Technical Manual for Dams

Section 1 - Modeling, Mapping, and Consequences Technical Manual for Dams Updates

This section summarizes the Modeling, Mapping, and Consequences (MMC) Production Center standard operating procedures (SOP) updates between the FY2022 to FY2023 SOP technical manuals.

• CTS worksheet fields and tabs updated. Modeling responsible for the pertinent data, H&H data, and H&H timing tabs.
• Software versions updated for recommended/required software.
• Updated RMC file share folder structure for final delivery.
• Removed all references to Consequences Assessment Summary reports and Model Reports for Hydraulics as they are no longer used.

The approach currently practiced by the MMC for dam breach risk assessments is to develop hydraulic models using a software suite composed of USACE Hydrologic Engineering Center software including the River Analysis System (HEC-RAS), RAS Mapper, and the Hydrologic Modeling System (HEC-HMS). The Life Loss Estimation model (LifeSim) uses the results from the hydraulic models to compute life loss.

Section 2 - Initial Procedures for Dams

This section summarizes the initial sequence of procedures used by the Modeling, Mapping, and Consequences (MMC) Production Center to complete a new flood risk management or navigation dam study and update to an existing dam study.

2.1 District Coordination

The first step of a new study, following work acceptance by the MMC Director, begins with the project manager (PM) leading development of the project work plan (PWP), data collection worksheet completion, and district coordination. The district Dam Safety Program Manager (DSPM) and Dam Safety Officer (DSO) are contacted by the PM or documentation lead to complete the initial MMC data collection worksheet. The data collection worksheet outlines details regarding available dam specifications, manuals, previous models, and data. The DSPM and DSO recommend district points of contact for the facility project manager, hydrology and hydraulics (H&H) engineer, geographic information systems (GIS) specialist, and economist, if resources exist. The PM utilizes this information and works with the MMC project delivery team (PDT) to complete the PWP. The PWP will include an initial description of the work to be conducted by the MMC and the projected schedule for each work item. The MMC PDT and district points of contact (POCs) walk through the PWP during the project kickoff meeting. The district will have an opportunity during the kickoff to describe existing project criteria and conditions to begin modeling the dam or appurtenant structure assigned to the MMC.

2.1.1 Develop Project Work Plan

The PM is the lead to create an external and internal PWP, and coordinate with the modeling technical lead for input. The documentation lead will create the project directories on the MMC file share and MMC Team SharePoint Site. More detailed discussion of the MMC dams folder structure can be found in Appendix 4.3.1. The MMC folder structure will be delivered to the assigned modeler and used throughout the entire process.

2.1.1.1 External Project Work Plan

An external PWP will be developed for the dam project. The documentation team will develop the PWP and provide it to the PM for revision. Prior to the project kick-off, the PM will notify the members of the kick-off meeting of information that will be required to fill out the dam PWP.

2.1.1.2 Internal Project Work Plan

An internal PWP will be developed for the dam project as needed. The PM develops the internal PWP and provides it to the modeling team lead to add the modeling scope, confirm funding amounts, and confirm internal schedules. As part of the work plan development effort, dam information will be collected and modelers identified by the modeling technical lead.

2.1.2 Project Kick-off Meeting

The MMC PM will schedule a project kick-off meeting after the draft external PWP has been developed. At a minimum, the invitees will include: the district DSPM, district DSO, MMC modeling lead, assigned MMC modeler, MMC mapping lead, and MMC consequences lead.

The kick-off meeting will clarify scope of the study as well as the schedule and budget. The MMC PM and modeler will discuss key technical information with the district personnel, and these technical details will be highlighted within the PWP. Primary data sources will also be identified, such as existing hydraulic models, high-resolution DEMs, and project datum conversions.

2.2 New Dam Study

Once work acceptance and initial district coordination are completed, the next step for a new dam study involves the production of pre-model GIS data.

2.3 Update to an Existing Study

If an update of an existing dam study is being performed, the initial step is still district coordination, and the existing data collection worksheet is updated to determine if new or supplemental data exists that should be used during the update. All district model independent quality review (IQR) comments and mapping/documentation IQR comments should be reviewed for items that were deferred to future study. The existing digital elevation model (DEM) should be evaluated by the MMC mapping production team member to determine if the elevation data has been updated since the previous study. The assigned modeling production team member will evaluate any existing modeling provided by the district. The evaluation will be based on map projection, file structure, model layout, and model setup to determine to what extent it meets current MMC modeling guidelines. The evaluation will be reviewed by the modeling team lead; a recommendation will be made regarding whether to use the existing model or create a new one.

2.4 Pre-Model Geographic Information System Data Production

This step generates the internal GIS deliverable needed by the modeler to begin model development.

The mapping production team member is responsible for providing the assigned modeler the GIS data necessary for the initial model setup using national data sets as described in Appendix 4.1.1. The data will be provided to the modeler using the standards described in Appendix 4.3.1. If it is determined that additional efforts are required to include levee elevations from the National Levee Database (NLD) in the pre-model DEM, Appendix 4.1.11 describes these methods.

2.4.1 Create File Structure

The mapping team member creates the MMC folder structure in the MMC file share following guidance in Appendix 4.1.1. More detailed discussion of the MMC folder structure can be found in Appendix 4.3.1. The pre-model data will be delivered to the assigned modeler via the MMC file share. Upon request, data will be delivered on an external hard drive to the assigned modeler. Figure 2-1 is an example of the MMC folder structure.

The MMC file share is for use by MMC members only, and the members are required to request permission to access this resource. Members can contact the MMC Mapping and Documentation Branch Chief (Michelle Carey) or the Documentation Lead (Tabetha Hesseldenz) to request access. The pre-model data is posted to the project folders located on the MMC file share: \\wpc-netapp3.eis.ds.usace.army.mil\RMCSTORAGE4\Production\Dams.

Figure 2-1. Modeling, Mapping, and Consequences Delivery File Structure

2.4.2 Projections

The standard projection for all MMC projects within the projection boundaries is USA_Contiguous_ Albers_Equal_Area_Conic_USGS_version. The linear units are set to U.S. feet. The MMC Production Center uses the North American Vertical Datum of 1988 (NAVD 88) for all elevation data within the datum extents.

The standard horizontal projection for Hawaii, Alaska and Puerto Rico (or other locations where the Albers projection listed above does not reach) is the state plane that the majority for the modeled area is located within.

Alaska is within the range of the NAVD 88 system and will use this datum for all vertical data. The standard vertical datum for Hawaii is local mean sea level (LMSL). The standard vertical datum for Puerto Rico is the Puerto Rico Vertical Datum of 2002 (PRV 02).

Detailed projection parameters are provided in Appendix 4.1.1.

The MMC projection is used for the pre-model data and throughout the modeling process. When alternate projections are in place, some additional steps are needed to add data to the MMC data viewer.

2.4.3 Create Centerline and Banklines

Digitize the river centerline and banklines from the study dam downstream, following the guidelines set in Appendix 4.1.1. If previous studies included coincident digitizing, the previously completed data may be used.

The dam will be located using the National Inventory of Dams (NID) database. The location will be verified against the most current aerial imagery available (see Appendix 4.1.1).

The Environmental Systems Research Institute (ESRI) world imagery service is used to digitize the centerline and banklines at a scale of 1:15,000 from the dam to the downstream extent provided in the PWP. If the centerline is stopped at a confluence, the centerline should proceed downstream past the confluence to account for any impacts at that confluence. The objective of this guideline is to minimize the chances of needing to develop additional data at a later time, and in many cases a longer study reach is developed than will need to be modeled.

2.4.4 Create Study Area

Create a study area boundary based on the digitized centerline or the preliminary depth grid (see Appendix 4.1.1). The preliminary depth grid would ensure backwater areas are captured. The depth grid is converted to a polygon and buffered by a specified distance.

The study area is used to define the maximum DEM extent to be included for modeling; the study area will include areas 20 miles from either side of the river centerline as well as cover the entire pool of the study lake at the top of dam (TOD) elevation.

There is some subjectivity in the creation of the study area; care should be taken to include all areas that could be inundated and include all areas provided in the downstream extent provided in the PWP. Overestimate the extent of the study area-the modeler can eliminate extraneous elevation data during the modeling phase. Underestimating the extent of the study area will cause the modeler to request additional data, which will cost time and effort.

The study area is included in the pre-model data deliverable.

2.4.5 Produce Digital Elevation Models

Merge source DEM tiles that intersect with the study area and project the DEM in the MMC projection. DEMs will be provided in native projection and in the MMC projection. Providing the native projection DEM allows the modeler to use a projection other than Albers. A general rule for all MMC team members is to minimize the number of projection steps for raster data, as some quality is lost during each step. The DEM production steps are detailed in Appendix 4.1.1.

The DEM is included in the pre-model data deliverable.

2.4.6 Create Preliminary Depth Grid

Create a preliminary depth grid in the MMC projection by developing a triangulated irregular network (TIN) that represents an elevated water surface (WS) that is intersected with the DEM to estimate the flood plain extent. See Appendix 4.1.1 for details.

The preliminary depth grid is included in the pre-model data deliverable.

2.4.7 Top of Dam Contour Polygon

The TOD contour polygon represents the maximum pool behind the study dam at the TOD elevation. The polygon is generated by intersecting a raster dataset representing the WS and the study digital elevation model. The resulting raster depth grid is then re-classified to represent either inundated area or non-inundated area. Convert the re-classified raster to a polygon feature class and delete the non-inundated area features from the resulting dataset. See Appendix 4.1.1 for details.

The TOD contour polygon is included in the pre-model data deliverable.

2.4.8 National Levee Database

Levee information from the National Levee Database (NLD) is provided to all modelers by the mapping technical lead independent of the pre-model data deliverable. The mapping technical lead coordinates with the NLD database manager and obtains updated NLD data layers at least once a year. The NLD includes information related to the levee centerline. The centerline should be represented as a line element and points containing the elevation from the latest survey of the levee. The mapping technical lead or delegate will need to confirm a levee line of protection (LOP) is available that combines the levee segments with closures and other structures that complete the levee alignment.

2.4.9 Create .mxd File

Create an .mxd file with the following layers:

• Conversion points
• Centerline
• Banklines
• Study area
• TOD contour polygon
• Preliminary depth grid
• Native and MMC-projected DEM
• ESRI Layers-street map, imagery, and topography
• Vertical datum conversion grids

Appendix 4.1.1 details the .mxd production steps. The .mxd file is included in the pre-model data deliverable.

2.4.10 Review Deliverable

Review the deliverable for content and conformance to the standard defined in Appendix 4.1.1. Use the checklist in Appendix 4.3.2; ensure all deliverables are included.

2.4.11 Deliver Data to Assigned Modeler

The mapping production team member will package the data and post it to the project folder in the MMC file share. The PM and Production Team Lead shall be copied on the transmittal email to the modeler.

The mapping production team member sends the data to the identified modeler unless the Modeling Team Lead directs otherwise. Any revisions or additions to datasets should be requested through the mapping production team member and will be transferred in the same manner as described above.

Once the deliverable is provided to the modeler, the task in the schedule database "Pre-Model" is complete.

2.4.12 Load Data in Modeling, Mapping, and Consequences Geodatabase

The mapping technical lead will save a full copy of the deliverable in the MMC Production Center Pre-Model Data Geodatabase. See Appendix 4.1.3 for more information on the geodatabase schema.

2.4.13 Update Project Schedule

The mapping production team member shall communicate status regularly, especially at task completion, to the PM. The PM will mark the task as complete.

2.5 Supplemental Data Research and Processing

The modeling production team members will use the district data collection worksheet and further coordination with district POCs to identify relevant H&H data needed for model setup and data that may assist or streamline the modeling process. If necessary, the mapping production team member will identify existing GIS data that may be of better quality than the national datasets used in the rapid data development process. To warrant processing costs, care should be taken to ensure that elevation data identified are sufficiently better than the National Elevation Dataset (NED). Of special interest is Light Detection and Ranging (LiDAR) that is not already incorporated into the NED, including any bathymetric data available that would support surface generation. Scattered cross section bathymetry may be useful to the modeler; however, this should not be incorporated into the elevation models. Supplemental data documentation is delivered to the modeler for reference. The data research will be conducted as a collaborative effort between the modeler and the mapping team in accordance with Appendix 4.1.2.

2.5.1 Deliver Research and Acquisition

The PM should notify the study dam project's district DSO and DSPM that the project will be studied and request updated data POCs to confirm the information in the data collection worksheet.

2.5.2 Existing Hydraulics and Hydrology Data

Modeler will contact the district H&H POC to request any available information on the study dam. Copy the PM on any communications. Catalog any existing data. See Appendix 4.1.2 for additional details.

2.5.3 Existing Geographic Information System Data

Mapper will contact the district GIS POC to request any data relevant to the MMC study. Copy the PM on any communications. Catalog any existing data according to Appendix 4.1.2.

2.5.4 Documentation of Findings

As part of model setup, the modeler will determine what information is necessary. In general, all existing H&H data should be obtained. Existing GIS data should only be requested if deemed necessary by the modeler.

2.5.5 Data Transfer

Data from districts can be transferred electronically via the MMC file share or, if district personnel do not have access, data can be transferred via file transfer protocol (FTP) using the following site. If necessary, temporary media or storage devices can be used for transferring data.

• \\wpc-netapp3.eis.ds.usace.army.mil\RMCSTORAGE5
• Safe Access File Exchange (DoD SAFE): https://safe.apps.mil/.

2.5.6 Data Review, Processing, and Delivery

The mapping production team member will review the district-provided GIS data and, after completing required post-processing, will deliver necessary GIS data to the assigned modeler. Any GIS data is processed following the standard procedures defined in Appendix 4.1.1.

2.5.7 Update Project Schedule

The mapping production team member shall communicate status regularly, especially at task completion, to the PM. The PM will mark the task as complete.

Section 3 - Modeling

This process begins with modeling production team member research of the data collection worksheet, additional communication with the district, and model setup using the pre-model GIS data deliverable. Completed hydraulic models and hydraulic data for consequences models are finalized and sent to consequences and mapping team members for further processing and product development.

Communication with the district will begin after the data collection worksheet has been sent. The modeling team lead and PM will contact district personnel to discuss the PWP. The PM will confirm the initial estimates of work schedule and design parameters prior to beginning the modeling process. The final PWP is filed in the project SharePoint folder.

Meeting modeling expectations will be documented by modeling team leads using the following metrics: model quality and meeting project schedule due dates. Modeling team leads are available to provide guidance on measurable MMC metrics (for metrics definitions, see Appendix 1.7).

3.1 Modeling Procedural Outline

• Develop Internal and External Project Work Plans
• Project Kickoff Call with District
• Collection and Inventory of Model Setup Data
• Begin Development of CTS Worksheet on SharePoint
• Begin Hydraulic Modeling Documentation
• Begin Model Setup
• Develop MMC Maximum High (MH) Pool Non-Breach Scenario
• Develop Breach Parameters for the MH Pool Breach Scenario
• Develop the MH Pool Breach Scenario
• Develop remaining Non-Breach Scenarios
• Develop Remaining Breach Parameters
• Develop remaining Breach Scenarios
• Generate required mapping products for all Scenarios
• Complete draft report and Modeling CTS entry
• Internal MMC Model Review
• Upload Preliminary Inundation Maps to the FIM Viewer
• District Model IQR
• Hydraulics Model Report Review
• Final Model Approval

For more details describing each step, see the Technical Manual for Program Management and MMC modeling SOP appendices.

3.2 Model Development

3.2.1 Getting Started With Modeling

Modeling files and results are key MMC Production Center products that feed the consequences, documentation, and mapping production efforts. Product development is complex and time consuming; this effort is the most demanding phase of the MMC Production Center process. In most instances, an unsteady HEC-RAS one-dimensional (1D) and/or two-dimensional (2D) model will be developed in support of the MMC program. This section of the SOP will outline HEC-RAS 1D and 2D hydraulic model development within the MMC Production Center.

3.2.2 Hydraulic Modeler Training Requirements

To successfully complete hydraulic modeling for an MMC dam breach study, a high level of training and experience using HEC-RAS software is required. In addition to practical experience, the following USACE PROSPECT courses are highly recommended to prepare modeling team members.

• Steady Flow with HEC-RAS
• Advanced Steady Flow with HEC-RAS
• Unsteady Flow Analysis with HEC-RAS
• Advanced 1D/2D Modeling with HEC-RAS
• H&H for Dam Safety Studies.

The MMC training plan is available on the Team SharePoint site for additional information on required and recommended classes and experience.

3.2.3 Computational Requirements, Data Resources and Data Transmission

The following section outlines the resources needed for model development as well as information on MMC SharePoint collaboration sites which house the latest MMC program guidance. Information on data transmission for the modeling, mapping, and consequence production process is also covered in this section.

3.2.3.1 Hardware

The team member will need to be assigned a USACE ACE-IT desktop/laptop that has the Science and Engineering specifications. The team member may need to request an external hard drive to store production model scenario data sets locally. Requests for external hard drives can be submitted to the MMC team lead or MMC technical lead; however, available resources may be limited.

3.2.3.2 Software

The MMC team members will not receive administrative rights on assigned equipment. If a user has a need for software installation, the ACE-IT Service Track system will be used to enter a request. Modelers should use the latest approved version of all software applications. Modeling team leads can provide guidance on software versions.

3.2.3.3 SharePoint; Modeling, Mapping, and Consequences file share; and ProjectWise (Collaboration) Sites

The MMC Team SharePoint site contains program information, reports, documentation, and policies. This collaboration site supports MMC members only. MMC Team SharePoint site link:

https://team.usace.army.mil/sites/NWK/pdt/MMC/default.aspx

The MMC Community of Practice (COP) SharePoint site contains program information, policies, documentation, and reports and is open to Corps employees. Personnel with a common access card (CAC) can connect to the collaboration site. MMC COP SharePoint site:

https://cops.usace.army.mil/sites/HHC/CoPs/DS/MMC/SitePages/Home.aspx

The MMC file share is located in the Western Processing Center (WPC) and contains draft and final model data within project folders. MMC file share access is required. The MMC file share link is:

\\wpc-netapp3.eis.ds.usace.army.mil\RMCSTORAGE4\PRODUCTION\DAMS

The MMC program requires the use of a virtual production team for GIS data production, modeling, consequence assessment, and review. Because of data transfers required for analysis, a project folder is assigned to each study dam on the MMC file share. The project folder houses all data used for the study throughout the entire process. The project folder adheres to a standardized structure and will originate with the pre-model GIS data prepared by the mapping team.

A project hard drive will be assigned and used for the delivery of large project data files that cannot be transferred across the wide area network (WAN), as needed.

It is important that all data on the project hard drive and within the project folder adheres to the standardized folder structure presented in Figure 2-1. Non-pertinent and legacy data is not to be uploaded to the hard drive or within the MMC file share project folder in order to maintain clarity.

The MMC project folders for model production and reviews will be housed on the MMC file share to maximize MMC data and file management during the production process. Once the production process is complete, final project data and reports will be uploaded to the MMC data viewer and the CEDALS ProjectWise server described in Section 4.1.4 of this document.

3.2.3.4 Scope/Schedule/Budget

The schedule, scope, and budget of the modeling effort is captured in the work plans described in Section 2. The assigned hydraulic modeler should discuss specifics with the modeling team lead. The work plans are loaded to the project folder on the MMC Team SharePoint site, link available in Section 3.2.3.3.

3.2.3.5 Funding Requests

Funding requests for MMC levee modeling work are entered through the online funding request system:

https://geo1.mmc.usace.army.mil/frs/

3.2.4 Collection and Inventory of Data for Modeling

3.2.4.1 Sources of Data

After the scope of the modeling effort is established, the first step of the hydraulic modeling process is to take an inventory of the available base data. As described in Section 2.4, the pre-model dataset that includes NLD GIS data, NLD levee profile data, land cover data, DEM, and dam pertinent information will be included. Additional data from the home district may be provided if identified during the kick-off call.

It is the responsibility of the assigned modeler to examine the quality and completeness of the pre-model dataset. The modeler should coordinate with the MMC mapping team lead and the home district contacts to ensure the best available data is being used from the beginning.

New unsteady HEC-RAS models will be prepared utilizing existing USACE and local data (when available) to supplement new model inputs derived from the pre-model GIS dataset. Because of the large scale of the models and simulation requirements, it is important only to use data sources that are not cost or time prohibitive and will improve model accuracy. Once the modeler receives the data from the mapping team, the modeler should review the data to get an overview of the entire study to be performed.

Data for MMC studies will come from two sources: existing district data and the pre-model GIS data package.

3.2.4.2 Existing District Data

Much of the pertinent data regarding the dam and area downstream will come from the district office in which the dam is located (owning district). Data should be requested from the owning district using the MMC Data Collection Worksheet (Section 2.1), and subsequent follow up with the owning district POC. This worksheet is sent to the owning district of the subject dam to catalogue the information that is available for the dam. This worksheet will inform the modeler of what existing data is available. The modeler will then do a data call to the district contact noted on the district data collection worksheet to request the data pertinent to model development. At a minimum, information required for MMC Dam breach modeling will include the dam water control manual (WCM), daily period of record pool elevation dataset (or a previously developed pool elevation duration exceedance curve), and information related to the latest approved PMF or design flood study.

Existing district data may include, but is not limited to:

• Project WCM
• EAPs
• Spillway adequacy studies
• Probable maximum flood (PMF) analysis
• Conversion factor for datum conversion from project datum to NAVD 88
• Water surface and thalweg profiles
• High-water marks
• Existing dam breach inundation mapping/GIS files
• Elevation duration exceedance and frequency curves
• Rating curves-spillway/gates
• Existing hydraulic models
• Lake elevation/storage curves
• Other existing model data
• Cross section data (from existing models)
• Bathymetric data
• Stream flow records (flow and stage; data storage system [DSS] format preferred)
• Reservoir period of record (DSS format preferred)
• Study dam design memorandum
• Study dam engineering drawings
• Levee data
• Reports
• Existing ground surface data
• Screening portfolio risk assessment (SPRA) for dams
• Inspection reports
• Dam rehabilitation (i.e., dam safety modifications)
• Federal Emergency Management Agency (FEMA) Flood insurance studies (FIS).

NOTE:

Ground surface data obtained from outside sources for use in MMC Production Center dam studies should meet minimum accuracy and resolution requirements. Minimum resolution for the MMC Production Center is 10-meter grid format. Minimum accuracy for the MMC Production Center is NED. More accurate data (possibly at the same 10-meter resolution) may be used if available and not production prohibitive.

3.2.4.3 Pre-Model Geographic Information System Data

For new studies, standard pre-model data will be provided to the modeler by the mapping production team. See Section 2.4 in this document for additional information regarding pre-model data development. The intent of the MMC Production Center is for the modeler to be able to prepare a model suitable for analysis using this data in conjunction with the water control manual. Certain cases may require additional data. Pre-production data will include the following information:

• DEM
• Digitized stream centerline
• Digitized banklines
• Hillshade
• TOD contour
• Preliminary inundation grids (upstream and downstream)
• NLD geodatabase
• ESRI ArcGIS Online Services (Imagery)
• ArcMap .mxd file containing the above data.

The digitized stream centerline and banklines should be verified by the modeler. If changes or corrections are made by the modeler the mapping team should be notified in order to maintain a consistent dataset for the production process.

NOTE:

At a minimum, the mapping production team member will supply 10-meter cell size NED. If better data exist in the form of LiDAR, bathymetry, or other elevation data, the modeler must decide whether or not to augment the initial pre-model GIS product, balancing tradeoffs between improvements to model quality and increased production time and costs. The modeler should coordinate with the mapping team member, who can support the modeler if needed to perform processing of any district-supplied elevation data.

3.2.4.4 Developing Supplemental Geographic Information System Data

The most common beneficial enhancements to the pre-model GIS dataset are incorporating bathymetric data into the DEM, "burning in" levee elevations, and using topographic data sources that are better than what is available in the NED. These enhancements may be performed by either the assigned modeler or the mapping production team member. However, exact steps to follow are contingent upon the format, quality, content, projection(s), and datum(s) of the source datasets. Extreme care must be taken during processing to limit the introduction of errors into the final compiled elevation model. For further information on pertinent data included in dam breach models refer to the RAS Mapper user's manual and the HEC-RAS 2D modeling user's manual, which details physical features that can be incorporated into HEC-RAS geometry using RASMapper.

3.2.5 Update Project Work Plan

The Modeling Team Lead and PM will update the PWP with data received from the district. If the district does not provide additional information, the MMC will utilize initial estimates and design parameters identified prior to beginning the modeling process.

3.3 Navigation Dam screening

For certain types of navigation dams and other dams, such as flood retarding structure and hurricane protection barriers, downstream flooding and consequences due to dam breach may be negligible, limiting the need for, or the benefits of, modeling and inundation mapping. A screening assessment tool has been developed to quickly estimate whether dam breach for these assets will result in significant consequences, which will drive the need for modeling and mapping. Figure 3-1 demonstrates the step-by-step flowchart required for screening low-to-medium head and navigation dams. Benefits lost and other economic consequence estimations will be conducted for all projects, regardless of modeling and mapping needs.

The companion flow chart elements have alphanumeric identifiers. The narrative sections that follow correlate to these identifiers. Elements labeled D(i) indicate decision elements, P(i) indicate process elements, and F(i) indicate final elements.

Figure 3-1. Modeling, Mapping, and Consequences Model Screening Process

NOTE:

The modeler is expected to use engineering judgment while using this screening process and should err on the side of conservative when a decision point is unclear. The engineer is encouraged to use available SPRA data as supplementary information to make informative decisions about each step. Any major deviation from the screening process requires appropriate coordination from the MMC team.

D1: DOES DAM OBVIOUSLY REQUIRE COMPLETE ANALYSIS?

This first decision box is the common-sense test. If, due to size and obvious downstream hazards, a dam should have a full analysis completed, the modeler can skip the entire screening process and flag the dam for further analysis. An example of a dam obviously requiring complete analysis is a high-head dam (>40 feet head differential) with a population center immediately downstream.

D2: ANY DOWNSTREAM CONSEQUENCES (PER AERIALS, AVAILABLE INUNDATION MAPPING, OR FEDERAL EMERGENCY MANAGEMENT AGENCY FLOOD INSURANCE SURVEY)?

The modeler should utilize current aerial photography or land use mapping to determine if there are potential consequences in the downstream routing reach. The engineer should use judgment regarding the length of the downstream reach. In general, the downstream reach should extend to a point where the flood wave is expected to be less than two feet above normal river stages. If needed, this can be estimated using the head differential ratio graph presented and discussed in Step P3.

If no potential downstream consequences are observed and the engineer is confident that the base mapping is current and accurate, the engineer selects no and the process for this dam ends. Conversely, a yes or unknown continues the process.

D3: OVER FIVE FEET MAXIMUM HEAD DIFFERENTIAL (FOR COASTAL, COMPARE TO HIGH TIDE)?

The modeler should use design or operational documents, topographic mapping, or other readily available information to determine if the maximum head differential across the dam is more than five feet (for most low head and navigation dams the largest differential will occur during under non-flood conditions). If yes, the screening process continues.

Background: Compilation of results from previously completed dam breach analyses has shown the maximum breach flood wave height for low head dams is approximately 40 percent of the total head differential at the time of breach. Five feet was chosen because it translates to approximately a two-foot maximum flood wave which is deemed to be generally low hazard in consequence analysis.

The modeler should use judgment at this phase. If, for example, there is a low-lying recreation area or some other hazard immediately below a five-foot head differential dam, further analysis may be warranted.

D4: IS EXISTING, SUITABLE HYDRAULIC MODEL AVAILABLE?

The modeler should research whether an appropriate, easily useable digital model is available and suitable to produce a dam breach. A no at this step takes the modeler to process 1 (P1): compute Qbreach using an empirical method. A yes at this step takes the modeler to process 2 (P2), in which the existing model would be converted to an unsteady-flow dam breach model.

P1: COMPUTE QBREACH

The modeler shall compute Qbreach for the study dam. The intention at this step is to use a simplistic, empirical method to estimate the breach peak. Several potential methods include:

• The NWS Simplified DAMBRK model (or accompanying equations).
• Equations provided in the USACE SPRA spreadsheet to compute maximum regression breach flows.
• The Natural Resource Conservation Service (NRCS) technical release (TR) TR-60 approach. While developed and intended for earthen dams, this method could provide a screening level estimate for Qbreach, including a breach outflow hydrograph.
• Manual Calculation. Assume breach occurs during maximum head differential and six monoliths experience immediate breach. A weir calculation can be performed or hydraulic model developed to estimate Qbreach.

If deemed appropriate, attenuation to the maximum Qbreach can be computed. This would likely involve an estimate of the breach hydrograph shape using engineering judgment, with the computed Qbreach being the peak discharge just downstream of the study dam. A simple HEC-HMS, hydrologic (or HEC-1), or HEC-RAS unsteady flow model could be developed to route the breach hydrograph downstream through the study reach, simulating attenuation.

It is suggested that the modeler calculate Qbreach using two methods, when practical, for verification.

D5: IS QBREACH ≥ MINIMUM FLOOD STAGE FLOW?

The modeler should compare Qbreach to the published minimum flood stage flow for the downstream hazard reach. Flood stage and flood stage flows may be taken from stream gage data and/or FEMA FIS reports, especially near population centers. However, an established flood stage may not be available in all study reaches.

P2: CONVERT EXISTING MODEL AS APPROPRIATE AND ESTABLISH INUNDATION ELEVATIONS.

Assuming an existing, suitable model was identified in step D4, the modeler converts the model to simulate a dam breach and route the breach hydrograph downstream. If available, the engineer could truncate an existing model to the area of interest and execute the model to estimate inundation elevations.

P3: PLOT INUNDATION ELEVATIONS USING EXISTING MODEL RESULTS, HEAD DIFFERENTIAL RATIO, OR OTHER ENGINEERING METHODS.

Assuming maximum breach elevations have been established or estimated for the downstream study reach, the modeler should utilize geographic information system (GIS) methods to plot the maximum breach inundation limits on the best available terrain data.

If no breach profile is available, the modeler can use the head differential ratio relationship if appropriate for the study dam.

Compiled results from previously computed dam breach models have shown there are fairly consistent trends in the breach flood wave height compared to the maximum head differential of a dam. These trends are plotted against the downstream distance and used to estimate the inundation elevation as a function of distance and starting head difference. Figure 3-2 illustrates data collected to date. This method will continue to be refined as more data is gathered.

Figure 3-2. Head Differential Ratio versus Distance Downstream

Note

In some scenarios, the difference between the TIN elevations and the peak profile will be negligible to the point that no inundation limits are plotted. In this case, proceed to step D6 and utilize breach elevations for comparison downstream to determine consequences.

D6: ANY DOWNSTREAM CONSEQUENCES INUNDATED?

The modeler should compare the maximum breach inundation limits against available aerial imagery or other mapping sources to determine if downstream consequences are predicted to be inundated from a dam breach. Hazards include, but are not limited to, habitable structures, crucial infrastructure, recreation areas (campgrounds), casino boats, etc. The modeler must be confident that the base mapping is accurate and current.

If inundation limits could not be established in step P3, the modeler may compare the breach profile elevations against other known flood stages downstream, such as reported minimum flood stage elevations at gages.

F1: NO COMPREHENSIVE MODELING/MAPPING NEEDED

This step reveals that the low head or navigation dam is unlikely to cause significant damages should a dam breach occur. Comprehensive analysis is not required. Evaluator should complete the consequences evaluation without comprehensive modeling or mapping.

F2: REQUIRES COMPLETE DAM BREACH ANALYSIS AND CONSEQUENCES MAPPING

This step reveals that the study dam may pose significant risk to downstream hazards should a dam breach occur. Additional analysis is required.

Figure 3-3. Navigation Dam (Screened Out) Scenario-Pool Relationships

3.4 Model Development for Flood Risk Management and Navigation Dams

3.4.1 Overview of Model Development

The current state of practice in hydraulic modeling for USACE projects utilizes the HEC's suite of software and GIS tools for developing hydraulic models, modeling various scenarios, efficiently updating models, and exporting results to the consequence estimation model. The software is endorsed by the Hydrology, Hydraulics, and Coastal Engineering (HH&C) COP and maintained by the HEC.

The goal of the MMC modeling team is to create geo-referenced unsteady 1D and 2D models capable of producing accurate mapping and consequence analysis across a wide range of scenarios. Most dams modeled as part of the MMC program are located in a typical riverine system which a 1D model can accurately model. However, some projects may have conditions where a 2D model is absolutely necessary which include extremely flat areas, large interior areas, complex topography with multiple flow paths, and/or highly urbanized areas. In general, the preferred methodology for these cases are to use a 2D hydraulic model.

The key products delivered by the MMC Production Center's modeling team members for dam safety projects are as follows:

• Geo-referenced hydraulic model capable of simulating a full range of hydrologic loading and breach and non-breach conditions
• Breach and non-breach scenario model inundations and mapping output
• Input data for HEC-LifeSim model
• Formal documentation of the hydraulic modeling effort

3.4.2 General HEC-RAS Model Set Up for Modeling, Mapping, and Consequences

Modeling specifics have been adopted by the MMC to maintain consistency and integrity for all models created as part of the program. This section will cover HEC-RAS Project specifics such as naming conventions and description field information used by MMC.

• Naming Conventions. All models created for the MMC Production Center will have specific naming conventions to provide consistency across the MMC program.
• Project Name. The HEC-RAS project file will be named with the project name: "<NID Name of Dam>_NIDID" Example: TuttleCreek_KS00000.
• Geometry Name. All models created or MMC will have utilize a single geometry with the following naming convention: "<Name of Dam>MMC Geometry"
• Projection. The HEC-RAS geometry will use the standard MMC Projection of Albers Equal Area (detailed projection data included in Appendix 4.1.1).
• Vertical Datum. HEC-RAS geometry elevations must be in feet using the North American Vertical Datum (NAVD 88).

Each scenario, breach and non-breach, created for the MMC Production Center will have a separate plan file named as detailed in the table that follows. Detailed description of these scenarios are presented in Section 3.4.4. Depending on whether the dam is a run-of-river navigation dam or flood risk management dam, each dam loading condition will share an unsteady flow file named according to the tables that follow.

• HEC-RAS Model Description. All models created for the MMC Production Center will include a thorough description field that provides potential users with pertinent information. The following items will be listed in the HEC-RAS Model Description field:
• Name of dam
• NID ID
• Location of dam and district
• Vertical datum and units
• Horizontal projection and units
• MMC Modeler
• Interim reviewer
• Final Reviewer
• MMC Modeling Team Lead
• District H&H Contact Person
• Status of model
• Date of last modification
• Program and version
• Controlled Unclassified Information

The HEC-RAS model geometry represents the physical constraints over which flow from the dam breach scenario will be routed. In order to have a complete model, constraints on both flow and time must be developed for analysis. These constraints will represent a range of loading conditions within the reservoir.

A HEC-RAS plan file is required to set the time constraints, computational settings, and model output for each modeled scenario. In addition, the breach plan is housed within the plan file. Specifics on the model plan files for MMC models is presented in this section of the SOP under "Plan Files for MMC Scenarios."

A HEC-RAS flow file is required to specify inflow hydrographs, downstream flow conditions, and gate operations at the dam. Specifics regarding model flow files for MMC are presented in this section of the SOP under "Flow Files for MMC Scenarios".

The combination of geometry, flow, and plan files is used to compute each model scenario. The model scenarios for MMC efforts are presented below.

3.4.3 HEC-RAS Model Geometry Set Up for Modeling, Mapping, and Consequences

3.4.3.1 Projections and Model Extents

• Projections. The standard projection for all MMC projects is as follows:
• USA_Contiguous_Albers_Equal_Area_Conic_USGS_version
• The linear units are set to U.S. Feet
• The MMC Production Center will use the NAVD 88 for all elevation data
• Detailed projection parameters are provided in Appendix 4.1.1
• Downstream Model Extents. The downstream model extent will be discussed during the model planning process. Initial estimates of the downstream extent may be obtained from inundation areas identified within existing EAP and other studies for the study dam or other dams along the same river reach. Depending on district feedback, the model extent may extend past the current EAP, or extend downstream from the assigned dam to the point of no significant damages or until floodwaters are no longer out of bank, or to a location where the flood conditions are the same for the breach and non-breach scenario. The initial estimate will be provided in the PWP. Determining this extent may be an iterative process and require the addition of cross sections after initial model development. When establishing model extents, downstream sources of significant inflow, such as tributaries, that may have an effect on the dam breach flood wave should be considered.
• Upstream Model Extents. Models created by the MMC Production Center will be created so that the area inundated upstream of the study dam due to the rise in pool level for a given scenario can be fully mapped in the inundation mapping process and can be considered in the consequence analysis. This will require delineation of the entire reservoir backwater area at the MH pool level. A shapefile defining the potential upstream inundation area will be supplied with the pre-model GIS data to aid in digitization of the area.
• Model Division for Large Systems. MMC Production Center dam studies may have to be divided into multiple reaches or segments based on study length.
• System Models. Layout procedures for system models with multiple dams (e.g., Columbia River, Missouri River, etc.) will be decided by project leads with input by the district/division of the system.
• Appurtenant Structures. Appurtenant structures are relatively common among USACE dams. Examples of such structures include upstream/within-pool levees protecting communities from high pool conditions or wing dikes and saddle dikes that act as an extension of the damming surface away from the main embankment. Appurtenant structures should be included in the model as appropriate.
• Dams Located Downstream of the Studied Dam. Every effort should be made to model significant downstream dams and they should be operated according to the WCM for the dam. Small low head weirs located downstream can be modeled as simple inline structures and if elevations are not provided for the structure, the elevation may be estimated using terrain data.
• Studies Ending in a Downstream Reservoir. In the case that significant damages end at a downstream reservoir, the controlling dam shall be included in the model, along with necessary downstream cross sections to properly model the structure. The dam should be operated according to the water control manual for the inflow conditions.
• Studies Ending at a Downstream Confluence. In the case where the model study ends at a downstream confluence with a major river, the model should not stop at the confluence, but should include a portion upstream and downstream of the major river to prevent sudden drops in the WS elevation at the confluence.
• Studies Ending along the Coastline. In the case that the model ends along the coastline, the model should extend beyond the coastline and the downstream boundary condition should be set to the mean high water (MHW) or tidal time series (coordinate with district) in that area. The MHW can be found for several stations on the National Oceanic and Atmospheric Administration (NOAA) Tide and Currents website: http://tidesandcurrents.noaa.gov/stations.html?type=Datums.

3.4.3.2 HEC-RAS Geometry

Standard pre-model GIS data will be utilized as the base for building the HEC-RAS model when an appropriate existing model is not available. DEMs and all shapefiles shall be developed in accordance with specifications set in Section 1.4.

Web imagery data sources linked to the HEC-RAS application are used for development in RASMapper.

• Data Processing. RASMapper will be utilized for processing model framework. For specifics on how to use RASMapper, the modeler should refer to the latest HEC-RAS 2D Modeling User's Manual respectively. Typical model data to be processed in RASMapper may include, but are not limited to:
• Stream centerline
• Cross sections
• Flow paths
• Bank lines
• Lateral structures
• Storage areas (where applicable)
• Storage area connections (not currently available in RASMapper)
• Inline structures (not currently available in RASMapper)
• Bridges/Culverts (not currently available in RASMapper)
• Ineffective flow areas (not currently available in RASMapper)
• Blocked obstructions (not currently available in RASMapper)

NOTE

A stream centerline shapefile will be provided by the mapping team for use in the model. The assigned modeler may adjust the initial centerline as necessary. If changes to the stream centerline occur during the modeling process, coordination with the mapping team must occur to ensure consistency between the model and the mapping. The mapping production team member is available to assist upon request.

• One-Dimensional Model Geometry.
  Models for the MMC Production Center will generally include only one geometry file. To provide consistency across the program, the following model geometry specifications have been adopted:
• Naming Convention. The following naming convention will be used for all geometry files produced for the MMC program: "<Name of Dam> MMC Geometry"
• Stream Centerline. Stream centerlines will be provided by the mapping team. If changes to the stream centerline occur during the modeling process, coordination with the mapping team must occur to ensure consistency between the model and the mapping. The stream centerline should be consistent with the channel shown in the orthophotography provided by the mapping team.
• Cross Sections. Cross sections should be spaced in accordance with guidance listed in the table that follows. Cross sections will be named as river miles from major downstream confluence. Bathymetric data and data from existing models should be incorporated when feasible. For areas where channel data is not available, a channel should be approximated based on aerial photography and cut into the cross sections. The channel should be sized to carry the full regulatory discharge as described in the water control manual. For additional guidance, see the HEC-RAS User's Manual.

Table 3-4. Recommended Cross Section Spacing

Channel Bed Slope (per river mile)	Cross Section Spacing (feet)
2 feet or less	2,000-2,500
2-10 feet	1,500
10 feet or greater	500-1,000



• Interpolated Cross Sections. Interpolated cross sections are only used when necessary to facilitate model stability. Interpolated cross sections are permitted for use in MMC Production Center modeling, but only on an extremely limited basis. Cross section interpolation should not be used in order to reduce the effort involved in the pre-model process or to create cross sections in pre-existing models that do not meet the spacing requirements listed above. Interpolated cross sections are acceptable if the cross section does not misrepresent the actual channel and overbank geometry. Additional guidance is available in the HEC-RAS user's manual.
• Reach Lengths/Flow Paths. Reach lengths and flow paths are to be adjusted to represent actual flow lengths to properly account for volume in the model computation. For additional guidance, see the HEC-RAS user's manual. This manual provides information on adjusting flow paths and their use in calculation.
• Manning's "n" Values. Manning's "n" values shall be increased immediately downstream of the dam to account for accumulation of debris and turbulence created during the breach. As general guidance, Manning's values can be doubled in this area. Cross sections should contain a minimum of three of Manning's "n" values: left overbank (LOB), channel, and right overbank (ROB). For additional guidance, see the HEC-RAS user's manual and the HEC-RAS Hydraulic Reference Manual.
• Ineffective Flow Areas. Ineffective flow areas are to be used in locations that do not have effective flow to properly account for flood plain storage. If interpolated cross sections must be used in the model, ensure applicable ineffective areas are translated to the interpolated cross sections. For additional guidance, see the HEC-RAS User's Manual.
• Blocked Obstructions. The use of blocked obstructions is acceptable for use in MMC models when an obstruction exists at a cross section. Blocked obstructions are not permitted to be used for subtracting storage volume at cross sections where permanent obstructions do not exist.
• Bridges and culverts. Bridges and culverts are generally not modeled as part of MMC Production Center efforts for dam breach analysis; however, bridges that may significantly influence hydraulic modeling results should be included when practical. If bridge data is not available and the embankments will have a significant impact on flood levels, the embankments should be at least modeled by placing a cross section on top of the embankment. However, bridge data may be readily available from the district or can be found from sources such as existing models, FIS, local district, etc. An approximation of bridge geometries is acceptable based on limited data from photos and other available sources.
• Lateral Structures/Levees. Lateral structures may be needed to model levees, road embankments and overland flow connected to a backwater storage area. Levees available in the NLD are provided as part of the pre-model GIS data and will be included in all MMC models. If additional data is needed, all NLD data requests will be met by the mapping technical lead assigned to the study dam.
• In HEC-RAS, for all NLD levees protecting areas that will experience significant damages due to levee overtopping. These levees are assumed not to breach for MMC Production Center scenarios. The recommendation is that levees being modeled in HEC-RAS be extracted from the NLD and added as a geo-referenced lateral structure. For additional information see Appendix 4.1.8.
• Levees that are picked up in the ground surface data are also to be included in the model.
• Flooded areas behind levees that overtop in the model are to be mapped as wet. Areas that are behind and protected by levees are to be removed from the flood boundaries created by that particular event. Coordination with the mapping team is required to ensure these areas are accurately mapped.
• For additional guidance, the HEC-RAS Hydraulic Reference Manual and the HEC-RAS 2D Modeling User's Manual. These manuals provide information on extracting storage area information from ground surface data as well as methodology for levee modeling as it pertains to HEC-RAS.
• For areas where a lateral structure is needed for a backwater 1D or 2D storage area and the lateral structure represents overland flow, the weir crest shape should be changed to the zero height option for the lateral structure and the weir coefficient should be adjusted to a value between 0.1 to 1.0. Overland flow is less efficient than weir flow and so the weir coefficient should be lowered to account for the lower efficiency. Lateral structures connected to 2D storage areas have 2 options to compute flow going over the top of the structure (Overflow Computational Method). The flow over the structure can be computed by either the Weir Equation or the Normal 2D Equation Domain. Generally, the "Normal 2D Equation Domain" is faster and more accurate but may not be good for true weir type structures. The "Normal 2D Equation Domain" should not be used for structures that are high where the flow over the structure will go into free fall (like a waterfall). The 2D equations cannot solve a stable solution through a waterfall. For these types of situations, the user should choose the "Weir Equation" option.
• Overbank Storage Areas. Floodplain and backwater storage is an important aspect of dam breach analysis and flood routing. Storage can be modeled by adding HEC-RAS storage areas in the model coupled with a lateral structure, extending cross sections up tributaries coupled with ineffective flow areas, or by adding an additional reach up the tributary.
• It should be noted for consequence analysis that the consequence analysis program will calculate consequences differently when modeling 1D or 2D backwater storage areas in HEC-RAS as storage areas versus modeling backwater storage using cross sections with ineffective area. When there is significant population in a backwater storage area, it should be modeled using a HEC-RAS storage area/2D area.
• HEC-RAS storage areas are to be named as river miles to include the river name and overbank (e.g., Susq Riv 16 IL) in accordance to their location along the river reach.
• For the MMC program, tributaries that are inundated by at least 10 miles of backwater flooding or contain a USACE-operated dam are to be modeled as separate reaches in the model.
• Reservoir. Reservoirs can be modeled several ways within HEC-RAS. The reservoir can be modeled with a 1D storage area, a 2D storage area, or cross sections. For the last two methods, bathymetric data would be needed (or approximated) in order to produce reasonable results. For most MMC models, reservoirs are typically modeled as 1D storage areas since bathymetric data is usually limited for reservoirs. When 1D storage areas are used, the latest storage curves (i.e., elevation versus volume curve) should be used unless bathymetric data exists which could then be used to calculate a new storage curve. If the existing curve does not capture the elevation-volume relationship up to the TOD or the MH pool level (whichever is higher), other sources can be used to supplement the elevation-volume relationship. Most USACE projects have storage curves in their WCM. The area times depth method should not be used unless no other data is available.
• Inline Structures (Dams). Dams modeled for MMC Production Center studies, as well as dams located in the downstream model extents, are to be included in the model as inline structures. Operating data should be obtained from the corresponding structure's WCM where available.
• Gates. All gates in a study dam shall be represented in the inline structure modeled in HEC-RAS. Rating curves from the water control manual corresponding to each gate should be input into the model as user-defined curves. Published curves may need to be extrapolated to maximum simulated pool elevations. Any gate curves that are extrapolated should be documented. For cases where rating curves are not available and other gate types are used (e.g., sluice, radial, overflow, etc.) adjustments to the appropriate coefficients should be made in order to reasonably target known stage/discharge relationships. Gate locations in the HEC-RAS model should approximately correspond to their physical location in the dam.
• Gate operations (opening and closing) will correspond to the water control manual. Elevation control and rules are the preferred methods of operation; however, certain scenarios will require the use of time series control. For additional guidance, see the HEC-RAS User's Manual and the HEC Hydraulic Reference Manual, which provides information on gate modeling options within HEC-RAS.
• Two-Dimensional Model Geometry
  The modeling production team lead will confer with the modeling production team member if a 2D model is required (i.e., when it is determined that a 1D model is not accurately representing flow and inundation extents). The standard 2D computational engine currently being used by the MMC Production Center is the latest approved version of HEC-RAS.
• 2D Area Breaklines. Significant interior restrictions to flow such as road embankments can have a major impact in the resulting inundation for a levee breach model and must be accounted for by modifying the computational mesh using a 2D area breakline. Openings or holes in embankments (such as highway underpasses) are also critical to achieving an accurate inundation result.
• 2D Area Internal Connections. The use of 2D area internal connections is an alternative to the use of breaklines. They have a great advantage in that they allow for the modeling of either gates or culverts directly within the structure, which is a convenient method for modeling a roadway embankment with underpasses. Internal hydraulic structures in 2D areas have two options to compute flow going over the top of the structure (Overflow Computational Method). The flow over the structure can be computed by either the Weir Equation or the Normal 2D Equation Domain. Generally, the "Normal 2D Equation Domain" is faster and more accurate but may not be good for true weir type structures. The "Normal 2D Equation Domain" should not be used for structures that are high where the flow over the structure will go into free fall (like a waterfall). The 2D equations cannot solve a stable solution through a waterfall. For these types of situations, the user should choose the "Weir Equation" option.
• 2D Grid Spacing. Select appropriate grid spacing for the computational mesh that fits with the area being modeled. This will take some trial and error and should be discussed during model development. Appropriate grid cell spacing will vary based on factors such as the slope of the terrain, number of breaklines used, and practicality of file sizes/runtimes.
• 2D Time Step Options: It may be necessary to use a different computation time step for the 2D flow area than the 1D river reach. This can be controlled by entering a value for number of time slices under 2D flow options for each 2D flow area.
• 2D Equation Set: Initial production runs will typically use the default 2D equation set diffusion wave. During the model verification process, it is recommended that the modeler make at least one run using the full momentum equation set to check for any significant impacts to the flood extent, peak stages, or arrival times when compared to an identical scenario using the diffusion wave equation set. If there are significant differences between the two runs, the modeler should assume the full momentum equation is more accurate and proceed with that equation set. For breaching analysis, the flood wave will rise and fall extremely quickly and the change in velocity (acceleration) will be dramatic both over time and spatially. The diffusion wave equations exclude the local (changes in velocity with respect to time) and convective (changes in velocity with respect to distance) acceleration terms. These terms are extremely important in order to model rapidly-rising flood waves.
• 2D Boundary Conditions: Appropriate boundary conditions should be added to the 2D computational grid when needed to prevent artificial pooling. Similar to 1D modeling, coastal areas should consider a stage hydrograph or rating curve for a downstream boundary.
• Channel Bathymetry: If channel bathymetry is not included in the terrain where 2D flow areas are implemented and it is expected that the bathymetry could impact the water surface elevations, it is recommended that bathymetry should be included in the terrain. If bathymetry data is not available, previous 1D models that have bathymetry data may be used to create a bathymetric surface or bathymetry data can be estimated from aerial or other reference material to create an estimated bathymetric surface.
• Spatially Varied Manning's "n" values: It is recommended that the roughness values should be varied spatially in 2D flow areas. This can be accomplished by either drawing 2D area Manning's "n" regions or importing a land coverage dataset within RAS Mapper in HEC-RAS. A recommended source for land cover is the National Land Cover database (NLCD) which can be downloaded from the Multi-Resolution Land Characteristics Consortium ( http://www.mrlc.gov/). Typical ranges for Manning's "n" values for some of the NLCD Land Cover types are provided in the table below. The "n" values in Table 3-6 are not meant for very shallow overland flow like those found in hydrologic modeling. For shallow overland flow, typically seen in hydrologic models, roughness values are generally much higher due to the relative roughness compared to the flow depth. In addition, the "n" values in Table 3-6 assume a bare earth terrain where the values factor in potential obstructions to the conveyance. If the terrain includes obstructions (e.g., buildings) or building footprints are imported as an additional land cover type, the "n" values should be adjusted to account for these differences. In some cases, the use of aerial photography to identify land cover and roughness may be preferable if there are significant discrepancies between current land use and those shown in the land cover database.

For additional details on HEC-RAS 2D, see the HEC-RAS 2D Modeling User's Manual.

3.4.4 Flood Risk Management Dam Scenario-Pool Relationships

The USACE has established a standard set of five modeling scenarios covering a range of pool elevations, representing minimum and maximum normal operating conditions as well as select extreme loading conditions designed to capture the upper limit of potential downstream consequences (Figure 3-4). The MMC program will consider alternative scenarios for flood risk management, dry flood risk management, navigation, and other dams such as flood retarding structures and hurricane protection barriers. To assess consequences more thoroughly, scenarios will be run for both breach and non-breach conditions.

Figure 3-4. Flood Control Dam Scenario-Pool Relationships

• Maximum High (MH) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for the MH pool water level. The most current inflow design flood hydrograph, antecedent pool, and routing will be provided by the district. If an antecedent pool is not provided, the pool should be initially set to the TAS pool and then adjusted until the district-provided maximum pool is met. If the antecedent event causes downstream flooding, additional coordination with the consequence team member is recommended.
• The MH scenario corresponds to the peak inflow design flood (IDF) elevation. This scenario is associated with the occurrence of an extreme flood event and routed using the emergency operation procedures from the WCM. It includes full utilization of available conservation, flood, and surcharge storage. Allowances for freeboard, wind setup, wave run up, and wedge storage (due to sloping reservoir WS) are typically not considered. Typically, uncontrolled spillway discharge will occur during the MH scenario resulting in significant downstream inundation for both with and without breach conditions. The MH scenario typically results in the greatest areal extent, depth of downstream inundation, and total economic consequences.
• Intermediate High (IH) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for the IH pool water level. Starting reservoir pool will correspond to the initial elevation used for MH. Reservoir inflow will be a scaled IDF hydrograph. The scaled hydrograph will be developed by trial and error. Gate operation procedures from the latest water control manual will be applied to the hydrograph routing. Consequence analysis will include damage and life loss (LL) estimates. A consequence analysis simulation for the non-breach condition will be necessary as damaging releases should result from the IH pool event.
• The IH scenario corresponds to an elevation that would occur in an unusual event, specifically an elevation that corresponds to a maximum peak discharge approximately halfway between the maximum TAS discharge and the maximum MH pool discharge. It does include some surcharge storage and will likely result in a significant increase in discharge above downstream channel capacity based on the physical properties of the project and/or operation procedures from the latest WCM.
• Top of Active Storage (TAS) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for the TAS water level. Starting reservoir pool will correspond to the 10-percent exceedance duration pool elevation. Reservoir inflow will be a scaled inflow design flood hydrograph. This hydrograph will be developed by scaling the MH hydrograph using trial and error to produce a peak pool equal to the TAS elevation. Gate operation procedures from the latest WCM will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates; however, computed consequences are not expected from the non-breach scenario, since non-damaging releases are assumed for the TAS event.
• The TAS scenario corresponds to the highest elevation which can be obtained under normal regulated operating conditions for authorized purposes (i.e., without damaging releases). This scenario is associated with the occurrence of an unusual flood event. It does not include surcharge storage but should represent the pool elevation that, if exceeded, would result in significant increase in discharge based on the physical properties of the project and/or operation procedures from the latest WCM. The term active storage has similar meaning as the terms full pool and flood control pool. For typical flood risk management dams with uncontrolled spillways, the TAS corresponds to the emergency spillway crest elevation. For dams with controlled or gated spillways, the TAS commonly corresponds to an elevation that, if exceeded, the gates would begin to release damaging discharge. For some cases this may be at or near the top of the spillway gates.
• Security Scenario (SS) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for a 1-percent exceedance duration pool elevation. Starting reservoir pool will correspond to the 10-percent exceedance duration pool elevation. Reservoir inflow will be a scaled inflow design flood hydrograph. This hydrograph will be developed by scaling the MH hydrograph using trial and error to produce a peak pool equal to the one-percent exceedance duration pool elevation. Gate operation procedures consistent with the latest WCM will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates; however, computed consequences are not expected from the non-breach scenario, since non-damaging releases are assumed for the SS event.
• The SS scenario corresponds to the one-percent exceedance duration pool elevation (exceeded about one percent of the time or three to four days per year on average) which can be obtained under normal regulated operating conditions. Depending on the dam, this scenario may or may not be associated with a flood event. This scenario is used for the CIPR program to provide a security-based scenario. It is also utilized for the Dam Safety Program to provide better definition of the pool versus consequence relationship.
• Normal High (NH) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for a NH water level, the 10-percent exceedance duration pool elevation. Starting reservoir pool will correspond to the 10-percent exceedance duration pool elevation. Reservoir inflow will be a constant inflow hydrograph as required to maintain the 10-percent exceedance duration pool under normal gate operations. Gate operation procedures consistent with the latest WCM will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates; however, computed consequences are not expected from the non-breach scenario, since non-damaging releases are assumed for the NH event.
• The NH scenario elevation corresponds to the ten percent exceedance duration pool elevation (exceeded about 10 percent of the time or 36 to 37 days per year on average) which can be obtained under normal regulated operating conditions. This scenario represents a relatively-high, but normal, pool condition which can be expected to occur every year. This scenario is not associated with the occurrence of a flood event.
• The hydraulic and hydrologic loading conditions for each breach scenario to be analyzed for flood risk management dams are listed in Table 3-6.

• Standard 3 Dams. Dams designated as standard 3 in ER 1110-8-2(FR) where the IDF is half of the PMF, the full PMF should be routed as a sixth scenario. This is to verify that incremental consequences are not expected with the full PMF. This only applies for Standard 3 dams that are not screened out and full products are developed.
• Dry Flood Risk Management Dams. Scenarios for dry flood risk management dams are to be the same as modeled for normal flood risk management dams. If the reservoir is dry for a particular event, this should be noted in the report. In cases where the reservoir remains dry in all scenarios except TAS, IH, and MH pool, a special scenario may have to be developed based on judgment of the project lead to capture an event less than TAS. This additional scenario will be a pool elevation that is halfway between the SS and TAS pool elevations and will be named Intermediate Low-Dry-Pool (ILD). Starting reservoir pool will correspond to the 10-percent exceedance duration pool elevation. Reservoir inflow will be a scaled inflow design flood hydrograph. The scaled hydrograph will be developed by scaling the MH hydrograph using trial and error to produce a peak pool equal to the ILD pool.
• In-Pool Levees (Appurtenant Structure). Levees that are located in a reservoir and are assigned within the NID, will have an additional scenario equal to a loading at the top of levee (TOL). Starting reservoir pool will correspond to the top of active storage pool elevation. Reservoir inflow will be a scaled inflow design flood hydrograph. The scaled hydrograph will be developed by scaling the MH hydrograph using trial and error to produce a peak pool equal to the TOL pool. In some cases, an in-pool levee may be modeled more appropriately with the MMC SOPs for levees. This may be the case for an in-pool levee that has a loading source other than (or in addition to) the pool, long levees where breach location may be critical, or high consequence potential. The decision of which SOP to follow is made in conjunction with the modeling lead, the district, and RMC.
• Site-specific scenarios that may impact consequence estimation may also be considered on a case-by-case basis; these scenarios will be reviewed and approved by the MMC technical lead.
• Appurtenant Structures. Appurtenant structures are relatively common among USACE dams. Examples of such structures include upstream/within-pool levees protecting communities from high pool conditions or wing dikes and saddle dikes that act as an extension of the damming surface away from the main embankment. All dams to be modeled by the MMC should be screened for the inclusion of appurtenant structures. Reference to the NID, the WCM, and/or discussion with the DSPM of the home district are among the actions that can be taken to determine whether appurtenant structures exist for a project. The determination about modeling an appurtenant structure is made based on the consequence zone. Appurtenant structures with consequence zones separate of any other appurtenant structure or dam will have its own NIDID and be modeled. Any of the base scenarios for the main dam that significantly load the appurtenant structure should be modeled to determine potential consequences. For some cases this may only include the MH scenario depending on the toe elevation of the appurtenant structure.
• Dams Located Downstream of the Studied Dam. Downstream dams should be operated according to the WCM for the dam. If modeled scenarios on the dam being assessed create conditions that exceed the storage or discharge capacity of the downstream dam(s) and overtopping occurs, the downstream dam(s) should be considered for breach. Should conditions warrant consideration for cascading breaches for a given loading condition an additional model simulation and associated consequences will be developed. The MH, and top of active storage (TAS) scenarios will be the only scenarios considered for a cascading breach scenario. IH, SS, and NH are not considered for cascading breach. Breach of the downstream dam will occur at the peak overtopping elevation unless the overtopping exceeds five feet, in which case the breach will be triggered at a maximum of five feet of overtopping. The non-cascading breach response will be considered as the official scenario for a given loading condition, but modeling assumptions and consequences for the cascading scenario will be documented as additional information in the model report and CTS spreadsheet. Cascading breach is not required for small water supply or run of river navigation dams that would not increase consequences if breached.

3.4.4.1 Flow Files for Modeling, Mapping, and Consequences Flood Risk Management Dam Scenarios

• Modeling of dam breach and non-breach scenarios requires inflow flood hydrographs for areas both upstream of the dam and inflow hydrographs for downstream tributary reaches. Inflow flood conditions into the reservoir and coincident tributary flow into the modeled reach downstream of the dam can have a significant impact on consequence determination in a dam breach analysis. In addition to consequence estimation, these inflow hydrographs should be used to ascertain the appropriateness of the model for future use in Risk Analyses (RAs). Presented below are inflow conditions, antecedent pool levels, and downstream boundary conditions for MMC scenarios.
• Inflow Hydrographs. Inflow hydrographs and reservoir operations for the study dam will be consistent between breach and non-breach for all scenarios. Dams located downstream may be modeled with different operational procedures between breach and non-breach scenarios if up-to-date emergency release procedures exist in the respective WCM.
• Inflow hydrographs for reservoirs upstream of the study dam are presented for each scenario below:
• MH Pool. Inflow Design (IDF) Flood hydrograph (e.g., PMF, SDF, SPF, etc.).
• IH Pool. Scaled IDF hydrograph producing an elevation that corresponds to maximum discharges approximately halfway between maximum TAS discharge and maximum MH pool discharge with gate operations defined by the WCM
• TAS. Scaled IDF hydrograph producing the required TAS elevation under normal gate operations.
• SS. Scaled IDF hydrograph producing the one-percent exceedance duration pool under normal gate operations.
• NH Pool. Constant inflow hydrograph as required to produce the 10-percent exceedance duration pool under normal gate operations.
• Hydrograph ordinates will be scaled by a constant factor through an iterative process until the desired pool elevation for the particular scenario is obtained.

NOTE

The MMC will use the district-provided IDF which for most cases will factor in the operation of upstream reservoirs. For the base MMC scenarios, the MMC will not consider alternate operations of the upstream reservoirs other than what was done in the computation of the IDF.

• Antecedent Pool Levels. Initial pool levels for MMC scenarios will come from exceedance duration curves obtained from the USACE district based on current operational procedures and most current pool data available. This relationship may be published in the WCM. If the WCM was not published within a reasonable timeframe, then a duration curve can be developed using the period of record daily stage data received from the district. For additional guidance, see Appendix 3.1.1.
• Antecedent pool levels for reservoirs upstream of the study dam are presented for each scenario below:
• MH: Pool elevation used in routing the IDF hydrograph. If an antecedent pool is not provided, the pool should be initially set to the TAS pool and then adjusted until the district-provided MH pool is met.
• IH: Same initial pool as that used for the MH scenario
• TAS: 10-percent exceedance duration pool level.
• SS: 10-percent exceedance duration pool level.
• NH: 10-percent exceedance duration pool level.
• Downstream Flow Conditions. Lateral or uniform inflow hydrographs shall exist in the model at significant confluences to produce base flow conditions downstream of the study dam. The magnitude of the inflow shall be consistent with the scenario being modeled. For instance, without detailed information, the base flow condition will be defined by stream conditions ranging from average daily releases for NH and SS, to channel capacity for TAS and IH). The values will be input as a constant inflow based on stream gage statistics or appropriate data based on availability. Gage data used for calibration can also be used for developing statistics or obtaining reasonable values. For the MH scenario, the most up-to-date data available shall be used for defining lateral or uniform inflow hydrographs, such that the data is readily available or can be determined within a reasonable timeframe such that the expected modeling schedule does not require adjustment. Multiple methods to develop lateral or uniform inflow hydrographs shall be used to determine model sensitivity to different flow rates. These methods include:
• Use of a readily available runoff model for the reach utilizing appropriate rainfall data coincident with the reservoir inflow event
• Use of 50-percent or 10-percent annual chance exceedance flow rates (either peak flow rates or duration specific) through Bulletin 17C techniques or appropriate regional regression equations
• Use of the residual runoff method and an appropriate spatial distribution, and rainfall reduction factors that are coincident with the reservoir inflow event
• Development of lateral inflow based on the highest historical flow value measured along the tributary reach, but not less than bank full capacity.
• Gages should be used to calibrate the model to ensure that initial stages and flows are within an acceptable range and do not produce flooding conditions at the start of the simulation. Gage data may be obtained from the sites listed below:
• USGS: http://waterwatch.usgs.gov/?id=ww_current
• USACE: http://www.rivergages.com/
• NWS: http://water.weather.gov/ahps/
• For additional guidance on how to incorporate gage rating data into HEC-RAS for calibration, see the HEC-RAS User's Manual.
• Initial Flow Conditions. Initial flow at a cross section should be equal to the added first flow ordinates from the inflow hydrographs upstream of that particular location. Initial flows should only be set at flow change locations in the model.
• Gate Operations for Modeling, Mapping, and Consequences Models. Gate operations will correspond to the WCM for the given dam. Elevation control and rules are the preferred methods of operation; however, certain scenarios will require the use of time series control.
• Downstream Boundary Conditions. Downstream boundary conditions will be set to appropriately model conditions at the downstream extent of the study. Normal depth will generally be used for models with typical riverine characteristics at the downstream boundary. For areas that are affected by tidal influences, the downstream boundary condition should be set to the MHW in that area. The MHW can be found for several stations on NOAA's Tide and Currents website (http://tidesandcurrents.noaa.gov/stations.html?type=Datums). Other boundary conditions may be used with approval from the project lead.

3.4.4.2 Plan Files for Modeling, Mapping, and Consequences Flood Risk Management Dam Scenarios

Every scenario modeled for the MMC Production Center will have a separate HEC-RAS plan file. The plan file contains data designating the geometry and flow files associated with the model scenario. The plan file also contains information on the simulation time window and computational settings. Breach parameters are also stored within the plan file for breach scenarios. Each model created for the MMC Production Center will contain a plan file for each of the ten scenarios (five breach and five non-breach) presented in the Table 3-7.

Plan Naming Conventions. The unsteady flow file presented in the right had column should be used in conjunction with the geometry to create a plan which represents an MMC Scenario.

• Simulation Times. Computational times for the MMC Production Center model plans should follow the following specifications:
• Computation intervals are generally to be set between 1-60 seconds in order to satisfy the courant condition. The Advanced Time Step Control option in HEC-RAS allows for the use of a dynamic time step throughout simulations using one of two criteria: based upon a maximum/minimum Courant number or using a time series of divisors at defined dates/times. Using this feature may decrease the overall HEC-RAS computation time by utilizing a smaller time step only when depths and velocities are changing rapidly; at all other times, a larger time step can be utilized.
• Hydrograph output interval should be set to ensure the peak stage and inflow is captured in the output hydrographs. Typically this should be 5-15 minutes. For each scenario, the breach and non-breach output intervals must match.
• Detailed output interval can be set to larger intervals compared to the hydrograph and mapping output intervals; however, there may be cases where a smaller detailed output interval could be needed to help troubleshoot problems. Small detailed output intervals can produce longer post-processing times and very large output files that can sometimes become unmanageable.
• The mapping output interval should be set to ensure that arrival time information is appropriately captured. This interval directly affects the arrival times utilized in the modeling of consequences. The mapping output interval matches the hydrograph output interval.
• Simulation Start Time. All simulations should begin February 2, 2099 at 2400 hours to avoid confusion with actual future flood events and maintain consistency between models.
• Simulation End Time. Simulations should run until the peak of the flood wave has been routed through the model extent and WS elevations at the most downstream cross section have begun to recede. The simulation end time should be the same for both the breach and non-breach scenarios.
• Stage and Flow Output Locations. For MMC dam analysis, stage and flow output locations are required at a minimum for the main study reach. This data is needed to produce the timing data for the facing profile pages in the MMC map books.
• For additional guidance, see the HEC-RAS User's Manual.

3.4.5 Navigation Dam (Not Screened Out) Scenario-Pool Relationships

The USACE has established a standard set of five modeling scenarios covering a range of pool elevations, representing minimum and maximum normal operating conditions as well as select extreme loading conditions designed to capture the upper limit of potential downstream consequences (Figure 3-5).

Figure 3-5. Navigation Dam (Not Screened Out) Scenario-Pool Relationships

• Maximum High (MH) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for the MH pool water level. The most current design flood hydrograph, antecedent pool, and routing will be provided by the district. If an antecedent pool is not provided, the pool should be initially set to the navigation pool channel capacity (NPC) pool and then adjusted until the district-provided maximum pool is met. If the antecedent event causes downstream flooding, additional coordination with the consequence team member is recommended. The MH scenario corresponds to the maximum design flood elevation. This scenario is associated with the occurrence of an extreme flood event and routed using the emergency operation procedures from the WCM. The MH scenario typically results in the greatest areal extent, depth of downstream inundation, and total economic consequences.
• Intermediate High (IH) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for the IH pool water level. Starting reservoir pool will correspond to the same initial pool as used for the MH scenario. Reservoir inflow will be a scaled IDF hydrograph. The scaled hydrograph will be developed to produce a peak pool that corresponds to a downstream maximum peak discharge approximately halfway between the maximum NPC peak discharge and the maximum MH peak discharge. Gate operation procedures from the latest water control manual will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates for breach and non-breach conditions.
• This scenario is associated with the occurrence of an unusual flood event. It results in significant increase in discharge above downstream channel capacity based on the physical properties of the project and/or operation procedures from the latest WCM.
• Navigation Pool Channel (NPC) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for the navigation pool with discharges equal to the downstream channel capacity. Starting reservoir pool will correspond to the normal navigation (NN) pool elevation. Reservoir inflow will be a scaled IDF hydrograph. The scaled hydrograph will be developed to produce a peak pool equal to the NPC loading. Gate operation procedures from the latest WCM will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates; however, computed consequences are not expected from the non-breach scenario, since non-damaging releases are assumed for the NPC condition.
• The NPC scenario corresponds to the highest elevation which can be obtained under normal regulated operating conditions that allows releases equal to the downstream channel capacity. This scenario may or may not be associated with the occurrence of a flood event.
• Intermediate Low (IL) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for an IL pool elevation. Starting reservoir pool will correspond to the NN pool elevation. Reservoir inflow will be a scaled IDF hydrograph. The scaled hydrograph will produce downstream peak discharges approximately halfway between the maximum NN peak discharge and the maximum NPC peak discharge. Gate operation procedures consistent with the latest WCM will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates; however, computed consequences are not expected from the non-breach scenario, since non-damaging releases are assumed for the LL condition.
• The IL scenario is obtained under normal regulated operating conditions. Depending on the navigation dam, this scenario may or may not be associated with a flood event.
• Normal Navigation (NN) Pool. An unsteady flow simulation for non-breach and breach scenarios will be modeled for a NN pool level under normal operating conditions. Starting reservoir pool will correspond to the NN pool elevation. Reservoir inflow will be a constant inflow hydrograph as required to produce the NN pool under normal gate operations. Gate operation procedures consistent with the latest WCM will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates. A consequence analysis simulation for the non-breach condition is not necessary since non-damaging releases result from the NN pool event.
• This scenario represents a normal pool condition. This scenario is not associated with the occurrence of a flood event.
• The hydraulic and hydrologic loading conditions for each breach scenario to be analyzed for navigation dams are listed in Table 3-9.

3.4.5.1 Flow Files for Modeling, Mapping, and Consequences Navigation Dam Scenarios

Modeling of dam breach and non-breach scenarios requires inflow flood hydrographs for areas both upstream of the dam and inflow hydrographs for downstream tributary reaches. Inflow flood conditions into the reservoir and coincident tributary flow into the modeled reach downstream of the dam can have a significant impact on consequence determination in a dam breach analysis. In addition to consequence estimation, these inflow hydrographs should be used to ascertain the appropriateness of the model for future use in RAs and IESs. Presented below are inflow conditions, antecedent pool levels, and downstream boundary conditions for MMC scenarios.

• Inflow Hydrographs. Inflow hydrographs and reservoir operations for the study dam will be consistent between breach and non-breach for all scenarios. Dams located downstream may be modeled with different operational procedures between breach and non-breach scenarios if up-to-date emergency release procedures exist in the respective WCM.
• Inflow hydrographs for reservoirs upstream of the study dam are presented for each scenario below:
• MH Pool. (IDF) Inflow Design Flood hydrograph (e.g., PMF, SDF, SPF, etc.).
• IH Pool. Scaled IDF hydrograph producing an elevation that corresponds to discharges approximately halfway between channel capacity and maximum MH discharges with gate operations defined by the WCM.
• NPC Capacity. Scaled IDF hydrograph producing the required navigation pool elevation under normal gate operations that produces discharges equal to the downstream channel capacity.
• IL Pool. Scaled IDF hydrograph producing a navigation pool under normal gate operations that corresponds to a discharge approximately halfway between the maximum NN pool discharge and the maximum NPC discharge.
• NN Pool. Constant inflow hydrograph as required to produce the NN pool under normal gate operations.

Hydrograph ordinates will be scaled by a constant factor through an iterative process until the desired pool elevation for the particular scenario is obtained.

NOTE

The MMC will use the district-provided IDF which for most cases will factor in the operation of upstream reservoirs. For the base MMC scenarios, the MMC will not consider alternate operations of the upstream reservoirs other than what was done in the computation of the IDF.

• Antecedent Pool Levels. Initial pool levels for MMC scenarios will come from exceedance duration curves obtained from the USACE district based on current operational procedures and most current pool data available; typically, this information is located in the WCM. If the WCM was not published within a reasonable timeframe, then a duration curve can be developed using the period of record daily stage data received by the district.
• Antecedent pool levels upstream of the study dam are presented for each scenario below:
• MH Pool: Pool elevation used in routing the IDF hydrograph. If an antecedent pool is not provided, the pool should be initially set to the TAS pool and then adjusted until the district provided MH pool is met.
• IH Pool: Same initial pool as that used in the MH scenario.
• NPC Pool: NN pool level.
• IL Pool: NN pool level.
• NN Pool: NN pool level.
• Downstream Flow Conditions. Lateral or uniform inflow hydrographs shall exist in the model at significant confluences to produce base flow conditions downstream of the study dam. The magnitude of the inflow shall be consistent with the scenario being modeled. For instance, without detailed information, the base flow condition will be defined by stream conditions ranging from average daily releases for NN and IL, to channel capacity for NPC and IH. The values will be input as a constant inflow based on stream gage statistics or appropriate data based on availability. Gage data used for calibration can also be used for developing statistics or obtaining reasonable values. For the MH scenario, the most up-to-date data available shall be used for defining lateral or uniform inflow hydrographs, such that the data is readily available or can be determined within a reasonable timeframe such that the expected modeling schedule does not require adjustment. Multiple methods to develop lateral or uniform inflow hydrographs shall be used to determine model sensitivity to different flow rates. These methods include:
• Use of a readily available runoff model for the reach utilizing appropriate rainfall data coincident with the reservoir inflow event
• Use of 50-percent or 10-percent annual chance exceedance flow rates (either peak flow rates or duration specific) through Bulletin 17C techniques or appropriate regional regression equations
• Use of the residual runoff method and an appropriate spatial distribution, and rainfall reduction factors that are coincident with the reservoir inflow event
• Development of lateral inflow based on the highest historical flow value measured along the tributary reach, but not less than bank full capacity.
• Gages should be used to calibrate the model to ensure that initial stages and flows are within an acceptable range and do not produce flooding conditions at the start of the simulation. Gage data may be obtained from the sites listed below:
• USGS: http://waterwatch.usgs.gov/?id=ww_current
• USACE: http://www.rivergages.com/
• NWS: http://water.weather.gov/ahps/ .

For additional guidance on how to incorporate gage rating data into HEC-RAS for calibration, see the HEC-RAS User's Manual.

• Initial Flow Conditions. Initial flow at a cross section should be equal to the added first flow ordinates from the inflow hydrographs upstream of that particular location. Initial flows should only be set at flow change locations in the model.
• Gate Operations for Modeling, Mapping, and Consequences Models. Gate operations will correspond to the WCM for the given dam. Elevation control and rules are the preferred methods of operation; however, certain scenarios will require the use of time series control.
• Downstream Boundary Conditions. Downstream boundary conditions will be set to appropriately model conditions at the downstream extent of the study. Normal depth generally will be used for models with typical riverine characteristics at the downstream boundary. For areas that are affected by tidal influences the downstream boundary condition should be set to the MHW in that area. The MHW can be found for several stations on NOAA's Tide and Currents website (http://tidesandcurrents.noaa.gov/stations.html?type=Datums). Other boundary conditions may be used with approval from the project lead.

3.4.5.2 Plan Files for Modeling, Mapping, and Consequences Navigation Dam Scenarios

Every scenario modeled for the MMC Production Center will have a separate HEC-RAS plan file. The plan file contains data designating the geometry and flow files associated with the model scenario. The plan file also contains information on the simulation time window and computational settings. Breach parameters are also stored within the plan file for breach scenarios. Each model created for the MMC Production Center will contain a plan file for each of the ten scenarios (five breach and five non-breach) presented in the table that follows.

Plan Naming Conventions. The unsteady flow file presented in the right had column should be used in conjunction with the geometry to create a plan which represents an MMC Scenario.

Table 3-10. Modeling, Mapping, and Consequences Plan and Flow File Naming Conventions for Navigation Dams

Event	RAS Plan Name	Short ID	Unsteady Flow Data Name
1	Maximum High Pool-Breach	MH Breach	Maximum High Pool
2	Maximum High Pool-Non-breach	MH Non-breach	Maximum High Pool
3	Intermediate High-Breach	IH Breach	Intermediate High Pool
4	Intermediate High-Non-breach	IH Non-breach	Intermediate High Pool
5	Nav Pool Channel Capacity-Breach	NPC Breach	Nav Pool Channel Capacity
6	Nav Pool Channel Capacity-Non-breach	NPC Non-breach	Nav Pool Channel Capacity
7	Intermediate Low Pool-Breach	IL Breach	Intermediate Low Pool
8	Intermediate Low Pool-Non-breach	IL Non-breach	Intermediate Low Pool
9	Normal Nav Pool-Breach	NN Breach	Normal Nav Pool
10	Normal Nav Pool-Non-breach	NN Non-breach	Normal Nav Pool

• Simulation Times. Computational times for the MMC Production Center model plans should follow the following specifications:
• Computation intervals are generally to be set between 1-60 seconds to satisfy the courant condition. The Advanced Time Step Control option in HEC-RAS allows for the use of a dynamic time step throughout simulations using one of two criteria: based upon a maximum/minimum Courant number or using a time series of divisors at defined dates/times. Using this feature may decrease the overall HEC-RAS computation time by utilizing a smaller time step only when depths and velocities are changing rapidly; at all other times, a larger time step can be utilized.
• Hydrograph output interval should be set to ensure the peak stage and inflow is captured in the output hydrographs. Typically, this should be 5-15 minutes. For each scenario, the breach and non-breach output intervals must match.
• Detailed output interval can be set to larger intervals compared to the hydrograph and mapping output intervals; however, there may be cases where a smaller detailed output interval could be needed to help troubleshoot problems. Small detailed output intervals can produce longer post-processing times and very large output files that can sometimes become unmanageable.
• The mapping output interval should be set to ensure that arrival time information is appropriately captured. This interval directly affects the arrival times utilized in the modeling of consequences. The mapping output interval matches the hydrograph output interval.
• Simulation Start Time. All simulations should begin February 2, 2099 at 2400 hours to avoid confusion with actual future flood events and maintain consistency between models.
• Simulation End Time. Simulations should run until the peak of the flood wave has been routed through the model extent and WS elevations at the most downstream cross section have begun to recede. The simulation end time should be the same for both the breach and non-breach scenarios.
• Stage and Flow Output Locations. For MMC dam analysis, stage and flow output locations are required at a minimum for the main study reach. This data is needed to produce the timing data for the facing profile pages in the MMC map books.

For additional guidance, see the HEC-RAS User's Manual.

3.5 Breach Parameter Estimation for Modeling, Mapping, and Consequences Models

Breach parameters for the breach scenarios should follow the guidance presented below. It is recommended that the modeler successfully execute a non-breach scenario model run before running the breach scenario.

If the project has both an earthen and a concrete section, conduct a MH breach scenario on each. The results are used as a consideration when determining which segment to model further.

• Earthen Dams. All earthen dams will use the <MMC_Breach_Parameters.xls> spreadsheet to calculate breach formation time (t_f) and breach bottom width (W_b). This spreadsheet calculates four sets of breach parameters using the following four regression equations: MacDonald and Langridge-Monopolis, Froehlich (1995a), Froehlich (2008), and Von Thun & Gillette. Because each scenario modeled for MMC will have different loading conditions, a separate tab within the spreadsheet has been developed for each scenario. MMC guidance for using the breach spreadsheet is as follows:
• Breach invert should be set to the elevation of the downstream streambed for all scenarios unless specified differently in the project kickoff meeting. The breach invert should be consistent across all breach scenarios.
• Do not average breach parameters computed by the spreadsheet for use in the model. Select one set of equations that seem reasonable using engineering judgment. The selected equation should be used for all breach scenarios at the dam.
• Use the breach formation time that was calculated by the selected equation.
• Formation time of breach should typically fall in the range of 0.1-4 hours. However, longer formation times may be reasonable, especially for dams with significant volume.
• Breach width should typically be one to five times the height of dam (check the bottom width of the dam between abutments; in some cases, this may limit the breach bottom width).
• HEC-RAS breach data editor requirements for the MMC are:
• Breach progression should utilize the sine wave option. For additional guidance, see TD 39, Using HEC-RAS for Dam Break Studies.
• Manning's "n" values immediately downstream of the dam should be increased in order to simulate accumulated debris and turbulence in the channel.
• Breach mode is to be piping for scenarios not overtopping the dam. The piping elevation should be set to the breach invert.
• It is recommended the trigger for breach scenarios be set to "Set Time" in the HEC-RAS Breach Data Editor. The time should correspond to the peak water surface elevation achieved in the equivalent non-breach scenario and for navigation dams, the time should correspond to the time of peak flow for the equivalent non-breach scenario. However, the NH pool for flood risk management dams and NN pool for navigation dams breach initiation times will be set to 03 FEB 2099 at 2400 since they will maintain a steady pool and flow for the duration of the non-breach scenario.
• Concrete Dams. All gravity concrete dams are to have a breach width equal to one to six monoliths of the study dam. For arch dams, assume the entire dam is destroyed. The breach width of an arch dam is the distance between the abutments.

3.6 HEC-RAS Model Execution and Model Output

Models developed for the MMC Production Center should compute all scenarios with minimal computational error. Instability in unsteady HEC-RAS model runs is probable during initial simulation. It is likely to take the modeler several iterations before instabilities are fully addressed in the model. The acceptable level of computational error is relative to the specifics of the project being modeled, but acceptable values will be addressed during the model review period and can be discussed with the production team lead.

HEC-RAS has an option to run in a mixed-flow regime mode. This mode is discouraged unless engineering judgment determines the system is a mixed-flow regime river system. If mixed flow is used for runs, then reasons for its use should be discussed in modeling portion of the documentation report. For further guidance see the HEC-RAS User's Manual.

It is recommended that the MH pool scenario be executed before other scenarios have been entered into the model. Once the model has been adjusted so that all MMC Production Center requirements are met, the modeler should enter plan and flow data for all remaining MMC scenarios.

3.6.1 HEC-RAS Model Output and Review

Once the model is stable for all scenarios, it is ready for the interim review. In order to maintain clarity in the data and reduce potential error in data interpretation the following standards on output data have been adopted by the MMC.

HEC-RAS model output is stored in model output files (.O1), HEC-Data Storage System (.DSS) format, and Hierarchical Data Format, version 5 (e.g., *.g0n.hdf and *.p0n.hdf). It is imperative that models delivered for review and ultimately delivered to mapping contain only output data for the finalized scenario runs. It is good practice, once the model has been finalized, to delete all extraneous plans and output files including the .DSS file and re-run all plans so that only HEC-RAS output associated with the 10 scenarios is maintained and ultimately delivered for review and mapping. This can also be accomplished by executing a "File/Save As" to a new location and then re-running all 10 MMC plans. Ideally, all scenarios should be written to a single DSS file rather than having a separate DSS file for each scenario. However, depending on data constraints, separate DSS files may be needed.

All stage and output locations should be selected in the model plan file under the options/stage and flow output locations. This should include any interpolated cross sections within the geometry.

Changes in flow or stage at the beginning of the model run must be addressed. These drops will create problems in the consequence and mapping stages of the MMC production process. These drops are typically caused by differences in initial flow conditions and cumulative inflows upstream of a particular location. Initial flow at a cross section should be equal to the added first flow ordinates from the inflow hydrographs upstream of that particular location. Initial flows should only be set at flow change locations in the model.

The following model output checks should be performed to ensure the model is accurately computing flows and WS elevations at all cross sections:

• Changes in WS occurring before the breach wave arrival should be removed
• All model output profiles should be reviewed for WS spikes and energy grade spikes
• Simulations should run until the peak of the flood wave has been routed downstream through the entire model extent.

3.6.1.1 Removal of Intermediate Outputs from Dataset

The final dataset should include only the relevant output from the final runs and all output from intermediate runs should be removed.

3.6.1.2 HEC-RAS Model Output Deliverable

Final MMC Production Center HEC-RAS model deliverables are listed below. File extension numbers .01 may vary from the following example. Green text should be modified for specific project.

• Name of Dam NIDID.prj
• Name of Dam MMC Geometry.g01
• Maximum High Pool-Breach.p01
• Maximum High Pool-Non-breach.p02
• Intermediate High Pool-Breach.p03
• Intermediate High Pool-Non-breach.p04
• Top of Active Storage-Breach.p05
• Top of Active Storage-Non-breach.p06
• Security Scenario-Breach.p07
• Security Scenario-Non-breach.p08
• Normal High Pool-Breach.p09
• Normal High Pool-Non-breach.p10
• Maximum High Pool.u01
• Intermediate High Pool.u02
• Top of Active Storage.u03
• Security Pool.u04
• Normal High Pool.u05
• Name of Dam MMC.DSS.

Corresponding run (.r01), output (.o01), and hdf (.p01.hdf and .g01.hdf) files should also be included. DSS files will contain only model runs required by the MMC Production Center.

The following deliverables are produced within RASMapper.

• Depth Grids: A resulting maximum depth grid must be stored to disk for each modeled scenario. This process will be accomplished using HEC-RAS RASMapper tools. The grids will be saved in the default location as a sub-folder within the HEC-RAS folder.
• Water Surface Elevation Grids: A resulting maximum water surface elevation grid must be stored to disk for each modeled scenario. This process will be accomplished using HEC-RAS RASMapper tools. The grids will be saved in the default location as a sub-folder within the HEC-RAS folder.
• Inundation Boundaries: A resulting maximum extent of inundation boundary shapefile will be stored to disk for each modeled scenario. This process will be accomplished using HEC-RAS RASMapper tools. The shapefile will be saved in the default location as a sub-folder within the HEC-RAS folder.
• HEC-RAS Geometry Shapefiles: River, cross sections, storage areas, 2D flow areas, and bank lines shapefiles should be exported from RAS Mapper and placed in a "Shapefiles" sub-folder created in the HEC-RAS folder.
• Location of Mapping Outputs: Copies of the above files/folder will be saved in the HEC-RAS folder within the MMC standard folder structure

See the HEC-RAS 2D Modeling User's Manual for further information.

3.6.2 Consequences-based Top Screening-H&H and Facilities Information Tabs

All modelers will complete the pertinent data tab, the H&H data tab, and the H&H timing tab, and fill in contact information for the modeler in the MMC contact info tab during the initial stages of the modeling process. On the pertinent data tab, the modeler will validate the values within column C, and in column H enter the date, his or her first and last name initials, and the resource where the numeric or textual value was found (e.g., 8/28/19 AB: WCM, pg. 4). If a change is made, column H should include the data that was changed (e.g., Changed from 32,000). The resource information is a critical piece of information to have during the product review stage. The modeling lead will review the completed H&H data and sign off as the reviewer in the MMC contact info tab.

The modeler should use the CTS worksheet facility info tab to fill in tabular values in the documentation report. In using this strategy, the MMC products will be consistent for the district customer use.

3.6.3 Modeling Documentation

All models completed for MMC will have a corresponding Hydraulic Modeling and Consequences Summary (HMCAS). This report summarizes pertinent aspects of the modeling effort associated with each scenario. Within the report is a discussion of the inputs needed by the modeler. The modeler should fill in the change table on page ii of the report indicating the date the report was developed or changed.

The HMCAS is housed in the MMC Team SharePoint project folder because multiple members of the MMC production team collaborate to prepare the report throughout the production process. Marked up and edited versions of the report are to be maintained on SharePoint at all times.

Pertinent model data will be inserted within the HMCAS that is on the MMC Sharepoint website and provided for both the interim and compliance review.

A summary of model assumptions and difficulties should be included within the HMCAS to support and facilitate initial review.

3.6.4 Reporting Breach Initiation Time

In order to create consistency in reported breach times by all members of the MMC production team a standardized method for reporting breach initiation time has been adopted. The breach time for a particular scenario is found by opening the HEC-RAS models and selecting the "View Runtime Messages" in the options menu of the breach plan file. The time of breach initiation will be reported in the runtime messages for the selected breach plan. The NH pool for flood risk management dams and NN pool for navigation dams breach initiation times will be set to 03 FEB 2099 at 2400.

3.6.5 Reporting Breach Wave Arrival Time

The breach wave arrival time for MMC is defined as the time at which increased WS elevation at a given point is the result of a breach of an upstream impoundment structure such as a dam. The breach wave arrival time is calculated by comparing hydrographs at a given location for breach and non-breach scenarios. The conditions of the non-breach scenario should only differ from the breach scenario in the fact that the structure in question breaches, increasing the flow capacity at its location. The two hydrographs, plotted together should be identical until the time at which the WS elevation in the breach hydrograph rises above the non-breach hydrograph, indicating increased flows as a result of the breach. A difference of two feet between hydrograph values has been chosen as the indicator value for the breach wave arrival.

3.6.6 Model Review Processes

Model review is an extremely important part of the MMC production process. Several review steps are required to ensure that models consistently represent all project scenarios and that the model will accurately represent the consequences associated with each scenario. A review checklist will be used to track comments regarding aspects that are checked through the review process. The review checklist will live with the model and be used throughout the entire review process (i.e., interim review and final review). A copy of the review checklist is available in the SharePoint project folder.

The model itself will go through a series of three reviews (listed below) during the production process.

All MMC products for review will be delivered via MMC share drive or the project hard drive.

• Initial Progress Review Web Meeting
• Interim Review. The deliverable will include the following:
• Working model with standard MMC scenarios as specified in SOP Section 3.4.4 Flood Risk Management Dam Scenarios-Pool Relationships or 3.4.5 Navigation Dam (Not Screened Out) Scenarios-Pool Relationships
• Output files for breach scenarios and non-breach scenarios. Model reviewer will ensure floodplain inundations for all scenarios are accurately representing flooding conditions
• Modeling sections of the report that are pertinent to review at this level should be filled out and saved. Reports are worked from the project folder on the MMC Team SharePoint site. Reviewer to verify modeling difficulties and assumptions write-up. See Section 3.4.2.
• The following CTS worksheet tabs should be filled out: MMC Contact Info, Pertinent Data, and H&H Data.
• Master review checklist with modeler comments section completed for all comments. This will ensure all aspects of the model to be reviewed have been addressed by the modeler.
• Breach parameter worksheet.
• WCM(s) and other reference material.
• Compliance Review. The deliverable will include the following:
• Working model with standard MMC scenarios as specified in Section 3.4.4 Flood Risk Management Dam Scenarios-Pool Relationships or 3.4.5 Navigation Dam (Not Screened Out) Scenarios-Pool Relationships
• Output files for all breach scenarios and non-breach scenarios
• Modeling sections of the report that are pertinent to review at this level should be filled out and saved. Reports are worked from the project folder on the MMC Team SharePoint site. Reviewer to verify modeling difficulties and assumptions in write-up. See SOP Section 3.4.2.
• Previously completed CTS worksheets should be updated as appropriate, and the H&H Timing worksheet should be completed
• Master review checklist with Resolution of Reviewer Comments by Modeler section completed for all comments
• Breach parameter worksheet
• WCM(s) and reference material.
• District Model IQR. Once the compliance review is complete, the Modeling Technical Lead will make the decision if there are additional items that need to be addressed or if the model is complete and ready to proceed to district review. If no additional review is needed the model will be sent by the modeling technical lead to the district DSPM for IQR. At this juncture, depth grids should be loaded to the USACE Inundation Data Viewer (for additional information, see the guide Uploading Data for Dams). The following steps will be completed for preparation and result of model IQR:
• Model data will be reviewed and standardized within the MMC folder structure displayed in Figure 2-1.
• All data will be uploaded via a transfer system available to the district by the modeling team lead.
• Modeling technical lead packages the preCTS worksheet, IQR checklist, and model data within a zip file and notifies district by email that model is available to be reviewed for a designated time period.
• Comments are posted by the district to the MMC CoP SharePoint IQR Comment Database.
• Model data will be updated based on IQR district and peer review comments.

3.6.7 Final Model Approval

The model team lead will submit HMCAS to the modeling technical lead after a technical review of the documentation and CTS is accomplished. The model reviewer will sign off on the CTS worksheet MMC Contacts tab verifying a model review has been accomplished. The technical lead will sign off on the CTS as the reviewer in the contacts tab. The following steps are taken to officially finalize a modeling effort:

• The model reviewer and model technical lead will sign off on the CTS worksheet MMC Contacts tab verifying a model review has been accomplished.
• The technical lead will conduct a final format review to standardize project data within the MMC folder structure displayed in Figure 3-6.
• The model team lead will verify that the latest modeling data has been uploaded to the RMC File Share production folder (E. Final Model).
• Modeling technical lead notifies the documentation lead, consequence lead, and mapping team lead by email that the final model is available to begin consequences, mapping, and documentation development
• The documentation report will undergo a technical edit by the documentation team before being finalized. The modeling production process is not complete until the documentation has been fully reviewed and submitted to the documentation and mapping teams.
• If comments from the mapping peer review significantly change modeling or consequence estimates, the model technical lead or model team lead will be immediately notified to incorporate corrections.

3.6.8 Model Deliverables

The peer review and IQR comments will be incorporated into the model data. Care should be given to assure that both the documentation report and CTS are consistent with model data. Once the district model IQR and peer reviews are complete and all edits have been made, the modeling technical lead will make the decision if there are additional items to be addressed. If no additional review is needed, the model is declared final by modeling technical lead. Modeling data should then be packaged and uploaded to the RMC file share production folder (E. Final Model). If a project hard drive has been used, its contents will be moved to file share at this point. See Figure 2-1 for MMC delivery file structure.

3.6.8.1 HEC-LifeSim Deliverables

HEC-LifeSim consequence modeling requires the final HEC-RAS model itself with the terrain and RAS Mapper grid outputs included. The only extra step required is to create a folder within the HEC-RAS model that includes the model geometry exported from RAS Mapper. These files include shapefiles for items such as the stream centerline, cross sections, storage areas, bank lines, and 2D storage areas.

The workflow process for delivering data to the consequences team is as follows:

• Go to the SharePoint MMC Project Reports folder for the project and verify the following CTS worksheets have been completed.
• Put the contact info on the Contacts tab
• Fill out the H&H data tab completely
• Fill out the H&H timing tab completely
• Fill out the Pertinent Data tab completely
• If changes are made to existing data, add a source note next to documentation's.
• Change status to H&H Added
• Alert modeling team leads, consequences team leads, and economist that data is ready.

3.6.8.2 Geographic Information System Modeling Deliverables

GIS modeling deliverables will include files and data used in interfacing GIS data with the HEC-RAS model. Final GIS deliverables will include final maps, DEMs used in creating models, supplemental ground surface data, pre-HEC-RAS geodatabases, pre-HEC-RAS GIS export files used in model creation, and any additional shapefiles used in modeling.

3.6.8.3 HEC-RAS Deliverables

The final HEC-RAS deliverable will contain the final model with the file structure (Figure 2-1).

3.6.8.4 Reference Material

The reference material deliverable is to contain all materials used in model development that do not fall under the GIS_Modeling folder. All data supporting the model should be included. This may include, but is not limited to, the following:

• Existing models
• Data collected from the district
• Hydrology data
• Period of record (POR) data

3.6.8.5 Report Deliverable

Go to the SharePoint MMC Project Reports folder for the project and verify the modeling portion of the associated project report is complete with all edits from previous review incorporated. Modeling data is required in the HMCAS, HMCAS NAV, and ASH.

3.6.8.6 MMC Project Overview PowerPoint Presentation

The MMC project handoff PowerPoint is used to present hydraulic model findings overview. The PPT template is in the project folder on the Team SharePoint project folder.

PPT is filled in by the modeler following model district IQR.

Section 4 - Consequences

This section summarizes the process performed by the consequences team member once the consequences team receives modeling internal deliverables.

Specific how-to instruction documents for much of the consequences work can be found on the Consequences Wiki system on the MMC Team SharePoint site:

https://team.usace.army.mil/sites/NWK/pdt/MMC/consequences/

4.1 Structure Inventory

The primary structure inventory is developed from the USACE National Structure Inventory (NSI). The NSI is a data service with a base dataset containing estimated information regarding the locations, building types, population, values, and other relevant information for all residential, commercial, industrial, agricultural, public and private structures across the nation. The base version 2 dataset developed in 2019 utilizes parcel data, Census data, Microsoft building footprints, and several other sources that serve as a basis for estimating flood hazard consequences. Population and structure values are estimated from a variety of sources, but are intended to reflect 2017 population levels and 2018 price levels.

The NSI is clipped to the study area. The population and dollar values are indexed from their base year to the most recent year available. If possible, structures within the highest non-damaging inundation zone are redistributed outside of that zone.

4.1.1 Emergency Planning Zones

Emergency planning zones (EPZs) are based on the study area boundary and include polygons which delineate the in-pool area and any downstream double warning area. This is accomplished by combining the study area with the non-breach inundation boundary (typically the MH and IH non-breach scenarios). When double warning is not required (typically TAS and lower), any EPZ file can be used. If multiple scenarios with different non-breach inundation areas require double warning, those scenarios use separate EPZs.

4.1.2 Damage Reaches Shapefile

A damage reaches polygon shapefile is developed in order to aggregate the consequence results to specific damage reaches in the simulation. The damage reaches polygon delineates the following six reaches: in-pool, 0-3 miles, 3-7 miles, 7-15 miles, 15-60 miles, and greater than 60 miles.

4.1.3 Town/City Area Shapefile

A nationwide town/city area shapefile is intersected with the study area. The resulting polygons are extracted to a new file and used in the simulations to aggregate consequence results.

4.1.4 Road Network and Evacuation Destinations

Evacuation on roads will typically not be modeled on a standard MMC dam breach assessment. Exceptions may be made when evacuation will be a known risk driver.

4.1.5 Consequence Model Parameters

Figure 4-1. Conceptual diagram illustrating the flood warning and evacuation timeline.

4.1.6 Hazard Identification Relative Time (Alternative Parameter)

The hazard identification value is the time, in hours, from the imminent hazard defined by the selected hydraulic data. Typically, the hazard is identified relative to breach initiation time. There are two different warning scenarios with different ranges of hazard identification time: minimal warning and ample warning. Minimal warning scenarios have the hazard identification relative time set as a uniform distribution between two hours prior to breach and the time of breach (-2 to 0 hours). Ample warning scenarios have the hazard identification relative time set as a uniform distribution between six hours prior to breach and two hours prior to breach (-6 to -2). In-pool areas and non-breach areas on double warning scenarios are set at least 72 hours prior to the simulation start in order to allow for maximum mobilization. Warning times for in-pool and non-breach zones should be in a 24-hour increment relative to the breach in order to maintain an equivalent daytime/nighttime population distribution in the results.

4.1.7 Hazard Communication Delay (Alternative Parameter)

The hazard communication delay is the time it takes from when the hazard is identified to when the EPZ representatives are notified. For example, if a breach occurs when no one is observing the project, the emergency managers could be notified one hour after the hazard is identified. The hazard communication delay is set as a uniform distribution between 0.01 to 0.5 hours.

4.1.8 Warning Issuance Delay (Emergency Planning Zone Parameter)

The warning issuance delay is the time it takes from when the emergency managers receive the notification of the imminent hazard to when they issue an evacuation order to the public. The warning issuance delay is set at the preset configuration of Preparedness Unknown, which utilizes a Lindell uncertainty distribution. The delay is randomly sampled from 0-6 hours, but is positively skewed such that results from 0-1.5 hours are more likely.

4.1.9 Warning Diffusion/First Alert (Emergency Planning Zone Parameter)

The first alert parameter defines the warning diffusion curve for daytime and nighttime. The diffusion curve represents the rate at which the PAR receive a first warning alert over time relative to the hazard identification. The first alert curves are set at the preset configuration of Unknown, which samples from a uniform uncertainty distribution where the percent of the PAR warned increases up to 100 percent just after 1.5 hours for the upper bound and 6 hours for the lower bound.

4.1.10 Mobilization/Protective Action Initiation (Emergency Planning Zone Parameter)

The protective action initiation (PAI) parameter defines the mobilization curve. The PAI curve represents the percentage of the population which will take protective action over time from when the first alert is received. For areas downstream of the dam the PAI/mobilization curve is set at the preset configuration of Preparedness: Unknown/Perception: Unknown which samples a uniform uncertainty distribution with maximum mobilization rates between 83 percent and 100 percent after 72 hours. For in-pool areas, the curve is set at the preset Preparedness: Unknown/Perception: Likely to Impact which samples a uniform uncertainty distribution with maximum mobilization rates between 94 percent and 100 percent after 72 hours.

4.1.11 Number of Iterations (Simulation Parameter)

The number of iterations determines the number of Monte-Carlo iterations the model will run for each event. The number of iterations is typically set at 1,000, although this can be changed to accommodate long run times if necessary.

4.1.12 Results Summary Polygon (Simulation Parameter)

The results summarization polygons should include the damage reach polygon shapefile and the town/city area shapefile.

4.2 Running the Consequences Model

The consequences model includes Monte Carlo simulations utilizing uncertainty around public warning issuance, warning diffusion, and protective action initiation. The mean results of the TAS breach model runs are used for CTS worksheet inputs; the statistical results of those runs are included as supplementary tables in the workbook. Typically, H&H will only provide data for the maximum non-damaging scenario (often TAS non-breach) for use in calibration, but this should be reported as zero in the CTS worksheets when it is known to be a non-damaging event.

The consequences model is simulated for all evaluated scenarios. LL and damage results are checked for reasonableness. The individual structure damage report is reviewed for abnormal results.

In some cases, the largest hydrologic event will not cause the largest LL. This is due to the surprise factor that occurs when the PAR downstream of the dam is warned prior to dam breach. For hydrologic events that are large enough to result in non-breach releases that exceed the downstream channel capacity, some of the PAR will already be warned and will be leaving the area when the dam breach occurs. While larger hydrologic events won't necessarily cause larger LL, the PAR and economic damage should always increase as the non-breach or breach release increases (i.e., PMF should always show the largest PAR and economic damage).

4.3 Facility Repair Costs and Project Benefits Foregone

Comprehensive consequence assessments require estimates of total economic impact. These estimates are developed and documented in the consequence toolbox spreadsheet. The following economic consequence categories should be evaluated:

• Facility (asset) repair or replacement costs
• Water supply
• Hydropower
• Flood risk management
• Navigation
• Recreation
• Other lost benefits.

4.3.1 Facility (Asset) Repair or Replacement Costs

Repair costs are estimated based on the original construction cost of the project. That cost is indexed to current value, and then a percentage of that updated cost is used as the repair cost. Typically, 33 percent is used, however if the breach width divided by the dam length is greater than 33 percent (meaning that the breach takes out more than 33 percent of the dam), the higher percentage may be used to reflect a higher repair/replacement cost. More detailed estimates from a risk cadre or other analysis may also be used.

4.3.2 Water Supply

Annual water supply benefits are based on the project's total contracted yield in millions of gallons per day (MGD) and the average contract cost of water storage reallocation per acre foot. The average reallocation costs are based on post-1986 reallocation contracts which have been judged as the best way to estimate willingness to pay for water using the data available on a national scale. To estimate the annual value, the total contracted yield in MGD is converted to acre-feet per year, and the national average post-1986 reallocation cost per acre foot is applied to estimate the annual value. Population served by water supply is estimated by assuming 1,200 gallons per day (GPD) per person unless better data is available.

Water supply intakes within navigation pools typically are not contracted with USACE, meaning there is often no data on the amount of withdrawals and how intakes would be impacted by pool loss. Therefore, the value of water supply within navigation pools will not be estimated unless data is available. However, known water users may be listed under critical infrastructure impacted by project breach.

The annual value of irrigation water of evaluated projects will be based on the Federal cost for irrigation by project from the Institute for Water Resources (IWR) Water Supply Database report. The price levels of the Federal cost for irrigation in this table are those at the time the project was built. Unless otherwise indicated, it will be assumed the price level is that of the year the project was completed for purposes of this estimate. The Corps' Water Supply Handbook indicates that a 30-year period of analysis is used to calculate annual costs of irrigation water supply. The federal discount rate for water supply is obtained from the annual Economic Guidance Memorandum for discount rates. The annual value of irrigation will be the Federal Cost to Irrigation indexed to current price level and amortized over a 30-year period (using the appropriate federal discount rate).

4.3.3 Hydropower

Annual lost hydropower benefits are based on a five-year average annual hydropower production amount and a regional average electricity price. The annual hydropower production for the last five years is obtained from the enterprise data warehouse (EDW) for every federal hydropower project in order to estimate the average annual kilowatt hours (KWh) generated at each project. The electricity price is obtained from the Energy Information Administration (EIA) which provides regional average electricity prices weighted by residential, commercial, and industrial uses. That average price represents the average cost of the most likely alternative power supply in the case of a hydropower loss.

4.3.4 Flood Risk Management

An average annual value is used to measure the lost benefits based on historic flood damages prevented that are calculated for the Annual Flood Damage Report. Each district uses either discharge-damage or stage-damage relationships for areas downstream of the dam to estimate flood damage with and without the project; these are reported to Congress on an annual basis. To determine an average annual value, the historical records of damages in each year are indexed to current value and divided by the number of record years to estimate an annual average. If only a cumulative value is available (no annual records), the value is indexed from the midpoint year and divided by the years of project operation to develop the annual.

4.3.5 Navigation

Lost navigation benefits are sourced from the Shipper Carrier Costs (SCC) data prepared by the Planning Center of Expertise for Inland Navigation (PCXIN) in conjunction with assistance from a Navigation Advisory Team (NAT). The SCC provides a basis for estimating the impact of unscheduled lock closure or disruption to navigation as a result of loss of navigable pool or lock closure. The SCC data provides navigation impacts based on transportation savings rates for outage durations ranging from a single day to an entire year.

4.3.6 Recreation

Annual recreation benefits lost due to breach are based on project average annual visitation and unit day value (UDV) per visit. Estimates are developed for the project pre-breach (existing condition) and post-breach; the lost benefit is the increment between those two conditions. Average annual visitation is obtained from the most recent five years of the Visitation Estimation & Reporting System (VERS) records. Visitation is then broken out into general recreation and general hunting and fishing using percentages developed from the recreation activities on the value to the nation website. UDV scores for each recreation sub-area are pulled from RecBEST and a visit-weighted average UDV is developed to represent the entire project (pre-breach condition). The total visitations for the post-breach condition are estimated by assuming a percentage loss based on activity; water based visits are reduced by 100 percent, while non-water based visits are reduced by 50 percent. UDV scores are also reduced by 80 percent in the post-breach condition, except for the availability of opportunity which remains unchanged. The UDV values are based on the latest version of the annual Economic Guidance Memorandum (EGM) for Recreation Unit Day Values.

4.3.7 Other Lost Benefits

Some projects have benefits/damages that will not be included in the categories above. An example is non-federal hydropower plants just downstream of a dam. This would not be included in the hydropower lost benefits if it is not an authorized purpose of the project, but can be included in the other lost benefits section because loss of the plant is an economic impact that needs to be included in the overall consequence estimate.

4.4 Consequences Deliverables

4.4.1 Consequences-based Top Screen Worksheet

A draft CTS worksheet will be on SharePoint in the project's folder. This should have the facility info tab completed by the documentation team and the pertinent data and H&H data tabs completed by the modeler. The consequence team member edits the CTS worksheet in SharePoint, and does not create or download a new version of the worksheet. The member adds the economics data to the CTS worksheet that is already posted to the SharePoint site, making sure to maintain all review and source comments on the already completed tabs. This worksheet is used by the documentation lead to validate the consequences portion of the report deliverables.

In addition to adding data from the Consequences Toolbox, a life loss results map of the TAS breach life loss results, along with other supporting figures from the analysis, is also required in the CTS worksheet.

The consequence team member will fill in the MMC Contacts tab when development is complete. The consequence reviewer will also fill in the Contacts tab after data is verified and final. The status should be listed as Ready for Econ Review.

4.4.2 Consequences Toolbox

The HEC-LifeSim and Lost Benefits Excel toolboxes used to process results are posted to the SharePoint project folder.

4.4.3 MMC Project Handoff PowerPoint Presentation

The MMC project handoff PowerPoint used to present consequence findings during the handoff meeting is developed using the template provided in the MMC Team SharePoint project folder.

4.4.4 Consequences Model Data

The HEC-LifeSim model and input data files (not the HEC-RAS model data) are posted to the RMC file share production folders.

4.5 Review Procedures

The life loss, damages, repair cost, and lost benefits estimates are reviewed internally before consequences are considered complete. Reviews are coordinated by the MMC Production Center consequences branch chief and are typically accomplished via webinar and the use of the MMC Consequence Team Checklist.

After the products are approved by the branch chief, the economist addresses any comments. At this time, the economist uploads the finalized consequences model to the appropriate consequences folder on the RMC file share. The modeler, consequences branch chief, and team leads are informed via email of the upload and location.

The consequences QC review team member is responsible for filling in consequences data in the MMC reports. The CTS worksheet, model data, and report are reviewed by the consequences QA review team member and details compared to ensure consistency during the report review process.

Section 5 - Documentation

5.1 Modeling, Mapping, and Consequences-Reports

A standard report is written for each dam studied by the MMC summarizing modeling and consequences results. MMC internal drafts of the reports are stored on and edited within the MMC Team SharePoint project folders. Reports differ for each project type. The documentation team is responsible for working with the project manager to ensure the correct report template(s) and CTS spreadsheet are available. The documentation team will load any report template that may be needed to the project folder (e.g., HMCAS, HMCAS NAV, ASH etc.). This reduces confusion relating to current templates or type of reports to develop for the project.

The report template(s) associated for each project are loaded to the MMC Team SharePoint project folder.

The report files shall be edited directly from the MMC Team SharePoint project folder. This ensures edits from all assigned team members are made to one copy of the document.

Project folders are organized by project name, then by fiscal year. Upon district acceptance, final reports and CTS worksheets are loaded to the final project folder on CEDALS ProjectWise server during project closeout.

5.1.1 Develop Draft Report Folder and Initiate the Report

During the project kickoff phase, the MMC documentation production lead creates the project folder within the MMC Team SharePoint site and includes current, relevant templates. A production folder is created for the project on the RMC file share and references, including a cover photo, are stored in folder F. References. The cover photo shall be used for the cover pages of the project work plan, the report, and the inundation atlases.

The assigned documentation team member will initiate the project work plan, fill in the CTS facility tab, and populate initial data in the report template.

5.1.2 Draft Consequences Input

The assigned consequences team member prepares the remaining consequences and updates the CTS worksheet on the MMC Team SharePoint project folder. The CTS worksheet template is designed to guide the consequences team member in drafting language that is suitable for incorporation into the report. The consequences technical lead assigns internal review of the CTS worksheet, and finalizes it based on feedback received. This review should be completed prior to entering consequences content within the report to minimize potential for rework. The consequences QC review team member is responsible for filling in consequences data in the MMC reports. The CTS worksheet, model data, and report are reviewed by the consequences QA review team member and details compared to ensure consistency during the report review process.

The CTS worksheet is populated for eventual entry into the Engineering Data Module (EDM). Population of the CTS worksheet is a joint effort between the modeling cadre member and economic cadre member. Hydraulic data will be found from multiple sources including, but not limited to, the water control manual, HEC-RAS model, SPRA data, and the dam safety program management tool (DSPMT) database.

5.1.3 Draft Modeling Input

The modeler is responsible for using the CTS and model output values to draft the modeling portions of the documentation reports. A modeling data documentation review is conducted by the model review team prior to a technical edit of the report by the documentation team.

5.1.4 Draft Mapping Input

The assigned documentation team member will develop the system and detail maps for the reports.

5.1.5 Technical and Management Reviews

Once modeling, mapping, and consequences inputs are drafted, the assigned documentation team member performs a technical review of the report, involving the assigned team members from the disciplines to resolve comments as necessary. The technical review includes review of the consequences section based on content of the previous-reviewed CTS worksheet and focuses on technical content accuracy. The technical reviewer will contact MMC members to modify the report language if an error is found. The assigned member will use the quality control checklist to verify correct information was entered within the report. This serves as the initial MMC review of the report.

After the technical review has been completed, and the report is error free, the report is sent forward for management review. The management reviewer looks at the report holistically, and will make comments, if needed.

5.1.6 Report closeout

Report closeout procedures consist of a final technical edit and format review, then the Word document is printed as a portable document file (PDF). The documentation member will identify the completed report and CTS products as pre-IQR final in the project folder and notify the PM and MMC leads that the files are ready for district IQR.

5.1.7 District Independent Quality Review

There are two instances when the preCTS and HMCAS will be reviewed by the district. The first is during district model IQR, and the second is during district documentation/mapping IQR.

The preCTS worksheet with Facility Info tab complete is sent with the model geometry for model IQR. The district review comments received will be reviewed, and the report will be updated.

The district is notified once the pre-IQR draft report and map atlases are ready for district IQR. The pre-IQR draft report, final draft map atlas PDF, and data are posted to the RMC storage 5 file share for review by the district.

District map atlas and documentation IQR comments are uploaded to the COP SharePoint site, and resolved by the MMC staff via input from the assigned team members from the disciplines as necessary. The final reviewed and approved copy of the report is reposted to the COP site by documentation. The documentation and map atlas are moved to the appropriate project folder on the Dam Safety ProjectWise server upon project completion.

5.2 Mapping

This section discusses the process to develop inundation maps based on model outputs delivered by the modeling production team member. All steps are performed by the mapping production team member unless otherwise noted.

Map production should be performed for both dam breach inundation map and non-breach inundation map (NBIM) atlases.

5.2.1 Review Hydraulics and Hydrology and Consequence Models

The mapping production team member reviews all H&H and consequences data to ensure consistency and completeness of models and documentation prior to mapping.

5.2.1.1 Folder Structure

Review the model data folder structure according to Appendix 4.3.1 and complete the model data review checklist in Appendix 4.3.4.

5.2.1.2 Data, Report, and Model

Review the modeling data to include consequence analysis and HEC-RAS models, model output data, and reports to verify that the data meet the checklist requirements for data inclusion and that the data meet the data structure requirements.

5.2.1.3 Request Additional Information (if needed)

If additional data are needed, the GIS/mapping team member should request additional data from the assigned modeler for the study dam. Common missing elements are required model scenarios and model time steps.

5.2.1.4 Put Data in the Appropriate Location

Once data has been reviewed and the data checklist has been satisfied, the mapping production team member should transfer all of the received data to the mapping technical lead for upload to the MMC server.

5.2.2 Model Data Dissemination

The mapping technical lead verifies that all necessary model data are properly organized in MMC file share. The data is also viewable through the MMC data viewer, which results in the following for the study area:

• Model data layers are loaded within the MMC geodatabase
• Flood plain time series data is reloaded if necessary
• The map viewer and web applications are updated with the latest model data.

5.2.3 Mapping Data Preparation

The mapping production team member develops and customizes datasets for use in all MMC Production Center maps. Detailed steps for preparing the mapping data can be found in Appendix 4.1.5. Most steps are performed for any model that is to be mapped; however, some steps are specific to the model type (i.e., 1D versus 2D).

5.2.3.1 Create Working Geodatabase

Create a new empty file geodatabase within the mapping folder called "Inundation_study_area_name.gdb." This geodatabase stores all of the data for use in the individual map series (see Appendix 4.3.1 for file schema information).

5.2.3.2 Create Inundation Areas for Mapping

Use the breach inundation areas for MH and NH scenarios included in the model output to create inundation polygons for the mapping process (see Appendix 4.1.5). Include the non-breach inundation areas for MH and IH scenarios if the NBIM atlas series is to be produced. The GIS/mapping team member will store the inundation polygons in the working geodatabase for map production.

Any major edits made to inundation areas during the mapping process should be reviewed with the modeler and modeling team lead.

5.2.3.3 Create Map Grids

Determine the mapping scales for the study area. Most of the study areas will use standard grids for use at a scale of 1:31,680 (1 inch=½ mile) and detail grids for use at a scale of 1:15,840 (1 inch=¼ mile) for use in densely populated areas. The number of grids to map is determined by the extent of the maximum breach scenario, plus upstream area to be mapped if the UNIM atlases are to be produced. Non-breach inundation scenario mapping may be limited to upstream mapping of the elevated pools, or upstream in conjunction with downstream non-breach inundation.

A national standard grid layer for use at 1:31,680 and a detail grid layer for use at 1:15,840 are maintained by the mapping technical lead. The mapping production team member will create custom map grids based on existing national map grids when standard scales are not appropriate.

The map grids will be used as the sheet index for map production.

5.2.3.4 Create Sheet Numbering Draft Map

Use the standard sheet number guidelines in Appendix 4.1.5 to draft a preliminary map. This map should be sent to the mapping technical lead for review and approval before sheet numbering is considered final. In some cases, the mapping technical lead will review the sheet numbering schema with the district DSPM for the study area.

5.2.3.5 Create Reference Miles

Use the centerline from the model output to create reference mile points to be stored in the working geodatabase.

5.2.3.6 Select Cross Sections for Mapping

Cross sections are used from HEC-RAS models to display arrival time and elevation data on the map sheets. Use the cross section data from the model output to select and display a single cross section for each standard map sheet that intersects with the centerline within the map sheet. Each cross section is assigned a letter designator.

Use the MMC Utilities Toolbar for cross section development as described in Appendix 4.1.5.

5.2.3.7 Create Two-Dimensional Flood Info Points

The output datasets for 2D models should include raster datasets for arrival time and depth information. A point in each sheet should be used to display the arrival time and elevation information for the sheet, similar to the HEC-RAS lettered cross sections.

5.2.3.8 Create Breach Wave Arrival Time Points

The breach wave is defined by comparing the model output for non-breach scenario to the breach scenario for each load case. The toe of the breach wave is defined as the time at which difference between the non-breach and breach hydrograph exceeds two feet. Use flow profile data from the cross section feature class to assign a flood wave arrival m-value to the centerline. Using linear referencing, create flood wave arrival time points from this new centerline. The breach wave arrival time points are displayed on the sheet index map.

5.2.4 Cover Page Development

All MMC Production Center projects will include a cover page to identify the study dam and location for each specific project. The cover page will be developed based on the information and standards set in Appendices 4.1.5 and 4.1.7. Inundation atlases are generated for dam breach and non-breach inundation scenarios. Non-breach inundation scenario mapping may be limited to upstream mapping of the elevated pools, or upstream in conjunction with downstream non-breach inundation.

The cover page will be provided to GIS/mapping team members in PowerPoint format and will serve as the standard for all study areas. Update the information in the title block for the assigned study area according to Appendix 4.1.5.

A photo of the dam is required for placement on the cover of the map atlas and model report. The following step will likely be completed by the MMC documentation lead during initial setup of the flood inundation modeling and consequence assessment report, during the initial phase of the project while pre-model GIS development is performed. The mapping team member should begin by checking the project's folder in MMC Team SharePoint to determine if a project photo has been selected. The intent is for the same project photo to be used on the cover of the report and the covers of the map atlases. If a photo has not yet been selected, the mapping team member will contact the documentation production lead to request a photo. Update the cover page template according to Appendix 4.1.5.

5.2.5 Map Notes Pages

Map notes pages will be created according to Appendix 4.1.5. Information shown on map notes pages should reflect the information and values located in the CTS worksheet located on the MMC Team SharePoint project folder.

5.2.6 Standard Map Sheet Development

The mapping team member incorporates modeling output into a standard sheet template for inclusion in the final map product, according to Appendices Appendix 4.1.5, 4.1.6, and 4.1.7. Mapping for upstream inundation will use the same templates and procedures but will only be included in the non-breach inundation atlas series.

5.2.6.1 Sheet Template

Verify that all elements in the .mxd file for standard sheets match existing graphic standards documented in Appendix 4.1.7.

5.2.6.2 Data Sources

Set the inundation layer data sources in the .mxd file to the appropriate study dam feature classes, according to Appendix 4.1.6. Verify that basemap data layers are sourced correctly.

5.2.6.3 Data Validation

Check the NID for data placement outliers. The location of the features will be verified based on the most current aerial imagery available.

In situations where data must be altered, the data will be changed in the local copy and all changes will be documented accordingly.

5.2.6.4 Data Frame Properties

Set the data frame scale and the coordinate system in the .aprx file for the study area. All map sheet data frames will use the Universal Transverse Mercator (UTM) coordinate system as specified in Appendix 4.1.5. Study areas that intersect multiple UTM zones should have individual tabs within the .aprx files created for each applicable UTM zone.

5.2.6.5 Create Map Series

Create a map series using Data Driven Pages.

5.2.6.6 Source Linked Text

Source text elements in the .aprx file to the standard sheet grid layer fields for text that dynamically updates during map series production.

5.2.6.7 Annotation

Create annotation for applicable data layers. Edit annotation according to guidelines in Appendices 4.1.5 and 4.1.7.

5.2.7 Detail Map Sheet Development

Detail sheet development follows the same process for standard sheets; however, it uses the detail sheet .aprx template. Detail sheets are developed for areas where a large scale is needed due to high feature density (e.g., metropolitan areas).

5.2.8 Sheet Index Map Development

The mapping production team member creates a location reference map for the study area in accordance with Appendices 4.1.5, 4.1.6, and 4.1.7. The numbering scheme shall ensure that all corresponding dam breach inundation map (DBIM) and NBIM map sheets have the same sheet number. If a downstream non-breach inundated area is to be included, NBIM map sheets should be produced to cover the entire extent of corresponding DBIM map sheets to the point downstream where non-breach inundated areas are constrained in the channel. This will eliminate confusion that would result if NBIM map sheets with no non-breach inundated area were omitted from the set.

5.2.8.1 Map Template

Sheet index map .aprx files are maintained by the mapping technical lead. The mapping production team member will determine an appropriate scale for the sheet index map based on the inundation area and information in Appendix 4.1.5.

5.2.8.2 Data Sources

Set the layer data sources in the .aprx file to the appropriate feature classes according to Appendix 4.1.6. Verify that basemap data layers are sourced correctly.

5.2.8.3 Data Frame Properties

Set all data frame scales and extents based on the size of the standard sheet grid. Set the coordinate systems in the .aprx file to the UTM coordinate system as specified in Appendix 4.1.5.

For study areas that intersect multiple UTM zones, set the coordinate system as the UTM zone containing the majority of standard sheets.

5.2.8.4 Annotation

Create annotation for applicable data layers. Edit annotation according to guidelines in Appendix 4.1.5.

5.2.9 Critical Infrastructure Lookup Table Page Development

Every standard sheet in a dam breach inundation atlas that has critical infrastructure points in the depth grid will have a corresponding lookup table. Critical infrastructure lookup tables are not currently developed for non-breach inundation.

If a printed map atlas was opened on a table top with a map sheet on the right, or front side of the pages, the critical infrastructure lookup table would be on the left, or back side of the pages. The critical infrastructure lookup tables contain information that references the data in the map on the adjacent sheet. Critical infrastructure lookup tables contain the structure type, name, address, inundation depth, arrival time, peak time, arrival elevation and peak elevation for each affected critical infrastructure point within the associated standard sheet. If there are more critical infrastructure points affected than can fit on one sheet an ellipsis will appear at the bottom of the table.

5.2.9.1 Critical Infrastructure Lookup Tables

Use ESRI ArcGIS Pro and the MMC Utilities Toolbar to process data to create the critical infrastructure lookup tables from the information in Appendix 4.1.5 and according to the standards set in Appendix 4.1.7.

5.2.10 Export to Portable document File

All MMC Production Center projects will have .pdf files created for the inundation atlas assembly. All files will be created according to Appendices 4.1.5, 4.1.7, and 4.3.7.

5.2.10.1 Export Cover Page

Use print to .pdf functionality within Microsoft PowerPoint to convert the cover page PowerPoint file into a .pdf document.

5.2.10.2 Export Map Notes Pages

Use ESRI ArcGIS Pro to export both pages to .pdf documents.

5.2.10.3 Export Standard and Detail Sheets

Use the series export function within Data Driven Pages to export each map sheet to .pdf documents.

5.2.10.4 Export Sheet Index Map

Use ESRI ArcGIS Pro to export the index map to a .pdf document.

5.2.10.5 Export Critical Infrastructure Lookup Table Pages

Use ESRI ArcGIS Pro to export the critical infrastructure lookup table series to a .pdf document.

5.2.11 Map Atlas Development

The map atlas is a consolidated mapping product of all the mapping outputs. See Appendices 4.1.5 and 4.1.7 for information on the contents of the inundation atlas.

Standard and detail sheets and facing pages are all exported as stand-alone .pdf files. The files will be stored individually and be combined into the inundation atlas. The file naming and storage parameters described in Appendix 4.1.5 should be followed for all .pdf files. Individual pages should be maintained in full-resolution and optimized formats. The full-resolution files should be used to generate the combined inundation atlas .pdf file.

5.2.11.1 Combine Pages

Use the Atlas Builder tool on the MMC Utilities Toolbar to combine .pdf files into inundation atlases as in Appendix 4.1.5.

5.2.11.2 Optimize .pdf Files

After saving a full-resolution version of the map atlas, use the optimization tool in Adobe Acrobat Professional to reduce the file size of the inundation atlas for Web delivery. Use Appendix 4.1.5 to reference best practices to optimize the .pdf map book.

The mapping production team member will need to send both optimized and full-resolution versions of the .pdf files to the mapping technical lead for distribution and archival purposes.

5.2.12 Map Review (Draft)

The mapping products produced for the MMC are reviewed at two levels within the MMC and, optionally, additional reviews are performed outside the MMC. The internal review is performed by a GIS/mapping team member. All products are then provided for mapping technical lead review using the MMC file share.

5.2.12.1 Internal Review

The mapping production team member is responsible for organizing an internal review of the inundation atlas and files used to create the inundation atlas within the mapping production team. The reviewer should review the atlases for cartographic and graphical completeness in accordance with Appendices 4.3.7 and 4.3.8.

5.2.12.2 Technical Lead Review

The inundation atlas is reviewed in .pdf format by an independent reviewer assigned by the mapping technical lead. The checklist in Appendix 4.3.3 is filled out and comments for revision are documented and returned to the original mapping production team member.

The inundation atlas is reviewed and all comments are provided to the mapper for edits. The .pdf inundation atlas is submitted for a second round review where it will be cleared for MMC and District IQR in most cases. In some cases, additional rounds of technical lead review are necessary. The technical lead review is tracked in the schedule database by the task mapping complete. Once all review comments are resolved, the task is complete.

5.2.12.3 Update mapping product

The mapping production team member updates the map series based on comments from the mapping reviewers. The inundation atlas is then re-created after editing. Appendix 4.3.5 is used to verify that data is complete for the deliverable product. The revised files are then submitted to the mapping technical lead who continues with the steps in Appendix 4.1.5 to finalize the .pdf product.

5.2.13 Develop KMZ Files

Use Google Earth Pro to convert the vector modeling data layers to .kmz files for use in Google Earth desktop applications. Save the .kmz files in the GoogleEarth folder within the MMC file structure. All symbolization should match the guidelines set for the mapping process in Appendix 4.1.7.

5.2.14 Load Data into Modeling, Mapping, and Consequences Geodatabase (Draft)

Load the data from the mapping portion of the project into the consolidated geodatabase for display in the MMC Production Center web map application.

5.2.15 Final Reviews: Modeling, Mapping, and Consequences and District Independent Quality Review

The district the dam is located in will be offered the opportunity to review all MMC products. The PM will coordinate with the district Dam Safety Officer and Dam Safety Program Manager to schedule and begin the review. The .pdf inundation atlas and documentation is sent to the district for review. All district IQR map atlas and documentation comments will be recorded and responded to within the MMC COP SharePoint site.

District review comments are provided to the MMC and addressed by the modeling, mapping, or consequence team members as appropriate. Once final review is complete and all issues have been addressed, the MMC member converts the suffix of the year root folder name in the MMC file share from Year-Draft to Year-Final. The study area is migrated from the draft product MMC geodatabase and map viewer to the final product MMC geodatabase and map viewer. Once the study area has been migrated from draft to final the District Review Products task in the schedule database is complete.

Section 6 - External Deliverables

This section summarizes the products available at the end of an MMC study, the review steps undertaken during the production process, and USACE policy and guidance for product handling and dissemination.

6.1 Modeling, Mapping, and Consequences Products

MMC Production Center deliverables produced using this SOP document are listed below and are accessible from the servers as noted.

6.1.1 Modeling, Mapping, and Consequences External SharePoint Site

The MMC external SharePoint site is known as the MMC COP SharePoint site ( https://cops.usace.army.mil/sites/HHC/CoPs/DS/MMC/SitePages/Home.aspx ).

• Dam Safety Data Viewer and Status Map
• Comment/response database for district IQR of MMC products
• Comment/response database for MMC SOP
• MMC status map
• MMC study status summary for each assessment
• Links to online maps for each dam (CorpsMap, MMC data reviewer and CorpsMap USACE Operations Center [UOC])
• MMC quarterly status report
• Geospatial metadata-Federal Geographic Data Committee (FGDC) metadata for features in the following MMC databases. Further discussion of metadata is available in Section 3.6.
• Pre-model database
• Model results database
• Mapping database

6.1.2 CorpsMap Modeling, Mapping, and Consequences Viewer

• Final modeling data layers
• Final inundation mapping data layers
• Inundation atlas map sheets and profiles (PDF format)

6.1.3 CorpsMap UOC Viewer

• Final inundation mapping data layers

6.1.4 Corps of Engineers Dam and Levee Safety ProjectWise

• Consequences Model Deliverables. A complete consequences model with all scenarios as well as input rasters, shapefiles, and study-specific Hazards U.S. (HAZUS) data are to be included in the final deliverable.
• GIS Modeling Deliverables. GIS modeling deliverables will include files and data used in interfacing GIS data with the HEC-RAS model. Final GIS deliverables will include final maps, DEMs used in creating models, supplemental ground surface data, pre-HEC-RAS geodatabases, pre-HEC-RAS GIS export files used in model creation, post-HEC-RAS export files, post-HEC-RAS geodatabases, and any additional shapefiles used in modeling.
• Model Deliverables. The final model deliverable contains the final model with the file structure as specified in this manual.
• Reference Material. The reference material deliverable is to contain all materials used in model development. All data supporting the model should be included. This data may be, but is not limited to the following:
• Existing models
• Data collected from the district
• Hydrology data
• POR data
• VDF analysis data
• Breach worksheets
• Water control manual.
• Hydraulic Modeling Report Deliverable. An HMCAS is to be developed for each MMC Production Center model that is developed. The report is intended to summarize the dam conditions, assumptions, and difficulties, as well as HEC-RAS model results. See Section 5.6 for further details.
• Review Deliverable. This deliverable will contain all review comments and correspondence pertaining to the model. These comments should contain a response from the modeler. The review checklist should be utilized for model review.
• Consequence output files and reports.
• Mapping file geodatabase, output files, KMZ files for Google Earth, and PDF map products.

6.2 Review Process Summary

This section lists the review steps that are performed as part of the SOP. Internal MMC reviews and external reviews are described in detail within Section 5. District IQR is the final step in the review process. District coordination begins with the initial request to complete the data collection worksheet and continues with model review and the final District IQR.

6.2.1 Internal (Modeling, Mapping, Consequences, Documentation) Review

• Pre-model GIS data review-Mapping team member
• Pre-model GIS data review-Modeling lead
• Model interim review-Modeling assigned reviewer
• Model compliance review-Modeling assigned reviewer
• Model final review-Modeling lead
• Consequence analysis model review-Consequences team member
• Consequences internal review-Consequences technical lead
• Model data consistency review-Mapping team member
• Report internal review-Documentation technical reviewer
• Report internal review-Documentation management reviewer
• Mapping internal review-Independent mapping team member
• Mapping initial-Mapping technical lead
• Report final internal review-Documentation production lead

6.2.2 External Review

• Model district-District POC
• Dam Safety Review-Risk cadre-all dams funded by Dam Safety
• CIPR program review-CIPR staff-all dams funded by CIPR
• Data collection worksheets
• CTS worksheet
• Documentation Reports
• HEC Review-HEC staff-minimum one dam per production team per year
• Annual rollup-MMC, HEC, CIPR, and Dam Safety staff-after action review
• Mapping/Documentation District IQR-see below

6.2.3 District Independent Quality Review

District IQR is now performed in two phases. First, the district is provided opportunity to review the hydraulic model once it is substantially complete and before development of consequences and mapping products begins. The second phase of district IQR occurs once all consequences and mapping products have been completed and is the final step before formal close out of a project. District IQR gives the district responsible for operating the project an opportunity to review the MMC products for adherence to the MMC SOP and to make final comments on questions or concerns with the products as the district begins to incorporate the MMC materials into local products such as EAPs. District comments are crucial to the MMC-addressing these comments improves the quality of USACE products and the processes and procedures used to develop them. The MMC commonly responds to district IQR comments with:

• Concurrence-Editing products to address the comment
• Concurrence-Logging the comment and deferring the edits to a future study (such as an upcoming Issue Evaluation Study (IES) or PA)
• Concurrence-Adjusting the MMC SOP to ensure similar issues do not occur in future studies
• Providing information to further explain MMC procedures and assumptions.

During the first phase of IQR the district should review the model and provide comment on issues that could affect consequences or mapping results. During the second phase of IQR the district should focus on the inundation map atlases, as their contents are the end result of the MMC production process and they are to be incorporated into EAPs. Other topics to be considered during this final review include:

• Consistency of consequences results-understanding that results reported by MMC will be refined during dam safety risk assessments.
• Completeness of the inundation modeling and consequence assessment report-does it serve as a good summary of methods, assumptions and results that can be used by others in the future to evaluate and refine the models?
• Completeness of products and documentation-are all files present, located in correct folders, and properly named? Is there sufficient documentation, including documentation of reviews?
• Are model results reflected in the map atlases (inundated areas and flood elevation and timing information/profiles) consistent with district input provided during the prior district review of the model?

6.3 Data Handling

The MMC is responsible for maintaining and managing MMC products. Districts are responsible for data dissemination to external stakeholders. The MMC will not disseminate products to external stakeholders except in special circumstances with either the concurrence of or at the request of a DSPM or DSO (district, division, or USACE).

MMC products are finalized via resolution of comments received in the reviews discussed above. The district DSO and DSPM are notified via email once products have been finalized. Final products are available to the district for download via CEDALS. Upon receipt of the transmittal memo further dissemination of the data to other stakeholders becomes the responsibility of the dam safety community (district, division, or USACE). The district is primarily responsible for determining the proper use and distribution of the data, including dissemination to local governments or emergency response agencies in accordance with current USACE policy on release of information.

Appendix 6 provides copies of the following guidelines and policies for dissemination of MMC products:

• USACE RMC, 18 May 2010, "Safeguarding Sensitive Information-Modeling, Mapping and Consequences Production Center."
• Draft usage agreement for submittals to external stakeholders.

Glossary

1-Percent Duration Exceedance Elevation (feet) . The reservoir elevation that is exceeded on average 1-percent of the time on an annual basis (approximately 3-4 days per year). Note: This is not the same as the 1-percent probability exceedance elevation, which is commonly referred to as the 100-year flood.

Active Storage Water Elevation (feet) . Maximum reservoir water surface obtained when the reservoir is fully utilized for all purposes, including conservation and flood storage. This elevation represents the highest elevation obtained under normal regulated operating conditions. This water surface elevation corresponds to the top of active storage level.

Antecedent Pool Level . The initial reservoir pool level associated with a model run.

Banklines (Pertaining to HEC-River Analysis System [HEC-RAS]) . A Geographic Information System (GIS) shapefile that represents where banks are located along a particular river reach.

Bathymetric Data . Underwater topography of oceans, seas, or other large bodies of water.

Blocked Obstructions (Pertaining to HEC-River Analysis System [HEC-RAS]) . Areas within cross sectional flow areas that are blocked from containing water in a particular cross section.

Breach Progression (Pertaining to HEC-RAS) . The progression in which dam embankment material is removed from the structure due to dam breach.

Centerline (River Centerline) . Water surface course centerlines for a waterway defined by digitizing centerlines atop a contiguous imagery source. Centerlines begin from the confluence upstream to the dam at a scale 1:15,000.

Conversion Points . Nationwide point features containing interpolated values at point locations. Conversion points contain the elevation difference between National Geodetic Vertical Datum of 1929 (NGVD29) and North American Vertical Datum of 1988 (NAVD88). This point shapefile can be used to update raster value fields. See the National Geodetic Survey website for additional information: http://www.ngs.noaa.gov/.

Consequences . Potential loss of life or property damage downstream of a dam caused by floodwaters released at the dam or by waters released by partial or complete dam breach. Consequences also include effects of landslides upstream of the dam on property located around the reservoir.

Consequence-based Top Screening (CTS) . CTS methodology is used to quickly identify dam projects whose breach or disruption could trigger significant consequences. CTS allows the dam's sector to establish common methods, assumptions, and measures to consistently quantify different types of consequence elements across the sector.

Critical Infrastructure . Defined in the U.S. Patriot Act as those systems and assets, whether physical or virtual, so vital to the United States that the incapacity or destruction of such systems and assets would have a debilitating impact on security, national economic security, national public health or safety, or any combination of those matters.

Cross Section. A n elevation view topography formed by passing a plane through the topography perpendicular to the axis.

Dam Safety Action Classification . A dam classification system created by U.S. Army Corps of Engineers dam safety professionals to group dams that exhibit certain characteristics for potential safety concerns.

Depth Damage Curves . A relationship between water depth and the associated economic damages.

Depth-Percent Damage Curve . A relationship between water depth at a damageable property (e.g., structure or vehicle) and the associated damages. The value of the property is multiplied by the percentage corresponding to the flood depth at the property to make the damage estimate.

Depth-Direct Dollar Damage Curve . A relationship between water depth at a damageable property (e.g., structure or vehicle) and the direct (actual) dollar damage value. A percentage of property is not applied when direct dollar damage curves are used.

Depth Grid . Depth raster datasets that represent the depth (elevation) to the water table encountered throughout the inundation area.

Design Memorandum . Notes or plans corresponding to a design.

Design Water Elevation (feet) . Maximum level pool reservoir water surface elevation, including surcharge, that a dam is designed to withstand excluding any allowance for freeboard. This water surface elevation corresponds to the maximum storage. Same as "design water level" in the Federal Emergency Management Agency (FEMA) Federal Guidelines for Dam Safety - Glossary of Terms, April 2004.

Drainage Area (square miles) . Surface area that drains to a particular point (in this case, the dam) on a river or stream. Same as data field 33 in the National Inventory of Dams, Version 4.0, April 2008.

Emergency Action Plan (EAP) . A plan of action to be taken to reduce the potential for property damage and loss of life in an area affected by a dam breach or large flood.

Exceedance Duration Elevation . Elevation in a reservoir that is equaled or exceeded a certain percentage of the time. Example: 10-percent exceedance duration elevation for a particular reservoir is equaled or exceeded only 10 percent of the time.

External Deliverables . Deliverables produced during and from the MMC Production Center's production cycle that are to be considered final end products for the intended customer.

Flood Storage (acre-feet) . Storage space in the reservoir exclusively allocated for regulation of flood inflows. This storage space includes the increment of storage volume between the top of conservation storage and top of active storage.

Flow Path . The center-of-mass of a particular flow area within a model cross section.

Formation Time (Pertaining to Dam Breach) . The amount of time between the instant a significant uncontrolled flow of water leaves the dam due to breach to the time breach formation is complete.

Geodatabase . An ArcGIS geodatabase is a collection of geographic datasets of various types held in a common file system folder, a Microsoft Access database, or a multiuser relational database (such as Oracle, Microsoft SQL Server, or IBM DB2).

Hillshade Creation . The hillshade surface area is generated from the 10-meter digital elevation model (DEM). Hillshades are primarily used to identify changes to topology or to approximate topology.

Historical Maximum Pool Elevation (feet) . The highest elevation attained in the reservoir since construction.

Hydrograph Routing . The act of accounting for inflow and outflow rates, water storage characteristics, and losses for a particular river reach or reservoir.

Ineffective Flow Areas (Pertaining to HEC-RAS) . Areas within a cross section representing flood plain flow that do not convey water downstream.

Inflow Design Flood (IDF) . The flood used in the design of a dam and its appurtenant works particularly for sizing the spillway and outlet works, and for determining the maximum temporary storage and height of dam requirements.

Inline Structures (Pertaining to HEC-RAS) . A physical feature that generally lies perpendicular to flow and impounds water (such as a dam). Water may be routed through or over this structure.

Internal Deliverables . Deliverables created during the MMC Production Center production cycle and disseminated between team leads and/or team members.

Interpolated Cross Sections (Pertaining to HEC-RAS) . A cross section within the model geometry that is created from an interpolation of the ground surface data for the cross sections immediately upstream and downstream.

Lateral Structures (Pertaining to HEC-RAS) . A physical feature that generally lies parallel to flow. Water may be routed through or over this structure.

Life Loss Estimates (Loss of Life) . Estimate of potential life loss using approved life loss estimating methodology. May be for individual breach modes, or total for specified loading scenario.

Loading Conditions . The reservoir pool level that corresponds to a particular dam outflow event.

Manning's "n" Values . A scale of relative roughness pertaining to stream channels and overbank areas and used in Manning's equation.

Maximum Flood Control Elevation (feet) . The highest elevation of the flood control storage.

Maximum High Pool (Type of Condition) . An unsteady flow simulation for non-breach and breach scenarios will be modeled for the maximum high pool water level. The maximum high pool event will be defined by the inflow design flood

Maximum Operating Pool . The highest elevation achieved in the reservoir under normal operating conditions. This represents the upper limit or top of active storage.

Maximum Storage (acre-feet) . Total storage space in the reservoir below the design water elevation. This storage space includes surcharge, flood, conservation, inactive, and dead storage. Maximum storage is determined based on a level pool assumption excluding any allowance for freeboard or wedge storage due to sloping water surface. This measurement is the same as data field 30 in the National Inventory of Dams, Version 4.0, April 2008.

Minimum Operating Water Elevation (feet) . The lowest elevation the reservoir is drawn down to under normal operating conditions excluding any special provisions for drought operations. This water surface elevation corresponds to the bottom of active storage. This measurement is the same as "minimum operating level" in the FEMA Federal Guidelines for Dam Safety, April 2004.

Model Geometry (Pertaining to HEC-RAS) . A representation of the physical features that influence flow in a particular modeled reach.

Normal High Pool (Type of Condition) . An unsteady flow simulation for non-breach and breach scenarios will be modeled for a normal high water level, the 10-percent exceedance duration. Starting reservoir pool will correspond to the 10-percent exceedance duration pool elevation. Reservoir inflow will be a constant inflow hydrograph as required to produce the 10-percent exceedance duration pool under normal gate operations. Gate operation procedures consistent with the latest water control manual will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates. A consequence analysis simulation for the non-breach condition is not necessary if non-damaging releases result from the normal high pool event.

Normal Water Elevation (feet) . Maximum reservoir water surface elevation obtained when the reservoir is fully utilized for conservation purposes (e.g., municipal and industrial water supply, industrial water supply, irrigation, hydroelectric power generation, navigation, etc.) excluding flood and surcharge. This water surface elevation corresponds to the top of conservation storage level.

Normal Storage (acre-feet) . Total storage space in the reservoir below the normal water elevation excluding any flood or surcharge storage. This storage space includes conservation, inactive, and dead storage. This amount of storage space corresponds to the top of conservation storage level for dams with seasonal variations. This measurement is the same as data field 31 in the National Inventory of Dams, Version 4.0, April 2008.

Population at Risk (PAR) , For Dam Safety risk assessments, it is the population downstream of a dam that would be subject to risk from flooding in the instance of a potential dam breach; usually documented in numbers of persons at risk.

Dam Portfolio Risk Assessment . A tool for prioritizing structural and non-structural measures for reducing dam safety risks across a group of dams. A dam portfolio risk assessment can also be used to prioritize further investigations and analyzes and to give a basis for the evaluation of other dam safety activities (e.g., monitoring and surveillance, inspections, and emergency planning).

Portfolio Risk Management . A risk-informed approach for improved management of dam safety for a portfolio of dams in the context of the owner's business.

Security Scenario Pool (Type of Condition) . An unsteady flow simulation for non-breach and breach scenarios will be modeled for a 1-percent exceedance duration pool elevation. Starting reservoir pool will correspond to the 10-percent exceedance duration pool elevation. Reservoir inflow will be a scaled probable maximum flood (PMF) or reservoir design flood hydrograph. The scaled hydrograph will be developed by scaling the available hydrograph using trial and error to produce a peak pool equal to the 1-percent pool elevation. Gate operation procedures consistent with the latest water control manual will be applied to the hydrograph routing. Consequence analysis will include damage and loss of life estimates. A consequence analysis simulation for the non-breach condition is not necessary if non-damaging releases result from the 1-percent pool event.

Stage Damage . The relationship of damage to a range of flood stages at a structure or the aggregated values of damage by damage categories for a range of stages at some form of index location, such as a HEC-LifeSim Common Computation Point.

Storage . The retention of water or delay of runoff either by planned operation, as in a reservoir, or by temporary filling of overflow areas, as in the progression of a flood wave through a natural stream channel. Definitions of the specific types of reservoir storage are as follows:

• Active Storage. The volume of the reservoir that is available for some use such as power generation, irrigation, flood risk management, water supply, etc. The bottom elevation is the minimum operating level.
• Dead Storage. The storage that lies below the invert of the lowest outlet. This type of storage cannot readily be withdrawn from the reservoir.
• Flood Surcharge. The storage volume between the top of the active storage and the design water level.
• Inactive Storage. The storage volume of a reservoir between the crest of the invert of the lowest outlet and the minimum operating level.
• Live Storage. The sum of the active and inactive storage.
• Reservoir Capacity. The sum of the dead and live storage of the reservoir.

Storage Area Connectors (Pertaining to HEC-RAS) . A physical feature that lies between two HEC-RAS storage areas over which water may be routed.

Storage Curves (Pertaining to Reservoir Storage) . A relationship between reservoir pool elevation and corresponding storage volume.

Streambed Elevation . The lowest elevation of the original natural ground surface (prior to dam construction) along the centerline axis of the dam. This elevation is typically located where the original stream channel intersects the centerline axis.

Study Area . An estimated inundation area created by GIS from buffering the centerline to create the 10-meter digital elevation model (DEM) for pre-model GIS process.

Surface Area (acres) . The surface area of the impoundment at normal water elevation (normal storage). This measurement is the same as data field 32 in the National Inventory of Dams, Version 4.0, April 2008.

Thalweg . The middle of the main channel of a waterway.

Top of Active Storage (Type of Condition) . An unsteady flow simulation for non-breach and breach scenarios will be modeled for the top of active storage water level. Starting reservoir pool will correspond to the normal operating pool elevation. Reservoir inflow will be a scaled PMF or reservoir design flood hydrograph. The scaled hydrograph will be developed by scaling the available hydrograph using trial and error to produce a peak pool equal to the top of active storage elevation. Gate operation procedures from the latest water control manual will be applied to the hydrograph routing. Consequence analysis will include damage and LL estimates. A consequence analysis simulation for the non-breach condition is not necessary if non-damaging releases result from the top of active storage event.

Top of Active Storage Elevation (feet) . The reservoir elevation attained if the reservoir is fully utilized for all project purposes (i.e., power generation, irrigation, flood risk management, water supply, etc.). The pool elevation that, if exceeded, would result in significant increase in discharge based on the physical properties of the project and/or operation procedures from the latest water control manual.

Two-Dimensional Model . The MMC Production Center standard for two-dimensional (2D) modeling is HEC-RAS 2D. HEC-RAS 2D is a finite volume hydraulic model that can simulate channel flow and unconfined overland flow.

Unsteady Flow Modeling . Hydraulic modeling that involves routing a hydrograph though a system.

USACE Dam Safety Program . The USACE Dam Safety Program effectively attempts to apply the utmost care and competence to every aspect of dam design, construction, operation, and maintenance.

Warning Time. The difference in time between the warning issuance and flood arrival times.

Water Control Manual . Document containing pertinent information pertaining to a dam and or reservoir. It may include construction plans, operational procedures, and exceedance duration curves.

List of Acronyms and Abbreviations

1D	one-dimensional
2D	two-dimensional
CAR	Consequences Assessment Report
CEDALS	Corps of Engineers Dam and Levee Safety Database
CIPR	Critical Infrastructure Protection and Resilience Program
COP	Community of Practice
CTS	consequence-based top screen
CUI	Critical Unclassified Information
DEM	digital elevation model
DBIM	dam breach inundation map
DHS	Department of Homeland Security
DM	design memorandum
DSO	dam safety officer
DSPM	dam safety program manager
DSPMT	Dam Safety Program Management Tool
DSS	data storage system
DVD	digital video disc or digital versatile disc
EAP	Emergency Action Plan
EGM	Economic Guidance Memorandum
ESRI	Environmental Systems Research Institute
FEMA	Federal Emergency Management Agency
FGDC	Federal Geographic Data Committee
FIS	flood insurance studies
FSA	Farm Service Agency
FTP	file transfer protocol
GIS	geographic information systems
HAZUS	Hazards US (Geodatabase data from FEMA)
HEC	Hydrologic Engineering Center
HEC-HMS	Hydrologic Modeling System
HEC-LifeSim	Life Loss Analysis
HEC-RAS	River Analysis System
H&H	hydraulics and hydrology
HH&C	hydrology, hydraulics, and coastal engineering
HMCAS	Hydraulic Modeling and Consequences Summary
HTML	hyper text markup language
IDF	inflow design flood
IES	Issue Evaluation Study
IH	intermediate high
IL	intermediate low
IQR	independent quality review
IWR	Institute for Water Resources
KML	keyhole markup language
KMZ	keyhole markup (file), zipped
LiDAR	light detection and ranging
MH	maximum high
MMC	Mapping, Modeling and Consequences Production Center
MXD	map document files
NAV	navigation
NAVD	88 North American Vertical Datum of 1988
NED	National Elevation Dataset
NBIM	non-breach inundation map
NGVD	29 National Geodetic Vertical Datum of 1929
NH	normal high
NHD	National Hydrography Dataset
NID	National Inventory of Dams
NL	normal low
NLD	National Levee Database
NN	normal navigation
NPC	navigation pool channel
NWK	U.S. Army Corps of Engineers, Kansas City District
NWS	National Weather Service
OHS	Office of Homeland Security, U.S. Army Corps of Engineers
PAI	protective action initiation
PAR	population at risk
PDF	portable document format, a file extension from Adobe Systems
PDT	project delivery team
PMF	probable maximum flood
POC	point of contact
POR	period of record
PWP	project work plan
RA	risk assessment
RMC	Risk Management Center
SOP	standard operating procedures
SPRA	Screening Portfolio Risk Assessment
SS	security scenario
TAS	top of active storage
TIN	Triangulated Irregular Network
TOD	top of dam
UOC	USACE Operations Center
UNIM	upstream non-breach inundation map
USACE	U.S. Army Corps of Engineers
USGS	United States Geological Survey
UTM	Universal Transverse Mercator
VDF	volume duration frequency
WCM	water control manual
WS	water surface