FEMA Floodplain Mapping (DFIRM)
The Federal Emergency Management Agency (FEMA) is undertaking a nationwide, 5-year, $1 billion program to update FEMA’s Flood Insurance Rate Maps (FIRMs) and convert them to a countywide, digital format (DFIRM) that will be available through the internet. Existing paper FIRMs may no longer reflect current flood risks (due to changes in drainage patterns resulting from erosion, land use practices and land development). WRMA engineers are Certified Floodplain Managers (CFM’s) and have acquired extensive experience to provide solutions to the challenges facing FEMA’s MAPMOD digital flood mapping program. WRMA staff is proficient with the application and integration of ARC HYDRO GIS and LiDAR/SAR-derived Digital Elevation Models (DEMs) for digital flood plain mapping per the requirements of FEMA’s new Map Modernization (MAPMOD) program. WRMA’s flood hazard study and floodplain mapping services include:
- Base Flood Elevation Determination;
- LiDAR Aerial Surveys for FEMA Mapping;
- Floodplain/Floodway Delineation & Mapping;
- FEMA Flood Insurance Studies;
- Hydraulic modeling of river systems, in both 1-D and 2-D, using steady-state and unsteady modeling techniques;
- Evaluation and delineation of floodplains and floodways in normal, split flow and looped flow situations;
- FEMA DFIRM Database & Map Development;
- Use of industry standard automated tools, as well as the development and use of in-house automated tools, for hydrologic and hydraulic modeling applications, floodplain and floodway delineation, and DFIRM/FIS production;
- Preparation of FISs, PMRs, CLOMRs and LOMRs with acceptance by FEMA.
Urban and Agricultural Flood Analysis Modeling
The Hydrologic Engineering Center's Flood Damage Analysis (HEC-FDA) program is a risk-based analysis model developed by the US Army Corps of Engineers for flood-damage-reduction studies (EM 1110-2-1419). The approach explicitly incorporates descriptions of uncertainty of key parameters and functions into project benefit and performance analyses. Flood damage in urban or agricultural land uses require a very specific approach. The urban flood Damage Calculation (DAMCAL) and Agricultural Flood Damage Analysis (AGDAM) programs, two subset models within the HEC-FDA software package, are designed to evaluate the urban and agricultural flood damage potential of floodplain areas. The primary purpose of these programs is to calculate expected annual damage and areas flooded by: urban land use, crop category and damage reach. Calculations are based on the urban property loss, and crop loss potential throughout the year, crop distribution patterns, and weighted seasonal frequency flood events.
AGDAM/DAMCAL flood damage analysis entails evaluation of floodplain areas, calculation of expected annual damage, reach damage, structural damage categories, historic records, hydrologic data, ungaged location analysis, periods-of-record, buildings category damage, reach crop impacts/crop loss potential, crop distribution patterns, weighted seasonal frequency, flood, events, crop loss-duration values, and exceedance frequency events. WRMA engineers are trained in HEC-FDA methodology and apply state-of-the-art LiDAR/RADAR Hyper Spectral airborne/satellite-based remote sensing data of crop damage to perform AGDAM/DAMCAL model simulations.
Project Risk & Cost Analysis
WRMA engineers are well versed in flood risk and cost analysis using the HEC-FDA methodology to perform basin-wide economic evaluations. Basin-wide economic evaluations which incorporate risk-based analysis entail the application of the US Army Corps of Engineers (USACOE) Flood Damage Analysis Model, or HEC-FDA. This model uses risk-based analysis to express economic performance in terms of expected annual damages (EAD). A WRMA economic analysis is based upon the Principles and Guidelines (P&G) published in 1983 by the U.S. Water Resources Council. A primary WRMA objective in flood damage reduction studies is to determine the expected annual damage along a river reach, taking into account all possible flood scenarios, and to compare changes in the damage resulting from various alternative plans. Although not an economics program, the use of geographic information system software allows for the efficient identification of thousands of structures within a floodplain where digitized parcel maps are available. Critical input into HEC-FDA is derived from UNET (river channel stage-frequency relationships) and FLO-2D (floodplain depths and delineations). WRMA's risk based economic analyses can provide valuable insight for large scale projects undergoing NEPA regulated evaluations.