The flood mapping partner responsible for model review will compare the models in the submitted or scoped version of HEC-RAS and HEC-RAS 3.1.1 or the latest version accepted by FEMA, and document the differences. Studies and restudies that are in progress (e.g., submitted to or contracted by FEMA) at the date of this Memorandum and that use versions of HEC-RAS prior to 3.1.1 will be completed in the submitted or scoped HEC-RAS version. After the date of this Memorandum, new modeling in studies, restudies, and LOMCs must use HEC-RAS 3.1.1 or a later version. The latest version of HEC-RAS, accepted by FEMA for NFIP studies, is to be used for all new modeling in studies, restudies, and Letters of Map Changes (LOMCs). Final Procedure: The following steps are recommended: 1. HEC-RAS 2.2 has been used to design flood-control projects if WSELs increase as a result of HEC-RAS version changes, these projects may be decertified due to inadequate freeboard.Īction Taken: The purpose of this Memorandum is to establish and clarify the decision-making processes that flood mapping partners apply to flood map revision requests involving HEC-RAS. 4.Ī large number of FEMA’s effective studies are based on HEC-RAS 2.2 or HEC-RAS 3.0.1. Models with bridges coded in the HEC-2 special bridge format are especially susceptible to differences. In contrast, models with bridges originally imported from HEC-2 models and not upgraded to HEC-RAS standards are the most susceptible to differences in WSELs and floodway surcharges.
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Models with bridges that are coded according to theĢ HEC-RAS User’s Manual are the least susceptible to differences in WSELs and floodway surcharges. The issue of varying WSELs and floodway surcharges is directly related to the quality of the bridge modeling in a simulation. The WSELs and floodway surcharges are often higher in HEC-RAS 3.0+ models than in HEC-RAS 2.2 models.Īt times, floodway surcharges significantly increase between HEC-RAS 2.2 and HEC-RAS 3.0+ estimates, violating maximum surcharge standards. For some cases, HEC-RAS 3.1.1 produces different WSELs and floodway surcharges than HEC-RAS 3.0.1. Issue: HEC-RAS 3.0 and later versions (HEC-RAS 3.0+) produce different water-surface elevations (WSELs) and floodway surcharges than HEC-RAS 2.2 with the same channel geometry and flow rates. The HEC-RAS program may be downloaded from the USACE website at. The USACE no longer supports HEC-RAS 2.2.
![hec ras downloads hec ras downloads](https://download.comet.ucar.edu/memory-stick/hydro/damfailure/applications_int/media/graphics/hec-ras-website.jpg)
In addition to adding new features, errors found in earlier versions were also corrected. HEC-RAS Version 3.1.1 was released by the USACE in May 2003 and the latest version, HEC-RAS 3.1.2, was released in June 2004. In April 2003, the HEC-RAS 2.2 version was removed from FEMA’s Nationally Accepted Models list and replaced with the HEC-RAS 3.0 and 3.1 versions. For your convenience, this memorandum is posted on FEMA’s Flood Hazard Mapping website at.
![hec ras downloads hec ras downloads](https://www.hec.usace.army.mil/software/hec-dssvue/images/main-page1.png)
FEMA issued a memorandum dated April 30, 2001, on the use of HEC-RAS for the National Flood Insurance Program (NFIP).
![hec ras downloads hec ras downloads](https://image1.slideserve.com/1963706/slide1-l.jpg)
Army Corps of Engineers (USACE), HEC-RAS is a widely used hydraulic model for the development and revision of flood studies. Regional Engineers, Regions I-X Bill Blanton, Project Officer Central Studies Team Max Yuan, Acting Project Officer Western Studies Teamĭoug Bellomo, P.E., CFM, Acting Chief Hazard Identification Section īackground: Developed by the U.S.