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Guide For Approximate Zone A Areas Developinq BFEs differ significantly depending on the Manning's "n" values used; therefore, care should be taken to ensure that the Manning's "n" values selected accurately reflect conditions at the site being analyzed. Manning's "n" values should be selected based on field inspection, field photographs, and topographic mapping. A list of accepted Manning's "n" values has been included in Appendix 5. Various methods for computing normal depth are described below. Computer Proqrams for Computinq Normal Depth In addition to QUICK-2, the following Federal Government computer programs have the capability to perform normal depth computations: Computer PrOqram HEC-2 HEC-RAS WSPRO WSP2 SFD PSUPRO Aqencv U.S. Army Corps of Enqineers U.S. Army Corps of Engineers U.S. Geological Survey NRCS FEMA FEMA Please note that HEC-RAS is still being tested and had not yet been released to the general public when this guide was published. Furthermore, FEMA has not yet approved the model for requests to revise NFIP maps. Please contact our Headquarters office to determine the current status of HEC- RAS. In addition to the above-referenced programs, there are other engineering computer programs and models, which perform normal depth calculations, that are available through various commercial vendors. References for the hydraulic computer programs listed above are in Appendix 7. Normal Depth Hand Calculations If a computer is not available, it is possible to perform hand computations to calculate normal depth for the 10D-year flood at a cross section by following steps 1-11 listed below. Step 1 - Obtain a topographic map or conduct a field survey to obtain a cross section at the site where normal depth should be determined. If a topographic map is used, the channel geometry should be obtained from measurements taken in the field. The cross section should be oriented perpendicular to the expected 100-year floodplain. V-24