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CITY OF SANTA ANA <br />CYI <br />Section 5: Base Flood Elevation Approved <br />FOR PERMIT ISSUAN E <br />Per "A Guide for Obtaining and Developing Base (100-year) Flood Elevations" published by FEMA <br />in April 1995, since this is a development of less than 5 acres project, the "Normal Dep is <br />adequate for determining Base Flood Elevation (BFE). Date: <br />Normal depth is the depth expected for a stream when the flow is uniform, steady, one dimensional, <br />and is not affected by downstream obstructions or flow changes. For uniform flow, the channel <br />bottom slope, water -surface slope, and energy slope are parallel and are, therefore, equal. For normal <br />depth computations, the flow is considered steady because the discharge is assumed to be constant; <br />therefore, the depth of flow does not change during the time interval under consideration. <br />Normal depth calculation computes BFE at a cross section. The standard formula for determining <br />normal depth at a cross section is Manning's formula. <br />Manning equation: Q= (1.49/n) x A x R11 x S12 <br />A = 230 SF <br />R = A/P = 230/44 = 5.227 ft <br />S = 0.0118 <br />n = 0.03 <br />Qca1= 3,737 cfs > Qioo= 1,600 cfs. <br />4 BFE = 67.02 + 10 = 77.02 ft. <br />Adding 1' for safety, we can interpolate a BFE of 78.02' will be sufficient to protect against flooding <br />during a 100-year event <br />