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<br />k lot z 4~. ass 0 cia t e s <br /> <br />water level which is the lower of the top of bank or ground levels in areas immediately <br />beyond the berms forming the banks of the channel. <br /> <br />3.4.2 Non-FEMA-Modeled Channels <br /> <br />When a FEMA model is not available for a primary channel or major tributary, an <br />approximate model is created by assuming the flow in the channel to be at normal depth. <br />Available data, including field survey data collected for this study, are used to define the <br />in-channel cross sectional shape of the channel in question. Representative bottom slope <br />is obtained from field survey data. With representative channel shape and slope <br />determined, the depth versus discharge relation for the chmmel can be determined using <br />the Manning equation. <br /> <br />The hydraulic model, therefore, for a non-FEMA models station is the set of data <br />defining channel shape and slope and the Manning equation which uses these data. <br /> <br />3.5 Evaluation of Storage Requirement <br /> <br />Storage is determined when a detention pond is to be sized to reduce peak discharge in a <br />channel. Depending upon the available model for the channel, the information available <br />to compute storage, and the purpose of the detention storage, somewhat different methods <br />are used to compute required storage volumes. <br /> <br />3.5.1 Mitigation Storage for Channel Widening <br /> <br />For mitigation of channel improvements involving channel widening, the mitigation <br />storage was estimated as the volume of excavation for the widening. <br /> <br />3-7 <br /> <br />Klotz Associates Project No. 0127.008.000 <br />January 2009 <br /> <br />La Porte Citywide Drainage Study <br />City of La Porte <br />