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<br />k lot z ~~. ass 0 cia t e s <br /> <br />3.3 Hydrologic Models <br /> <br />Hydrologic models were used to describe runoff magnitudes and flow in channels. For <br />evaluation of primary channels and major tributaries, hydrologic models were available <br />from TSARP studies or were developed for evaluation of primary channels and major <br />tributaries. <br /> <br />3.3.1 HEC-HMS Hydrologic Models for Primary Channel Drainage Areas <br /> <br />HEC-HMS hydrologic models for entire drainage areas defined by most of the primary <br />ch8.1mels are available as a consequence of the TSARP program (these models are <br />available online from HCFCD). These models use the Tc+R method (a specialized <br />version of the Clark unit hydro graph method) developed and used by HCFCD. Key <br />parameters in these models are drainage area, time of concentration Tc, storage parameter <br />R, channel length L, and level of development as characterized by the DLU parameter, <br />the latter affecting Tc, R, and imperviousness values. Each watershed for which a HEC- <br />HMS model was available has a separate HEC- HMS model with its own set of <br /> <br />par8.1neters. <br /> <br />These models are used to define not only peak discharge for the storm event frequency of <br />interest but also the entire shape (i.e., discharges) of the runoff hydro graph. <br /> <br />3.3.2 Hydrologic Models for HEC-HMS Sub-Areas <br /> <br />For drainage areas within a drainage area with a HEC-HMS model but of lesser size than <br />the full drainage area for which a HEC-HMS model is available, the peak discharge and <br />hydro graph discharges were determined by prorating discharges according to drainage <br /> <br />area SIze. <br /> <br />3-4 <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 />