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FLOOD05134
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Last modified
1/25/2010 6:48:21 PM
Creation date
10/5/2006 1:17:08 AM
Metadata
Fields
Template:
Floodplain Documents
County
Jefferson
Community
Lakewood
Stream Name
South Lakewood Gulch
Basin
South Platte
Title
Flood Hazard Area Delineation
Date
7/1/1977
Prepared For
Lakewood
Prepared By
UDFCD
Contract/PO #
&&
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />., <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Equations. There are two basic equations used in defining the limits <br />of the synthetic hydrograph. The first equation defines the lag time <br />of the basin in terms of time to peak, tp, which, for CUHP is defined <br />as the time from the center of the unit storm duration to the peak of <br />the unit hydrograph. This study used a 10 minute storm duration. <br /> <br />I <br /> <br />tp <br /> <br />= <br /> <br />Ct (L Lca).3 <br /> <br />(HA-1) <br /> <br /> TABLE HA-2 <br /> CUHP BASIN CHARACTER I ST I CS <br /> _ 9ls.!.i!!.9_ _i.u.!.u.!:e_ <br />Subbasin Area L Lca S Ct 2- Ct ~ <br /> 0.27 1. 23 0.63 0.04 0.45 0.72 0.45 0.72 <br />2 0.54 1. 32 0.57 0.04 0.54 0.78 0.39 0.68 <br />3 0.27 0.66 0.38 0.025 0.45 0.72 0.43 0.72 <br />4 0.2t 0.66 0.28 0.02 0.40 0.68 0.40 0.68 <br />5 0.31 1.25 0.83 0.02 0.39 0.68 0.39 0.68 <br /> <br />where tp <br /> <br />= <br /> <br />time to peak of hydrograph from midpoint of <br />unit rainfall in hours <br /> <br />I <br /> <br />L <br /> <br />= <br /> <br />length along stream from study point to upstream <br />limits of the basin in miles <br /> <br />I <br /> <br />Lca <br /> <br />= <br /> <br />distance from study point along stream to the <br />centroid of the basin in miles <br /> <br />I <br /> <br />Ct <br /> <br />= <br /> <br />a coefficient related to time to peak <br /> <br />I <br /> <br />qp <br /> <br />= <br /> <br />(HA-2) <br /> <br />DETERMINATION OF DESIGN FLOWS - MITCAT <br /> <br />As previously mentioned, the MITCAT computer model was used fo~ stre~m <br />routing of the CUHP-generated subbasin hydrographs. A brief diScuSSion <br />of MITCAT is presented below, with emphasis on stream routing. <br /> <br />Introduction to the Catchment Model. The Catchment Model, developed at <br />MIT under the U.S. Department of Interior, Office of Water Resources <br />Research Grant No. 14-01-0001-1576(1), is a general purpose simulation <br />model of a watershed. The model is formulated in a problem oriented <br />language with a flexible command structure that permits selection from <br />many input/output and computational options available in the mode~. <br />The basic coding language of the model is Fortran IV. The fol~owlng <br />paragraphs are excerpts from a paper explaining the model, entitled, <br />"Evaluation and Control of Urban Runoff," by John C. Schaake, Jr., Guy <br />Leclerc, and Brendan M. Harley, which was presented at ASCE Annual and <br />National Environmental Engineering Meeting, October 29 through November <br />1, 1973, in New York City. <br /> <br />"Urban hydrology research during the past two decades at the Johns <br />Hopkins University and Massachusetts Institute of Technology has <br />led to the development of practical mathematical models for simu- <br />lating the occurrence of storm rainfall and the movement of th~s <br />water through the environment. These models assume that dynamiC <br />water movement is governed by underlying physical principles of <br />conservation of mass and momentum. There is a sound basis in pro- <br />bability theory for the models to estimate recurrence int7rvals of <br />ungaged events. Tests with limited available data have given <br />splendid results, and the models have been applied to many practi- <br />cal engineering problems. <br /> <br />The second equation defines <br /> <br />the unit <br />C 640 <br />p <br />t <br />p <br /> <br />peak of the unit hydrograph <br /> <br />I <br /> <br />The Cp and C values are empirical and should be based on similar <br />basins that ~ave been instrumented to obtain the actual rainfall- <br />runoff relationships. The Cp and Ct values used in this study are <br />based on values determined from Figures 4-2 and 4-3 of the Urban <br />Drainage Criteria Manual. When selecting the Cp and Ct values f0r <br />the various basins, the area, the shape, and slope were considered <br />along with probable future conditions such as type or development <br />and percent of impervious area. <br /> <br />I <br /> <br />I <br />I <br /> <br />The process of computing excess precipitation, and then the unit <br />hydrograph, was followed by multiplying the two to obtain the design <br />storm hydrograph. This is lengthy and time consuming if done by <br />hand. For this reason, a computer was used. The data fed into the <br />computer for each basin consisted of: the area, the basin length <br />parameters, Cp' Ct, percent pervic~s area, and the precipitJtion <br />infiltration, along with the design retentions for the pervious and <br />impervious areas. <br /> <br />I <br /> <br />I <br /> <br />Table HA-3 tabulates the various coefficients that were used for the <br />CUHP. Areal values are shown in square miles, with all lengths <br />expressed in miles. The coefficients, Ct and Cp, (as well as slope <br />values) are dimensionless. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br />
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