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<br />I <br />I <br />:1 <br />'I <br /> <br />Page Five <br />Battlement Ilpsa Development Storm Drainage and Flood Plain Study <br /> <br />2. Extend the precipitation values obtained <br />from the Precipitation - Frequency Maps for <br />Colorado by use of the rainfall depth-duration <br />diagram contained in Technical Paper 40. <br /> <br />3. Use the Depth-Duration-Frequency Graphs in <br />the Urban Storm Drainage Criteria Manual to <br />determine precipitation amounts for very short <br />dura tion E; torms . <br /> <br />I <br />:1 <br />I <br />I <br />II <br />II <br />il <br />I <br />II <br /> <br />The design rainfall values obtained by this method are <br />shown in FigurE' 1, Rainfall Depth-Duration-Frequency Graphs <br />for the Battlement r.1esa region. This data has also been converted <br />into Intensity-Duration-Frequency Curves as shown on Figure 2. <br /> <br />III. Hydrological /1ethods <br /> <br />Three basic methods of hydrological analysis have been <br />reviewed and compared before selecting the methods utilized <br />for the storm drainage study. Those methods analyzed consist <br />of the following: <br /> <br />1. Soil Conservation Service (SCS) method from <br />"Procedures for Determining Peak Flows in Colorado," <br />dated December, 1972, and published by the U. S. <br />Department of ~griculture Soil Conservation Service. <br /> <br />2. Rational method with modifications as recommended <br />in the Urban Storm Drainage Criteria Manual, March, <br />1969, published by the Denver Regional Council of <br />Governments. <br /> <br />3. Colorado Unit Hydrograph Procedure as outlined <br />in the Urban Storm Drainage Criteria Manual <br />previously referenced. <br /> <br /> <br />I <br />I <br />I <br /> <br />These methods represent both empirical and synthetic <br />approaches to modeling storm water runoff. They are based upon <br />accepted rainfall-runoff relationships characteristic of the <br />area and account for around cover, soils, ground slope and <br />other basin parameters. The best method of selecting the <br />coefficients and characteristics of empirical and synthetic <br />hydrology approaches is to compare them with recorded events <br /> <br />I <br />I <br />I <br />