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RED MESA WARD SITE HYDROLOGY <br /> FLOOD HYDROLOGY <br /> Background <br /> The purpose of this section is to detail the prediction of the Inflow Design Flood(IDF) generated <br /> by the Probable Maximum Precipitation(PMP) for Red Mesa Ward Reservoir. Since the dam is <br /> classified as a Class I structure, the full PMP is applicable. The approximate latitude and <br /> longitude of Red Mesa Ward Reservoir is 37°10'00" and 108°08'30", respectively. The dam is <br /> located in the NE1/4 of Section 27, Township 34 North, Range 12 West of the New Mexico <br /> Principal Meridian. The PMP was developed according to the procedure outlined in <br /> Hydrometeorological Report No. 49 (National Oceanic and Atmospheric Administration <br /> [NOAA]). The tributary basin was divided into eight subbasins ranging in size from 2.88 to 4.79 <br /> square miles. Unit hydrographs were developed for each basin using Excel spreadsheets. Unit <br /> hydrographs and precipitation data were entered into.the HEC-1 program to carry out runoff <br /> simulations. <br /> Probable Maximum Precipitation <br /> The PMP estimate was developed using Hydrometeorological Report No. 49, Probable <br /> Maximum Precipitation Estimates, Colorado River and Great Basin Drainages, a NOAA <br /> publication, hereafter referred to as HMR No. 49. The procedure gives PMP estimates for both <br /> the general storm and the local storm (thunderstorm). In the case of the general storm, PMP <br /> estimates are developed for several durations, specifically 6, 12, 18, 24,48 and 72 hours. For the <br /> local storm, a duration of 6 hours is implicit. It is left to the engineer to determine which storm is <br /> the more critical based on the problem at hand. For the purpose of determining the feasibility of <br /> enlarging Red Mesa Ward Reservoir, the local storm is the controlling precipitation event <br /> because of the intensity. This is consistent with the United States Bureau of Reclamation <br /> (USBR) experience in this region. Table 1 below summarizes the results of PMP estimates for <br /> local and general storms. <br /> 991-077.070 Wright Water Engineers, Inc. Page 1 <br /> September 2002 <br />