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I I Page Six Battlement Ilesa Development Storm Drainage and Flood Plain Study I through existing gauging stations. At the present time, there are no satisfactory gauging stations with rainfall-recording gauges in the immediate vicinity of the site. As data becomes available from the numerous environmental analyses stations being constructed throughout the oil shale area, it is possible that far better calibration of rainfall-runoff relationships may be obtained. However, at this time, the best procedure is to compare various methods to determine the most reasonable set of rainfall-runoff relationships to be applied to the project area. I II ,- , II i II I I The Monument c,ulch basin was selected for the trial basin as its drainage basin boundaries are unaffected by the develop~ent. The basin also incorporates virtually all the types of land to be encountered in the overall project. The gulch has an area of 4.99 square miles, a lenqth of 6.16 miles, a length to centroid of the basin of 3.22 miles and an average slope of 10.46%. Soils analyses of the basin indicate that the soil has a moderate infiltration rate. CO'ler types predominant within the basin consist of juniper/pinon woodlands, scrub oak woodlands and juniper/big sagebrush. The comparative analysis among the three hydrological procedures vTas conducted on rainfall return frequencies of once in two years, ten years and 100 years. This analysis of different frequency storms allowed the relative effects of the three procedures to be tested against both varying rainfall intensities and varying soils and cover types. I I I The SCS method was evaluated using curve numbers of 65, 70 and 80. Th,~se curve numbers are characteristic of conditions ranging from sage grasslands with 50% cover density on moderately permeable soils to juniper grass with a 30% density on moderately permeable soil. The sensitivity analysis results obtained are shown in Table I. I I I TABLE I SCS METHOD SEIlS ITIVITY ANALYSIS Return Freauency CN = 65 Cll = 70 CN = BO 100 year 437 cfs 655 cfs 1185 cfs 10 year 103 cfs 196 cfs 506 cfs 2 year 0 cfs 35 cfs 173 cfs I I I