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. . . regional regression equations for California. The regression equations are published in the USGS Water-Resources Investigations Report 77-21 entitled "Magnitude and Frequency of Floods in California" dated June 1977. The flood frequency analysis of gaged data was performed in accordance with the Water Resource Council's Bulletin 17-B. A test for low and high outliers was performed using the recommended procedures. Two low outliers were detected, and no high outliers were detected. A general skew value of -.2 was assumed for the study area. Based on the computerized analysis, the resulting flood frequency relations are presented in the table below. An additional hydrologic analysis was performed for the purpose of comparing results from more than one methodology. The USGS regional regression equations are based on flood frequency analyses of streamflow data from USGS gaging stations located within California. The regional regression equations relate flood magnitude (the dependent variable) to drainage basin and climatic characteristics (the independent "explanatory" variables). California was divided into six (6) distinct hydrologic regions because of widely ranging, complex basin physiography and climate. The 6 hydrologic regions include the North Coast, Northeast, Sierra, Central Coast, South Coast, and South Lahontan-Colorado Desert. The study area for this report is at the north end of the Central Coast region as defined by the USGS. The explanatory variables for the Central Coast region flood-frequency equations include drainage area, mean annual precipitation, and altitude index. For the purpose of this study, the drainage area and altitude index for the watershed of interest were estimated from the San Jose, California USGS I :250,000 scale topographic map. The mean annual precipitation for the basin was estimated using available information in the USGS WRI 77-21 document. There are several reservoirs located in the upper portion of the arroyo's watershed including the previously mentioned Del Valle Reservoir. The Del Valle Dam was constructed in 1968 by the California Department of Water Resources. That reservoir was not originally constructed for the sole purpose of providing flood control for downstream properties and interests. Therefore, it was asswned that peak flood flows at the subject property would not be reduced substantially during a major flood event. The reservoir would release or pass-through the high flows in cases where it was already filled to capacity. Reservoir storage and routing for flood control purposes is not accounted for in the regional regression equations, and was not performed for this study. In addition, the affects of increased urbanization have not been specifically accounted for in the USGS regression equations which date back to 1977. Hvdrolol!ic SUmmary The results of the hydrologic analyses are presented in the table below. 3