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Flooding <br /> Flooding could occur from runoff in Jahant Slough or from peak flows in the <br /> Mokelumne River. During the February 1986 storm, substantial inundation occurred from <br /> both sources. In the analysis of flood risk, Jones & Stokes Associates will: <br /> ■ refine the estimate of watershed runoff from Jahant Slough prepared by <br /> Kjeldsen-Sinnock&Associates using regional rainfall intensity-duration-frequency <br /> relationships and detailed watershed characteristics; <br /> ■ estimate long-term effects of possible future urbanization of the Jahant Slough <br /> watershed on runoff intensity; <br /> ■ estimate the frequency and rate of flood overflow from North and South Lakes; <br /> ■ refine and evaluate 100-year floodplain and designated floodway areas for the <br /> Mokelumne River using detailed site topography (maximum 2-foot contours) to <br /> be provided by Catwil Corporation; <br /> ■ evaluate effects of the proposed bridge, berms, and structures on conveyance <br /> capacity and 100-year floodplain for the Mokelumne River; and <br /> ■ evaluate the adequacy of the project design for flooding, including sizing of lakes, <br /> spillways, and pumping plants, land use, hydraulic capacity of the proposed <br /> bridge, and building pad elevations. <br /> Water Use <br /> The project will alter patterns of water use on the site. Presently, the lakebeds are <br /> dry farmed, and the only substantial use of water is for irrigating approximately 65 acres of <br /> grape vineyard in the southeast comer of the project site. With the project, overall water <br /> use would increase to meet the needs of evaporation and seepage from the lakes, irrigation <br /> of approximately 70 acres of golf course and pasture, and domestic use at 26 homesites. <br /> Three sources of water have been proposed: runoff from Jahant Slough, diversions from the <br /> Mokelumne River, and groundwater. The seasonal and long-term availability of these <br /> sources has not been determined. Environmental impacts would vary depending on the <br /> source of supply. In the analysis of water use and supply, Jones & Stokes Associates will: <br /> ■ calculate net consumptive water use for the entire site with and without the <br /> project under normal and dry climatic conditions; <br /> ■ calculate monthly water budgets for the lakes under normal and dry climatic <br /> conditions; <br /> III-12 <br />