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r 4.6 WATER RESOURCES Vineyard Irrigation The existing vineyard on the site is planned to be retained and will require a continuing supply of water. Water for the 65 acres of grapes currently in production is supplied from an existing on-site agricultural well, which is expected to be retained for this purpose. The estimated annual water demand for the vineyard(current and future) is 100 to 130 acre-feet, based on an annual irrigation water demand of 18 to 24 inches. Golf Course. Pasture and Restoration Irri age tion The proposed golf course would have an estimated 68 acres of greens and fairways requiring irrigation. Additionally, irrigation would be needed for approximately 19 acres of new pasture plus 20 acres of restored riparian vegetation and 45 acres of restored savanna. The irrigation needs will vary seasonally, from essentially zero in the winter months, to a maximum of about 540 gallons per minute during the summer (or about 780,000 gallons per day). The total annual water demand for the golf course, pasture and restoration area is estimated to be approximately 400 acre-feet. (This calculation is shown in Table 4.6-3 and is less than the applicant's estimate of 540 acre-feet per year.) The applicant proposes to meet this irrigation requirement by drawing upon water stored in the Tracy Lakes. Irrigation requirements are subject to change when landscape plans for the entire development are finalized and the forest and oak/savanna restoration projects are established. Lake Water Level Maintenance The proposed project calls for converting the North Lake to a year-round water body,with a relatively constant lake level. The South Lake would serve effectively as a water storage reservoir, from which make-up water for the North Lake (i.e.,to compensate for evaporation),and irrigation water for the golf course and pasture would be supplied. The water level in the South Lake would fluctuate seasonally, but with the intent of always maintaining a minimum water level. Evaporation and lake water levels will vary from year-to-year according to rainfall runoff conditions. The actual evaporative losses from the lakes are estimated to range from about 800 to 1,100 acre-feet per year. In wet years, this water requirement can be expected to be met from the storage of local runoff from the Jahant Slough watershed. However, in drier years, and especially in periods of successive dry years (e.g., such as the past five years), additional water would need to be obtained from the Mokelumne River and/or from pumping of local groundwater to maintain the proposed water level conditions in the lakes, while also supplying irrigation needs. The following section presents a detailed water balance analysis for estimation of the probable needs for surface water diversion or groundwater pumping to support the water supply needs of the project. 4.6-9