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46 WATER RESOURCES ENVIRONMENTAL SETTING The project site is located in the central portion of California along the eastern edge of the San Joaquin Valley. The site is adjacent to the area known as the Sacramento-San Joaquin River Delta. Elevations of the region vary from 20-to 35-feet above mean sea level (MSL). The average annual rainfall at the i project site and surrounding watershed ranges from 16 to 18 inches. The climate of the region is characterized as Mediterranean, with wet winters and dry summers. The region's "rainy" season extends between the winter months of November and April, with relatively dry conditions for the remainder of the year. Temperatures may range from below freezing in the winter to above 100 degrees Fahrenheit during the summer months. The area's drainage is characterized by large perennial streams, flowing from the western slopes of the Sierra Nevada mountain range. These streams broaden and slow as they reach the lower elevations around the site. Many of the streams have been dammed and their water is used for water supply or irrigation in the surrounding agricultural areas of the San Joaquin Valley. The Buckeye Ranch development is designed around the hydrologic features of the site. These features include Jahant Slough,the Mokelumne River, and a series of ephemeral lakes known as the Tracy Lakes. Tracy Lakes represent the terminal drainage point for the Jahant Slough watershed. These lakes were probably created by sediment deposition from the adjacent Mokelumne River, cutting-off the hydraulic connection between Jahant Slough and the river. There are two lakes, North and South. The northern lake is the smaller of the two, covering approximately 85 acres and draining an area of approximately one square mile. The southern lake drains an area of 16.5 square miles and covers approximately 265 acres. When both lakes are full, the maximum water surface elevation is about +25 National Geodetic Vertical Datum(NGVD). Water above this level spills over and flows into the Mokelumne River. The water surface elevation of the lakes fluctuates based upon the amount of rainfall and local runoff received during the winter months. Lake levels in normal or dry years are below capacity and there is no out flow to the Mokelumne River. Witnessed accounts reveal that it usually takes a "wet" winter (at least 20 inches of rainfall) to fill the existing lakes completely (Catwil Corporation, 1990). The Mokelumne River has a watershed of 661 square miles. This river, flowing year round,has a yearly average discharge of 600 cubic feet per second (cfs), an average dry season discharge of approximately 20-30 cfs, and a total average water yield of approximately 434,700 acre-ft per year (USGS, 1991). 4.6-1