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Mokelumne River. For ten miles downstream of the Camanche Reservoir, natural runs of anadromous Chinook salmon and steelhead utilize the river for spawning and rearing (Wixon, L. Pers. comm.). Between Clements and the San Francisco Bay Delta, the Mokelumne River ordinarily flows across its flood plain within a channel averaging 75 to 150 feet wide, and 15 to 30 feet deep. Under natural conditions the river would overflow this channel during peak discharge events, occupying intermittent flood channels and inundating its flood plain. However, this natural regimen has been modified by the construction of levees so that floodwaters are more frequently confined to the active river channel. The climate of the Mokelumne River basin is characterized by wet, cool winters and hot, dry summers. Precipitation varies widely with elevation, and ranges up to approximately 100 inches in the upper elevations. In the vicinity of the proposed project, average annual rainfall is approximately 17 inches (Sar? Joaquin County, 1973). The USGS maintains a streamflow gaging station 1.0 mile downstream from Camanche Reservoir (i.e., 3.4 miles northeast of Clements). The average annual discharge at the gaging station between 1929 and 1982 was 809 cubic feet per second (cfs), with a peak discharge of 28,800 cfs in 1950. Since the creation of Camanche Reservoir the peak discharge has been considerably reduced, reaching a maximum streamflow of 5,000 cfs in 1986. Groundwater A substantial amount of groundwater recharge occurs adjacent to the Mokelumne River, particularly over lands within the historic flood plain (Sedway Cooke Associates, 1989). These are lands with deep and youthful soils developed from alluvium, particularly in the middle section of the Central Valley plain. The Eastern San Joaquin County Groundwater Basin is the principal aquifer underlying the region, and has been subject to critical conditions of overdraft (DIVR, 1980). Seepage loss from the river into the alluvium of the flood plain tends to be intermittent and alternates with seepage gain (USGS, 1939). The rate of loss or gain can lag months behind the fluctuations of river stage. Rising river stages cause water to be 27