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stored within the alluvium, and falling stages allow some of the stored water to percolate back into the river. Project Area Surface HvdroloQy The proposed 120 acre gravel extraction site is located within the historic flood plain of the Mokelumne River. The flood plain is surrounded on the south, east, and west, by bluffs reaching elevations 50 feet above typical project site elevations. In the project area most of the historic flood plain of the Mokelumne River no longer functions as the active flood plain because of the confinement of the river on the south side by man-made levees and the construction and operation of Camanche Reservoir. Natural river banks form the north side of the river channel and the generally higher banks on the south side of the river channel were created as man-made levees (San Joaquin County, 1974). Field inspection of the levees revealed no undercut banks or surface erosion, except in one localized area immediately downstream of the Mackville Bridge. Approximately 30 feet of the south levee face has been eroded, exposing the sand substrate to continued degradation. Streambed sediments consist primarily of sands, with very few deposits of gravel. There is no deposition in the form of point bars, and only two small riffle sites were observed. In the late 1800's and early 1900's the channel in the project area was dredged for gold. This activity altered the course of the river (Sal: Joaquin County, 1974) and the dredged sediments were probably used to build up the natural river banks to form the levees which currently protect the surrounding farmland. The maximum controlled release from Camanche Dam is 5,000 cfs under US Army Corps of Engineers (COE) prescriptions for reservoir operation (U.S. Army Corps of Engineers, 1981). At this maximum planned release, the river would be expected to reach an elevation of approximately 76 feet in the project vicinity, which is from 1 to 30 feet below the top of the existing banks and levee. Figure 3.2-1 shows the location of the proposed project in relation to the 100 and 500 year floodzones. The floodzones were based on the Flood Insurance Rate Map 28