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reducing the capacity of the river to transport sediment close to the quarry site. Because the potential for the project to impact channel alignment is small, this potential impact is considered less than significant. Bridee Relocation The approximate site for bridge relocation has a south bank levee elevation of 83 feet and a north bank levee elevation of 78.8 feet. The water surface elevation at this location with 5,000 cfs discharge would be 75.8 feet based on predicted river stages (USGS, 1972). At an 18,000 cfs discharge (discharge for the 100 year flood), the river would reach an elevation of approximately 85 feet. Therefore, the bridge, if constructed at the top elevation of the south side levee, would be inundated by 2 feet of water with the 100 year flood. The analyses of flood stage by USGS was based upon conditions surveyed in 1970 and makes the following assumptions: (1) no levee failures; (2) no additional encroachment in channel by land reclamation and levee construction; (3) no additional encroachment by trees and brush; and, (4) no change in streambed elevations. If any of these assumptions are no longer valid, then inundation of the bridge and surrounding farmlands could occur with a smaller discharge than those indicated in the USGS report. If the bridge span requires construction of structural supports in the channel or fill and pilings on the levee, then the channel capacity could be reduced. Any constriction of the channel would decrease flood carrying capacity, resulting in a higher river stage for a given discharge. Flow velocities would also become greater, increasing the probability of scour on the channel bottom and erosion along the levee banks. A reduction in channel capacity would increase the chance that levees would be breached during flood flows, inundating land adjacent to the channel and possibly damaging the levees. If the levee were to fail, the extent of flooding would cover an area larger than the floodzones delineated in the FIRM. The quarry site could become inundated during flood flows and any exposed topsoil stockpiled could be entrained, increasing siltation to the Mokelumne River. Increased sedimentation may also occur due to the demolition of the old bridge site and construction at the relocation site. Sediments deposited 33