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<br />Flood Control <br /> <br />Lake Mead is operated in accordance with updated flood <br />control regulations which are specified in the Field Working <br />Agreement between Reclamation and the Corps of <br />Engineers, signed in 1982, The regulations stipulate the <br />minimum release levels needed from Lake Mead to route the <br />reasonable maximum inflow, The reasonable maximum <br />inflow is the estimated inflow volume that, on the average, will <br />not be exceeded 19 out ofWtimes. This volume is derived by <br />adding an "uncertainty' term to the most probable runoff <br />forecast. In 1983, unusual hydrometeorological events <br />resulted in unprecedented large forecasting errors. <br />Subsequent reassessment of the estimate of the "uncertainty" <br />term led to adoption of larger values for use in determining <br />the reasonable maximum inflow in 1984 and thereafter, <br /> <br />No flood control releases are scheduled for 1990, but in future <br />years, as Lake Mead refdls and flood control releases are <br />again required by the Hoover Dam flood Control <br />Regulations, consideration will be given to making those <br />releases over the fall and winter months to avoid high flow <br />rates during the January to July runoff season, This <br />distribution of water reduces the chance of bypassing <br />hydroelectric powerplants below Hoover Dam and avoids the <br />adverse impacts of higher flood control releases on fish and <br />wildlife, recreation, water quality, and river stabilization, <br /> <br />Routine maintenance and repair of banklirie damage was <br />carried out during water year 1989. As in the previous year, <br />some bankline erosion was experienced in the Lower Basin of <br />the Colorado River, In some river reaches, especially the <br />Mohave Valley, greater than normal bankline repair was <br />necessitated in part by increased wave action from boating <br />and other recreational river traffic, During water year 1989, <br />the river channel in the Lower Basin has remained in good <br />balance, neither aggrading nor degrading significantly in any <br />particular reach, <br /> <br />Total Colorado River reservoir system storage at the start of <br />water year 1989 was approximately 52,404,000 acre-feet and <br />about 48,183,000 acre-feet at the end of the water year, <br />representing a 4,221,000 acre-foot increase in total remaining <br />available reservoir space, <br /> <br />Alamo Dam on the Bill Williams River (in the Lower Basin) <br />received minor flood inflow during water year 1989, During <br />water year 1990, Painted Rock (Gila River) and Alamo <br />Reservoirs are scheduled to be operated in accordance with <br />established flood control criteria to maximize the available <br />flood control space in their respective reservoirs, <br /> <br />22 <br />