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River Regulation The runoff into Lake Powell during water year 1988 was approximately 70 percent of normal and water year 1989 runoff was approximately 54 percent of normal, The low runoff years of 1988 and 1989 have caused a drawdown in each of the Colorado River system reservoirs, The October I, 1989, system vacant space was approximately 13,1 maf, This vacant space has resulted from the two successive years of low inflow and the requirement to maintain the minimum deliveries to meet obligations pursuant to "The Law of the River." Daily releases are provided from the storage reservoirs in the Lower Basin to meet the needs of water user agencies, for river regulation and as needed for flood control. When possible, all water passes through the powerplant units. The daily releases are regulated on an hourly basis to meet, as nearly as possible, the power needs of the hydroelectric power customers. At appropriate locations, minimum instream. flow objectives have been established, which preserve the present aquatic resources downstream of certain Colorado River dams. In many cases, these resources were poor or nonexistent prior to the time of dam construction. and the subsequent minimum, cool water releases have provided an improved environment for aquatic resources and sport fisheries, fn general, controlled releases allow for an extended recreation season, and reduce the high flow periods in May and June. Water years 1988 and 1989 have been drier than normal and a return to more normal runoff levels in future years will provide increased benefits to fish, wildlife and recreation uses as it will to the other project purposes, Remedial modifications, including construction of a relief well and seepage collection system downstream of Senator Wash Dam, were completed and a seepage evaluation program performed in March of 1989. Normal water conservation operations of Senator Wash reservoir have resumed; however, the collector ditch required some further modification to meet design specifications, Senator Wash reservoir was drawn down for about a month at the beginning of water year 1990 to accomplish these modifications, Water deliveries were lower during this period, and the cooler fall temperatures promoted health and safety of the work force and resulted in a lesser impact on fish and wildlife resources, The water conservation operation of Senator Wash will now allow regulation of water deliveries to Mexico without over-deliveries except during rainstorm events, Operational objectives at and below Laguna Dam are to conserve water, control sediment, and maintain the river channel. Storage of water above Laguna Dam in the reservoir, in surcharge, and in bank storage provides for controlled flows in the river at Yuma, which combined with seepage and drainage, allows a continuous live stream serving recreational and fish and wildlife purposes, On a few occasions each year, higher daily flows below Laguna, caused by rainstorms or user rejected water orders, are used to maintain sufficient river channel capacity. This occasional practice reduces channel maintenance expense without impairment to water conservation or power production. Because of existing reservoir conditions and river regulation operations below Hoover Ilanl,flie total water year 1989 delivery to Mexico was approximately 200,000 acre-feet in excess of the scheduled treaty delivery of 1,500,000 acre-feet for the calendar year. Of that amount, 136,000 acre-feet of drainage waters were bypassed to the Gulf of California via the Bypass Drain during water year 1989, This bypass channel was constructed pursuant to provisions of Minute No. 242 of the International Boundary and Water Commission. 21