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<br />River Regulation <br /> <br />Daily releases lICe made from the storage reservoirs in the <br />Lower Basin to meet the incoming orders of the water user <br />age.ncies or for the regulation of higher flood control and <br />releases of excess water, When possible, aU water passes <br />through the powerplant units. The daily releases are regulated <br />on an hourly basis to meet as nearly as possible the peaking <br />power needs oflhe hydroelectric power customers, Minimum <br />daily flow objectives are provided in the river to maintain <br />flsbery habitat. <br /> <br />The combination of high runoff conditions and river <br />regulation below Hoover Dam resulted in a total water year <br />1987 delivery to Mexico of approximately 4,7 MAP in excess <br />of the scheduled treaty quantity (1.7 MAF per calendar year). <br />Of that amount, 125,000 acre-feet of drainage waters were <br />bypassed to the Gulf of California via the Bypass Drain during <br />waler year 1987, This bypass channel was constructed <br />pursuant to provisions of Minute No, 242 of the International <br />Boundary and Water Commission, <br /> <br />Flood Control <br /> <br />Lake Mead is operated in accordance witb updated flood <br />control regulations which are specified in the Field Workiug <br />Agreement between Reclamation and the Corps of <br />Engineers, signed in 1982, The regulations stipulate miuimum <br />release levels from Lake Mead to route the reasonable <br />maximum inflow, The reasonable maximum inflow is the <br />estimated inflow volume that, on the average, will not be <br />exceeded 19 out of 20 times. This volume is derived by adding <br />an "uncertainty" term to the most probable ruooff forecasLln <br />1983, unusual hydrometeorological events resulted in <br />unprecedented large forecasting errors. S ubseq uent <br />reassessment of the estimate of the "uncertainty" term led to <br />adoption of larger values for use in determining the probable <br />maximum inflow in 1984 and thereafter, <br /> <br />Routine maintenance and repair of bankline damage was <br />carried out during water year 1987. The majority of the <br />bankIine erosion problems experienced io the Lower Basin <br />stemmed from increased boating and other recreational river <br />traffic, <br /> <br />Scouring in some reaches of river channel has continued, <br />tberefore river levels bave been lower in some areas than they <br />were with the same release levels during the last 4 years. In a <br />few areas, however, reaches have refilled due to heavy <br />sediment loads, <br /> <br />Total Colorado River reservoir system storage at the start of <br />water year 1987 was approximately 55.61 MAP and about <br />54,92 MAP at the end of the water year, representing a 691,000 <br />acre-foot increase in total remaining available reservoir space, <br /> <br />In addition to the mainstem structures, Namo Dam on the <br />Bill Williams River (in the Lower Basin) received minor flood <br />in~ow during water year 1987. During water year 1988, <br />Pamted Rock and Namo Reservoirs are scheduled to be <br />operated in accordance with established flood control criteria <br />to maximize the available flood control space in their <br />respective reservoirs. <br /> <br />21 <br />