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<br />- - - -- <br /> <br />001688 <br /> <br />in accordance with the regulations as published in Exhibit A of the <br />Water Control Manual for Flood Control (December 1982), also <br />described in Appendix F of the report Review of Flood Control <br />Regulation - Colorado River Basin - Hoover Dam (July 1982). Both <br />reports are by the United States Army Corps of Engineers, Los Angeles <br />District. The data values described throughout this section are <br />taken from these reports and are normally used in CRSS simulations. <br />The values are part of the CRSM input data and can be readily changed <br />to investigate or evaluate alternative flood control plans. <br /> <br />There are three different flood control procedures that are in effect <br />during different times of the year. The first procedure is used <br />during the runoff forecast season, January through July. This is the <br />period from the earliest reliable runoff forecast to the conclusion <br />of the snowmelt runoff. The objective during this period is to route <br />the forecasted maximum inflow through the reservoir system, using <br />specific rates of Hoover Dam discharge, so that the reservoir system <br />is full by the end of July. The second flood control procedure is <br />used during the space-building or drawdown season, August through <br />December. The objective during this period is to gradually draw down <br />the reservoir system to create space for the next spring's snowmelt <br />runoff. The third flood control procedure is in effect all year. <br />The objective of this procedure is to maintain a minimum space of <br />1.5 million acre-feet in Lake Mead for rain floods. <br /> <br />Forecast Season <br /> <br />The first flood control procedure is used each month during the fore- <br />cast season, January through July. The flood control regul ati ons <br />contain a table for each month of the forecast season that gives the <br />minimum average release in cubic feet per second based on the maximum <br />forecast, the available space in Lake Mead (below elevation 1229), <br />and the available space in Lake Powell (below elevation 3700). The <br />maximum forecast is the amount of inflow that, on the average, will <br />not be exceeded by the actual runoff 19 times out of 20. The CRSM <br />uses an iterative procedure each month of the forecast season to <br />determine this minimum average flood control release from Lake Mead. <br />The iterative procedure is the same procedure that is used to develop <br />the minimum average release tables in the flood control regulations. <br /> <br />The first step in the iterative procedure is to compute a value of <br />minimum average release using a mass balance equation that considers <br />the forecasted inflow, available space, losses, and an assumed Mead <br />release for the remainder of the forecast season. The computation <br />consists of taking the available space in Powell and Mead, sub- <br />tracting the exclusive flood control space (1.5 million acre-feet), <br />adding losses from Powell and Mead, subtracting the maximum fore- <br />casted inflow, and adding the discharge from Lake Mead for the <br />remainder of the forecast season at an assumed level 1 discharge rate <br />(see below). Losses consist of evaporation and changes in bank <br />storage at Lakes Powell and Mead, and depletions from Lake Mead. The <br />maximum forecast value used in the computation is described in <br /> <br />38 <br />