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<br />0017J1 <br /> <br />11.2 Rule Curves <br /> <br />The CRSM utilizes reservoir target storage levels in determining monthly <br />releases. Each reservoir has a set of 12 monthly target storage levels <br />that make up what is known as a rule curve. Each month, releases from <br />any given reservoir are initially computed to bring the reservoir's con- <br />tents in line with its rule curve. If the reservoir's contents are <br />below its rule curve, then the release is set to the minimum monthly <br />release. If the reservoir's contents are above its rule curve, then the <br />release is computed as necessary to reduce the contents to the target <br />storage. Releases in excess of powerplant maximum will not be made to <br />bring reservoirs down to their monthly target storages. If downstream <br />demands exist which require a release higher than the rule curve- <br />dictated release, then the release is later increased to satisfy these <br />downstream demands. <br /> <br />Target storage values are obtained or computed in different manners, <br />depending on the reservoir. Initially, target storage values for all <br />reservoirs are read from the CRSM control file. These values can be <br />changed as the modeling run progresses. Blue Mesa, Flaming Gorge, <br />Navajo, and Lake Mead are given additional consideration. The target <br />storage values for Blue Mesa, Flaming Gorge, and Navajo are recomputed <br />each month depending upon the elevation of Lake Powell. If Lake Powell <br />is above its rated power generation head (elevation 3570) then the <br />target storage values for these three reservoirs are dete~mined from <br />desired drawdown quantities. The drawdown quantities for months August <br />through December are specified in the model. The drawdown quantities <br />for months January through July are computed using a simulated forecast <br />procedure which varies the quantity of drawdown as a function of <br />upcoming runoff. This produces a greater drawdown in wet years and a <br />lesser drawdown in dry years, which simulates what is done in actual <br />practice. <br /> <br />If Lake Powell is between rated power generation head and mlnlmum power <br />pool (elevation 3490), then the target storage values for Blue Mesa, <br />Flaming Gorge, and Navajo are set at either their own rated power <br />generation head contents or a computed percentage of their maximum con- <br />tent, whichever is greater. This percentage is computed by dividing the <br />current total Upper Basin contents by the total Upper Basin storage <br />capacity. This procedure tends to keep the Upper Basin reservoirs near <br />the same percentage of full content when Lake Powell is below its rated <br />power generation head elevation. <br /> <br />As Lake Powell approaches its minimum power pool, the target storage <br />values for Blue Mesa, Flaming Gorge, and Navajo are set to their minimum <br />power pool contents. This causes these reservoirs to evacuate storage <br />at their maximum powerplant capacity, tends to keep Glen Canyon <br />powerplant on-line longer, and allows all of the Upper Basin reservoirs <br />to reach their minimum power pools together. <br /> <br />'I <br />~ <br /> <br />i <br />f <br /> <br />The target storage values for Lake Mead in months January through July <br />are the values that were read from the input control file. The target <br /> <br />~ <br />