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<br />. <br /> <br />. <br /> <br />. <br /> <br />, <br />~ <br /> <br />The Colorado River Storage Project has flood control as an authorized project purpose. but only <br />Blue Mesa and Navajo Dams have actual flood control allocations and Corps flood control <br />diagrams. Glen Canyon Dam has no such flood control diagram, but through the years an <br />acceptable method of determining monthly release volumes has been developed though the AOP <br />process. Because Glen Canyon Dam has no flood control diagram currently, it is appropriate to <br />consider a process that will provide support to this AOP process and also flexibility to respond to <br />the AMWG mission and goals, especially as relates to environmental opportunities associated <br />with managing spring flows. Filling the reservoir while avoiding spills is a prime objective <br />during full reservoir conditions. The 1970 Operating Criteria prepared in response to the 1968 <br />Act further provided a minimum objective annual release volume of 8.23 MAF. When <br />combined with the requirement to equalize storage. these constraints effectively provide limits <br />on monthly release volumes and patterns. <br /> <br />Despite the lack of a formal flood control diagram, flood control operations at Glen do exist <br />when the forecasted runoff is expected to fill Lake Powell. When the monthly release volumes <br />approach powerplant capacity, release options are significantly reduced from the perspective of <br />avoiding spills (bypasses). The issue of planning for beachlhabitat building flows complicates <br />this process. Various interpretations exist regarding the timing and the threshold level of <br />initiating these bypasses under the 1995 agreement with the Basin States. <br /> <br />How do we use forecasts in our operation at Glen Canyon Dam? What is the <br />frequency of forecasts? How are annual and monthly and daiiy release ~'olumes <br />determined? <br /> <br />Inflow forecasts which have been coordinated between the National Weather Service and the <br />Natural Resource Conservation Service are issued monthly, usually the fifth working day of the <br />month. Specific predictions for the critical April through July snow runoff period are made as <br />pan of the January through July forecasts. Additionally, the National Weather Service issues <br />mid-month updates which reflect changed snowpack and runoff conditions. These forecasts are <br />input into a monthly planning computer model which then accounts for upstream dam operation <br />and regulation. Annual and montWy release volumes then are determined by Reclamation to <br />accomplish the objectives cited above. <br /> <br />Annual release volumes are determined by either the storage equalization or minimum objective <br />flow provisions of the 1968 Act or the practical necessity of safely controlling runoff during <br />high reservoir conditions. Monthly release patterns are sometimes more flexible and can take <br />into account such things as desirable flow levels for downstream sediment transport, power <br />production, and recreation. An example of this circumstance occurred in the spring of 1995, <br />when flows were purposely kept below 20,000 cfs because the risk of an anticipated spill was <br />small and we believed larger releases could be avoided. The prime focus for this decision was to <br />limit sediment transport. However, when the risks associated with uncontrolled spills and dam <br /> <br />Reclamation Discussion Paper -- Working Draft -- 3/24/97 version <br />