WSP01533 - Laserfiche WebLink

Home Browse Search

Regardless of the target protection level assumed, the surplus threshold capacity will rise sharply after use exceeds 11.8 maf. However, alternative concepts could be considered for a shortage strategy. For example: In the analysis the target protection level was set at elevation 1050 feet or about 7 maf for determining storage that could be made available for surplus. While elevation 1050 feet may be an appropriate target for determining water that can be surplused, it may be less appropriate as the target for basing a shortage determination. The assumed strategy sets the shortage threshold at elevation 1120 to protect storage from falling below elevation 1050. Other levels of protection could be considered which would reduce the risk of shortage, while increasing the risk of drawing Lake Mead below 1050. CONCLUSION Reclamation examined the effect of alternate provisions for determining surplus conditions. Operating scenarios were developed and simulated using the CRSS, and CRSS-EZ models. The results of each run were compared with a base case analysis. Following the comparison, the results were examined and the model runs were reformulated to address specific questions. Initial alternatives focused on arbitrarily setting a surplus threshold capacity or a percentage assurance of avoidance of spill capacity and examining the long-term effects on shortage, normal, and surplus occurrences. During these exercises understanding of the system increased, however the studies and discussions did not appear to generate consensus. Consensus building had been based around developing a method which achieved some "middle ground" in its long-term effects. Over the course of the study, as hydrologic and water use changes occurred, the long-term effects changed. As the long-term effects of a specific method could not be reliably predicted consensus and confidence deteriorated. Finally Reclamation was asked to, "just make a recommendation" . The studies highlight how the strategies, initially considered, were more or less arbitrary. Strategies were evaluated based on the end results the strategy would achieve and not on whether there was technical merit to the strategy. If there is no legal or technical rationale for a strategy, there is no foundation that maintains the strategy over time and change. The upper basin objective minimum release is to supply 8.23 maf to the lower basin. To assure that this supply can be provided a critical period of record was established for the upper basin. The upper basin maintains sufficient storage in upper basin reservoirs such that an average 8.23 maf of minimum flow can be provided to the lower basin through the critical period of record without impairment to upper basin uses or without impacting the minimum power pool. 38