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<br />d - High spring runoff is highly sediment laden, With the tunnels open, sediment <br />would be bypassed downstream under a natural !low and sediment regime, It is <br />likely that the Grand Canyon would be brought back near to pre-dam conditions, <br /> <br />e - One would expect that under this action, the "Law of the River" would likely <br />be revisited, however, only the 8,23 MAF minimum objective release and the <br />obvious equalization provisions might need to be eliminated, With an average <br />annual natural inflow during the historic critical hydrologic period of about 12 <br />MAF and current upper basin use of 4,2 MAF, the difference of7,8 MAF is <br />, enough to satislY the Colorado River Compact obligation of75 MAFflO years to <br />the lower basin without needing the storage of Lake Powell. In addition, <br />recovered evaporation losses from Lake Powell would help to meet any potential <br />deficiency in the Mexican Treaty obligation, <br /> <br />However, future increases in upper basin depletions will depend on the <br />ability of Lake Powell to supplement upper basin outflow during drought <br />periods. This drawing from storage is the foundation purpose for the <br />construction of Glen Canyon Dam. The most serious impacts of emptying <br />L:lke Powell is th:llthere would no longer be reservoir storage to support <br />additional upper basin uses lmd that the lower basin would receive <br />uncontrolled flow. If flows to the lower basin were to fall below 75 MAFflO <br />years, then upper b:lsin use would have to be curtailed to meet the delivery <br />requirement of the 1922 Colorado River Compact. <br /> <br />f - The loss of existing benefits from Lake Powell itself are self evident: power <br />generation, lake recreation, downstream trout fishery, and the extended and <br />moderated white water Grand Canyon boating season. The entire ecosystem <br />of the Grand Canyon would likely change with the loss of the current food <br />base, llnd non-native predator !ish from Lake Mead could be a major <br />concern to native fish species in the Grand C:myon. <br /> <br />g - Significant increases could occur in lower basin consumptive uses as the <br />result of curt:liled upper basin uses, perhaps as much as 2 MAF annually <br />during surplus conditions (equal to the foregone additional upper basin <br />development up to the upper basin yield). Lower basin shortages could be <br />eliminated as an alternative to increased uses since future risks of shortages to <br />lower basin uses are primarily due to increases in upper basin use, The risk of <br />!lood control releases from Lake Mead would rise dramatically, meaning extra <br />deliveries and !lood !lows to Mexico, As a result of these higher flows along the <br />Parker - Davis !loodway, river channel maintenance costs in the lower basin could <br />also rise, Since upper basin increases in consumptive use would end, projected <br />increases in salinity impacts might also decline, decreasing the need for additional <br />salinity control projects, <br /> <br />6 <br />