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. ~ o >- to . . HISTORY OF WATER RESOURCE DEVELOPMENT Water exported from the Upper Basin during the period 1941-70 averaged about 360,000 acre-feet per year. \,'ith completion and diversions by the lar~e projects such as the Colorado-Big Thompson. Duchesne Tunnel. Roberts Tunnel, and the more recent projects such as the San Juan-Chama Fryingpan-Arkansas. and Hornestake. The transmountain diversion from the Upper Basin increased to about 690,000 acre-feet in 1973. Reservoir evapora t ion vaT ies from year- to-year but the var ia tions have little effect on average streamflow depletions. For the period of record considerl'd. average reservoir evaporation in the Upper Basin was not large unci I about 1963 when the Colorado River Storage Project Res- ervoir started to store loater. In 1973 about 550.000 acre-feet were eVAf'nrated from the reservoirs. Under normal operating conditions. evap- ur4~itJn from the Colorado River Storage Project reservoirs is expected to average about 568,000 acre-feet annually. In the Lower Basin above Imperial Dam, loater is exported to the Southern California coastal areas through the Colorado River Aqueduct ;lod to the Imperial and Coachella Valleys through the All-American Canal. Along the river. the main IoBter diversions are to the Southern ~evada Water Project, Colorado River Indian Reservation. Palo Verde Irrigation District. Gila Project, and the Yuma Project. Below the Imperial Dam. water is delivered to l'luxico as required by the treaty with Mexico. There is essentially no flow below ~orellos Diversion Dam except for the bypassed Silline flows from the We 11 ton-Mohawk Drain Extension. C. Legal Aspects 1. Colorado River Compact \.,'a ter of the Colorado River was divided between the Upper and Lower Colorado River Basins by the Colorado River Compact ...'hleh was signed in 1922 by a commissioner of each of the seven States of the river basin dnd by a representative of the United States. All States but Arizona ratified the compact prior to its effective date in 1929. The dividing point on the river between the Upper aOO Lower Basins is at Lee Ferry ....hich is def ined as a point 1 mile below the rrnuth of the Paria River. (i.llt to be confused ...ith Lees Ferry which is the site of the gaging station just above the Paria River.) The compact apportions from the Colorado River system to each of the Upper and Lower Basins in perpetu- ity for exclusive beneficial consumptive use a total of 7,500.000 acre- feet annually. In addition to the apportionment of 7,500,000 acre-feet, the Lower Basin is given the right to increase its beneficial consumptive use of Wlter from the Colorado River system by 1 million acre-feet annually. The compact further provides that the States of the upper division will 16