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o Qj ...t <.0 HIsrORY OF iiATER RESOORCE DEVELOPMENT Water exp::Jrted from the Upper Basin during the sa.'Ile period averaged about 357,000 acre-feet per year. Since completion of the Colorado-Big Thompson Project with initial diversions made in year 1947, the Duchesne Tunnel completed in 1953, and the Roberts Tunnel completed in 1963, the transmountain diversions have increased to around 500,000 acre-feet. Consumptive use of water for municipal and industrial purposes in the Upper Basin produced a minor depletion of about 30,000 acre-feet annually. Reservoir evaporation varies from year to year but the variations have little effect on average streamflow depletions. For the period of record considered, average reservoir evaporation in the Upper Basin was minor as the large reservoirs of the Colorado River Storage Project did not begin filling until late in the period. Under normal operating conditions, evaporation from the Colorado River Storage Project neser- voirs is expected to average about 600,000 acre-feet annually. For the 1941-68 period of record, streamflow depletions in the Upper BAsin totaled about ? million acre-feet. In the Lower Basin above Imperial Dam water is exported to the Southern California coastal areas and to Imperial and Coachella Valleys and delivered to irrigated areas along the river in Arizona and Cali- fornia, principally to the Colorado River Indian Reservation, Palo Verde Irrigation District, Gila Project, and Yuma Project. Water is also de- livered to Mexico at the International Boundary as well as consumed by phreatophytes or evaporated. C. Legal ~spect~ 1. Colorado River ComE,:>:ct Water of the Colorado River was divided between the Upper and Lower Colorado River Basins by the Colorado River Compact which was signed in 1922 by a commissioner of each of the seven States of the river basin and 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 a!1d LO'Ner Basins is at Lee Ferry which is defined as a point 1 mile below the mouth of the Faria River. The compact apportions from the Colorado River system to each of the Upper and Lower Basins in perpetuity for exclusive beneficial consumptive use a total of 7,500,000 acre-feet annually. In addition to the appor- tionment of 7,500,000 acr~-feet, the Lower Basin is given the right to increase its beneficial consumptive use of water from the Colorado River system byl million acre-feet annually. The compact further provides that the States of the upper division will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 75 million acre-feet for any period of 10 consecutive years. 13