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I. ~' ~s~~s ~ «~s3 ~~~ ~N ~ sa" . _ ~~ i~~~ BRIEF ~~ , Overview of Water Development in the Colorado River System (see Attachments III. and N.) Lower Basin: Majority of water development occurred between 1909 and 1966 with the development of 17 dams plus other major water diversions. All water has been allocated and most appropriated: BR estimates that only 230,000 AF is available from the Upper Basin for future appropriation. Little natural riverine habitat remains, especially in the tributaries. Only major river section not significantly altered is the 220 miles between Lee Ferry (Utah/Arizona border) and Lake Mead, however this stretch is affected by the operation of Glen Canyon Dam (see Map page 3). Upper Basin: Major water development began in 1952 and continued with project development under the Colorado River Storage Project Act in the early 1960's, resulting in an initial average flow depletion of abqut 18% (2.0 million acre-feet). Presently, there are 9 major dams plus other major water diversion projects in the Upper Basin, resulting in a total flow depletion of 35% (3.9M AF) (see Map page 4), `, Water diversion projects have altered the riverine habitat by reducing spawning/rearing areas, altering river channel characteristics, affecting water temperature, salinity, and turbidity, and obstructing migrational habits of the fish. Presently, BR estimates there is only 1.6M AF (149'. of total river flow) still available for appropriation under the Colorado River Compact in the Upper Basin. Projects proposed or planned for construction between 1980 and 1990 will deplete 1.3M AF of the 1.6M amount. The total flow in the river system is measured at Lee Ferry (Utah/Arizona border). The Colorado River Compact estimates a total flow of 14M acre-feet for equal allocation between the Upper and Lower Basins, however reliable data indicates that the average yield of the Green and Colorado Rivers is only 11M AF actually available (5.5M AF a11ocated to each Basin, based on a 10-year average). The above figures (and percentages) are based upon the 11M figure.