| OCR Text |
Show APPENDIX XII XII-29 acre-feet to Mexico annually from the Colorado River. 5. The Colorado River Storage Project Act of 1965 which authorized several long-termed carryover reservoir storage units in the upper basin which permit the upper basin to maximize the consumptive use of water within its Colorado River Compact apportionment. 6. The Supreme Court Decree in Arizona vs. California of March 9, 1964, which apportioned the lower basin supply of Colorado River water among the States of Arizona, California, and Nevada. 7. Colorado River Basin Project Act of 1968 which directed that diversions to the Central Arizona project in times of shortage shall be so limited as to, in effect, guarantee California the use of 4.4 million acre-feet of Colorado River water annually. It also declared that the satisfaction of the Mexican Water Treaty from the Colorado River constitutes a national obligation which shall be the first obligation of any water augmentation project planned pursuant to the act. 8. The Federal Water Pollution Control Amendments Act of 1972 which gives the Environmental Protection Agency certain responsibilities and authorities for controlling water quality on the Nation's rivers. 9. Minute 242 (1973) of the International Boundary and Water Commission, United States and Mexico, which requires the initiation of several actions which will reduce the salinity of Colorado River water deliveries to Mexico under the Mexican Water Treaty. 10. Colorado River Basin Salinity Control Act of 1974, which authorized construction of a desalting complex and salinity control units to control salinity and improve the quality of Colorado River water. In negotiations leading to a number of the above documents, a water supply yield of the Colorado River was assumed that records of the past several decades have proven to be overly optimistic. For instance, at the time the Colorado River Compact was negotiated, existing records indicated that the average virgin runoff of the Colorado River at Lee Ferry was in excess of 18 million acre-feet. As of today, the long-term record (1906-1970) indicates a virgin yield at Lee Ferry of 14.9 million acre-feet, while for the period 1931-1964 the yield was only 12.9 million acre-feet. With the above background in mind, attention can be focused on the current water supply problems of the Colorado River Basin. Today and for some years to come, the Colorado River should be able to meet all quantitative physical water demands. The upper basin States are meeting their Compact requirements and demands being placed on the river are being met. Lake Powell and Lake Mead are filling and, assuming average annual runoff conditions for the next few years, Lake Powell and Lake Mead will "spill" in the sense that they will be required to release water, other than Mexican Treaty waters, for which there will be no consumptive use in the United States. However, assuming a long-term average annual supply of 14.9 million acre-feet, sometime after the Central Arizona project is fully operational, the Colorado River will not yield enough water under normal circumstances to meet upper and lower basin demands, the Mexican Treaty obligations, and system losses. Thus, the Colorado River Basin faces future water shortages unless its natural flows are augmented or water-dependent basin development is curtailed. The extent and timing of these shortages will depend on the rate of future consumptive use development and the volumes of annual runoff. There are several categories of potential shortages: 1. When California is first cut back from its present 5.1 million acre-feet annual consumptive use to 4.4 million acre-feet consumptive use a legitimate current demand on the river will not be 39 |
