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OOJ145 I. EXECUTIVE SUMMARY Unless the water supply of the Colorado River is increased within the next two decades, shortages will almost certainly occur. The need for additional water in the Colorado River Basin has been recognized and studied for many years. The Secretary of the Interior is specifically charged with the responsibility for development of the water resources of the Colorado River Basin (Colorado River Basin Act, 1968; Public Law 90-537), and with the protection of water quality (Colorado River Basin Salinity Control Act, 1974; Public Law 93-320). CREST (Colorado River Enhanced Snowpack Test) is an 8-year program to demonstrate the capability of cloud seeding to augment the flow of the Colorado River and thereby also improve the quality of the water in the river. The Secretary of the Interior has determined that this is the most cost effective and promising means of providing the additional fresh- water supplies at this time. Current cloud seeding technology appears to be able to increase winter snowpack by 10 to 15 percent in many mountainous areas of the Colorado River Basin. CREST will seed clouds in two hi9h-yield areas of the Basin to determine the amount of additional precipitation that current weather modifi- cation technology can provide. It will also determine the pertinent charac- teristics of other subbasins so the technology demonstrated in these two areas could be applied Basin-wide. The two CREST demonstration projects are expected to result in an additional 410,000 acre-feet of water per year. A subsequent Basin-wide operational program has the potential of producing 2.26 million acre-feet of water per year. The cost of the 8-year CREST Program is $88 million (FY83 dollars). The additional water produced by the demonstration projects is valued at $11.9 million per year in increased hydroelectric capacity, energy produc- tion, salinity reduction, and water supplies for agriculture, industry, and recreation. Benefits from Basin-wide operational application of the tech- nology are estimated to average nearly $140 million per year with an associ- ated cost of $12 to $16 million per year resulting in a benefit/cost ratio between 9:1 and 12:1. Cloud seeding is an attractive approach to streamflow augmentation because it does not require major permanent construction or large fixed operation and maintenance costs. A decision to employ cloud seeding can be made on a year-to-year basis or even on a storm-to-storm basis within a season. More importantly cloud seeding presently is the most cost-effective means for securing additional water in the Basin. Other options considered were importation, desalination, evaporation suppression, and vegetation manage- ment. Importation and desalination have high construction costs. Current evaporation suppression technology is not adequate for reservoirs on the Colorado River. Vegetation management appears to be effective, and studies show that the combined effect of weather modification and vegetation manage- ment on the same area increase streamflow more than if the two were applied separate 1 y. Six major runoff-producing areas in the Colorado River Basin have been identified as candidates for snowpack augmentation by cloud seeding in the CREST Program. The Central Colorado, the Park Range, the San Juan,