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Some providers also implemented measures to increase their supplies and reduce their draw on storage reservoirs. These measures included cooperative arrangements with farmers, invoking special drought clauses to relax minimum bypass flows, drilling supplemental wells, trading supplies between users, building facilities to allow better use of existing water rights, and sharing the burden of shortages where the State Engineer was willing to relax administration of the priority system. Agricultural water users employed a wide variety of strategies to cope with the drought and irrigators were generally more adept than cities at anticipating its onset. Responses included reductions in the amount of acreage planted, changes in cropping mix from full season crops (e.g. feed corn) to partial season crops (e.g. I- or 2 -cut hay and corn for silage). Some farmers decided not to farm this year (2002), and to lease their water supplies to cities instead and many livestock owners sold off significant percentages of their herds in expectation of high - priced and reduced feed supply. Mechanisms to Meet Existing & Future Water Demands Looking to the future and the assessment of storage augmentation in managing Colorado's water needs, not all basins are created equal. Some can be eliminated from consideration given current conditions either of hydrology, adequacy of existing storage capacity, economics, project proposals that are already well along (e.g., Animas/La Plata), downstream delivery requirements (e.g., Rio Grande Compact), or some combination of the above. The Rio Grande, the San Juan/Dolores, the Yampa/White, and the North Platte fall into this category. In all of these basins at least two of these factors are relevant. For these reasons, the report concentrates on the question of storage in the Colorado /Gunnison, the Arkansas, and the South Platte. Reservoirs have been part of Colorado's water development strategy since the late 1800s, in response to its highly variable stream flows. Today, Colorado has more than 7.5 million acre -feet of reservoir storage. About 25% of this capacity directly supports municipal water uses and this fraction is steadily growing, mostly as cities acquire agricultural water rights with their associated storage. In addition, there is the natural storage provided by Colorado's principal underground aquifers. The Denver Basin aquifers contain approximately 150 million acre -feet of recoverable groundwater and aquifers elsewhere within the South Platte, Arkansas and Rio Grande basins contain over 15 million acre -feet. The traditional purpose for building reservoirs has been to capture excess runoff, which usually occurs relatively infrequently and in large volumes. Consequently, traditional reservoirs are fairly large and located directly in a stream channel. Apart from their well - documented environmental impacts, such large on- stream reservoirs have other major limitations. First, they are relatively costly to build and cannot be built incrementally in response to gradually growing demands. Rather, they must be fully paid for and constructed "up front," which increases their financial risk and diminishes their economic viability. Second, as a basin becomes over - appropriated, additional runoff - capture storage produces ever - diminishing returns in terms of water supply yield, because unappropriated runoff occurs less frequently and storage carry -over periods become ►W