Hydrologic effects of reducing irrigation to maintain a permanent pool in John Martin Reservoir, Arkansas River Valley, Colorado

The U.S. Geological Survey has evaluated a plan by the Colorado Division of Wildlife to maintain a permanent pool of 10,000 acre-feet (1.2x10⁷ cubic metres) in John Martin Reservoir on the Arkansas River. The proposed pool would be maintained through the use of water formerly diverted by the Catlin Canal Company to irrigate land in the Arkansas River valley. This plan was evaluated using a mathematical simulation model developed to test management alternatives in a stream-aquifer system. A 25-year period from 1949 through 1973 was simulated using monthly time intervals. Based on this simulation, it is concluded that (1) the proposed change in water use would be adequate to maintain a permanent pool of the proposed size, (2) surface-water diversions by most other canals in the study area would increase slightly under the proposed plan, (3) the flow of the Arkansas River at the Colorado-Kansas State line would increase slightly under the proposed plan, and (4) the ground-water system would not be significantly affected by the proposed change in water-use plan.