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I. I I I I I I I I I I I I I I I I I I Executive Summary A feasibility level study was made to evaluate the benefits of constructing an augmentation reservoir near the Colorado-Nebraska state line. The purpose of the reservoir would be for providing supplemental flows to the South Platte River during times when the compact call could be enforced. The supplemental flows are intended to allow GASP well owners to continue to divert water. The study is an extension of previous studies that evaluated a proposed site near Sedgwick and several uplands reservoir sites on the south side ofthe river. The site in this study is located on the north side of the river approximately 1 mile west of the Town of Ovid. The project was evaluated as a standard off-channel storage project that would make controlled releases back to the river. A storage reservoir with controlled releases would provide much greater impact in reducing compact calls. There are some water rights issues that do need resolution on how the reservoir would operate in sync with the lower river and the compact. Water supplies would be delivered to the reservoir through the Peterson Ditch by gravity. Deliveries back to the South Platte would be through an existing flood and drainage control channel that protects the Town of Ovid. Permitting issues were evaluated. The project site has jurisdictional wetlands that will require obtaining an individual 404 permit. Preliminary meetings with the Corps of Engineers received indication that they would be supportive in issuing a permit for this project in light of the environmental benefits that the river would see. . Preliminary cost estimates were prepared for two alternate sized reservoirs. These costs include the reservoir embankment and appurtenant structures, a diversion structure on the Peterson Ditch, land acquisition costs and permitting costs. The total cost of the project to develop 4,000 acre-feet of water storage would be approximately $2,400,000. The total cost of the project to develop approximately 5,800 acre-feet of water storage would be $3,900,000. The long-term annual cost ranges between $600 to $700 per acre-foot. The proposed reservoir was evaluated using the past 10 years of historic flow records for the South Platte River. The evaluation was based on a refined model that was developed in conjunction with the State Engineer looking at how the lower river is administered. Based on these records there is sufficient water available for diversion during the winter months to allow this project to operate under a junior diversion decree. 2