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I I I I I I I I I I I I I I I I I I I A. Location The proposed reservoir site is located approximately 1/2 mile west ofthe Town of Ovid, Colorado. Figure 1 represents the proposed site, which is located in Section 6, Township 11 North, Range 45 West, in the County of Sedgwick, State of Colorado. The site consists of approximately 350 acres, which is presently pastureland and irrigated cropland. The site is approximately 13 miles upstream of the Julesburg Gage, which is the designated measuring point for compact deliveries. The proposed site location was chosen based on proximity to the gage. This site offers the main advantage of direct proximity to both the Peterson Ditch and the South Platte River. B. Project Scope The scope of work includes identifying known environmental, constructional, or operational constraints that would affect the completion of the proposed reservoir. The constraints that were evaluated included review of the geotechnical information of the on-site materials and their engineering properties as related for dam construction. Geologic information for the underlying formations was compared to existing USGS data. Groundwater information including depth and formation transmissivity was calculated from field tests and compared to existing USGS information. Preliminary survey data was collected for the reservoir site and the Peterson Ditch where a new reservoir turnout structure could be located. The U.S. Army Corps of Engineers was contacted on 404 permit questions. A field meeting was held with the Corps to determine the requirements for a permit. A preliminary opinion of probable cost was compiled using construction costs of known projects of similar scope, and conducting interviews with contractors experienced in this type ofproject. Two alternative configurations ofthe reservoir were studied at the feasibility level. The two reservoir alternatives that were studied were a 3,900 acre-foot capacity and a 5,400 acre-foot capacity. The alternative sizes were studied to evaluate ability to divert excess water into the reservoir, make deliveries back to the river, preliminary site layout ofthe reservoirs, the effectiveness of increasing flows in the South Platte River during target periods, and preliminary construction costs for the reservoir and appurtenant structures. Historically the flows in the river during the compact period have dropped below the benchmark flow of 120 cfs. A flow rate below 120 cfs at the state line does not automatically coincide with a compact violation, but the potential for interruptions in water diversions needs to be minimized to give more certainty for water users including the irrigation wells for GASP members. An off-channel reservoir is one that does not dam a flowing stream. This study site has no discernible drainage basin due to the flat nature ofthe area. There are three irrigation canals that lie upstream from the property that intercept drainage. Due to the lack of grade change across the site a ring dike will be required to form the reservoir. A ring dike simply means that a dam will be constructed around the entire perimeter because of the lack of topographic relief. Plate I and II are preliminary site plan layouts of the alternate reservoir sizes based on the assumptions outlined in this report. The dam geometry would use a 6h: 1 v slope on the upstream side and a 3h: 1 v slope on the downstream side. The shallow upstream slope was chosen in lieu of a steeper slope that would require imported riprap shoreline protection. The shallow slope will help dissipate wave energy and reduce shoreline erosion. However, this configuration will probably require more annual 4