C150094 Application (2) - Laserfiche WebLink

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River. In dry and average years,the reservoir is totally drained to meet irrigation water demands. Harris Water Engineering conducted a Red Mesa Reservoir Enlargement Feasibility Study that focused on assessing the availability of water for filling the enlarged reservoir to 4,070 AF, to provide both agricultural and domestic water. That study indicated that the current dam's earth embankment has a height of 59 feet, a length of 420 feet, and a crest width of 10 feet. The normal storage capacity of the reservoir is 1,172 acre-feet (AF), with a maximum storage capacity of 1,454 AF. The spillway, located on the left abutment of the dam, is 35 feet wide and approximately 6 feet deep. The spillway has a capacity of 2,126 cubic feet per second(cfs). The outlet works, a 2-foot by 4-foot arched tunnel near the left abutment of the dam, have a capacity of 138 cfs. The Harris study identified a need to repair the existing outlet tower and enlarge the spillway, and recommended consideration of the reservoir enlargement since the repair work would present an opportunity to conduct the enlargement work in an efficient manner. It is important to note that some critical permitting has already been obtained for the proposed enlargement. As part of the initial feasibility work, a Clean Water Act Section 404 Permit was obtained and the U.S. Fish and Wildlife Service (USFWS) issued a biological opinion under Section 7 of the Endangered Species Act. Renewal of this permit is now being reviewed by the Army Corps of Engineers. A minimal amount of time has been included in the scope of work and cost estimate for the Section 404 permit renewal work. The Harris Water Engineering study of the Red Mesa Reservoir enlargement relied upon geological and geotechnical studies completed in 1975 by the Soil Conservation Service (SCS) in cooperation with the La Plata Soil Conservation District. The SCS field investigation consisted of drilling eight geotechnical test holes to investigate the condition of the abutment of the dam and possible emergency spillway areas; 41 test pits dug with a backhoe; and the collection of six disturbed soil samples for analysis by a soils laboratory. WWE has reviewed the SCS files. Although they provide valuable and useable information, the feasibility study will require collection and evaluation of some additional geotechnical data. Little site-specific information is available relative to topography, wetlands, hydrology, cultural resources and threatened/endangered species, other than the endangered fish in the San Juan River. These items have been included as part of the proposed work plan for this application. Study Objective The objective of this study is to investigate the technical, financial and institutional aspects of a limited number of alternative dam and reservoir configurations to increase the Reservoir's capacity to approximately 4,000 AF. The need for enlargement of this facility was established in previous studies (Western La Plata County Water Management and Conservation Plan, Red Mesa Reservoir Enlargement: Feasibility Study). Enlargement of the Reservoir will improve the currently inadequate water supplies in the 2