C153607L Feasibility Study - Laserfiche WebLink

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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 Mountain Home Reservoir is located in Costilla County, Colorado and is approxi- mately 2 miles south and 2 miles east of Fort Garland, Colorado. The dam was originally constructed in about 1910 and not been significantly modified since the initial construction. The reservoir is filled by an appropriation of water from Trinchera Creek and its tributaries. Mountain Home Reservoir is impounded by one dam that runs in approximately a North to South direction. The dam is approximately 450 feet long with a structural height at the outlet of approximately 153 feet and a hydraulic height of 126 feet. The dam embankment slope at the upstream face is approximately 3H (horizontal) to 1 V (vertical) with the downstream siope varies from approximately 1.5H to IV to 2.5H to IV. The crest width is approximately 20 foot with a 36 foot wide berm approximately 8 feet below the crest with an access road running across the berm. The crest of the dam is slightly depressed in some areas but is relatively uniform in elevation. The upstream slope protection on the dam is in good condition and consists of hand laid riprap approximately 18-inches in thickness. The upstream face of the dam is in good condition and uniform in shape and slope. The downstream face consists of dumped rock with boulders up to 6-feet in diameter. The downstream face is rough in shape and slope but is stable and in good condition. The emergency spillway for the reservoir is located in a natural swale to the southeast of the dam. The spillway inlet is approximately 1400 feet southeast of the dam with the spillway control section located approximately 800 feet from the dam. The control section is approximately 80 feet wide consisting of a rock- filled embankment. The spillway control section is at Elevation 8202 feet and the crest of the dam is at Elevation 8210 feet for a freeboard of 8 feet. The spillway channel is has a total length of approximately 3500 feet and discharges into Trinchera Creek approximately 1500 feet downstream of the dam toe. The outlet works consists of a cast in-place concrete, modified horseshoe shaped conduit. The outlet works is in good condition and no rehabilitation work is being considered at this time. The Colorado State Engineer has imposed a storage restriction on the reservoir at Gage Height 87.5 feet due to an inadequate emergency spillway. On January 7, 1992 the Trinchera Irrigation Company Board of Directors at their monthly meeting passed a resolution to conduct a feasibility study for the renovation of Mountain Home Reservoir and to apply for funding of the project through the Colorado Water Conservation Board(CWCB). That funding was approved by the CWCB and the Colorado Legislature in 1992 contingent on the completion and acceptance of the feasibility study. This report was prepared by SMITH GEOTECHNICAL/Engineering Consultants to fulfill the requirements of the CWCB to complete the application for funding. 1.