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I I I I I I I I I I I I I I EXECUTIVE SUMMARY Twin Lakes Dam is an earth embankment with a maximum height of about 35 feet and a crest 1 ength of 220 feet at el evati on 9300. It impounds a reservoi r, when full, of 278 acre-feet at the normal reservoir pool elevation of 9295. Releases from the reservoir are controlled by an outlet works that discharges into an unnamed creek downstream of the dam. The spillway is located in a low saddle in the northwest corner of the reservoir. The dam is located in Larimer County on a tri butary to the South Fork of the Cache 1a Poudre River, about nine miles south of Rustic, Colorado. The drainage basin for Twin Lakes Reservoir lies north of Rocky Mountain National Park in the Roosevelt National Forest. The basin divide is located at approximately 10,700 feet near the headwaters of the South Fork of the Cache la Poudre River. The drainage area is 0.89 square miles, and the basin has an average slope of 922 feet per mile. The distance from the basin divide to the reservoir is approximately 1.5 miles. Water is also supplied to the reservoir by a filrer ditch diverting water from a stream to the west of the drainage basin. The dam was constructed in the early 1900's for irrigation supply. There is no record of the dam having been repaired since its original construction. The dam's operating level was voluntarily restricted to zero storage by the City of Greeley in September of 1984, due to the deteriorated condition of the outlet works and embankment seepage. On January 22, 1986, the restriction was formalized by the Colorado State Engineer's Office (SED). In February 1986, the City of Greeley applied to the Colorado Water Conservation Board (CWCB) for partial funding of a feasibility study to rehabilitate Twin Lakes Dam. That funding was approved by the CWCB in May 1986. Morri son-Knudsen Engi neers, Inc. (MKE) was se1 ected to perform the feasibility study in June of 1986. i