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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 North Poudre Reservoir No. 2 is impounded by two earth dams with an average height of 12 feet and a total crest length of 2000 feet. The dams impound a reservoir. when full, of 3910 acre-feet at a normal pool elevation of 5228.6 feet USGS or Gage Height 24 feet. Releases from the reservoir are through a 36 inch metal conduit that empties into a feeder ditch on the south and east end of the reservoir. Two spillways exist; one on each end of the two dams. The west spillway is approximately 15 feet wide and the east spillway is approximately 30 feet wide. The reservoir is located in Larimer County approximately 1~ miles north and 2 miles east of Wellington, Colorado. The dams were originally constructed in about 1890 and were raised at least once following the initial construction. The reservoir is filled by an appropriation of water from the North Fork of the Cache La Poudre River by means of the North Poudre Canal and from The Cache La Poudre River by way of the Ed Monroe Gravity Canal. Some runoff is captured out of Dry Creek and the drainage immediately above the reservoir. The dam's operating level has been restricted to Gage Height 18.0 feet since 1984 by the Colorado State Engineer's Office (SEO). This restriction reduces the reservoir storage capacity by 1532 acre-feet. from a maximum of 3910 acre-feet to 2378 acre- feet. This restriction was imposed due to seepage at the West Dam and due to inadequate spillway capacity. In February 1985 The North Poudre Irrigation Company Stock- holders at their annual meeting passed a resolution to provide assessments to rehabilitate Reservoir No.2. At that time the North poudre Board of Directors began a course of action to obtain partial funding for the rehabilitation of Reservoir No. 2 through The Colorado Water Conservation Board (CWCB). That funding was approved by the CWCB in 1985. This report prepared by SMITH GEOTECHNICAL/Engineering Consultants (SGC) was thus prepared to fulfill the requirements of the CWCB to complete the applica- tion for funding. This need to 1. 2. study found several problems or areas of concern that be addressed. The spillways are inadequate to pass a 0.75% PMP storm as required by the State Engineer. Seepage at the foundation contact on the West Dam must be controlled to prevent a piping type failure. The condition of the outlet conduit is poor and is in need of repair or replacement to avert a major failure due to pipi~g. The metal conduit has numerous holes through the pipe wall and is in general in a deterior- ated state. The upstream slope protection is poor and almost nonexistent in some areas. 3. 4. i