Laserfiche WebLink
2 Background <br />^ Monument Dam and Minnesota Reservoir are located on the Dry Fork of Minnesota Creek <br />approximately 6.5 miles upstream of Paonia, Colorado, in Section 32, Township 13 South, Range 90 <br />' West of the 6~' Principal Meridian District 40 of Division 4. The dam and reservoir are owned by <br />MCRC for the purpose of supplying water for irrigation. <br />' The original Monument Dam was constructed in 1899 to an unknown height. However, it was <br />smaller than its current height. The dam was subsequently raised twice, first in 1910 and again in <br />' 1933 to its current crest elevation of 7,340.2 (Wright Water Engineers, 1994). <br />In 1980, the Colorado State Engineer's Office (SEO) placed a restriction on the reservoir. The <br />t restriction required the reservoir to be at most 10 feet below the crest of the dam. In 1985, under <br />order from SEO, the spillway was excavated to Elevation 7330.2 to provide 10 feet of freeboard <br />~ below the dam crest. <br />In 1985, a crack on the downstream slope of the left abutment was observed. The crack extended <br />approximately 100 feet, measuring 1.25 inches wide by about 2 feet deep. The crack was excavated <br />and repaired, and a trench drain 29 feet deep was constructed about 130 feet across the downstream <br />shell of the dam (Norfleet and Marvin, 1995). <br />The dam and reservoir are currently operated under restrictive orders by the SEO. These restrictions <br />have been in place since 1980 because of an inadequate spillway capacity, seepage exiting at high <br />elevations on the downstream slope of the dam, and cracks observed in the dam crest and <br />downstream embankment. The most recent restriction was ordered in 1987 and requires the reservoir <br />be maintained at least 10 feet below the elevation of the emergency spillway (7330.2). The <br />restriction has been modified to allow increased storage up to the emergency spillway elevation for a <br />few months during the summer, subject to site inspection and verification of instrument data by the <br />SEO. <br />Installed monitoring instruments revealed that saturation and movement of the landslide was more <br />attributed to snowmelt water than leakage from the reservoir. Piezometer and inclinometer data <br />showed that the landslide movement was seasonal and triggered almost exclusively by porewater <br />pressures related to sources other than the reservoir-in particular, melting snow on the hillside <br />above the dam (Norfleet and Marvin, 1995). <br />Another dam safety concern is the cast-iron outlet conduit, which is subject to full reservoir head <br />pressure along its entire length through the embankment. This is because the flow in the outlet is <br />controlled by a valve at the downstream end of the conduit. <br />P:\Mpls\06 CO\26\0626067\WorkFiles\DesignReport\FTNAL\DesignReportFINAL.doc 2 <br />