SPDSS_Task5_KeyStructure_PrewittReservoir

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2) Prewitt Reservoir (Structure ID 6403552) Prewitt Reservoir is an off-channel storage facility located approximately 6 miles downstream from the upper boundary of Water District 64 on the south side of the South Platte River. The reservoir is situated between the Towns of Merino and Messex and on the Logan -Washington County line. The reservoir was completed in 1910 and is used for irrigation and recreational purposes. The embankment that impounds Prewitt Reservoir consists of two dams along the northern edge of the reservoir approximately 6,500 feet in total length. The embankments are earthen dams with concrete faces. The dams are considered to be in good condition and have never failed. There is currently no emergency spillway for the reservoir. Discussions with the State are ongoing to determine appropriate spillway design criteria. Storage water from Prewitt Reservoir is released to the Prewitt Outlet Canal, which conveys water to the South Platte River. Storage water may also be delivered to the South Platte Ditch via the Highline Canal. Prewitt Outlet Canal is approximately 3 miles in length with a capacity of approximately 900 cfs. Capacity: Total Storage: 32,164 acre-feet Currently restricted to 28,600 acre-feet (elevation 26.5 feet) pending determination of emergency spillway criteria. Active Storage: 28,600 acre-feet Dead Storage: none Area/Capacity Data: Unknown date of survey. Reservoir gage height, area, and cumulative capacity information are provided in Table 1. Table 1 Prewitt Reservoir Elevation-Area-Capacity Gage Height (ft) Area (acres) Cumulative Capacity (ac-ft) 0.0 43.9 0 5.0 292.0 840 10.0 688.0 3,290 15.0 1,216.6 8,051 20.0 1,737.7 15,368 25.0 2,212.8 25,198 28.0 2,430.7 32,164 Since original construction, sedimentation in the southwestern area of the reservoir has reportedly reduced the active pool by approximately 4,000 acre-feet. Historical Prewitt Reservoir.doc Page 9 of 15