FLOOD10780 (3) - Laserfiche WebLink

Home Browse Search

Uncompahgre River are minor structures around abutments and have no effect on the 100- and SOO-year floods. Significant flood protection from the 100- and SOO-year floods is provided by several irrigation canals that branch off from the river at different locations upstream of Delta County. These canals are part of the Uncompahgre Project which was completed in 1931. This project included many diversion dams and canals, as well as the Gunnison Tunnel and the Taylor Park Dam (Reference 12). Several of the irrigation ditches cross the Gunnison and Uncompahgre Ri ver basins, notably the South Canal, fed by the Gunnison Tunnel from Gunnison River, and the Loutsenhizer Canal, which draws from Uncompahgre River. The South Canal typically carries 900 to 1,000 cfs of flow, while the Loutsenhizer Canal conveys approximately 200 cfs. Other irrigation canals that branch off from Uncompahgre River include East Canal, Montrose and Delta Canal, and West Canal, upstream of the study area, in Montrose County. Concurrent with periods of snowmelt runoff, maximum allowable flow is usually in effect for the irrigation canals in order to meet the requirements of agricultural areas. During periods of excessively high flows on Uncompahgre River, transbasin diversions from Gunnison River to the Uncompahgre River valley are reduced to alleviate flood conditions. Numerous water storage and irrigation ponds are located in the Minnesota Creek watershed upstream of Paonia. These ponds significantly affect normal flow on Minnesota Creek; however, during periods of major flooding, they will not significantly reduce the peak floodflows. The natural flows of Surface Creek and Cedar Run are affected by numerous irrigation channels. Surface Creek is also regulated by several small reservoirs. The reservoirs and irrigation di tches were built primarily for storage and distribution, and do not reduce peak floodflows. No other flood-control measures exist. 3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods in the county, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude which are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or SOQ-year period (recurrence interval) have been selected as having special significance for floodplain management and for flood insurance premium rates. These events, commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the long-term, avera2e period between floods of a specific magni tude, rare floods could occur at short intervals or even wi thin the same year. The risk of experiencing a rare flood increases when periods 18