FLOOD08263 - Laserfiche WebLink

Home Browse Search

study area. 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 6). During periods of flooding, these struc- tures provide only incidental flood storage and protection. Concurrent with periods of snowmelt runoff, maximum allowable flow (all gates open) is usually in effect for the irrigation canals to meet the requirements of agricultural areas. During periods of excessively high flows on the Uncompahgre River, trans-basin diver- sions from the Gunnison River to the Uncompahgre Valley are reduced to alleviate flood conditions. On all the smaller streams other than the San Miguel and Uncompahgre Rivers, only incidental flood protection is provided by numerous irrigation reservoirs throughout the study basins. Montrose Reservoir (Cerro Summit Reservoir) is located at Cerro Summit at the extreme end of Cedar Creek. There is a small on-stream irrigation reservoir located approximately 1,200 feet downstream of the Ogden Road crossing of Montrose Arroyo. The capacity of this reservoir is estimated to be 2.5 acre-feet. There are other small reservoirs scattered throughout the basins, primarily for stock watering. The size, location, and condition of these reservoirs indicate their minimal effect on basin hydrau- lics. Several irrigation ditches cross the study basins, notably the South Canal (fed by the Gunnison Tunnel from the Gunnison River) and the Loutsenhizer Canal (which draws from the Uncompahgre River). The South Canal typically carries 900 to 1,000 cfs of flow, while the Loutsenhizer Canal conveys approximately 200 cfs. other irriga- tion ditches in the basin include the Vernal Mesa Ditch, the Hairpin Ditch, the Garrett Ditch, the AM Lateral, and the AB Lateral. These ditches carry significantly less water than either the South Canal or the Loutsenhizer Canal (i.e., 50 cfs or less). 3.0 ENGINEERING METHODS For the flooding sources studied in detail in the county, standard hydro- 10'1ic 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 averaqe during any 10-, 50-, 100-, or 500-year period (recurrence interval) have been selected as having special significance for flood plain mana'1ement 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 16