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<br />The climate of Orchard City is classified as semiarid. The mesa <br />areas north of Orchard City are subject to moderately heavy preci- <br />pitation. Elevation greatly influences the precipitation amounts. <br />Annual precipitation at Orchard City averages approximately 12 <br />inches, while higher elevations of the mesas receive from 20 to <br />40 inches of precipitation. Most winter precipitation occurs <br />as snow, and, in the higher elevations, a deep snowpack normally <br />accumulates. Snowpack ordinarily begins in late October and snow- <br />melt starts in late April. Snowmelt continues through early July. <br />The mean annual temperature at Orchard City is 49.30F (Reference 5). <br />Cooler temperatures prevail in the higher elevations. <br /> <br />The flood plains of Surface Creek, Cedar Run, and Tongue Creek <br />consist primarily of pastureland, however, some residences occupy <br />the area. Small businesses and residences adjoin the flood plain. <br /> <br />2.3 Principal Flooding Problems <br /> <br />The principal cause of flooding on Surface and Tongue Creeks is <br />the rapid melting of heavy snowpack which occurs during May, June, <br />and July. Rainfall on melting snow may hasten the melting process <br />and increase floodflows. <br /> <br />On Cedar Run, thunderstorms are the principal cause of flooding, <br />because the drainage area is at a lower elevation and is not subject <br />to heavy snows. <br /> <br />Records of past flooding at Orchard City were unavailable. The <br />largest flow on record at nearby Cedaredge occurred on May 13, <br />1941, on Surface Creek. The flow was 1190 cubic feet per second <br />(cfs) and is estimated to have been a 100-year flood. <br /> <br />2.4 Flood Protection Measures <br /> <br />The natural flows of Surface Creek, Tongue Creek, and Cedar Run <br />are affected by numerous irrigation channels. Surface Creek is <br />also regulated by several small reservoirs. The reservoirs and <br />irrigation ditches were built primarily for storage and distri- <br />bution, and do not reduce peak floodflows. No other flood control <br />measures exist. There is no flood plain management in Orchard <br />City. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied in detail in the community, standard <br />hydrologic and hydraulic study methods were used to determine the flood <br />hazard data required for this study. Flood events of a magnitude which <br />are expected to be equalled or exceeded once on the average during any <br />10-, SO-, 100-, or SOO-year period (recurrence interval) have been selected <br />as having special significance for flood plain management and for flood <br /> <br />5 <br />