FLOOD10717 - Laserfiche WebLink

Home Browse Search

early fall general rain over large areas, normally make August, September, and October the wettest months of the year. Most wintertime precipitation occurs as snow and, in the higher elevations, a deep snowpack normally accunulates. Average snowfall ranges from approximately 19 inches at Fruita and Palisade to approximately 72 inches at Collbran. Snowfall is generally dominated by a few large storms. Snowpack ordinarily begins in late October and snowmelt in late April; snowmelt continues through early July. The average monthly temperature at Grand Junction ranges from approximately 260F in January to approximately 78.30F in July. Grand Valley temperature extremes are evidenced by mean maximums ranging from approximately 380F in January to approximately 940F in July, and by mean minimums ranging from approximately lSoF in January to 620F in July. Cooler temperatures prevail in higher mountain areas. The lowest recorded temperature in the county was -360F at Collbran on February 8, 1933. In Grand Valley, record low' and high temperatures are -340F and 640F for January and 380F and 1110F for July, respectively. The growing season usually extends for approximately 190 days. Mesa County is principally mountainous, and native vegetation is mainly in the pinion-juniper and forest categories, with some salt desert shrub land in the west-central portion of the county and grass-covered valley land in the western portion. Agricultural operations and urbanization have taken place along several streams in the county, but have been concentrated principally in the Grand Valley region. Valley areas not changed by human encroachment retain desert shrubs, cottonwood trees, willow trees, and an understory of hardy grasses. Between elevations of 5,000 and 8,000 feet, pinon pine, juniper, oak, big sagebrush, and Douglas fir trees are prominent. From an elevation of 8,000 feet to the timberline, vegetation consists mainly of subalpine fir, aspen, Englemen spruce, and lodgepole pine trees. Hardy grasses, sedges, and alpine willow trees are found above timberline. 2.3 Principal Flood Problems Flooding in Mesa County IS caused mainly by snowmelt 10 the larger drainage basins and by cloudbursts over the smaller drainage basins. However, geni~ral rainstorms constitute the principal flood hazard on Roan Creek, whi le general rain on soowpack creates the most hazardous conditions in the basins of Plateau and Buzzard Creek. The Dolores Ri ver experiences flooding from both snowrnel t and general rains torms. Major floods on the Colorado and Gunni son Rivers result from rapid melting of the mountain snowpack during May, June, and July. Major floods on the other creeks, washes, and small streams in the study area, especially those with much of their drainage basin below an elevation of 8,000 feet, are most often caused by cloudburst storms. 11