FLOOD09534 - Laserfiche WebLink

Home Browse Search

may change rapidly due to movement of storm systems from west to east through the region. precipitation in the county ranges from 10 to 15 inches in the river valleys to 30 to 40 inches in the high mountainous northeastern areas. Average snowfall varies from approximately 40 inches at Rifle to approximately 70 inches at Glenwood Springs. Snowpack normally begins to accumulate in late October, and snowmelt begins in late April and continues into June or early July. Rain may occur over large areas of the county from late spring through late fall and convective-type cloudburst storms occur in summer. The largest amounts of precipitation occur from January through April, and in August. In the river valleys, mean maximum temperature varies from the mid 300F range in January to approximately 900F in July, and the mean minimums vary from 100F in January to 500F in July. The growing season is 136 days and lasts from mid-March through late October. Native vegetation in Garfield County varies from salt desert shrub and associated growth in the southwest corner to alpine and tundra- type cover in high mountain areaS. Agricultural operations and urbanization have drastically modified native vegetation in the main river valleys, the adjoining benchlands, and the lower portions of small tributary valleys. The surface cover of western Colorado ranges from substantially barren rock to deep fertile friable loarns and clays of good to excellent quality for plant growth. Along the north side of the Colorado River is a prominant escarpment known as the Roan or Book Cliffs near Rifle. Most of the area has fairly deep soils and steep slopes. Mancos shale outcrops follow West Rifle Creek. Sedimentary formations are nearly horizontal in the upper part of the Rifle Creek basin. Soil characteristics for the Glenwood Springs area consist of clayish to loamy textures with variable amounts of gravel, cobble, and stone throughout. 2.3 Principal Flood Problems Most of the annual precipitation in the Colorado River Basin occurs as snow resulting in a deep snowpack in the higher regions. General rainstorms can occur in the area from late spring through late fall, and convective type cloudburst storms can be expected fre- quently during the summer. Major flood flows on the Colorado and Roaring Fork Rivers result from rapid melting of the mountain snowpack during the period from late May through early July. Snowmelt floods are characterized by moderate peak flows, large volumes and long durations, and marked diurnal fluctuation in flow. Rainfall on melting snow may accelerate the rate of snowmelt adding to floodflows. Major floods on the dry washes, gulches, and smaller streams under study, especially those with much of their drainage area below 8,000 feet, are generally caused by cloudburst storms. This type of storm is 6