FLOOD02443 - Laserfiche WebLink

Home Browse Search

Threemile Creek drains approximately 15 square miles. The stream flows northeasterly to its confluence with the Roaring Fork River. Soil in the Glenwood springs area has mainly clayish to loamy tex- tures with variable amounts of gravel, cobble, and stone throughout. The surface is normally stone covered, due to weathering of over- lying bedrock exposures being carried downslope by gravity (Reference 4). The Colorado River has basically no vegetation along its rock- covered banks. Vegetation along the banks of the Roaring Fork River varies extensively and consists of medium to heavy growths of native grasses and willow bushes. The temperature in Glenwood Springs varies from a record low of -30oF in January to a record high of lOooF in July. Sufficient records are not available to determine accurately the average monthly temperatures. However, the approximate average low temperature for January is 230F, and the approximate average high temperature for July is 700F. Annual precipitation for Glenwood Springs during 1977 was 16.53 inches (Reference 5). The patterns of future residential and commercial development along flood plains in Glenwood Springs are of no major concern, because of the topographic conditions of the river channels. Most of the river channels have extremely well-defined deep channels, and development on the over banks of the rivers is hindered by the cost- effectiveness of building construction. 2.3 Principal Flood problems Flooding on the Colorado and Roaring Fork Rivers is caused by rapid melting of the mountain snowpack during the period from late May through early July. These snowmelt floods are characterized by moderate peak flows, large volumes, long duration, and marked diurnal fluctuation in flow. Rainfall on melting snow may accelerate the rate of snowmelt and thus augment floodflows. Major flooding on Threemile Creek is generally caused by cloudburst storms that occur mainly during the summer. This type of storm is characterized by high peak flow and short duration. However, flood- flows could result from snowmelt or a combination of rainfall and snowmel t. Although not recorded by river gage, the snowmelt flood that occurred on the Colorado River in 1884 is generally considered the most severe known, with a 300-year recurrence interval. A flood that occurred in 1971 is judged the most severe of record on the Roaring Fork River, with an 80- to 90-year recurrence interval. The largest recorded flow on the Colorado River is 30,100 cubic feet per second (cfs), which occurred in 1918. This flow is slightly greater than 5