FLOOD03422 - Laserfiche WebLink

Home Browse Search

1998. Colorado Flood Hazard Mitigation Plan (409) 2.2.1.1 General Rain Floods General rain floods can result from moderate to heavy rainfall occurring over a wide geographic area lasting several days_ They are characterized by a slow steady rise in stream stage and a peak flood of long duration_ As various minor streams empty into larger and larger channels, the peak discharge on the mainstream channel may progress upstream or downstream (or remain stationary) over a considerable length of river. General rain floods can result in considerably large volumes of water. The general rain flood season is historically from the beginning of May through Octo- ber. Because the rate of rise is slow and the time available for warning is great, few lives are usually lost, but millions of dollars in valuable public and private prop- erty are at risk_ The October 5, 1911, floods in Pa90sa Springs and Durango were a result of a general rain system over tributaries of the San Juan River Basin in southwest- ern Colorado_ The June 3, 1921 flood in Pueblo was a result of a general rain system in the Upper Arkansas River Basin_ The damaging floods of June 1965 in the Denver-metro area were a result of heavy to torrential rainfall over large portions of the South Platte River Basin, which lasted several days_ 2.2.1.2 Thunderstorm Floods Damaging thunderstorm floods are caused by intense rain over basins of relatively small area_ They are characterized by a sudden rise in stream level, short duration, and a relatively small volume of runoff_ Because there is little or no warning time, the term "flash flood" is often used to describe thunderstorm type floods_ The average number of thunderstorm days per year in Colorado varies from less than 40 near the western boundary to over 70 in the mountains along the Front Range_ The thunderstorm flood sea- son in Colorado is from the middle of July through October. The widely publicized Big Thompson Canyon flood disaster of July 31, 1976, was a result of an intense thunderstorm cell, which dropped up to 10 inches of rain in a few hours over the basin_ On May 15-16, 1993, a thunderstorm-induced flood event occurred at Rifle on Rifle and Government Creeks_ As is usually the case, the highest flows in the shortest period of time occurred when an estimated 125-year flood discharge impacted Rifle_ Structures and vehicles in harm's way suffered damages in ex- cess of $200,000_ On June 17, 1993, a flash flood occurred on Shooks Run in Colorado Springs_ Damages were confined to a File:FHMP.chapterw2.pub Chapter 2 - 3 1129/983:49 PM