Laserfiche WebLink
<br />The peak discharges for the 10-, 50-, 100-, and SOO-year recurrence <br />interval floods on Uncompahgre River were computed by the U.S. <br />Army Corps of Engineers in April 1979 and 1960 (References 3 and 7). <br /> <br />In the U.S. Army Corps of Engineers report, frequency curves for <br />rainfall and snowmelt events on Uncompahgre River at the Delta <br />and Colona stream gages were developed. The Delta gage is located <br />approximately 20 miles downstream of Olathe, and the Colona gage <br />measures flow on Uncompahgre River approximately 20 miles upstream <br />of Olathe. These frequency curves were computed by statistical <br />analyses of stream-gage data for 58 years of record at the Delta <br />gage and 57 years of record at the Colona gage. The independent <br />frequency curves for rainfall and snowmelt events were combined <br />statistically to get all-event frequency curves at the gage loca- <br />tions. As the two all-event frequency curves were nearly identical <br />at the two gage locations, the peak discharges for the 10-, 50-, <br />100-, and SOO-year floods were computed to be constant between <br />the gages. This indicates that attenuation and stream diversions <br />counterbalance tributary inflow between the stations. <br /> <br />Peak discharge-drainage area relationships for Uncompahgre River <br />are shown in Table 1. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of the flooding sources <br />studied in the community were carried out to provide estimates <br />of the elevations of floods of the selected recurrence intervals <br />along each of these flooding sources. <br /> <br />For Uncompahgre River, the water-surface elevations of floods <br />of the selected recurrence intervals were computed by the U.S. <br />Army Corps of Engineers (Reference 7) through use of their HEC-2 <br />step-backwater computer program (Reference 6). <br /> <br />The results obtained from the HEC-2 computer program were adjusted <br />in the vicinity of bridges to more accurately represent actual <br />flooding conditions (Reference 9). <br /> <br />Cross sections used in the hydraulic analyses of Uncompahgre River <br />were obtained from aerial photogrammetry (Reference 10). The <br />below-water sections were obtained by field measurement. All <br />bridges, dams, and culverts were field surveyed to obtain elevation <br />data and structural geometry. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). For stream segments <br />for which a floodway is computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Boundary and Floodway <br />Map (Exhibit 2). <br /> <br />10 <br />