FLOOD03496 - Laserfiche WebLink

Home Browse Search

hydrologic runoff response of the basin_ 9. Conclusions The quantitative perfonnance of the WSR-88D rainfall algorithm, PPS, is examined for a flash flood event along the Buffalo Creek in the town of Buffalo Creek, Colorado in July 1996. A total of 145 rain gauges were available to serve as a comparison to the radar estimates derived from the Denver WSR-88D rZldar, though only one actually sampled the flood-producing storm. Over the 230 Ian range domain of the WSR-88D, the PPS significantly overestimated the rainfall relative to the rain gauges by about 60%, however the radar estimate over the town of Buffalo Creek where the flood deaths and property damage occurred was within 6% of the gauge observation collected by a citizen of the town living on the banks of the river. The cause for the radar-wide overestimation is suggested to be due several error sources including the use of a l-R relationship which may not have been optimal for the environment and stOlms on that day, hail contamination of the radar estimates, below-beam evaporation, andlor improper radar hardware calibration of the reflectivity measurements. Determining the relative importance of these elTor sources is difficult to do and is not attempted in this study. The l-R relationship in use at the Denver WSR-88D on the flood day was the standard NEXRAD default of l=300 R" which has historically performed well for convective rainfall events in the u.s. A default rain rate threshold of75 mm h-I (corresponding to 51 dBl} was in use in the PPS adaptation data. at the Denver WSR-88D radar on this day, however the radar estimates would still have been overestimated on the average even if it were lowered to 54 mm h- 1(49 dBl) or even lower. Thl: 75 mm h'\ threshold could very well have been an appropriate 24