THE MAY1978 CANYON (TX) FLOOD - CALCULATION OF PEAK DISCHARGE IN PALO DURO CANYON STATE PARK

On the afternoon of May 26, 1978 severe thunderstorms formed in the watershed of the Prairie Dog Town Fork of the Red River just west of the town of Canyon, Randall County, Texas. It has been estimated that approximately 150 to 250mm (6-10 in.) of rain fell in the watersheds of the two major tributaries to the Prairie Dog Town Fork of the Red River west of the town of Canyon. Approximately 3000 acre-feet of runoff was captured by the Buffalo Lake Dam, approximately 10 miles southwest of Canyon on Tierra Blanca Creek, one of the major tributaries However, runoff on Palo Duro Creek, the other major tributary, produced major flooding that exceeded flood stage by more than 2.6m ( 8 ft) in the town of Canyon on the morning of May 27. From Canyon, the flood wave continued downstream into Palo Duro Canyon State Park. At the first water crossing in the park the water level at the peak of the flooding was more than 7.5m (24 ft) above the normal low flow. This study estimated the peak discharge of the May 27 flood at the first water crossing to be approximately 2260 cms (80,000 cfs) using standard Slope-Area Methodology. Sources of error in this calculation include uncertainties about the cross-sectional area of the active channel, the height of the water level, changes in the roughness coefficient due to vegetation growth and removal since 1978, and a less than ideal reach of the channel for use of the Slope-Area method. The USGS gaging station near Wayside, 32 km (20 mi) downstream from the first water crossing in the state park recorded a peak discharge of 1300 cms (46,400 cfs) from this runoff event, reflecting an attenuation of the peak discharge of about 42%.