Abstract

Major flooding occurred May 6, 2007, in the Willow Creek drainage basin in Harrison County following severe thunderstorm activity over west-central Iowa. More than 7 inches of rain were recorded for the 72-hour period ending 7 a.m., May 6, at the Logan, Iowa weather station. The peak discharge in Willow Creek at Medford Avenue near Missouri Valley, Iowa, was 17,000 cubic feet per second. The recurrence interval of the flood is 160 years, which was estimated using regional regression equations. Information about the basin, the storms, the flooding, and a profile of high-water marks measured at 10 locations along Willow Creek between the mouth at the Boyer River and State Highway 37 in Monona County, a distance of almost 33 river miles, are presented in this report.