Contraction scour at a bridge over the Iowa River

Flooding of the Iowa River during July and August 1993 caused extensive contraction scour at the State Highway 99 bridge over the Iowa River at Wapello, Iowa. At least 3.3 m of piling under the footing of the second pier from the right (west) abutment were exposed. The scoured streambed did not fill in again after the flood receded, and a bathymetric survey in November 1993 showed that the streambed had been scoured for a distance of about 500 m upstream from the bridge. The bridge was closed to traffic, first because of water over the roadway when a levee failed, and then remained closed because of the exposed piling. The bridge subsequently was reopened to traffic with a weight limit of 13.6 tons.