Flood-profile analysis, Big Darby Creek at State Route 762, Orient, Ohio

The U.S. Geological Survey, in cooperation with the Ohio Department of Transportation, made a hydraulic analysis of the 25- and 100-year floods on Big Darby Creek where State Route 762 crosses the stream at Orient, Ohio. Two proposed bridge plans were analyzed to determine the effects on flood profiles subsequent to the placement of a 376-foot-long, four-span deck bridge across the stream 90 feet upstream of the existing State Route 762 bridge. In plan 1, the brigde is set at a 25-degrees skew to the river and at sufficient elevation to pass the 100-year flood below it. In plan 2, the skew is 28 degrees and elevations are 3 feet lower than in plan 1, which result in partial submergence of the bridge during the 100-year flood.

This analysis shows that the 25-year flood profiles upstream of the new bridge would increase by 0.4 foot if plan 1 is adopted and by 0.3 foot if plan 2 is adopted. Both profiles converge with the present-condition profiles 5,750 feet upstream. The profiles for the 100-year flood would increase by 0.6 foot plan 1 and 1.1 feet for plan 2. This additional backwater affects profiles is 0.1 foot higher than for present conditions, and the plan 2 profile is 0.2 foot higher than profiles for present conditions.