Date of this Version
A physical model of Deadmans Run and a pair of railroad bridges was constructed to assess the impacts of the bridges on flood flows. Lower Platte South Natural Resources District is planning a series of improvements to Deadmans Run to improve flood conveyance capacity and remove approximately 500 homes and businesses from the floodplain. The rail bridges are located less than a mile from the confluence of Deadmans Run and Salt Creek, meaning the bridges present a significant bottleneck to the planned improvements. The physical model was used to characterize the drag effects caused by the bridges, which was used to improve computer models. Drag coefficients were determined from tests with individual bridges, then combined to predict losses for both bridges. These predictions aligned well with results from tests with both bridges. The model was modified with a flume to assess alternative designs to improve conveyance under the bridges. The addition of the flume caused a hydraulic jump to form at low tailwater depths, but the jump was drowned out for higher tailwaters. The addition of pier extensions and elliptical entrances to the spur bridge and flume, respectively, had similar effects: small benefits at high tailwaters and small detriments at low tailwaters. However, observed changes were only on the order of about 0.1 feet at prototype scale. On the other hand, removing the spur bridge completely provided substantial benefits to flume performance, with head reductions approaching nearly 1.0 ft upstream of the bridge.
Advisor: David M. Admiraal