United States Department of Transportation
i
Analysis and Potential Solutions to Sediment Deposition in Dean Road Bridge Watershed, Midland City, AL
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2018-11-01
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[PDF-4.70 MB]
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TRIS Online Accession Number:01688120
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Edition:Final Report
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Abstract:Land use changes in watersheds can create dramatic impacts to the environment as well to existing transportation infrastructure. A severe aggradation process is ongoing in Soapstone Branch, located in Dale County, Alabama, a tributary of the Little Choctawhatchee River. This aggradation has compromised most of the conveyance of the Dean Road Bridge (BIN 12930) as it crosses Soapstone Branch. Between February 2011 and April 2014, the clearance under the bridge, which exceeded 6 ft., dropped to near zero due to sediment accumulation brought from the upstream reaches of the watershed. Given this scenario, this research intended to: 1) study the causes for the ongoing sedimentation process in this stream, considering various competing processes happening within the watershed; and 2) propose alternative solutions to improve conveyance at Dean Road Bridge, with the goal of avoiding the need of a bridge replacement. This research included field investigations to help the calibration of hydrological and hydraulic modeling tools. The calibrated hydrological model supplied flow data for detailed, two-dimensional hydraulic simulations. The hydrological modeling also indicated that in recent years there was a 35% increase of 35% in sediment yield in the watershed. Hydraulic modeling showed that a stream modification strategy based on increasing stream slopes near Soapstone Branch consistently increased shear stresses in the stream bed, reducing the likelihood of sediment accumulation near the bridge. Further modeling indicate that, for long-term conditions including sediment transport in the stream, the solution is sustainable, and could be seen as a lower-cost alternative to bridge replacement at Dean Road.
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