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Highway Drainage
US 113 over Poplartown Branch
Maryland State Highway Administration
This project consisted of two components. The first was to determine existing and ultimate development conditions discharges at the Poplartown Branch, at the location of US 113 crossing, Worchester County, Maryland. The second component was to evaluate the hydraulic performance of the existing 5' x 9' box culvert under these flow conditions. Several hydrologic methods, such as the USGS Regression Equations, Tasker Program, and a NRCS TR-20 model, were used to estimate the 2-, 5-, 10-, 25-, 50-, and 100-year peak discharges. This photo shows the upstream side of the culvert.
ArcView-GISHydro2000 software of the Structure Hydrology and Hydraulics Unit of the Maryland State Highway Administration was utilized to delineate the 1.0-sq. mi. watershed as well as to calculate values required by the TR-20 model. It was also used to evaluate the parameters for the USGS peak-discharge regression equations. The base data set consisted of 100-ft Digital Elevation Model, digital maps of land use, and maps of soils.
To ensure that TR-20 peak discharges were representative of Maryland conditions, the TR-20 model parameters were adjusted, according to the Hydrology Panel (convened by Maryland State Highway Administration and Maryland Department of Environment) recommendations, so that the TR-20 peak discharges were within one standard deviation of the peak flows estimated by the USGS regression equations.
The existing culvert, above photo showing the downstream face, was evaluated using the FHWY HY-8 computer program. The hydraulic analysis revealed that overtopping of the US 113 roadway would not occur for the 100-year discharge under the ultimate development conditions (as shown in the figure on the right). A brief tidal influence analysis revealed minimal impact.
All field measurements required by this project, such as measurement of the culvert and road, survey of upstream/downstream cross sections, and verification of Manning’s n were performed by SAAD staff.
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