Engineering-based analysis of pre-development hydrology stormwater policy for transportation applications
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Ongoing concern over water quality impacts from development has prompted consideration of a return to pre-development hydrology as a possible solution strategy. The Environmental Protection Agency (EPA) has equated pre-development hydrology with retention of the 95th percentile storm. EPA Region III has issued a municipal separate storm sewer system permit for the District of Columbia (District) with a predevelopment hydrology goal. An engineering-based analysis of the entire set of requirements documents has revealed a number of technical and policy issues that must be resolved before this strategy can be extended nationwide and into transportation applications. Roadways under the jurisdiction of state departments of transportation may need to comply with the strategy because of the use of federal funding and would present unique challenges for stormwater management. Technical issues range from the short times of concentration to the need to specify a design rainfall intensity to the need to focus on dischargebased best management practices (BMPs) rather than on volumetric ones. Policy issues range from whether an improvement in water quality can substitute for the required change in hydrology and which BMPs can accrue compliance credit. The engineering-based analysis suggests a framework for assessing the impacts of the strategy and the current hydrologic and hydraulic tools available for design. On-site infiltration may require huge increases in standard right-of-way purchases, while in-situ conditions may make the District permit requirements impossible for other jurisdictions to meet. Additional tools are required for the design and evaluation of overland flow BMPs.
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