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Water Resources of Virginia

Palmer-Bowlus flume 
Palmer-Bowlus flume

Small Basin Runoff



Cooperating Agencies
Virginia Department of Transportation

Project Chief
Don Hayes

Period of Project
1997 to Present


Small Basin Runoff
H-flume for peak flow
H-Flume for peak flow measurement

The State of Virginia has excellent potential for economic growth and development. However, with economic growth, there is the responsibility of planning for construction of new or modifying the current statewide transportation infrastructure. Extensive hydraulic analysis and design are needed to reduce the impact of highways and bridges on the drainage basins which they cross. With any modification to existing basin drainage, there is potential for stormwater runoff to create flood and water-quality problems. Many government agencies are trying to mitigate the increased runoff and diminished water-quality associated with economic development through better drainage structure design. Detention structures and channel improvements have often proved to be good solutions for managing runoff volume and improving water quality.

On average, Virginia's highways contain one culvert or flow structure for every half mile of road constructed. A large percentage of these structures drain small basins with areas less than 200 acres.  The Virginia Department of Transportation (VDOT) follows several well documented, standard engineering methods to estimate runoff volumes and peak flows from small drainage basins. However, significantly different results are calculated for the same basin when using the separate methods for estimating flood hydrographs.

The objectives of the study are to evaluate existing methods used by VDOT to estimate flood hydrographs from small drainage basins, and evaluate the use of dimensionless hydrographs to estimate runoff volumes.

Relevance and Benefits
Data collection will enhance the knowledge of runoff from precipitation events in small drainage basins.  Current methods are inadequate for accurately determining runoff volumes and peak flows from small drainage basins. Because of the inaccuracies of the available methods to estimate runoff volumes and peak flows from small drainage basins, drainage structures are usually over designed. A better understanding of the runoff process and more accurate flow estimates will contribute to the protection of life and property.

Basins will be selected that are less than 200 acres in size and which have previous hydraulic design work by VDOT. The basins will be instrumented for precipitation and stage and rated for discharge. Weirs or flumes will be installed to assist in discharge determinations as appropriate. Rainfall data and stage data will be collected to obtain 6-8 single-peak runoff events per site (estimated 1.5 to 2 years per site). Runoff volumes and peak flows calculated in the initial hydraulic design by VDOT will be compared to single-peak rainfall-runoff data collected at each site. If at any time during the project, it is determined that the proposed analysis will not supply an adequate solution to the problem, two alternate methods should be addressed: the rainfall-runoff model, and regression equations.

Virginia Projects or: Water Resources of Virginia
U.S. Department of Interior, U.S. Geological Survey
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Last modified: Monday, May 23, 2005 07:35:27 AM