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Virginia Coastal Program: 2005 Coastal Grant Project Description and Final Summary

Project Task:



Virginia Institute of Marine Science - Eastern Shore Laboratory

Project Title:

Impervious Surfaces and Water Quality - Virginia Eastern Shore

Project Description as Proposed:

Virginia ranks second in the US in production value of aquacultured shellfish, almost entirely the result of hard clam (Mercenaria mercenaria) aquaculture. This aquaculture predominately occurs in small tidal creeks and coastal lagoons adjacent to two counties, Accomack and Northampton, which comprise Virginia’s Eastern Shore. Clam aquaculture is completely dependent upon good water quality. The shallow water environments where this aquaculture occurs are generally located within a few meters to kilometers from uplands. Thus, land use practices in the adjacent uplands are critical to the continued health of this industry. Excessive inputs of (1) sediments can bury shellfish, (2) nutrients can contribute to harmful algal blooms and, (3) fecal coliform bacteria can lead to harvest closures.

Both Accomack and Northampton County are undergoing transformative changes in land use. Traditional grain and vegetable farming is giving way to industrial poultry production and corporate “staked tomato” farming. The latter practice, sometimes called plasticulture, involves covering mounded rows with impervious plastic sheeting, which can enhance run-off into adjacent tidal creeks. The region is also facing tremendous residential and commercial growth pressure, which is increasing the amount of impervious surface (e.g., roads, parking lots, houses) in the watershed.

Research in other regions of the country has revealed positive relationships between the percent of impervious surfaces in a watershed and several water quality parameters, including fecal coliform bacteria. Both counties are currently undergoing revisions to their comprehensive plans and zoning ordinances and both are looking for guidance on how to protect water quality on which the clam aquaculture and other quality of life factors depend. In response to requests from local government, this project will (1) investigate the relationship between the % impervious surface in 10-12 watersheds on the Eastern Shore and water quality (suspended sediments, nitrogen, phosphorus, chlorophyll a and fecal coliform bacteria) in the receiving tidal creeks and (2) examine these relationships with and without the inclusion of plasticulture to determine the effects of this new agricultural practice on water quality.

Federal Funding:


Project Contact:

Mark W. Luckenbach; (757) 787-5816,

Project Status:

Project Closed

Final Product Received:

"Evaluating the Relationship between Impervious Surfaces within Watersheds and Coastal Water Quality on Virginia’s Eastern Shore" PDF

Project Summary Provided by Grantee:

In response to concerns over increasing development on the Eastern Shore of VA and the effects of impervious surface on water quality in the region, a study was undertaken to examine current water quality conditions in relation to impervious surfaces in 18 watersheds.   These watersheds spanned the length of both Accomack and Northampton counties and varied in total area, area of impervious surface from development and area of impervious surface from tomato cultivation.  Aerial photography, ground truthing and GIS mapping were used to produce detailed land-use maps for all 18 watersheds and estimate the amount of impervious surface within each. 
Water samples were collected bi-weekly from April 9 – October 25, 2007 and analyzed for fecal coliform bacteria, suspended solids, nitrogen, phosphorus and Chl a.  Mean concentrations and loadings were computed for all study sites and compared to the amount of impervious surface within their watersheds. 
The results reveal few significant trends between the mean concentrations of these water quality indicators in the creek headwaters and impervious surfaces in the watershed.  They do, however, show increasing loadings of these materials from the headwaters to coastal waters in relation to increasing watershed area and area of impervious surfaces within the watershed.  These results make it clear that the presence of impervious surfaces within the watershed contribute to loadings of these materials to coastal waters within the region, but they do not point to specific threshold values for the percent of impervious surface within a watershed above which critical pollution levels are observed.  Further, the results from this study do not reveal significant loading of bacteria, sediment or nutrients associated with tomato cultivation. 
This project has produced detailed GIS layers of land use in the 18 watersheds that can be used for additional studies and as the basis for estimating changes to land use in the future.  An overview presentation to county planners and government official on the findings from this work was given at a meeting on June 11, 2008 and VIMS staff will work with local governments in the coming months to make further use of the findings from this study.

Disclaimer: This project summary provides the federal dollars initially awarded to the grantee. Due to underexpenditure or reprogramming of grant funds, this figure may change. For more information on the allocation of coastal grant funds, please contact Laura McKay, Virginia Coastal Program Manager, at 804.698.4323 or email:

A more detailed Scope of Work for this project is available. Please direct your request for a copy to

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Virginia Department of
Environmental Quality
P.O. Box 1105
Richmond, VA 23218
(804) 698-4000

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