Computer Model Aids Management of Ground-Water Resources in Eastern Virginia

by E. R. McFarland



The U.S. Geological Survey (USGS), in cooperation with the Virginia Department of Environmental Quality (DEQ) and other State and local agencies, has constructed a computer model of ground-water flow in the Coastal Plain province in Virginia. As a result of large withdrawals from Coastal Plain aquifers in Virginia, ground-water levels have declined as deep as 160 feet below sea level near major pumping centers. The aquifers comprise a complex and interconnected hydrologic system, however, and withdrawals have wide-ranging effects that can be difficult to characterize. The model was constructed to provide information about how the ground-water flow system operates and is influenced by withdrawals. To help sustain a reliable, long-term water supply in the Virginia Coastal Plain, the model provides a valid and efficient means for systematically evaluating the combined effect of numerous actual and proposed withdrawals.

The model, which consists of a computer program and related data sets that simulate the ground-water-flow system, can synthesize a large amount of data to test ideas about how the flow system works: it can simulate current withdrawals to understand the existing flow system, and can also simulate possible future withdrawals to calculate how the flow system could respond. For example, results of model simulations influenced legislators to adopt the Virginia Ground Water Management Act of 1992, which fundamentally changed the withdrawal permitting process. In addition, the model has been used by USGS, DEQ and other agencies, and by applicants for withdrawal permits, to simulate the effects of proposed major withdrawals, to evaluate the cumulative effect of actual and proposed withdrawals, and to examine current and possible future trends in ground-water conditions.

Information continues to be gathered on the Coastal Plain aquifers, and revision of the model is essential to maintain its usefulness as a ground-water management tool. Several new sources of information now need to be incorporated into the model to improve the accuracy of simulations and to address increasing ground-water withdrawals. Better representation is needed of ground-water conditions in the Northern Neck and Middle Peninsula, which are among the least well-understood parts of the flow system. In addition, a better understanding is needed of how the aquifers are disrupted by a recently discovered, approximately 60-mile-wide crater that formed when a comet or meteorite struck the Earth about 35 million years ago near the mouth of the present-day Chesapeake Bay. Important connections of the aquifers with streams and rivers along the Fall Zone, a major regional recharge area, are also being found that could control the supply of ground water to much of the Coastal Plain. Lastly, withdrawals are increasing in areas near the model boundaries, where the current form of the model is least accurate. By incorporating the most up-to-date knowledge of ground-water conditions and addressing emerging demands on the resource, the Virginia Coastal Plain ground-water model will continue to provide an effective means to understand the aquifer system and to safeguard the water supply.


McFarland, E.R., 2000, Computer model aids management of ground water resources in eastern Virginia [abs.]: in 1999 Virginia Water Research Symposium--integrating science into the development and implementation of effective water resource policies, Richmond, Va.,  Proceedings: Blacksburg, Va., Virginia Polytechnic Institute and State University, p. 146.


Contact: GS-W-VArmd_webmaster@usgs.gov
U.S. Department of Interior, U.S. Geological Survey
Privacy Statement

Disclaimer