New Jersey Water Science Center
Great Falls of the Passaic River at Paterson, N.J.
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Changes in Base-Flow and Withdrawals
Project Title: Changes in Base-Flow and Withdrawals
The objective of this study is to determine the relationship between changes in base-flow and groundwater withdrawals for selected small-sized basins in the NJ Coastal Plain.
Statement of Problem
Groundwater withdrawals in the New Jersey (NJ) Coastal Plain, as well as other parts of the Northern Atlantic Coastal Plain, have increased significantly with the increase in population in recent decades. Future water-supply demands will cause a continuing increase in groundwater withdrawals. In 2000, the aquifers of the NJ Coastal Plain supplied over 300 million gallons per day to groundwater users. Local impacts of these groundwater withdrawals vary from complete elimination of small-stream base flow by nearby shallow pumpage to estimated declines of 5 to 10 % of stream base flow by groundwater withdrawals from deeper confined aquifers. Even small declines in stream base flow can result in unwanted effects on aquatic and wetland ecosystems. Current water-supply management practices in New Jersey rely, in part and increasingly, on groundwater flow models to provide estimates of reduction in stream base flow caused by future increases in groundwater withdrawals. Documenting the effect of coastal plain groundwater withdrawals on stream base flow will increase the understanding of long-term trends in surface-water discharge and aquatic and wetland communities and aid in the management of ground- and surface-water resources.
Strategy and Approach
The approach of this study will be to compile available periodic low-flow measurements and data on precipitation, stream regulation and groundwater withdrawals. This data will be used to evaluate which basins provide adequate low-flow data to determine changes over a period of record showing increased withdrawals and non-interference from stream regulation and precipitation. Estimates of changes in groundwater flow to and from the selected basins caused by changes in nearby withdrawals from deep confined aquifers will be made using appropriate simulations of the NJ Coastal Plain RASA model. A statistical analysis of changes in stream base flow to increases in groundwater withdrawals will then be completed on the selected basins. If significant relationships between base flow and groundwater withdrawals are found, this approach is applicable to other areas of the Northern Atlantic Coastal Plain.