A Quantitative Assessment of Water Inputs and Outputs to a Small Watershed in Northwestern Wake County: Evaluating the Effects of Human Water Use on Groundwater Resources.
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Date
2008-12-12
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Abstract
Sustained availability of safe drinking water is an increasingly important issue for Wake County planners due to the recent rapid and ongoing population growth in areas of the county that utilize groundwater for domestic water supply. Wake County planners need to know whether existing groundwater resources can be maintained in the event that the expected population increase takes place. Any anthropogenic influence can alter a natural system. The groundwater system responds to pumping with either a decrease in stored groundwater, a decrease in streamflow or both (Bredehoeft et al. 1982, Sophocleous, 2000).
Wake County is interested in developing a “risk†map as a planning tool to identify areas of Wake County which are at increased risk of groundwater overuse. There are neither adequate data on water table elevations nor stream flows in Wake County with which to assess the relation of current groundwater use to ground or surface water depletion. This case study considers whether insights into groundwater use and potential overuse could be derived from a watershed water-balance approach using existing data. This study is an exercise in identifying available data and data gaps necessary to fill in order to develop a planning tool. Data limitations (e.g., lack of stream discharge or groundwater level data) resulted in restrictions on specific conclusions regarding the study catchment, however, this aspect makes a case study on a specific, fairly typical Wake county catchment a good tool for quantitatively illustrating the significance of different types of hydrologic and water supply data in understanding the water balance and fluxes on a developed catchment with significant groundwater pumping. The study identifies available data sources, data sources that can be further developed, and existing gaps in the data necessary to increase our understanding of a Piedmont fractured bedrock aquifer system.
The results of this case study demonstrate that while the natural water balance components overwhelm the anthropogenic inputs and outputs, the impact of human water use on the catchment water balance does offer some useful insights. The quantification of the developed components of the system indicate that water is being moved within and across catchment boundaries in potentially significant ways. Community water systems may result in interbasin transfer of water on many scales. Water is also being transferred from low elevations to higher elevations as groundwater is removed from deep wells and discharged to onsite wastewater treatment systems just below land surface. The CWS groundwater withdrawals from BTC increase the effective housing density in the catchment. Water recharging the aquifer from onsite wastewater treatment systems may be increasing stream flow during drought and may lead to changes in water chemistry and stream health.
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Keywords
water resources, water balance, development, water use
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Degree
MS
Discipline
Marine, Earth and Atmospheric Sciences
