ASSESSING GROUND-WATER AVAILABILITY IN A REGIONAL BEDROCK AQUIFER USING NUMERICAL MODELING, SEACOAST REGION OF NEW HAMPSHIRE

The Seacoast region of southeastern New Hampshire has seen a population growth of nearly 40 percent over the past 20 years. With limited surficial aquifers, the region's bedrock aquifers are increasingly being developed to meet the growing demand for water. The availability of water in the bedrock aquifers, particularly fractured crystalline bedrock aquifers, and the effects of increased stresses, generally are unknown.

To assess the availability of ground water, and the potential effects of future growth on the hydrologic system of the Seacoast region, a regional ground-water-flow model was developed for a 240 mi² coastal area. The finite-difference model was constructed to account for complex hydrologic boundaries; hydrogeologic characteristics of major rock types; and domestic, commercial, industrial, and municipal water withdrawals and returns. The model was calibrated, using parameter-estimation techniques, with more than 1,000 water levels, discharge measurements from 17 watersheds covering about 26 percent of the model area, and ground-water age data. The model provides an improved understanding of the regional ground-water-flow system by 1) quantifying the availability of water in the system, 2) determining stream-aquifer interactions, and 3) assessing the potential effects of increased withdrawals and sewering to 2025. This model provides insight into the implications of future water demands on the hydrologic system and provides a tool for assessing ground-water availability and sustainability in the region.