Preliminary investigation of a shallow ground-water flow system associated with Connetquot Brook, Long Island, New York

Under natural conditions, about 95 percent of the flow in Long Island streams is derived from ground-water seepage. The ground-water system that feeds the streams is a shallow subsystem that overlies the regional subsurface flow system. The Connetquot Brook basin was selected for study because it has not been appreciably affected by urbanization. Studies in the basin indicate that the shallow ground-water flow system circulates to a depth of less than 30 feet below the stream channel. Directly beneath the stream, shallow ground-water flow is upward toward the stream channel, but elsewhere in the basin it is predominantly horizontal. Relatively large increases in head with depth in the first 3 feet below the streambed suggest local differences in hydraulic conductivity or in size of area through which the water flows, or both. Water-table contour maps of the area adjacent to Connetquot River for September 1977 and March 1978 indicate that the shape of the water table and the direction of flow lines change seasonally. Variations in ground-water levels and gradients directly affect the rates of ground-water seepage to the stream. (USGS)