Hydrogeology of the Tully Lakes area in southern Onondaga and northern Cortland Counties, New York

Water levels in a series of kettlehole lakes and ponds known as the Tully Lakes respond to seasonal water-level changes in the surrounding aquifer but often differ from ground-water levels in the aquifer because the lakebed sediments are poorly permeable and inhibit the exchange of water. Three sets of ground-water-level measurements were made from the spring recharge period of 2000 through the fall of that year. Seasonal ground-water-level declines ranged from 1.5 to 8 feet. Average annual water-level fluctuations in the three western lakes ranged from 2.5 to 6 feet, whereas those in the two eastern lakes were only about 1.5 feet because these lakes have natural outlets. The ground-water divide between the St. Lawrence and Susquehanna River Basins did not coincide with the surface-water divide and the ground-water divide moved southerly in response to lower water levels in the aquifer during the summer and fall.