Preimpoundment water quality in the Tioga River Basin, Pennsylvania and New York
The water quality in the Tioga River basin was studied from September 1973 to September 1978, prior to impoundment by the U.S. Army Corps of Engineers. Results of the investigation will be used in the operation of three reservoirs that were in the final stages of construction in late 1979. Annual suspended-sediment yields for the basin averaged 575 tons per square mile. Mill Creek near Tioga and Cowanesque River upstream from Nelson were the smallest contributors. The suspended-sediment yields for some sites on the Tioga River and Crooked Creek were affected by reservoir construction. Acid-mine drainage in the headwaters of the Tioga River increased the levels of sulfate, trace elements, and specific conductance, and decreased alkalinity and pH. For most of the river's length, nutrient levels are generally low, but high enough to support biological activity. Tioga Lake will be acidic and probably stratify chemically and thermally. High concentrations of heavy metals will accumulate near the bottom of the lake where oxidation of these metals will produce dissolved oxygen levels significantly lower than those near the surface. Hammond and Cowanesque Lakes will be alkaline and thermally stratified. They will probably support a warm-water fishery. The addition of Hammond Lake water to the outflow from Tioga Lake will probably improve the water quality of the Tioga River below Tioga Dam. Releases from the multi-level withdrawal system will allow the water quality of the river to stabilize, and not be subject to the extreme low-flow conditions that have historically damaged aquatic life.