Stream Pollution: Low-Flow Regulation by Pymatuning Reservoir

Pymatuning Reservoir, with a capacity of 8 365 000 000 cu ft, has been built in Northwestern Pennsylvania at a cost of approximately $3 700 000 for the primary purpose of regulating the flow of the Shenango and Beaver Rivers. A part of the project area is used as a Game Refuge, and there are opportunities for hunting, fishing, and other forms of recreation. These uses require careful evaluation of conflicting interests to determine how the project may be operated to serve best the needs of the region. Industries in the valley below require large quantities of water, especially for cooling purposes. The load on water-works filtration plants had been gradually increasing, and the State Department of Health was insisting upon the installation of sewage treatment plants to provide for the removal of settleable solids, oxidation, and chemical disinfection. Since the adoption of the reservoir plans, this high degree of treatment has not been required. Recreation interests demand that the reservoir be maintained at the highest possible elevation. Releases were made during the filling of the reservoir sufficient to satisfy the minimum industrial requirements. Since filling, tests under varying conditions of reservoir releases have been, and will continue to be, made at sampling stations established at a number of locations in the Beaver and Shenango Basins. The tests apparently show that the requirements for sanitation and public water supplies will be the criterion for releases, and a tentative operating schedule was adopted and used in 1937. Provision is made for flood regulation by the installation of flash-boards in the main spillway, and by maintaining the reservoir level below spillway elevation during the winter months. The reservoir was of material assistance in reducing flood heights during the floods of 1936 and 1937.