Ben Houston, GroundPoint Engineering
The operation of hydroelectric plants can cause serious ecological impacts. When estimating the volume of flow available to generate power, it’s important to remember that not all the flow in the stream can be routed through the turbines. A certain amount of flow needs to remain in the stream to help maintain consistent water quality and support healthy ecological function. In New York State, this “environmental flow” (also referred to as “in-stream flow”) is the subject of significant regulatory oversight and is a critically important factor in establishing realistic power production estimates.
Environmental flows are generally determined via monthly exceedance values and are a function of stream class and stream size (see: https://www.dec.ny.gov/docs/water_pdf/flowtogsfinal.pdf). The NYS DEC Bureau of Ecosystem Health's Instream Habitat Protection Unit primarily functions to mitigate the adverse environmental impacts from the operation of hydroelectric stations and can provide guidance on how to estimate and maintain proper stream flow conditions: