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36 BIOLOGICAL REPORT 90(5) Determination of Instream Flow Needs at Hydroelectric Projects in the Northeast Gordon W. Russell by U.S. Fish and Wildlife Service 400 Ralph Pill Marketplace 22 Bridge Street Concord, New Hampshire 03301 The Fish and Wildlife Service (Service) developed its New England Flow Method in 1981 in anticipa- tion of reviewing numerous applications for new hydroelectric projects. At the time, there were about 10,000 existing dams in New England that were not being used for hydropower, but whose development was possible with the passage of the Public Utility Regulatory Policies Act of 1978. The New England Flow Method continues to be used by the Service, although its incorporation by the Federal Energy Regulatory Commission into hydroelectric project licenses and its effectiveness in protecting aquatic habitat have not been evaluated until now. The New England Flow Method uses historical stream flow data to determine instream flow needs at a given hydroelectric project. The major biological assumption of the method is that instream flow equivalent to historical median discharge in August (base flow conditions) and during spawning and in- cubation periods will protect aquatic habitat to the degree that would be expected under a natural flow regime. Recommended flows are derived from historical flow data for the river on which the project is located. In certain circumstances, regional historical flow data are used, based on gaging information for unregulated rivers throughout New England. The regional median August flow is equivalent to 0.07 m3/s/km2 of drainage area (0.5 ft3/s/mi2). Using the New England Flow Method, the median August flow (Aquatic Base Flow) is recommended as the instream flow requirement that applies throughout the year unless higher flows are needed on a seasonal basis for migration, spawning, Of egg incubation. The method also allows for project releases to equal inflow to the project area, when the latter are lower than the prescribed flows. In- flows lower than historical monthly median dis- charges would be expected during natural drought conditions or when upstream projects are storing watef for peaking or flow augmentation. Since its inception in 1981, the New England Flow Method .has been the basis for instream flow re- quirements at 157 hydroelectric projects in New England (77% of a total 205 projects authorized by the Federal Energy Regulatory Commission). At 48 projects (23%), the Commission used alternate means for determining instream flows, including re- quiring run-of-river operation, which obviates the need for minimum flows. Lack of data on baseline and postproject condi- tions precludes direct observation of the level of habitat protection provided by flows derived from the New England Flow Method. However, an in- direct measure can be found by examining the results of 14 instream flow studies. These studies wefe conducted by project proponents between 1981 and 1988 and used habitat-based techniques, including the Instream Flow Incremental Method- ology. Flows supported by the results of the in- stream flow studies ranged from 63% below to 90% above those derived from the New England Flow Method (median 11.1% below the Aquatic Base Flow). In all but three cases, the instream flow studies gave results that were lower than corre- sponding values for Aquatic Base Flow. These results suggest that the New England Flow Method produces conservative results, favoring aquatic resource protection. Review of numerous hydroelectric projects under prescribed deadlines requires an efficient approach. Faced with a high workload and limited resources, Service biologists often need to quickly develop recommendations for instream flows that will ade- quately protect fish and wildlife resources. The New England Flow Method can be applied with minimal information and no field studies. In addressing issues related to minimum flows at hydroelectric projects