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C) 1990 by S.E.L & Associates <br />A Method to Refine the <br />New England Aquatic <br />Base Flow Policy <br />Brandon H. Kulik <br />Kleinschmidt Associates, Consulting Engineers <br />75 Main Street <br />Pittsfield, Maine 04967 <br />ABSTRACT. The New England Aquatic Base Flow (ABF) Policy, issued <br />by the U.S. Fish and Wildlife Service (USFWS), is used by New England <br />aquatic resource regulatory agencies to recommend instantaneous mini- <br />mum instream flow for water use projects. The intent of the policy is to <br />approximate the historic unregulated median August flow, determined by <br />USFWS to be 0.5 cubic feet per second per square mile (cfsm) of drainage <br />area. This paper presents the thesis that the ABF policy actually under- <br />recommends or over-recommends the instantaneous minimum instream <br />flow for individual projects. The ABF policy is refined by identifying <br />hydrologic regions and synthesizing gage data by the flow duration meth- <br />od. Separate ABF criteria of 0.6 cfsm and 0.3 cfsm, respectively, were <br />developed for Mountain Windward and Non-Mountain Windward re- <br />gions. This refinement provides a better approximation of historic unreg- <br />ulated median August flow. <br />KEY WORDS. Base flow, minimum flow, hydropower, water manage- <br />ment, decision-making. <br />T <br />INTRODUCTION <br />he instantaneous minimum instream <br />flow to be provided in water diver- <br />sion projects is often a major environmen- <br />tal concern. In 1981 the Northeast Region <br />(Region 5) of the U.S. Fish and Wildlife <br />Service (USFWS) developed its Aquatic <br />Base Flow (ABF) Policy to provide a rule- <br />of-thumb criterion for that agency's in- <br />stream flow recommendations for the six <br />New England states. The expressed pur- <br />poses of this policy are: (1) to encourage <br />instream releases that perpetuate indige- <br />nous aquatic organisms and (2) to identify <br />those projects that do not threaten nation- <br />ally important aquatic resources so that <br />permits or licenses for those projects can <br />be expeditiously issued without expensive <br />protracted environmental investigations <br />(USFWS 1981). The policy is applied to <br />stream diversion projects that involve <br />aquatic resources, ranging from diversions <br />for winter snowmaking to year-round hy- <br />droelectric generation. The aquatic re- <br />source agencies of the New England states <br />have generally adopted this same ABF pol- <br />icy. <br />The USFWS ABF Policy describes the bi- <br />ological basis for determination of accept- <br />able instream flows as follows (USFWS <br />1981): <br />The USFWS has used historical flow rec- <br />ords for New England to describe stream <br />flow conditions that will sustain and per- <br />petuate indigenous aquatic fauna. Low flow <br />conditions occurring in August typically <br />result in the most metabolic stress to aquat- <br />ic organisms, due to high water tempera- <br />tures and diminished living space, dis- <br />solved oxygen, and food supply. Over the <br />long term, stream flora and fauna have <br />evolved to survive these periodic adver- <br />sities without major population changes. <br />'N- 8 Rivers • Volume 1, Number 1 Pages 8-22