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National Water Summary 1987-Water Supply and Use: INSTREAM WATER USE 113 The long-term effects of continuously maintain- ing these artificial minimum flows seldom are the same as the infrequent, naturally occurring, short- term effects that appear in the historic record. As water projects were built and operated, it became apparent that, in many instances, the fishery resources were decimated as a result of imposing minimum-flow standards (Trihey and Stalnaker, 1985, p. 177). • Long-term imposition of low flow ignores the im- portance of periodic flushing events to the main- tenance of fish habitat. The channel shape and bedforms to which fish have adapted has formed in response to cycles of flooding and low flows. Continuous low-flow could drastically alter the na- ture of a channel so that it no longer is a viable habitat (Tennant, 1976, p. 7). • Minimum flows for fisheries were perceived as limits imposed on legitimate water uses rather than as legitimate uses in their own right. Within the water development community, instream flow tended to be viewed as water wasted. • Minimum flows were unenforceable because they were not based on water rights. They were only as good as the word of the operator of a dam or diversion. Even if minimum flows were provided, they were available for appropriation for other uses just below the dam or diversion. • The concept of minimum flows was too rigid to be a useful negotiating tool. It had an "all or nothing at all" ring to it. Water developers asked such questions as, "How much would a fishery be im- proved by a little additional water?" or "What would happen to the fishery with a little less water?". Biologists could not answer these questions. • The minimum-flow concept, as practiced in earlier years, failed to recognize the different water-flow requirements of the various instream uses. A commonly held belief was that fish required a greater minimum flow than all other uses. There- fore, according to the prevailing wisdom, if there is enough water for fish, there is enough water for other instream uses. During the early 1970's, as streamflows for fishery maintenance and management, recreation, water-quality maintenance, esthetics, and maintenance of estuarine ecosystems were recognized as legitimate uses of water, the terms "instream flow" and "instream-flow needs" began to replace the concept of minimum flow. Instream uses now were thought to have their own set of flow requirements that could not be satisfied by water "left over" after other uses were satisfied; for example, flow requirements for a particular instream use might not be just a single minimum, but could vary seasonally or even daily. Further, instream needs were found to be different for each use and often were in conflict with one another (fig. 58). Until 1976, the hydrographs shown in figure 58 for fish and wildlife, estuary inflow, waste assimilation, and recreation would have appeared as straight lines (constant minimum flow), if included at all, in an analysis of streamflow allocation. Two conferences-one on a description of existing instream-flow methodologies and the other on the major legal, institutional, and technical problems associated with instream flows-that were held in the 1970's focused national attention on this issue (Orsborn and Allman, 1976; Stalnaker and Arnette, 1976). Of the problems identified in both conferences, one was emphasized over and over-the need for an incre- mental methodology. A means was needed to determine the value of an increment of flow to assess adequately needs and to negotiate flow releases sufficient to satisfy those needs. Since the mid-1970's, instream-flow method- ology has advanced significantly; it now includes the development of incremental approaches for assessing r, r /Fish and wildlife . ,, •7,.- Estuary f inflow I /Hydroelectric ' power I generation -..--Navigation ................ . ,-Waste assimilation Recreation JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC Figure 58. Schematic of the nature of streamflow require- ments for instream uses throughout a calendar year. (Source: Modified from U.S. Water Resources Council, 1978, v. 1, p. 42.) TIME