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<br />source engineering profession. Looking at stream.
<br />!low through time (by constructing a hydrologic
<br />lime series) allows one to compare the frequency
<br />and duration of wet and dry periods, to examine the
<br />difference between snow-melt and rain-driven sys-
<br />tems. and to determine the Intensity and duration
<br />of short.term e\'ents such as cloud bursts and peak-
<br />ing cycles. To influence operating decisions \vithin
<br />large-scale water development settings, a tool was
<br />needed that underscored conflicts and complemen-
<br />tary water uses, considered 8Jld evaluated each
<br />user's needs, and was understandable, acceptable,
<br />and easy to use by a broad clientele, Such decision
<br />arenas involve a diversity of disciplines, including
<br />engineers, hydrologists, biologists, recreation plan,
<br />ners, lawyers, and political scientists,
<br />The U ,S, Fish and Wildlife Service Directorate
<br />requested direct input from other agencies in the
<br />development of this special methodology, Water
<br />resource professionals were assigned to work on
<br />this cooperative e!Tort for periods up to 4 years,
<br />Engineering, water quality modeling, and plan-
<br />ning expertise came from the U.S, Bureau of Rec-
<br />lamation, Soil Conservation Service. Army Corps
<br />of Engineers. Environmental Protection Agency,
<br />and university scientists. Expertise in aquatic
<br />ecology, fishery biology, water law. institutional
<br />arrangements, and planning came from state
<br />agencies, The Intergovernmental Personnel Act
<br />provided the vehicle for these assigrunents from
<br />state organizations.
<br />This interagency e!Tort led to the conclusion that
<br />an analytical methodology should handle a variety
<br />of in stream flow problems, from simple diversions
<br />from the stream channel to complex storage and
<br />
<br />Overview 01 Incremental Methodology
<br />
<br />
<br />Instil'Jtional
<br />analysis
<br />model
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<br />THE lNSfREA..M FLOW INCREMENTAL Mf::THOLOOLOGY 5
<br />
<br />release schemes involving hydropeaking schedules,
<br />pump-storage, and a network of interconnected res-
<br />ervoirs, For such a methodology to be suitable for
<br />evaluating alternatives, it had to be useful in iden.
<br />tifying, evaluating, and comparing potential solu-
<br />tions, be capable of being tailored to a specific
<br />stream reach, and be expandable such that reach
<br />information could be applied throughout a river
<br />basin, With this general charter, and building on
<br />historical planning practices using stream reach
<br />hydrology, IFIM has developed over a period of
<br />15 years into a river network analysis that incorpo-
<br />rates fish habitat, recreational opportunity, and
<br />woody vegetation response to alternative water
<br />management schemes (Bartholow and Waddle
<br />1986; Milhous et al, 1989; Auble et al. 199n Infor-
<br />mation is presented as a time series of flow and
<br />habitat at selected points within a river system
<br />(Milhous et at 1990). Figure 1.1 illustrates the
<br />general information flow within IFIM; we will dis-
<br />cuss the various components of IFlM throughout
<br />the remainder of this booklet.
<br />Optimizing for anyone use is contrary to the
<br />general philosophy of multiple use; efficiency of use
<br />is defined as the greatest return in the number and
<br />quantity of uses, with emphasis on simultaneous
<br />use, It is imprudent to use the simple, intermediate
<br />output (for example, flow/habitat or !low/recreation
<br />functions) to argue for a minimum release or flow
<br />standard chosen from the maximum value on a flow
<br />versus habitat graph, The timing of events across
<br />seasons is critical to the reproductive success and
<br />relative strength of year classes within fish popu.
<br />lations, The temporal distribution of strong .'ersus
<br />weak year classes shows the well-being of the fish
<br />
<br />Fig. 1.1. Overview of the I nstream Flow
<br />Incremental Methodology.
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