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14 BIOLOGICAL REpORT 29 that involve assessment of the impacts of alterna- tive project proposals. Incremental problems often create a labyrinth of choices for the analyst who tries to anticipate questions and design stream flow research to ac- commodate likely needs. A simple PHABSIM or HQI analysis will not be sufficient in this setting. New steps, however, can sometimes be added to mid-range processes to help them fit more de- manding problems. More often, as Olive and Lamb (1984) reported, a more comprehensive approach must be chosen. Although fish habitat is still the decision variable, when these more complex tools are used the analysis alone may require as long as 2 years to complete. Each study is preceded by negotiations covering study design and followed by negotiations in which results are debated. The total elapsed time for study design, data collection, and analysis may be more than 3 years. Replicate habitat sampling, biological sampling to develop habitat suitability criteria, and sediment and water routing studies, as well as physical habitat, temperature, and water quality simulations, may be necessary to accurately depict the effects of project operations (Sale 1985). These steps go far beyond what might be accomplished solely with PHABSIM. The IFIM is one process designed to accomplish this intricate research based on knowledge of fish response to habitat features. Trihey and Stalnaker (1985) pointed out that processes like IFIM should be properly called methodologies rather than methods. Whereas 'method' connotes a single tool or concept, 'methodology' implies the linking of procedures, perhaps from several disciplines, to tackle a multi-faceted problem. In IFIM, habitat suitability data come in two forms: macrohabitat and microhabitat. Macro- habitat suitability refers to variables that vary longitudinally downstream, such as water qual- ity, channel morphology, discharge, and tempera- ture. Microhabitat suitability refers to the same variables used in PHABSIM analysis: depth, ve- locity, substrate material, and cover. IFIM uses computer software to integrate these two meas- ures of habitat into habitat units that are then related to flow over time, resulting in a Habitat Time Series. Figure 2.4 illustrates an example habitat time series and a population-size time series. Note that the population does not track the magnitude of the habitat trace, but rather is a function of the habitat capacity established by the minima. Time Series of Population and Habitat Data ----to Limiting habilal event ----. Population size or growth 100X Ii I!! - II ,,::I i ~~ it ,,:8 10X .<:jo I IE :s E :s ~ S t- o .1 ~.. ...- ..... ~............. i . 3 4 5 6 7 8 9 10 11 Years Fig. 2.4. Example fish population size related to usable habitat area using the IFIM. The Habitat Time Series displays the availabil- ity of suitable habitat over a period of record. For example, if the period of record is 10 years (a good minimum number), the Habitat Time Series would display available habitat over that 10-year period. The time trace can be hourly, daily, or monthly. The analyst can answer many questions, such as What amount of habitat is available 90% of the time? What is the median habitat value? What would happen to the available habitat if the flow were reduced by 20% in high flow months? This information makes it possible to analyze the ef- fects of changes in flow on each life stage of every species for which habitat suitability data are avail- able. Where a standard-setting approach might result in a set of annual or seasonal minima below which flow could not fall, an incremental technique might result in a set of monthly or weekly flow envelopes, or windows, within which flow might vary depending on the water supply. With a complex technique such as IFIM, an analyst must be able to document the scientific acceptance of all the technologies used and must be able to extrapolate from the data collected. Especially in intense negotiations, the assump- tions of each method should be well understood, and careful planning should anticipate what spe- cial studies or modifications to a methodology are needed. The result should be the ability to predict changes in habitat over time, to make recommen- dations for wet and dry situations, and to quantify habitat duration phenomena similar to the firm yield concept in hydrology (Trihey 1981). Figure 2.5 illustrates the duration concept, which sum- marizes the availability of habitat values across time. For example, at least 15.5 habitat units are