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r 100 '0 90 CD 80 '0 CD 70 CD u )( 60 CD CD 50 E 40 :;::: - 30 0 ~ 20 0 10 0 0.0 3.1 I...... ....p~...... ..~~~/~~~.. OjflCt With mil' . . .... 'Qallon '. ..-.-----------!'!_oJ~____________.~ ... . ,. ': 6.2 9.3 12.4 15.5 18.621.724.827.931.0 Units of available habitat Fig. 2.5. Duration analysis of habitat available under baseline conditions, with-project, and after mitigation of project. present about 90% of the time under the baseline condition, but only 15% of the time under the with-project condition. An extension of these incremental, project-bar- gaining methodologies leads to predicting popula- tion responses to flow changes (Cheslak and Jacob- son 1990; Bartholow et al. 1993). In an approach such as IFIM, these predictions will typically re- quire hydrologic analyses, habitat models, sedi- ment transport, water quality, and temperature analyses, as well as trophic level studies, validation of species criteria, studies of biomass, and popula- tion dynamics (Bovee 1982). An alternative to combining these models into a predictive methodology would be long-term em- pirical observations offish behavior. Such studies would document population responses to carefully controlled changes in flow over perhaps 20 years. Recent research on the South Platte River, Colo- rado, by Bovee (1988) demonstrated the rigorous analysis required to show the relation between flow and population. Bovee's work highlights that these relations can be established in theoretically sound, intuitively satisfying directions. We have already seen (Fig. 2.4) the form that these popu- lation responses to changes in flow over time are likely to take. Conclusion Several instream flow quantification procedures are commonly used. The Tennant Method and wet- ted perimeter technique are widely used in the THE INSTREAM FLOW INCREMENTAL METHOLDOLOGY 15 early stages of planning throughout the country. The wetted perimeter and conceptually similar ap- proaches, concentrating on passage for upstream migrating salmon, are important first-cut analyti- cal tools. The PHABSIM method is commonly used as a way to look at hydroelectric power projects (Bovee 1985), to set standards for controversial streams (Washington Department of Ecology 1987), and to develop conditions on federal permits and licenses (Cavendish and Duncan 1986). The PHABSIM method is sometimes used in very com- plex problems (Olive and Lamb 1984), but care must be taken to consider several intervening vari- ables. IFIM is appropriate for the most controver- sial project assessments (Fig. 2.6; Trihey and Stal- naker 1985). Naturally, all of this experience with instream flow technology has led to a literature of evaluation and criticism. In particular, useful insights into choosing and employing instream flow assessment technologies were provided by Wesche and Re- chard (1980), Bain et al. (1982), Orth and Maughan (1982), Loar (1985), Morhardt (1986), and Gore and Nestler (1988). In conclusion, experience and the critical litera- ture teach that there is simply no one best way. The choice of method or methodology depends on the circumstances. Literally dozens of approaches, models, and tools have been used, each developed to satisfy a specific need. To establish the necessary flow, the analyst must know the history and pur- pose of these techniques and must use this knowl- edge to make an informed choice of the best process to follow. Incremental vs. Standard Setting Problems Complexity of decision Complexity of system Fig. 2.6. Spectrum of problem-solving methodologies.