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THE INSTREAM FLOW INCREMENTAL METHOLDOLOGY 27 Table 4.3. IFIM models developed for integrating the spatial and temporal scales of habitat analyses. River perspective Longitudinal succession (river continuum) Habitat segregation and patchiness Variable meteorological. processes Type of model One-dimensional macrohabitat models-temperature, dissolved oxygen, dissolved chemicals. Indicators: degree- day accumulations of temperature, thresholds oftolerance, extent of optimum or acceptable conditions. Two-dimensional microhabitat models-depth/velocity distributions in association with substrate material and cover in small cells. Time series of the total amount of usable habitat present in the aggregate over the stream network or a specified portion. Indicators: seasonal occurrence and duration of ecological bottlenecks associated with flood, droughts, or human-induced hydro-peaking or flow depletions. simulation, can model the qualities and patchiness of the usable microhabitats. Microhabitat analyses can identify velocity boundaries important to drift feeders and velocity barriers to rearing immobile or velocity-intolerant life forms. Computer programs (Time Series Library; Mil- hous et al. 1990) allow the analyst to integrate the macro or longitudinal (one-dimensional) habitat data with the one-dimensional hydrologic data throughout a stream system to produce a time series analysis of the total amount of usable habi- tat available for specified species and life stages for particular periods. The spatial analyses are aggregated at the stream network or sub-basin level. Evaluations of atypical events (i.e., climatic disturbances such as droughts and floods) are made by examining the habitat time series for habitat bottlenecks; their magnitude, frequency, duration, and timing of occurrence; and the life stages they appear to influence. With such histori- cal analyses (back calculations), the analyst is better able to compare proposed operating alter- natives and document the probable impacts of those changes. These integrated analyses are termed effective habitat analyses (Bovee 1982). Effective habitat analysis and the identification of habitat bottle- necks have become the focus of instream flow stud- ies involving trout and salmon in the western United States (Bovee 1988). In these analyses, the investigator transforms the habitat time series into a quasi-population model (Waddle 1992). Effective habitat analyses aid the biologists by allowing them to use population dynamics theory and experience to interpret the likely outcome of stream water management options.