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(e.g., measurement methods, simulation, expert opinion) if it does not exist. The planning group must also agree on methods of quantifying the effects of each alternative to be analyzed. The hydrologic information chosen to represent the baseline or reference condition should be reex- amined in detail at this point in the study. All parties must understand and agree on one or more hydrologic time series that will be used for com- parison. The baseline hydrologic time series serves as a reference point for judging potential impacts. Often the reference baseline condition is not the actual historical hydrology used in problem iden- tification, but a synthetic time series representing present water uses, operational procedures, and waste loads superimposed on the variability found in the historical hydrologic records. (Occasionally, the baseline hydrology includes future operational procedures that are not yet in place but have been formally approved and are imminent.) Two or more reference hydrologic time series are commonly used for baseline conditions. The resource agency responsible for fisheries must describe the biological reference or bench- mark conditions. Identifying the geographic distri- bution and important times ofthe year (for spawn- ing, migration, etc.) is critical in evaluating different life history phases of the fish populations. A population benchmark may be constructed using historical habitat conditions (from best estimates of actual historical hydrology) and 'backcasting' to identify critical events that populations may have experienced due to physical or chemical limita- tions reflected as habitat bottlEmecks (Burns 1971). A written study plan should (1) determine when data collection must be completed in the field; (2) synchronize the collection of data needed for model input, calibration, and testing; and (3) esti- mate the labor, equipment, travel, and other costs required to produce the needed information by the agreed study deadline. An interdisciplinary plan- ning effort representing all the major interest groups can result in considerable savings of time and effort during the conflict resolution phase. A common mistake in planning is to go about describ- ing a 'set' of data and 'standard collection proce- dures' appropriate for commonly used models. This shortcut simplifies initiation of the data collection phase but often does not build a common under- standing of data needed or agreement on the ana- lytical approach. Lack of group planning may lead to polarization ofthe parties, which may stifle the negotiation process. THE INSTREAM FLOw INCREMENTAL METHOLDOLOGY 29 Study Implementation From the field biologists' and the resource agen- cies' perspective, the implementation phase is often the most interesting and scientifically chal- lenging. This phase consists of several sequential activities: data collection, model calibration, pre- dictive simulation, and synthesis of results. Proper implementation of the study is critical and can bring biological credibility to the decision process but will not, by itself, result in good decisions. During implementation, sampling locations are selected for collecting empirical data used in pre- dictive models. Data collected can include tem- perature, pH, dissolved oxygen, biological pa- rameters, and measures of flow such as velocity, depth, and cover. These variables are used in describing the relation between stream flow and stream habitat utility. IFIM relies heavily on models because they can be used to evaluate new projects or new operations of existing projects. Model calibration and quality assurance (Fig. 5.1) are keys during this phase and, when performed carefully, lead to reliable estimates of the total habitat within the study area during simulation of the alternative flow regimes. Total habitat is synthesized by integrating large-scale macrohabi- tat variables with small-scale microhabitat vari- ables (Fig. 5.2). An important intermediate prod- uct from this phase is the baseline habitat time series. This analysis determines how much habi- tat in total would be available for each life stage of each species over time. The baseline habitat time series provides the base from which rational judgements can be made about proposed alterna- tive management schemes. Inappropriate selection and use of models and failure to verify model assumptions can lead to major errors in application (Shirvell 1986; Scott and Shirvell 1987). Because all habitat-based in- stream flow models rely on empirical measure- ments of the stream channel as inputs, adequate understanding of sediment transport and channel dynamics must be incorporated into any habitat time series analysis. If a channel is not in dynamic equilibrium, the modelers may have to hedge on simulation of alternative futures and call for peri- odic adjustments, with empirical measurements at regular intervals. Some site-specific empirical evidence should be collected to ensure validity when applying instream flow models to the decision-making process. Site- specific data help reduce the large amount ofuncer- tainty in understanding how biological systems