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Output of Microhabitat Model (reach specific. life stage specific) E 11l !~ .J::. .J::. .!I!c, m .i Life stage specific =>'2 ::l ~ Flow (cis) Fig. 2.2. Flow-habitat relation developed by using PHABSIM. versus flow function showing how incremental changes in flow result in quantifiable changes in habitat value. Even the best mid-range techniques leave the analyst open to criticism. There are two fre- quently challenged features ofPHABSIM. First is the necessity for species suitability criteria (esti- mated species responses to stream variables, nor- malized onto a response curve). Figure 2.3 depicts example suitability criteria for two life stages of brown trout. The curves show that adults use deeper and faster water than do juveniles. These criteria may be established by several methods ranging from solicitation of expert opinion to site- specific collection and verification of field data (Bovee 1986; Modde and Hardy 1992, (Thomas and Bovee 1993). All of the criteria development methods have been challenged to some degree. 1.0 ~ ~ 0.5 'S C/) 0.0 o 5 1.0 ~ ~ 0.5 'S C/) 0.0 o 5 Depth (ft.) Brown Trout (Adult) 1.0 1.0 THE INSTREAM FLow INCREMENTAL METHOLDOLOGY 13 The second criticism concerns the requirement to analyze habitat species by species, which may not account for habitat selection affected by interspe- cies competition (Ross 1986; Hearn 1987; Modde et al. 1991). Note that the quality of habitat suit- ability data, along with the significance ofPHAB- SIM's driving variables (e.g., depth, velocity, sub- strate material, and cover), forms the basis for most criticisms of this technique (Morhardt 1986). To satisfy such criticisms, more in-depth analysis is needed than is usually undertaken in simple PHABSIM or HQI studies. PHABSIM is an incre- mental method in the sense that it predicts changes in habitat resulting from changes in flow, but it focuses on only a few variables affecting localized fish behavior and ignores the dynamics of habitat through time. The use of PHABSIM alone also ignores many other biotic factors such as inter- and intra-specific interactions. Incremental Techniques The mid-range techniques essentially provide temporal snapshots of stream resources. When the imperatives of negotiation or court proceedings re- quire a more dynamic look at the instream flow question, other techniques are needed. These pro- ject bargaining problems have been labeled 'incre- mental' (Trihey and Stalnaker 1985) because a deep knowledge of how aquatic habitat value changes as a function of incremental changes in streamflow is required. This detailed quantifica- tion must be developed to prepare for negotiations 10 5 10 4 8 12 Fig. 2.3. Suitability-of-use curves for Brown Trout (Juvenile) brown trout. 1.0 0.5 0.5 5 10 4 8 12 Velocity (fps) Channel index 0.5 0.5 10