Laserfiche WebLink
<br />Table 2. Criteria used to determine minimum flow requirements using R2CROSS single transect <br />method (Nehring 1979). <br /> <br />Stream Top Average Percent Wetted Average <br />Width (ft) 1 Depth (ft) Perimeter (%) 2 Velocity (ftlsec) <br /> (xd ) (% WP) (x, ) <br />1-20 0.2 50 1.0 <br />21-40 0.2-0.4 50 1.0 <br />41-60 0.4-0.6 50-60 1.0 <br />61-100 0.6-1.0 >70 1.0 <br /> <br />. <br /> <br />1 At bankfull discharge. <br />2 Percent of bankfull wetted perimeter. <br /> <br />Instream Flow Incremental Methodology (IFIM) <br />and the Physical Habitat Simulation System (pHABSIM) <br />IFIM is an incremental problem solving approach based upon systems analysis techniques <br />(Stalnaker et aI. 1995). PHABSIM is a specific model designed to calculate an index of the amount <br />of microhabitat available for different life stages at different flow levels (Stalnaker et al. 1995, <br />Millious et al. 1989). The IFIM methodology is coupled with the PHABSIM model to generate a . <br />habitat-discharge relationship (Figure 2). Habitat area is expressed in dimensionless units called <br />"Weighted Usable Area". The relationship between Weighted Usable Area and discharge is used <br />to predict changes in habitat under various streamflow scenarios. The IFIM approach is commonly <br />used in 38 states (Figure I) and it is the preferred method for developing instream flow <br />recommendations in 24 states (Reiser et. al1989). <br /> <br />IFIM/PHABSIM is a very flexible modeling tool. The methodology supports the use of at <br />least three separate hydraulic models. This flexibility allows the rnodel to predict instream hydraulic <br />parameters in a variety of stream habitat-types including, but not limited to, riffles, runs, pools, and <br />glides. <br /> <br />Habitat modeling in PHABSIM is based on habitat suitability curves. Habitat suitability <br />curves are estimated species responses to instream hydraulic variables that have been nonnalized <br />into a response curve. Suitability curves have been developed to reflect flow-related,' instream <br />hydraulic requirements for most lifestages of wannwater, coolwater, and coldwater fish species, <br />aquatic invertebrate species, and many other instream values, e.g. rafting and wading flows. In <br />addition, site-specific habitat suitability curves can be developed for practically any aquatic species <br />or instream value of interest. Consequently, IFIMlPHABSIM can be used to predict changes in <br />almost any environmental parameter that can be quantified in the form of a flow-dependent <br /> <br />7 <br /> <br />. <br />