habitat suitability index models and instream flow suitability curves

for a fish species as a function of streamflow. The output generated byPHABSIM can be used for several IFIM habitat display and interpretationtechniques, including:1. Optimization. Determination of monthly flows that minimize habitatreductions for species and life stages of interest;2. Habitat Time Series. Determination of the impact of a project onhabitat by imposing project operation curves over historical flowrecords and integrating the difference between the curves; and3. Effective Habitat Time Series. Calculation of the habitat requirementsof each life stage of a fish species at a given time by usinghabitat ratios (relative spatial requirements of various lifestages).Suitability Index Graphs as Usedin IFIMPHABSIM utilizes Suitability Index graphs (SI curves) that describe theinstream suitability of the habitat variables most closely related to streamhydraulics and channel structure (velocity, depth, substrate, temperature, andcover) for each major life stage of a given fish species (spawning, eggincubation, fry, juvenile, and adult). The specific curves required for aPHABSIM analysis represent the hydraulic-related parameters for which a speciesor life stage demonstrates a strong preference (i.e., a species that onlyshows preferences for velocity and temperature will have very broad curves fordepth, substrate, and cover).Four categories of SI curves are described below. All species curves forHEP and IFIM are referred to collectively as suitability index (SI) curves orgraphs. The designation of a curve as belonging to a particular category doesnot imply that there are differences in the quality or accuracy of curvesamong the four categories.Category one curves are the most common type presently available for usewith HEP or IFIM. Usually category one curves have as their basis one or more1iterature sources. Some SI curves may be derived from general statementsmade in the literature about fishes (i.e., rainbow trout spawn in gravel; fryprefer shallow water.). Some category one curves may come from literaturesources which include variable amounts of field data (i .e., from a sample sizeof 300, fry were observed in velocities ranging 0.0 to 3.0 ft/sec, and 80%were found in velocities less than 1.0 ft/sec). Other category one curves maybe based entirely on professional opinion, by using the Delphi technique oreducated guesswork (i .e., an expert believes that velocities ranging 1.0 to8.0 ft/sec are necessary for successful spawning of striped bass). Mostcategory one curves are the result of a combination of sources; the finalcurve may include information from the literature, combined with field data,and smoothed or modified using professional judgement. Category one curvesusually are intended to reflect general habitat suitability throughout theentire geographic range of the species and throughout the year, unless they22