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are made by simulating the effects of the proposed alternatives(s) on stream flows <br />and diversions in the central Platte River system assuming that the climatic <br />conditions occurring in 1947 through 1994 are replicated for the modeled <br />scenario." <br />Biological Models <br />1. Instream Flow Models - Two physical habitat simulation models developed for <br />the Platte River have been used by the Service, one for whooping crane roosting <br />habitat and one for forage fish habitat. These two models are based on <br />applications of Physical Habitat Simulations Methodology (PHABSIM). Each <br />model has two primary components: habitat suitability index models for the <br />species (described below); and channel hydraulics models of the study area. For <br />the hydraulics model, the 89-mile reach from Lexington to Chapman is stratified <br />into 16 river segments having differing hydrology or channel morphology. A <br />total of 85 transects were established within these river segments. Channel <br />profiles and hydraulics have been repeatedly measured for these transects at a <br />range of river discharges to describe how water-related variables such as water <br />width, depth, and velocity change in relation to river discharge. Sixty-two <br />complete sets of ineasurements have been collected from the 16 segments. <br />Hydraulic simulation programs provide detailed computations for various water- <br />related parameters (e.g., wetted surface area, river stage, depth, and velocity) as a <br />function of river flow. <br />a. Whooping Crane Model - The Whooping Crane Model was developed by the <br />PRMJS Biology Workgroup. The purpose of the Whooping Crane Model is to <br />predict the quality and spatial distribution of crane roosting habitat. The <br />functional relationships in the model include a series of biological suitability <br />indices for habitat criteria (e.g., channel width, water widths, and water <br />depths). The data for these indices were derived from hydraulic <br />measurements and channel profiles surveyed at whooping crane roost sites. <br />By combining input of these roosting habitat suitability indices and the <br />hydraulics models (described above), the whooping crane model generates a <br />roost habitat versus flow function that describes how habitat distribution and <br />quality varies with flow. This is produced for.each of the 16 river segments <br />and the entire study area. In addition, landscape features along the river <br />associated with crane disturbance (e.g., housing development, roads, and <br />bridges) are identified to adjust weighting for the amount of habitat in each of <br />the various river segments. The habitat versus flow curve produced by the <br />whooping crane model is combined with the hydrology time series (e.g. <br />OPSTUDY output) to generate a habitat time series that can be compared to <br />those of other hydrology alternatives. <br />b. Forage Fish Model - Several entities have contributed to the development of <br />habitat suitability index models for Platte River forage fish. Suitability <br />indices for microhabitat variables (i.e., depth, velocity, substrate, and cover) <br />have been developed for 24 species or species life stages. By combining input <br />of microhabitat suitability indices and the PHABSIM hydraulics models <br />(described above), habitat versus flow functions are generated. To facilitate