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<br />GSTARS 2.0 <br />GSTARS 2.0 was recently developed by the U,S. Bureau of Reclamation as a <br />Generalized Stream Tube Model for AIluvial River Simulation (Yang et aI, 1998). The <br />model was developed specifically for the Bureau's internal projects rather than the needs <br />of the general public, in contrast with how commercial models are designed. GST ARS <br />2.0 is a quasi-two dimensional model that utilizes a stream tube approach to <br />accommodate differential scour and deposition over the width of a cross section (Figure <br />3), Thus. vertical and lateral changes in cross sectional elevation can be simulated, <br />GSTARS 2.0 was selected for testing primarily to overcome the limitations encountered <br />with the use ofHEC-6, and to improve the accuracy of the output without substantially <br />increasing input effort. <br /> <br />Computer Modeling Methods <br /> <br />The modeling was conducted along the 400 m long study reach, with 19 cross <br /> <br /> <br />sections through two pools (the Ouzel and Tick Pools) and two riffles (Figure I). Both <br /> <br /> <br />HEC-6 and GSTARS 2.0 required similar input parameters, including cross section (x, y) <br /> <br /> <br />coordinates, relative roughness en'), moveable bed \vidth and depth. water discharge. <br /> <br /> <br />water temperature. flow duration, starting water surface elevation, discharge rating curve, <br /> <br /> <br />intlowing sediment load. sediment rating curve, bed material gradation, and a sediment <br /> <br /> <br />transport capacity equation. Many of the input requirements can be treated in HEC-6 <br /> <br /> <br />using a default option in situations where field-based measurements are not available. <br /> <br /> <br />Very few default options are available in GST ARS 2,0. Initially. three stream tubes were <br /> <br /> <br />specitied for the study reach, which is the default value in the manual (Yang et a!. ] 998), <br /> <br />Flushing Flow Scenarios <br /> <br />Two flushing flow scenarios were simulated by HEC-6 and GSTARS 2.0 <br /> <br /> <br />(Table I), The scenarios represent two discharge situations that occurred after the <br /> <br /> <br />sediment release from Halligan Reservoir, as depicted in the hydrograph of Figure 2. <br /> <br /> <br />Flushing Flow I represents a short duration, low magnitude discharge similar to the <br /> <br /> <br />experimental. stepped-up discharge from February-March 1997, Flushing Flow 2 <br /> <br />8 <br />