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<br />represent the internal resistance stresses of a Bingham fluid, The sum of the cohesive <br /> <br /> <br />yield stress and viscous stress defines the shear stress of a cohesive <br />, <br /> <br />hyperconcentrated sediment fluid in a viscous flow regime, The last term is the sum <br /> <br /> <br />of the dispersive and turbulent shear stresses, which is a function of the square of <br /> <br /> <br />the velocity gradient, <br /> <br />c, Methodology <br /> <br /> <br />The model was first run for clear water only, Rainfall (the 100-year and 10-year <br /> <br /> <br />storm events) was applied over the entire study area. Nodes were selected up- <br /> <br /> <br />gradient (south) of the City, and the flow hydrograph at each of these nodes was <br /> <br /> <br />determined. <br /> <br />These outflow nodes and hydro graphs were then converted to inflow nodes and <br /> <br /> <br />hydro graphs, After examination of the hydro graphs, sediment concentrations were <br /> <br /> <br />assigned for each time period and for each outflow node. The peak sediment <br /> <br /> <br />concentration by volume, C" was assigned to the time that the peak flow occurred, <br /> <br /> <br />Flows less than 10 cfs were assigned a sediment concentration of 20%, Sediment <br /> <br /> <br />concentrations for flows between the peak flow and 10 cfs were varied to provide <br /> <br /> <br />a smooth transition between the two values, <br /> <br />These hydro graphs with their associated sediment concentrations are then input <br /> <br /> <br />through the nodes up-gradient of the City, and the flow of water and sediment is <br /> <br /> <br />analyzed as it flows through the City to the Roaring Fork River. <br /> <br />The peak sediment concentration was varied until the water and sediment flow just <br /> <br /> <br />reached the river. This concentration would provide a conservative estimate of the <br /> <br /> <br />effect of a mudflow or mud flood on the City or any future development. This value <br /> <br /> <br />would optimize the area covered against the maximum depth of flow, Higher <br /> <br /> <br />sediment concentrations would cause a greater depth offlow but would not cover as <br /> <br /> <br />wide an area, Lower sediment concentrations would cause the flow to cover a greater <br /> <br /> <br />area, but the depth of flow would be less. <br /> <br />13 <br />