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modeling tuns are for a very limited duration, final closure scenario. Upon arriving closer to these <br />scenarios, Colowyo will re-evaluate the adequary of these channels. <br />2.0 BATIIURST EQUATION CALCULATIONS <br />Most of the flow resistance in channels with large-scale roughness is derived from the form drag of <br />the roughness elements and the distortion of the flow as it passes around roughness elements. <br />Consequently, a flow resistance equation for these conditions has to account for skin friction and <br />form drag. Because of the shallow depths of flow and the large size of the roughness elements, the <br />flow resistance will vary with the relative roughness area, roughness geometry, Froude number, and <br />Reynolds number. Bathurst's experimental work quantified these relationships in asemi-empirical <br />fashion (Chen et al, 1988), The results estimate flow depth and Flow induced shear stresses, which <br />determine the required dimensions of the designed channel. Velocity is not determined for channels <br />calculated with the Bathurst equation, as velocity through the channel varies dramatically depending <br />on proximity to riprap particles and is not directly rued in the determination of adequate riprap size. <br />3.0 RIPRAP SIZING <br />• Riprap sizes were detemuned using the SEDCAD 4.0 subroutine for designing riprap lined channels, <br />utilizing either the OSM/Simons Method or the PARER Method. <br />The OSM/Simons Method determines the flow induced shear stress on the channel lining and <br />compares this value to the permissible shear stress of the lining material. The permissible shear <br />stress is defined as the lowest shear force which will cause incipient motion of the DSO particle. To <br />ensure a stable channel, the D50 is selected by the program with an internally applied safety factor. <br />The PARER method compares the flow velocity to laboratory determined permissible velocities for <br />particle sizes. The PARER method assumes a specific gravity of 2.65 for riprap (Bureau of Land and <br />Water Conservation, 1996), which is considered appropriate for materials used by Colowyo at the <br />mine site. Given the uncertainty in deterrruning riprap sizes for steep grades using the PARER <br />method, the median riprap size was increased 3 inches as a safety measure to ensure a stable channel. <br />a.0 RESULTS <br />Based on the previously discussed input parameters and methodologies, the emergency spillways, <br />. temporary and permanent channels for the Colowyo mine site were designed and/or evaluated for <br />capacity and erosional stability. The following summary tables indicate a range of slopes and erosion <br />Page 2 <br />