Laserfiche WebLink
• CHANNEL DESIGNS <br />The surface water diversion dimensions were determined using Mannings Equation for open channel <br />flow. All channels will be either riprap, gravel, or vegetated lined channels. <br />All existing channels were evaluated assuming a worst case scenazio, which is; a V-shaped, vegetated <br />ditch with 3H:1V sideslopes. If the channel is stable assuming a worst case configuration, no <br />additional armoring is required. If not, the channel will be riprapped as indicated on the channel <br />design drawings. <br />For newly designed channels, if the flow velocity is less than 6 feet per second, the channel will be <br />gravel lined. If flow velocities exceed 6 feet per second the channels will be lined with riprap. Riprap <br />sized were determined using the SEDCAD+ subroutine for designing riprap lined channels, utilizing <br />either the OSM/Simons Method or the PADER Method. Given the uncertainty in determining <br />riprap sizes for steep grades where the PADER Method was used, a factor of safety of 3 inches has <br />been added to the Dso of riprap in most of these areas. <br />The hydrology modeling for Post Mine Channel SIIPM-1 (lower) has been revised for TR-36. SCC <br />believes that the use of a CN=62 is jusd£ed for the (originally graded spoil) areas that have now been <br />• successfully revegetated. <br />There are three approved land condition types in the original watershed model; reclaimed (vegetated <br />CN=62), undisturbed (CN=70) and graded spoil (CN=86). The original modeling was conducted in <br />1998 (ACZ, 1998) and used the SEDIMOT II model. The model was converted to the 4~ <br />generation of that model, SEDCAD4, in this technical revision. Since the time of the original <br />modeling, the graded spoil areas have been successfully revegetated. (I'he CN=70 for the <br />undisturbed sub-watershed was retained in the previous modeling. <br />The CN's for the other redesigned post mine channels have not been changed or revised, since these <br />channels were constructed using conservative design parameters. <br />SIIPM-8a and SIIPM-Sb Channel Design Demonstration <br />Background: During the spring 2004 rill and gully survey, two large gullies were identified <br />north of Pond 008. A rapid snowmelt directly up-gradient of the eroded area resulted in a <br />large flow of water which then caused the gullies to form. In addition, temporary diversion <br />channels constructed in the past to divert water from fenced vegetation plots also served to <br />concentrate the flow of water. <br /> <br />TR-36 7-12-5 Revised 11/04 <br />