Laserfiche WebLink
• The surface runoff diversion system for the waste pile is designed to conform with the requirements <br />of Rule 4.09.2 (~ Supporting calculations and details of the resulting channel design <br />specifications are presented on the following pages D-3 through D-32. The 100-yeaz, 24-hour <br />precipitation event (2.6 inches/24 hours) is utilized as the design criteria for the diversion network <br />providing perimeter drainage control for the waste pile. Peak flows are modeled over the final <br />configuration of the waste pile using Sedcad and are routed into stabilized diversion channels off <br />of the pile. <br />The designed diversion system consists of a combination of ditches established on the immediate <br />perimeter of the pile and ditches established on areas slightly removed and downgradient of the pile <br />(see Map 24 and Exhibit 26A, Figure 2). The location of selected ditch segments away from the <br />immediate pile perimeter is necessitated by topographic constraints existing in the field. <br />Trapezoidal vegetated channels provide stable configurations in all but three presented design <br />segments of the diversion channel network. Riprap lined channels are required for ditch segments <br />RDA-la and RDA-lb (see pages D-8 and D-9) due to the relatively steeper slopes prevalent in <br />these areas. The riprap specifications are indicated. A triangulaz channel design is utilized for the <br />contour ditch RDA-lc (see page D-10) in order to facilitate construction of this portion of the <br />channel. A small ephemeral drainage contributes runoff to ditch segment RDA-lc through a steep <br />natural pre-existing channel. The contributing watershed for this drainage will be slightly enlazged <br />• as a result of constructing the waste pile. TCC will monitor this drainage for erosional stability and <br />install rock check dams if necessary to reduce runoff velocities in this channel. Channel segments <br />RDA-ld and RDA-le are pre-existing trapezoidal ditches designed with 4' bottom widths. These <br />channels aze demonstrated to adequately convey the waste pile 100-yeaz event flows contributing to <br />them (see pages D-11 and D-12). The entire length of ditch RDA-2 consists of an 8' wide <br />trapezoidal vegetated channel (see pages D-18 through D-23). Consequently the individual design <br />segments for this channel are not indicated on Map 24 but are provided herein for reference. As the <br />channel slope steepens in the upper reaches of RDA-2, design flows decrease as a function of the <br />decreasing contributing watershed size. Consequently channel design deviations aze not required <br />throughout this reach. <br />The Sedcad input parameters utilized for generating of the 100-yeaz runoff estimates for the waste <br />pile diversion system contributing watersheds were also utilized to calculate the resultant runoff <br />contribution from the waste pile under the 10-yeaz event scenario (see pages D-3 through D-7 and <br />D-13 through D-17). The resultant runoff estimates totaling 16.4 cfs (see pages D-6 and D-16) are <br />added as base flow to the culvert design calculations presented for drainage PG-2 (see pages D-24 <br />through D-31). The culverts established in drainage PG-2 aze required to adhere to the 10-yeaz <br />design event criteria applicable to access roads. Two sets of culverts are established in drainage <br />PG-2. The upstream culverts (2 x 18" diameter) are designed to convey the 10-yeaz runoff from the <br />• contributing watershed east of permanent diversion ditch RDA-2. The downstream culverts (3 x <br />21" diameter) are designed to convey the same runoff plus the additional 16.4 cfs 10-year event <br />contribution derived from the waste pile. <br />TR 95-21 D-1 Revised 05/18/95 <br />