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WORK PLAN <br />The following presents a corrective action work plan to remove debris from the LDG and stabilize the <br />drainage channel. Based on the analysis conducted, the following design has been prepared to meet <br />the conditions imposed by DRMS as part of the approved 112d permit. This TR uses current <br />topographic data to further refine the design that was presented in the Original Work Plan and <br />prepare the final construction documents for the LDG and May Day 2. <br />Scope of Work <br />Design Analysis: <br />To repair the LDG back to its original configuration an analysis was completed of the slopes and <br />cross sections of the Gulch upstream and downstream of the disturbed area. Cross sections were <br />cut on a 25 -foot interval to determine approximate side slopes of the Gulch in an undisturbed state <br />as well as to determine the approximate longitudinal grade of the LDG in the vicinity of the May Day <br />2 portal. This provided a typical section for the LDG that could be used to estimate the maximum <br />drainage conveyed by the channel. <br />Based on this analysis, it was determined that the LDG could convey approximately 114 cfs of <br />stormwater run -off. This run -off was used to determine the required pipe size to allow the drainage to <br />pass beneath the access road. Calculations show that the flow could be conveyed in one 42" pipe. <br />Due to vertical constraints, two 24" CMP's must be used instead of the calculated single 42" CMP. <br />See Appendix A for drainage calculations. <br />Construction of Improvements: <br />Construction will begin with installation of necessary runoff and erosion BMP controls as shown on <br />Figure 1 — Initial SWMP in Appendix B. Following installation of these controls, construction will start <br />with the installation of the twin 24" CMP's. A plan and profile of the pipes was prepared showing the <br />required slopes and length of pipe (see Figure 3 — Culvert Plan & Profile). <br />All CMP used for this project shall use a typical 2 -2/3" x 1/2" corrugation, 16 gage steel (minimum <br />thickness = 0.064 ") and shall be installed in bedding material meeting the manufacturer's <br />specifications. Typical material used for bedding of CMP is squeegee (3/8" minus sand) due to how <br />easy it is to work with and the squeegee's ability to convey water through the material. <br />The upstream side of the pipes will be supported by an 18" deep by 6" thick concrete toe wall to <br />prevent undermining of the pipe in high flow situations. It is also recommended that a trash rack be <br />placed over the mouth of each pipe to prevent large debris from entering the pipes. <br />The downstream side of the pipes will use a multi -inlet CMP flared end section to disperse the water <br />to the greatest extent possible. Additionally, a 14 -foot by 15 -foot riprap pad will be installed to <br />prevent erosion of the channel as it exits the pipe. The riprap shall have a median rock size of 12" <br />and will be grouted in place, to prevent high velocity flows from dislodging the rock. <br />After installation of the culverts, grading operations can begin to reshape the LDG and restore it to <br />its original configuration. Figure 2 — Little Deadwood Gulch Grading Plan was prepared to show <br />proposed grading activities. <br />After completion of grading activities, the channel will need to be stabilized to prevent erosion and <br />degradation of the proposed alignment. Rock Check Dams will be placed along the flow line of the <br />channel to slow the velocity of run-off and prevent scouring. Seeding and mulch will be placed on all <br />disturbed areas. Due to the high probability that water will flow through this area, it is recommended <br />that all slopes disturbed during grading activities be covered with erosion control blankets. Erosion <br />control measures are shown on Figure 4 — Final SWMP. <br />Page 2 <br />