2012-07-10_PERMIT FILE - C1981041A (6)

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Roadside South Portal Area • Grated Drains Culvert Below Retaining Wall Rational: Calculated using SEDCAD 4 for Windows Areas, slopes and flow paths obtained from electronic media. Curve Numbers -reference page RSS-6 Culvert Below Retaining Wall 89 -Estimated between 86 and 92 Grated Drains 95 -Estimated between 92 and 98 10 year 24 hour storm event of 1.4" used for all run-off calculations There are three grated drains at the portal level. Two 6-inch diameter drains and one 4-inch diameter. The peak flow for the drainage area is 1.4 cfs. The combined capacity of the grated drains is 1.9 cfs (2-6" C~ 0.8, 1-4" ~ 0.3). See pages RSS-42 & 43 for pipe capacities. The two six inch drains combine into a single six inch pipe at the base of the retaining wall. Page RSS-44 demonstrates a single 6-inch pipe with 5-feet of head has adequate capacity (1.6 cfs) to handle the combined flow from the two 6-inch diameter grated drains. Flow from the single 6-inch pipe is routed over the steep slope below the retaining wall in a six inch flexible ADS pipe. Flow from the 4-inch grated drain and the drain pipe near the shop join below the retaining wall. The drain pipe near the shop is a 4 inch pipe, 175 feet long with a 2% grade. Page RSS-42i shows the peak capacity of this pipe is 0.1 cfs although it will probably never attain this flow. The combined flow in the 4-inch pipe of 0.4 cfs (0.3 + 0.1) is routed over the steep slope below the retaining wall in a 6-inch culvert/flexible ADS pipe. Page RSS-42ii shows that a 6 inch culvert/flexible ADS pipe has • adequate capacity to handle the 0.4 cfs combined flow. The culvert/flexible pipe below the retaining wall will see a peak flow of 0.74cfs (RSS-45). Page RSS-49 indicates the minimum pipe diameter for this culvert/flexible ADS pipe is 6 inches. All three 6-inch diameter culvert/flexible ADS pipes discharge a combined flow of 2.14 cfs (0.74 + 1.4) into the north collection ditch, (ref. Exhibit 66). The north collection ditch is ditch Section F-F as shown on Exhibit 6C. The design of this ditch is presented in Volume V, Appendix 14-6 at page 14- 6-18v. Page RSS-44i shows that increasing the design discharge in this ditch section F-F by 2.14 cfs, from 9.07 to 11.2 cfs only increases the flow depth 0.01 feet. Therefore, the additional 2.14 cis flow from the flexible pipes will not have a measurable impact on ditch Section F-F. Ditch section F-F flows into ditch section G-G as shown on Exhibit 6C. The design of this ditch is presented in Volume V, Appendix 14-6 at page 14-6-18vi. Page RSS-44ii shows that increasing the design discharge in this ditch section G-G by 2.14 cfs, from 13.39 to 15.53 cfs only increases the flow depth 0.03 feet. Therefore, the additional 2.14 cfs flow from the flexible pipes will not have a measurable impact on ditch Section G-G. ENGINEER'S CERTIFICATION The SEDCAD calculatio e~~G?Nt.Presented on pages RSS-36 through RSS-50 were prepared by me during ~V ~a° tl~of~~~ ver & October 2002, and the information presented is true and correct to the~~g!°~my know end belief. •7 a*Y ~* Y. L~9.~~ vo a ,o/z~~ a ,James E. Stoo~,~.E. ate F~~lstered Profess~~al Engineer ~i~•¢j°Hio~sh7o. 19230 RSS-36 10/02