Laserfiche WebLink
<br /> <br />' The design parameters and subsequent constfi#ffition is dlscussed in detail in <br />this section. Refer also to the "Design Calculations" section for additional <br />' design Information. <br />I. GRADING <br />' The contributing drainage basin has been dlscussed in the previous section. <br />The amount of area physically available to construct the sediment basin is <br />limited both in a horizontal configuration and topographically (vertically) 9'his <br />' constraint has resulted In the need to limit the amount of runoff entering the <br />sedimentation basin and subsequently leaving the permitted area. The qu~irry <br />operation is creating a large retention area as is demonstrated by the ..pot <br />elevations on Exhibit A. With a limited amount of grading within the quarry, <br />drainage that is currently leaving the quarry will be retained onsite allox~ing <br />the basins to function properly without beinglurcharvPd. This onsite grading <br />will be completed prior to the construction of the sediment basins. <br /> <br /> <br /> <br />1 <br /> <br />l~ <br />C <br /> <br /> <br /> <br />1 <br />A soil stability analysis conducted by CTL Thompson for disturbance areas <br />1-4 oP the CAP recommended ahaping slopes of 2:1 for dry conditions and 3:1 <br />Por wet conditions for the granular material encountered some 750 feet East oP <br />this site. These design parameters were confirmed as part of this final design <br />to be appropriate and applicable to the sediment basin construction. If, <br />however, rock is encountered In the excavation, the slopes can be steeper- <br />theoretically vertical. The majority of the area where the sediment ba:~lns <br />will be constructed will be excavation Lnto native material which 1~ kr~r in <br />be rock. There may be some fill (granular material) encountered at the tower <br />en oP the lower pond and likewise at the lower end of the upper pond. 'The <br />design contours and subsequent operational surface area reflect these <br />assumptions. Material excavated Prom the ponds will be transported to the `r5 ~'~ v~~ <br />quarry for suitable disposal. <br />A representative of the geotechnical firm 1s proposed to be on site for <br />inspection of the excavation. Rock surfaces are proposed to be cut at 1:1 but <br />in the case of the East side of the upper pond will likely eb- steeper to <br />minimize disturbance Into the existing hillside. IP ra ar material. is <br />encountered, the slope will be cut at 2:1 and armored with a 12.-thick~lanket <br />of lmperm As excavated and~~~onstructed basins will be <br />cross-sectioned to confirm available surface area ~ai4`ny as ustment necessary to 6 <br />match available area with contributing basin area will be made by additional <br />regrading oP Subbasin B Area North of the current access road. <br />IL HYDROLOGY <br />The contributing basin hydrology has been estimated with the TR-20 _ <br />computer modeling program. This software has been recognized Sn the <br />City/County Drainage Criteria Manual as an acceptable method for estimating <br />peak design runoff for watersheds of these characteristics and sizes. <br />1 <br />