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HomeMy WebLinkAboutSW5190201_2019-02-21 15 Inch RCP Drwy Cul 14 Riprap Outlet_7/16/2019User Input Data Calculated Value Reference Data Designed By: T Harrell Date: 2/25/2019 Checked By: D Blevins Date: 2/25/2019 Company: DEI Project Name: Cambridge Southeast Project No.: 16-154 Site Location (City/Town) Siler City Culvert Id. Driveway Pipe #14 Total Drainage Area (acres) 0.94 ,Step 1. Determine the tailwater depth front channel characteristics below the pipe outlet for the design capacity of the pipe_ If the tailwater depth is less than half the outlet pipe diameter. it is classified mitumum tailwater condition_ Lfit is greater than half the pipe diameter, It is classified maxinmi condition_ Pipes that outlet onto -Wide flat areas with no defined channel are assumed to ha-ve a n,;niinuni tailwater condition unless reliable flood stage elevations sho,kv otherwise - Outlet pipe diameter, Do (in.) 15 Tailwater depth (in.) 7.5 Minimum/Maximum tailwater? Max TW (Fig. 8.06b) Discharge (cfs) Q10 3.18 Velocity (ft./s) 9.5 Step 2. Based on the tailwater conditions determined in step 1, enter Figure S_U6aorFigure 8_06h, and determine d50riprap size and mininnun apron length (L). The d_, size is the median stone size iu a well -graded riprap apron_ Step 3. Determiine apron width at the pipe outlet, the apron shape, and the apron width at the outlet end fron7 the same figure used im Step 2_ Minimum TW Maximum TW Figure 8.06a Figure 8.06b Riprap d50, (ft.) 0.5 Minimum apron length, La (ft.) 4 Apron width at pipe outlet (ft.) 3.75 3.75 Apron shape Apron width at outlet end (ft.) 5.25 1.25 ,Step 4. Determine the inaxirnum stone diameter: drcax 1.5 x d5d Minimum TW Max Stone Diameter, dmax (ft.) 0.75 Step 5. Detemune the apron thickness - Apron thickness = 1.5 x dr1 ,: Apron Thickness(ft.) Maximum TW 0 Minimum TW Maximum TW 1.125 0 ,Step 6. Fit the riprap apron to the site by making it level for the rninimtun length, L. , from Figure 8.06a or Figure 8.06b_ Extend the apron farther downstream and along channel banks itntil stability is assured_ Keep the apron as straight as possible and align it with the fio%v of the recen-1-ug stream_ Make any necessary alignment bends near the pipe outlet so that the entrance into the recei7,-ing stream is straight_ Some locations may require lining of the entire channel cross section to assure stabilitv_ It may be necessary to increase the size of riprap where protection of the channel side slopes is necessary (Appendie 8.05_4'here a-erfalls exist at pipe outlets or flows are excessive, a phinge pool should be considered, see page 8.06.8_