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HomeMy WebLinkAboutWilliamston Subdivision - Williamston Rev Calcs_011818 (2)Job Name Williamston Subdivision Job No. Date 1/18/2018 Sheet Subject DIVERSION CHANNEL SUMMARY SHEET By KEH Chk By <4.5f/s <1.0'Design Diversion Drainage Average Bottom Side Slope Velocity Flow Depth for Top Width Channel Area (Ac) Slope (%) Width(ft) ft/ft ft/s Depth (ft) Liner (ft)T (ft) RD-1(9.0%) 0.93 9.00 0.75 3.5 3.85 0.42 1.00 7.75 RD-2(9.0%) 0.26 9.00 0.50 3.5 2.79 0.25 1.00 7.50 RD-3(8.0%) 0.40 8.00 0.50 3.5 2.99 0.32 1.00 7.50 RD-4(8.0%) 0.32 8.00 0.50 3.5 2.82 0.29 1.00 7.50 PD (5.0%) 0.80 5.00 0.50 3 3.73 0.44 1.00 6.50 SYNTHETIC MAT SYNTHETIC MAT Liner 6" ROCK RIPRAP Temporary SYNTHETIC MAT SYNTHETIC MAT Job Name Williamston Subdivison Job No. Date 1/18/2018 Sheet Subject PERMANENT DITCHES By KEH Chk By DETERMINE TEMPORARY LINER APPROACH: Channel Design calculated using NORMAL DEPTH procedure. Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design. Shear Stress is then compared to Permissable Shear Stress allowed. PROPOSED CHANNEL:PD (5.0%) DRAINAGE AREA: 0.80 Acres MAX SHEAR Td allowed: 2.00 AVERAGE SLOPE: 5.00 % VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth) Calculated VELOCITY of 5.66 is GREATER THAN 2 Feet per second TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN) PROPOSED LINER:6" ROCK RIPRAP *MANNINGS (n) of 0.036 used for design Calculated shear of 1.26 is less than the Permissable Shear*** of 2 Therefore can be used as a temporary liner for PD (5.0%) *Mannings Coefficient obtained from Table 8.05e **RATIONAL METHOD USED TO DETERMINE DISCHARGE Q=CIA Where C= 0.5 I=7.6 in/hr for channel design,Tc=5 min I=5.94 in/hr for 2 year storm REF: NOAA Atlas 14 Data ***Permissable Shear Stress Td obtained from Table 8.05g ****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft) Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted) Calculated Shear 6" ROCK RIPRAP 2.38 0.40 3.43 1.26 Q (cfs) d (ft) VELOCITY v (f/s) (Td) **** DISCHARGE** DEPTH Job Name Williamston Subdivison Job No. Date 1/18/2018 Sheet Subject PERMANENT DITCHES By KEH Chk By PROPOSED PERMANENT LINER:6" RIP RAP APPROACH: Channel Design calculated using NORMAL DEPTH procedure. PROPOSED CHANNEL:PD (5.0%) AVERAGE SLOPE: 5.00 % MAX VELOCITY allowed: 4.50 feet/sec MANNING'S (n) used: 0.035 MAX VR allowed: 8 DISCHARGE FLOW WETTED CRITICAL DEPTH Side Slope Bottom VELOCITY Q=CIA AREA PERIMETER DEPTH FROUDE (d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs) (sq ft) (ft) (ft) No. Fr VR 0.45 3 0.5 3.73 3.04 0.82 3.31 0.50 1.30 0.92 FLOW IS SUBCRITICAL VELOCITY CHECK Calculated velocity of 3.73 feet/sec is less than permissable velocity of 4.50 feet/sec VR CHECK 0.92 is less than the maximum allowable VR of 8 *Permissable Velocity Obtained from Table 8.05a **VR = Velocity * Hydraulic Radius = Velocity * Flow Area/Wetted Perimeter Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted) Calculated VR Job: Williamston Subdivision Job No. Date 1/18/2018 Sheet Subject: Apron A-2 By KEH Chk By APRON:A-2 Pipe Diameter, Do 0 Inches or 0 Feet Apron Length, L=10 Feet (from Fig 8.06a) Channel Width, b=0.5 Feet Side Slope, M:1 = 3 :1 H (2/3 Pipe Dia): =0.0 Feet Apron Width, W1 =0 Feet (3 * Pipe Dia.) Apron Width, W2 =10.0 Feet d50 Stone Size = 0.5 Feet (from Fig 8.06a) =6 inches Apron Thickness, t=13.5 inches RECEIVING OUTLET (CHANNEL / SHEET FLOW): SHEET FLOW