Williamston Subdivision - Williamston Rev Calcs_011818

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