SW6220907_Ditch Calculations_20221006

Project Data
Revisions
Project #
2021-026
No
Date
Description
Project Name
Mason Landing Subdivision
Date
9/27/2022
Ditch - 9
Peak Discharge Calculation (10 Year Design]
Drainage Area = 2.54 ac
C = 0.30 Bare Earth
I10 = 7.86 in/hr Assume Tc =5 min
A= 2.54 ac
Q10 = 5.99 cfs
Determine Ditch Flow Depth [d] and Velocity (A - Check for Temporary Conditions
Apply Manning "s Equation: V=1.49/n * R2/3*51/2, Q=AN
Ditch Characteristics:
n = 0.02 Bare Earth
Base Width (B) = 2.00 ft
M= 3
Ditch Slope (S] = 1.24% M:1
Permissible Max Velocity (Vp) = 2.00 fps
FBI
Apply the Following Analysis to Determine Actual "d"and "V"
d = flow depth = 0.46 ft
Area (A) = B*d + M*d2 = 1.56
Perimeter (P] = b + 2d*(M2+1 ].5 = 4.91
R = A/P = 0.32
VpR = V Permiss * R = 0.63
V = Flow Velocity = 3.85 fps
Q= design flow= 5.99 cfs checkQ: OK
Check Ditch Velocity for Lining:
Vp = 2.00 fps Vactual>Vallow,
Find Temp Lining
Vactual= 3.85 fps
Determine Temporary Liner
Recalculate with Liner:
Liner Material = Synthetic Mat
T,he-tre- = Shear stress =
g*d*s
n = 0.025 Table 8.05e NCESCPDM
g = density of water =
62.4 lb/ft3
Base Width (B) = 2.00 ft
d = flow depth =
0.52 ft
M = 3
S = channel slope =
1.24
Ditch Slope (S] = 1.24%
T,he-tre- = Shear Stress =
0.40
Tallow (Td) = 2.00 psf Compare Tshearstress to Td:
Apply the Following Analysis to Determine Actual "d"and "V"
T allow (Td)
2.00
d = flow depth = 0.52 ft
Tshearstress =
0.40
Area (A] = B*d + M*d2 = 1.83
Perimeter (P) = b + 2d*(M2+1).5 = 5.26
Tshear stress < Td => OK
R = A/P = 0.35
V= Flow Velocity = 3.28 fps
Summary
Q= design flow= 5.99 cfs checkQ: OK
Temporary Ditch Liner=
Synthetic Mat

Project Data
Revisions
Project #
2021-026
No
Date
Description
Project Name
Mason Landing Subdivision
Date
9/27/2022
Ditch- 2
Peak Discharge Calculation (10 Year Design]
Drainage Area = 3.64 ac
C = 0.30 Bare Earth
I10 = 7.86 in/hr Assume Tc =5 min
A= 3.64 ac
Q10 = 8.58 cfs
Determine Ditch Flow Depth [d] and Velocity (A - Check for Temporary Conditions
Apply Manning "s Equation: V= 9.49/n * R2/3*51/2, Q=AN
Ditch Characteristics:
n = 0.02 Bare Earth
Base Width (B) = 2.00 ft
M= 3
Ditch Slope (S] = 1.85% M:1
Permissible Max Velocity (Vp) = 2.00 fps
FBI
Apply the Following Analysis to Determine Actual "d"and "V"
d = flow depth = 0.50 ft
Area (A) = B*d + M*d2 = 1.75
Perimeter (P] = b + 2d*(M2+1 ].5 = 5.16
R = A/P = 0.34
VpR = V Permiss * R = 0.68
V = Flow Velocity = 4.90 fps
Q= design flow= 8.58 cfs checkQ: OK
Check Ditch Velocity for Lining:
Vp = 2.00 fps Vactual>Vallow,
Find Temp Lining
Vactual= 4.90 fps
Determine Temporary Liner
Recalculate with Liner:
Liner Material = Synthetic Mat
T,he-tre- = Shear stress =
g*d*s
n = 0.025 Table 8.05e NCESCPDM
g = density of water =
62.4 lb/ft3
Base Width (B) = 2.00 ft
d = flow depth =
0.56 ft
M = 3
S = channel slope =
1.85
Ditch Slope (S] = 1.85%
T,he-tre- = Shear Stress =
0.64
Tallow (Td) = 2.00 psf Compare Tshearstress to Td:
Apply the Following Analysis to Determine Actual "d"and "V"
T allow (Td)
2.00
d = flow depth = 0.56 ft
Tshearstress =
0.64
Area (A] = B*d + M*d2 = 2.06
Perimeter (P) = b + 2d*(M2+1).5 = 5.54
Tshear stress < Td => OK
R = A/P = 0.37
V= Flow Velocity = 4.17 fps
Summary
Q= design flow= 8.58 cfs checkQ: OK
Temporary Ditch Liner=
Synthetic Mat

Project Data
Revisions
Project #
2021-026
No
Date
Description
Project Name
Mason Landing Subdivision
Date
9/27/2022
Ditch - 3
Peak Discharge Calculation (10 Year Design]
Drainage Area = 1.18 ac
C = 0.30 Bare Earth
I10 = 7.86 in/hr Assume Tc =5 min
A= 1.18 ac
Q10 = 2.78 cfs
Determine Ditch Flow Depth [d] and Velocity (A - Check for Temporary Conditions
Apply Manning "s Equation: V=1.49/n * R2/3*51/2, Q=AN
Ditch Characteristics:
n = 0.02 Bare Earth
Base Width (B) = 2.00 ft
M= 3
Ditch Slope (S] = 1.49% M:1
Permissible Max Velocity (Vp) = 2.00 fps
FBI
Apply the Following Analysis to Determine Actual "d"and "V"
d = flow depth = 0.29 ft
Area (A) = B*d + M*d2 = 0.85
Perimeter (P] = b + 2d*(M2+1 ].5 = 3.86
R = A/P = 0.22
VpR = V Permiss * R = 0.44
V = Flow Velocity = 3.29 fps
Q= design flow= 2.78 cfs checkQ: OK
Check Ditch Velocity for Lining:
Vp = 2.00 fps Vactual>Vallow,
Find Temp Lining
Vactual= 3.29 fps
Determine Temporary Liner
Recalculate with Liner:
Liner Material = Synthetic Mat
T,he-tre- = Shear stress =
g*d*s
n = 0.036 Table 8.05e NCESCPDM
g = density of water =
62.4 lb/ft3
Base Width (B) = 2.00 ft
d = flow depth =
0.40 ft
M = 3
S = channel slope =
1.49
Ditch Slope (S] = 1.49%
T,he-tre- = Shear Stress =
0.37
Tallow (Td) = 2.00 psf Compare Tshearstress to Td:
Apply the Following Analysis to Determine Actual "d"and "V"
T allow (Td)
2.00
d = flow depth = 0.40 ft
Tshearstress =
0.37
Area (A] = B*d + M*d2 = 1.28
Perimeter (P) = b + 2d*(M2+1).5 = 4.53
Tshear stress < Td => OK
R = A/P = 0.28
V= Flow Velocity = 2.17 fps
Summary
Q= design flow= 2.78 cfs checkQ: OK
Temporary Ditch Liner=
Synthetic Mat

Project Data
Revisions
Project #
2021-026
No
Date
Description
Project Name
Mason Landing Subdivision
Date
9/27/2022
Ditch - 4
Peak Discharge Calculation (10 Year Design]
Drainage Area = 2.17 ac
C = 0.30 Bare Earth
I10 = 7.86 in/hr Assume Tc =5 min
A= 2.17 ac
Q10 = 5.12 cfs
Determine Ditch Flow Depth [d] and Velocity (A - Check for Temporary Conditions
Apply Manning "s Equation: V=1.49/n * R2/3*51/2, Q=AN
Ditch Characteristics:
n = 0.02 Bare Earth
Base Width (B) = 2.00 ft
M= 3
Ditch Slope (S] = 2.19% M:1
Permissible Max Velocity (Vp) = 2.00 fps
FBI
Apply the Following Analysis to Determine Actual "d"and "V"
d = flow depth = 0.37 ft
Area (A) = B*d + M*d2 = 1.14
Perimeter (P] = b + 2d*(M2+1 ].5 = 4.32
R = A/P = 0.26
VpR = V Permiss * R = 0.53
V = Flow Velocity = 4.50 fps
Q= design flow= 5.12 cfs checkQ: OK
Check Ditch Velocity for Lining:
Vp = 2.00 fps Vactual>Vallow,
Find Temp Lining
Vactual= 4.50 fps
Determine Temporary Liner
Recalculate with Liner:
Liner Material = Synthetic Mat
T,he-tre- = Shear stress =
g*d*s
n = 0.036 Table 8.05e NCESCPDM
g = density of water =
62.4 lb/ft3
Base Width (B) = 2.00 ft
d = flow depth =
0.50 ft
M = 3
S = channel slope =
2.19
Ditch Slope (S] = 2.19%
T,he-tre- = Shear Stress =
0.68
Tallow (Td) = 2.00 psf Compare Tshearstress to Td:
Apply the Following Analysis to Determine Actual "d"and "V"
T allow (Td)
2.00
d = flow depth = 0.50 ft
Tshearstress =
0.68
Area (A] = B*d + M*d2 = 1.73
Perimeter (P) = b + 2d*(M2+1).5 = 5.14
Tshear stress < Td => OK
R = A/P = 0.34
V= Flow Velocity = 2.95 fps
Summary
Q= design flow= 5.12 cfs checkQ: OK
Temporary Ditch Liner=
Synthetic Mat