ArthurLaneDitchAnalysis

Below are the 10-year and 100-year analysis for the 5' Base ditch along Arthur Lane. As shown
in the table, the 10-year (also 100-year) velocity is greater than 4.5 ft/s if the ditch is grass -
lined.
According the Hydraulics guidelines: "Grass -lined ditches tend to become unstable when flow
velocity approaches 4.5 ft/sec or greater, requiring a non -vegetative liner to maintain
stability."
In order to stabilize the ditch and maintain the physical integrity, the ditch is lined with rip -rap.
Arthur Lane 10 yr Detail Analysis
Drainage Area
75.4 ac
Time of Conc.
30 min
Intensity
3.9 in/hr
C-value
0.5
Flow (10-yr)
147 cfs
Grass
Rip -Rap
Manning n
0.035
0.065
Long. Slope
0.017 ft/ft
0.017 ft/ft
Depth
2.0 ft
2.7 ft
Velocity
6.48 ft/s
4.1 ft/s
Max Shear Stress
2.16 Ib/ft^2
2.89 Ib/ft^2
Arthur Lane 100 yr Detail Analysis
Drainage Area
75.4 ac
Time of Conc.
30 min
Intensity
5.2 in/hr
C-value
0.5
Flow (100-yr)
196 cfs
Grass
Rip -Rap
Manning n
0.035
0.065
Long. Slope
0.017 ft/ft
0.017 ft/ft
Depth
2.3 ft
3.1 ft
Velocity
6.99 ft/s
4.4 ft/s
Max Shear Stress
2.48 Ib/ft^2
3.29 lb/ft-2