SW3190701_Engineering Calculations (Riprap)_20190822

PROJECT: Harwood Autotmotive Shop Addition
DATE: 8/22/2019
LOCATION: Midland, NC
DESIGNED BY: M.S. Latham- LWE
V-DITCH DESIGN
1. LOCATION: Ditch 1
2. DRAINAGE AREA (ACRES)
C VALUE
INTENSITY (IN/HR.)
Q10=CIA =
DITCH SLOPE _
SLOPE RATIO, Z =
MANNINGS COEFF., N =
0.91 ACRES
0.45 Pavement and Grassed Areas
6.5 IN/HR., 10 YR STM, Tc=S MIN
2.7 C.F.S.
0.014 FT./FT. 1.37
3
0.03 FOR GRASS LINING
3. SOLVE FOR DEPTH OF FLOW USING VARIATON OF MANNING'S EQUATION
FOR 3:1 SIDE SLOPE.
d = ((N x Q)/(S^0.5 x 2.71))^(3/8) = 0.60 FEET
4. CROSS SECTIONAL
FLOW AREA
A=3dA2 =
5. VELOCITY
V = Q/A
I1]6YKIbXy[oleo
Grass lined ditch is stable.
1.07 SQUARE FEET
2.5 FEET PER SECOND
5.0 FT./SEC. ALLOWABLE,
SEE TABLE 8.05a, NCECM
100

Appendices
n
l
3
3 5 10 20 50 100 200 500 1000
Discharge (ft3lsec)
Curves may not be extrapolated.
Figure 8.06a Design of outlet protection protection from a round pipe flowing full, minimum tailwater condition ffW < 0.5 diameter).
Rev. IZ93
8.06.3