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23 September 1999 <br />V -DITCHES - CROSS-SECTION DESIGN <br />(For Minimum Ditch Slopes) <br />GEOSYNTEC CONSULTANTS <br />2. Flow depth is calculated using Manning's equation for the input parameters in this table <br />(ditch cross section geometry, slope, lining) and the peak flow rate. <br />3. Minimum ditch depth includes a minimum 0.5 ft of freeboard '_"' <br />4. Based on iterative approach for grass lining (class D)-exEp�ga <br />5. VR = V x R = Velocity x Hydraulic Radius <br />6. Tractive Stress (T) = y R S„ <br />7. Grass lining assumed to be retardance class D <br />8. Permissible tractive stress for vegetation with retardance class D [ASCE, 1992]. Use permanent erosion mat (e.g., PEC -MAT or equivalent) where permissible <br />tractive stress is exceeded. <br />J:\1LLI TEW-CADCLOSMCHANNELS.XLS(DITCHES) <br />Calc'd Parameters <br />Minimum <br />Tractive Stress (psf) <br />Bottom <br />Side Side <br />Manning <br />Flow <br />Flow <br />Flow <br />Wetted <br />Ditch <br />Calcul- <br />Permiss- <br />Ditch <br />Width <br />Slope Slope <br />Slope(') <br />Lining (7) <br />Roughness (4) <br />Rate <br />Depth(" <br />Area <br />Perim. <br />VR (5) <br />V <br />Depth(') <br />aced" <br />able(') <br />(ft) <br />1 2 <br />(efs) <br />(ft) <br />(ft) <br />(ft) <br />(ft2/s) <br />(fds) <br />(ft) <br />Subcatch 2 <br />0.0 <br />2HAV 2HAV <br />2.0% <br />Grass <br />0.085 <br />1.55 <br />0.79 <br />1.25 <br />3.54 <br />0.44 <br />1.24 <br />1.3 <br />0.44 <br />0.60 <br />Subcatch 3 <br />0.0 <br />2HAV 2H:1 V <br />2.0% <br />Grass <br />0.075 <br />2.05 <br />0.84 <br />1.40 <br />3.75 <br />0.55 <br />1.46 <br />1.4 <br />0.47 <br />0.60 <br />Subcatch 4 <br />0.0 <br />2HAV 2HAV V <br />0.5% <br />Grass <br />0.098 <br />1.60 <br />1.09 <br />2.40 <br />4.89 <br />0.33 <br />0.67 <br />1.6 <br />0.15 <br />0.60 <br />Subcatch 5 <br />0.0 <br />2HAV 2HAV <br />0.5% <br />Grass <br />0.140 <br />0.91 <br />1.01 <br />2.05 <br />4.53 <br />0.20 <br />0.44 <br />1.6 <br />0.14 <br />0.60 <br />Subcatch? <br />0.0 <br />2HAV 2HAV <br />2.0%a <br />Grass <br />0.098 <br />1.04 <br />0.72 <br />1.03 <br />3.21 <br />0.32 <br />1.01 <br />1.3 <br />0.40 <br />0.60 <br />Subcatch 8 <br />0.0 <br />2H:1 V 2HAV <br />2.0% <br />Grass <br />0.069 <br />2.43 <br />0.87 <br />1.50 <br />3.87 <br />0.63 <br />1.62 <br />1.4 <br />0.48 <br />0.60 <br />Subcatch 9 <br />0.0 <br />2HAV 2H:1 V <br />0.5% <br />Grass <br />0.160 <br />0.65 <br />0.94 <br />1.76 <br />4.20 <br />0.15 <br />0.37 <br />1.5 <br />0.13 <br />0.60 <br />Subcatch 10 <br />0.0 <br />2HAV 2HAV <br />0.5% <br />Grass <br />0.130 <br />1.10 <br />1.06 <br />2.24 <br />4.73 <br />0.23 <br />0.49 <br />1.6 <br />0.15 <br />0.60 <br />Subcatch 11 <br />0.0 <br />2HAV 2HAV <br />0.5% <br />Grass <br />0.170 <br />0.46 <br />0.84 <br />1.42 <br />3.77 <br />0.12 <br />0.32 <br />1.4 <br />0.12 <br />0.60 <br />Subcatch 12 <br />0.0 <br />2HAV 2HAV V <br />0.5% <br />Grass <br />0.160 <br />0.58 <br />0.90 <br />1.62 <br />4.02 <br />0.14 <br />0.36 <br />1.4 <br />0.13 <br />0.60 <br />Subcatch 13 <br />0.0 <br />2HAV 2HAV V <br />2.0% <br />Grass <br />0.095 <br />1.10 <br />0.72 <br />1.05 <br />3.24 <br />0.34 <br />1.05 <br />1.3 <br />0.40 <br />0.60 <br />NOTES: <br />1. Slope for sizing ditch <br />- approx. minimum slope in <br />ditch <br />_ / <br />4(4- t,65:5 Tmf j 2 Ft is <br />2. Flow depth is calculated using Manning's equation for the input parameters in this table <br />(ditch cross section geometry, slope, lining) and the peak flow rate. <br />3. Minimum ditch depth includes a minimum 0.5 ft of freeboard '_"' <br />4. Based on iterative approach for grass lining (class D)-exEp�ga <br />5. VR = V x R = Velocity x Hydraulic Radius <br />6. Tractive Stress (T) = y R S„ <br />7. Grass lining assumed to be retardance class D <br />8. Permissible tractive stress for vegetation with retardance class D [ASCE, 1992]. Use permanent erosion mat (e.g., PEC -MAT or equivalent) where permissible <br />tractive stress is exceeded. <br />J:\1LLI TEW-CADCLOSMCHANNELS.XLS(DITCHES) <br />