Using the velocity method, find the concentration time of a 1. 6 ha drainage area which is primarily forested, with a natural channel having a good stand of high grass. The data of Table 3. 3 can be used to estimate the time of concentration. The length and slope of the forested area are 100 km and 0. 2% and the channel length is 20 km with a slope of 0. 5%.

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TABLE 3.3 Parameters Used in Velocity-Slope Relationship ] K = Land Use/Flow Regime n Forest Dense underbrush 0.8 0.83 1.11 Light underbrush 0.4 0.73 2.03 Heavy ground litter 0.20 0.67 3.82 Grass Bermuda grass 0.41 0.50 1.54 Dense 0.24 0.40 2.26 Short 0.15 0.33 3.20 Short grass pasture 0.025 0.13 10.44 Conventional Tillage With residue 0.19 0.20 1.80 No residue 0.09 0.17 3.37 Agricultural Cultivated straight row 0.04 0.40 13.57 Contour or strip cropped 0.05 0.20 6.84 Trash fallow 0.045 0.17 6.73 Rangeland 0.13 0.13 2.01 Alluvial fans 0.017 0.13 15.35 Grassed waterway 0.095 3.33 23.49 Small upland gullies 0.04 1.67 35.14 Paved area (sheet flow) 0.011 0.20 31.09 Paved gutter 0.11 0.07 14.95