For the design of drainage, assume the coefficient of runoff, assume the time of concentration, use the rational method, and use the intensity of rainfall formula of i=3300/ t+ 19 (mm/hr). Assuming that the location of the outfall pipe will be on the river, you may use circular, trapezoidal, or rectangular concrete pipe for the lined canal and the outfall pipe is a circular pipe. n = 0.020, S = 0.0003. Table 2: Runoff coefficients. type of drainage area concrete and bituminous pavements gravel and macadam surfaces impervious soil impervious soils with turf slightly pervious soils pervious soils wooded areas (depending on slope and cover) For slopes from 1 to 2 percent runoff coefficients 0.70-0.95 0.40-0.70 0.40 0.65 0.30-0.55 0.15-0.40 0.05-0.10 0.05-0.20