From a topographic map and field survey, the area of the drainage basin upstream of the point of interest is found to be 35 hectares. The following data were measured: Length of overland flow = 45 m at an average slope of 2.0% with medium grass cover Length of main basin channel = 700 m Slope of channel = 1.8 % Mean annual rainfall = 498 mm Land Use 40% of the basin is for residential purposes while 60% is undeveloped Residential area consists of 15% streets (C=0.90), 15% parks (C=0.20) and 70% flats (C=0.70) Undeveloped area (2.0% slope) is composed of permeable grassland (i) Determine the maximum rate of runoff for a 10-year return period using the Rational method. Use the Rational method table in the Appendices. Use i = 1016/(t 20) where I is in mm/h and t in minutes. [12] (ii) Estimate the diameter of sewer required to convey the generated stormwater if the velocity of flow is 0.9 m/s