12. A new urban development is to be constructed near Pinetown KZN (coastal region), which has a mean annual rainfall (MAP) of 1000 mm. This development lies within the catchment of a small stream that is 4.0 km long. The flow characteristics of this catchment are that over the first 500 m of the catchment, runoff flow can be considered as overland flow (grassveld with medium grass) at a slope of 4.5 %. In the next stage, runoff flows in a small natural channel that is 1500 m long with a slope of 2.5 %, and the final stage to the outlet is a concrete-lined channel Page 8 TRANSPORTATION ENGINEERING 2A TRACIA2 laid to a slope of 1.5 % over the remainder of its length. The area of the catchment has been measured as 6.5 km?. The development is made up of 15 % asphaltic streets, 32 % downtown shopping malls, 38 % single-family residential and the remainder as parkland, which may be considered for runoff purposes as lawns with sandy soil - steep >7 %. Analyse this catchment for a 50-year return period storm. 12.1. Calculate the runoff coefficient currently prevailing in the catchment 12.2. Calculate the total time of concentration associated with the flow condition in the catchment 12.3. Calculate the rainfall intensity time of concentration 12.4. Calculate the peak discharge for a 10-year return period storm