Design the stormwater-collection pipes (concrete; minimum size of 12 in.) for the housing subdivision in Figure P11.8.13. The data for each drainage area (basin) contributing flow to the manholes is provided in the following table, including the inlet time (Ti) and the runoff coefficient (C). In addition, stormwater-pipe information is given, including the ground elevation at each manhole. The rainfall intensity-duration relationship for the design storm can be described by i = 18/(td0.50), where i = intensity in in./hr, and td = storm duration = time of concentration in minutes.

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Basin I O) Inlet/manhole Storm pipe Basin 3 Basin 4 Basin 2 Surface runoff Figure PI1.8.13 Stormwater Length Upstrean Basin (acres) (min) C Pipe (ft) Elevation (t Elevation (ft) 0.3 0.4 0.3 0.5 22.9 22.9 22.0 21.6 200 300 12 AB CB BD DR 24.9 24.4 22.9 22.0 2.2 2.2 1.2 10 200