A combined sewer of circular section is to be laid to serve an area of 100 ha with a population of 90,000 supplied with water at 200 litres per day. Assuming an impermeability factor of 0.50 and time of concentration of rainfall 't as 20 minutes. Calculate the size of the sewer when it has to run full with a velocity of 0.3 m/s. Assume suitable coefficients for 'a' and 'b' in the equation for R, intensity of rainfall relating to 't', the time of concentration.

Design a concrete sewer required to carry a maximum design discharge of 10 cfs on a slope of 0.003. The minimum expected discharge is 2.5 cfs. Check the velocity for self-cleansing. Assume that commercial pipes are available in steps increasing by 0.5 ft (i.e. davail = 1 ft, 1.5 ft, 2ft, 2.5 ft...etc.)

A pipeline is needed to drain water away from a hypermarket car park which regularly gets flooded during even moderate rainfall. The current drainage system starts to fail at a rate of 5m3/s, and it is estimated that a drainage rate of at least 15m3/s is needed so that flooding would only occur once every ten years. The drain has fall of 2m over a length of 200m. Estimate the smallest pipe diameter which would clear the water where the head available at the start of the drain is 1.5m. Assume that the Darcey Weisbach friction coefficient would be 0.012.