The physical changes in the landscape created by urbanisation considerably alter the
hydrological response of an area to rainfall through higher river flow magnitudes, faster runoff
response to rainfall periods, lower levels of groundwater recharge, and reduced base flow. A
drainage system within an urban area has to deal with these difficulties so as to mitigate the
arising effects, particularly when the design flood occurs or is exceeded. Flood and
precipitation runoff prediction for design of stormwater controls is a highly statistical process,