According to IPCC and other experts extreme weather events and very high levels of rainfall will be more frequent features of climate change. This increases the risk of fl ooding and the potential for subsequent damage. Depending on the local topography it may be necessary to protect residential areas from the effects of fl ooding by building storm water retention tanks or by the provision of storm water or combined sewer pumping systems to pump into the receiving water. This will ensure that predetermined high water levels are not exceeded. Otherwise there is the danger of back up and possible collapse of the sewer or channel system.