It pours down stormwater drains, carrying with it litter, organic matter and a range of pollutants washed off the urban streets. The vast area of hardened surfaces that characterises the urban environment provides not only the source of pollution, but results in an increased rate of run-off, channelled into ever more constrained areas. Many of our urban rivers, including those in Cape Town, have been canalised in an attempt to control them, to manage them, to make them obey our rules. But the forces of nature are not so easily constrained. Rivers burst their banks.
Small streams turn all too fast into raging torrents.
When coupled with a heritage of poor planning and lack of regulation, such events have the makings of disasters. Buildings are erected in the wrong place because of a desire to be close to the banks of a river or because there is nowhere better to put up a shack. These increase the risks not only to the inhabitants of such buildings, but to others downstream as the natural course of floodwaters is interrupted. The managers of cities face a different set of challenges to those managing water at the macro level. There is, of course, one challenge that they have in common - the protection and, in many cases, the restoration of a valuable environmental asset.