Author(s): David Stephenson
Linked Author(s): David Stephenson
Keywords: Culverts; Flooding; Hydrology; Low cost; Risk; Urban
Abstract: The problem of flooding is increased in low cost townships because of disregard for flood plains and obstructing the flow. Drainage systems are blocked with litter and water flows overland. Emergency water ways are required. Stormwater culverts in Alexandra township were originally designed to cope with a 10 year storm, and major floods were intended to flow along overland channels. Since the original design, there has been an influx of poor people building their dwellings on available land. including over the culverts. Now there are 1800 dwellings in the path of potential floods. Not only are the lives and properties of people endangered, their shacks also obstruct flows. Three culverts are affected. The northern culvert was estimated to be the worst and was the subject of hydrological calculations and modelling. Engineering solutions investigated included enlarged culverts, surface concrete channels and new culverts along other roadways to intersect flows. Non engineering solutions included relocation of residents, construction of high rise buildings adjacent to the drains and establishing lanes down the drainage routes. Lanes would facilitate garbage collection, a major contributor to reducing capacity of the culverts. The stormwater inlets can be improved in capacity, but the culvert capacity is the limiting factor. This cannot be increased easily without disrupting houses built in the waterways. The most practical solution appeared to be to construct additional drains on intermediate roads going eastwards towards the Jukskei river. Separate systems are envisaged for stormwater and sewage. This will minimize the pollution threat to the Jukskei river downstream. Sanitary lanes will also facilitate garbage removal.