G. Lebitsa, O. Pule, and D. Stephenson (Botswana)
Storm water, peak flow, modelling.
Stormwater drainage in cities is a relatively costly service. Underground drain pipes are larger than water pipes or sewers. On the other hand open channels take up space and are dangerous from the health point of view and for falling into. Concentration of water in the channel after storms adds further to the danger. Alternatives need to be developed. The paper discusses computer modelling that was undertaken on the Old Naledi area using RAFLS and StormCAD to calculate flows. The two modelling approaches are compared with conventional methods. Alternative management facilities were investigated. Detention storage is found to halve the peak storm flows. The paper also looked at various alternatives for drainage of these townships which included: channels which are easier to construct and maintain by local resources, open channels with flood plains that attenuate floods to reduce downstream intensity, management structures such as detention storage to reduce flood peaks and retention storage which could also be used as a supplementary water source. The paper further considers health risk due to pollution and design recurrence interval of flooding as well as the maintenance implications of drain types to be adopted in informal settlements such as Old Naledi.
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