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A major concern mentioned by residents of all four areas relates to the predictability of the flooding event. . . . In other words, even extensive inundation is bearable if expected. . . . Interventions aimed at ameliorating the effects of flooding should try to take account of these needs of the community to understand and adapt their coping strategies if necessary. |
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Residents in flat areas give equal, if not more, weight to the aftereffects of rains. . . .as compared to immediate effects. Water may stand for long periods in very flat areas. Respondents feel that this makes walking difficult and allows the breeding of mosquitoes. Faeces-contaminated mud caused by stormwater is seen as most problematic as it is also a perceived source of mosquitoes and noxious smells. |
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[In areas of the slum improvement programme. . .] residents had high expectations of drainage improvement when the projects were initiated and appear to have expected that flooding and inundations would cease or be reduced substantially. It is likely that the feeling that their expectations have not been met is in part an immediate sense of disappointment that flooding has not ceased altogether. |
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[Drainage] interventions would gain favour if residents understood and were clearly informed about the effects (good and bad) on the environmental risk which they perceive as inherently a natural event. This, of course, necessitates technical personnel being able to predict the consequences of technical interventions. Such a strategy might reduce the scale of expectation. |
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14.1.2
Conventional Drainage Practice |
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While the extensive literature of urban stormwater management describes many sophisticated techniques of analysis (e.g. DoE/ NWC, 1982; WEF/ASCE, 1992; Marsalek and Torno, 1993), drainage design as practised for small catchments is quite straightforward. Conventional practice defines the problem as designing a system to pass a flow generated by a storm of a specified return period or frequency. With this approach, the engineer can only hope to say 'This system's capacity will be exceeded on average once every x years' (but even x can be difficult to estimate with available data). The engineer cannot rationally predict how high the water will rise, how big an area will be flooded, or how long a flood will last. If residents are to understand that drainage networks cannot eliminate flooding, engineers need to know and explain what is likely to happen when it does flood. |
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