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Understanding performance during floods matters less where flooding is rare. Flooding in slums of developing countries, however, is a frequent occurrence for a variety of reasons. Rainfall is more intense in tropical climates than in temperate ones (Watkins and Fiddes, 1984; Shaw, 1994), but the funds available for drainage improvement projects are scarcer. In addition, the capacity of most slum drainage networks is greatly diminished by heavy solids deposits. These solids often include sediment loads from unpaved areas, construction debris, road metal and solid waste. While many have noted this problem, (e.g. Cotton and Franceys, 1991; Kolsky et al., 1992; Cairncross and Feachem, 1993) there has been no previous systematic study exploring the impact of such solids upon the performance of the drainage system as experienced by the community. |
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14.1.3
The Research Questions of this Study |
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The Notion of Performance |
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What are appropriate measures of drainage system performance? As noted above, the current standard measure is the return period of the design storm, which is inadequate for prediction of what will happen when it floods. Equally seriously, most engineers do not try to minimize the effects of such flooding when it inevitably occurs. Pioneering work has been done to develop the 'major/minor' or dual drainage design philosophy (Wisner and Kassem,1982; Argue, 1986) in which the role of (major) surface flow during flooding is explicitly recognized. However, field application of these ideas to slum drainage in developing countries has been minimal. Our initial definition of drainage performance as the depth, area, duration and frequency of flooding evolved in light of what could be measured and modelled. |
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Rubbish, construction debris and sediment inevitably end up in drains. What is their impact upon flooding? If drainage performance can be defined and measured, it may serve as a basis on |
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