|
|
|
|
|
|
|
more likely to enter drains in low-income communities in the developing world than in the industrialized world, where more resources are available to manage these wastes. We also suspect that the notion of 'self-cleansing' velocities is unrealistic for the particle size distributions likely to enter surface water drains in slums of developing countries. |
|
|
|
|
|
|
|
|
Ignoring solids would not matter if they were limited in depth or extent, or if they had no effect upon drainage performance. Our research and experience strongly suggest otherwise; solids deposition is common, substantial, and greatly affects drainage performance. Surface water drains are designed as sumps into which water can flow, but unfortunately serve as sumps for anything else on the ground. While open channels are particularly susceptible, gully pots of closed conduit systems do not stop all solids from entering the drain, particularly if they are not emptied (Butler and Karunaratne, 1995). |
|
|
|
|
|
|
|
|
14.4.3
An Alternative Approach |
|
|
|
|
|
|
|
|
Our research suggests that blockage of drainage conduits is likely to be a recurrent problem, and that frequent surface water flow along the streets of slums in developing countries is practically inevitable. If this is true, engineers should consider the deliberate routing of surface water over the streets of the slum, rather than depending on separate pipes or channels to carry these flows. Such an approach has been developed and used by the Indian consulting engineer Himanshu Parikh, who designed the infrastructure for the sites of the ODA-funded Slum Improvement Programme in Indore. Parikh (1990) adopted a variant of the major/minor drainage concept he had developed earlier, and used both pipes and the roads of the site to drain surface water. Given that water will flow over road surfaces anyway, why not try to design them to serve as effective drainage conduits? This may involve more expensive site grading, but will assure more reliable site and road drainage than any system based on conduits that are subject to solids deposition. Roads as drains are also easier to maintain; street sweeping is easier than drain cleaning, and residents have an interest in keeping roads reasonably clear for access. Solids in drains are not an immediate nuisance to residents and are difficult to clean; road obstructions, however, |
|
|
|
|
|