Abstract
Abstract Cities in South Asia are experiencing storm water drainage problems due to a combination of urban sprawl, structural, hydrological, socioeconomic and climatic factors. The frequency of short duration, high-intensity rainfall is expected to increase in the future due to climate change. Given the limited capacity of drainage systems in South Asian cities, urban flooding and waterlogging is expected to intensify. The problem gets worse when low-lying areas are filled up for infrastructure development due to unplanned urban growth, reducing permeable areas. Additionally, solid waste, when dumped in canals and open spaces, blocks urban drainage systems and worsens urban flooding and waterlogging. Using hydraulic models for two South Asian cities, Sylhet (in Bangladesh) and Bharatpur (in Nepal), we find that 22.3% of the land area in Sylhet and 12.7% in Bharatpur is under flooding risk, under the current scenario. The flood risk area can be reduced to 3.6% in Sylhet and 5.5% in Bharatpur with structural interventions in the drainage system. However, the area under flood risk could increase to 18.5% in Sylhet and 7.6% in Bharatpur in five years if the cities' solid waste is not managed properly, suggesting that the structural solution alone, without proper solid waste management, is almost ineffective in reducing the long-term flooding risk in these cities.
Highlights
Unplanned urban growth and development interferes with the natural flow of water and usually increases the risk of urban flooding (Booth, 1991; Douglas et al, 2008)
For the purposes of this paper, there are two consequences of urban development in South Asia: (i) it augments run-off and increases the risk of the breaching of embankments if a city abuts a river; and (ii) it reduces the flow of drainage by gravity due to drainage congestion, as urban drainage systems are unable to keep pace with urban development
We examine the existing designs of the drainage systems in Sylhet and Bharatpur to understand how the inadequate capacity of a drainage system and the unplanned dumping of solid waste result in higher risks of waterlogging and flooding in the low-lying areas of two South Asian cities
Summary
Unplanned urban growth and development interferes with the natural flow of water and usually increases the risk of urban flooding (Booth, 1991; Douglas et al, 2008). For the purposes of this paper, there are two consequences of urban development in South Asia: (i) it augments run-off and increases the risk of the breaching of embankments if a city abuts a river; and (ii) it reduces the flow of drainage by gravity due to drainage congestion, as urban drainage systems are unable to keep pace with urban development. Urban development, if unplanned, often reduces the effectiveness of urban drainage systems and increases the risk of flooding and waterlogging (Clemens & Veldhuis, 2010). Solid waste dumping in drainage routes reduces the carrying capacity of the drainage system, resulting in unwanted waterlogging in the event of heavy rainfall. Urban flooding is exacerbated as a result of rapid but unplanned urbanization and the resulting increased impervious surface (Huong & Pathirana, 2013)
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