The Effectiveness of Sustainable Drainage Systems In Highly Urbanised Areas: Bangalore, India
Heavy rainfall is commonplace during the south-west monsoon season in India. However, urban floods have recently become a more frequent occurrence in most of the cities and towns. As cities and towns started growing uncontrollably, the land use patterns have changed drastically, with increasing impervious areas due to construction activities, tarmac roads, etc. Often this problem is aggravated by old drainage systems which are not maintained properly. Also, the sharp peak discharge of typical flood hydrographs, which occurs because of high rainfall intensities, produces flows which exceed the drainage capacity of the system. This results in surface water standing on roads and open areas, and in urban flooding. The main consequences of this are disrupted communication and transport links, economic losses, social disruption and health impacts, and environmental damage. Overall, flooding disturbs the normal functioning of the city and town. Bangalore, the capital of Karnataka, is one of the fastest growing cities in India. During the last few monsoons, Bangalore city and its surrounding ULBs experienced unusual high-intensity rainfall for long durations, which caused severe flooding problems at several locations. This resulted in submergence of low-lying areas, causing water stagnation in many places. The disruption included submergence of footpaths, inconvenience to traffic and pedestrian movement for several hours, and extensive damage to both life and property. The causes of these problems can be linked to change in land use, formation of layouts in tank bed areas and also below high flood levels, the non-functionality of primary and secondary water ways as intended, inadequate size of drains and cross drains, improper networking & maintenance of tertiary drains, dumping of garbage/debris into the drains, poor gradients, lack of maintenance in the system, obstructions due to laying of utility lines, lack of co-ordination with other service providers, and a general lack of awareness about the importance of waterways. When compared to conventional drainage system, SUDS provide space within the city. A combination of conventional drainage systems with SUDS is the most practical solution to the problem of urban flooding. With this view, the project studies the effectiveness of SUDS in one of the highly urbanized areas of Bangalore and its surrounding ULBs. The study proposes to derive solutions within the existing system and/or propose new solutions that can be implemented. Rainwater harvesting, one of the many features of SUDS, is found to be most optimum solution in a city like Bangalore, which is densely developed and has no space available within the city to incorporate SUDS features like swales and basins and ponds.