Frequent Floods in Bangalore: Causes and Remedial Measures

Abstract

Floods in an urbanised landscape refer to the partial or complete inundation from the rapid accumulation or run-off resulting in the damage to property and loss of biotic elements (including humans). Urban flooding is a consequence of increased impermeable catchments resulting in higher catchment yield in a shorter duration and flood peaks sometimes reach up to three times. Thus, flooding occurs quickly due to faster flow times (in a matter of minutes). Causal factors include combinations of loss of pervious area in urbanising landscapes, inadequate drainage systems, blockade due to indiscriminate disposal of solid waste and building debris, encroachment of storm water drains, loss of inter connectivity among lakes, housing in floodplains and natural drainage and loss of natural flood-storages sites. Flood mitigation in urban landscape entails integrated ecological approaches combining the watershed land-use planning with the regional development planning. This includes engineering measures and flood preparedness with the understanding of ecological and hydrological functions of the landscape.
Bangalore is experiencing unprecedented urbanisation and sprawl in recent times due to concentrated developmental activities with impetus on industrialisation for the economic development of the region. This concentrated growth has resulted in the increase in population and consequent pressure on infrastructure, natural resources and ultimately giving rise to a plethora of serious challenges such as climate change, enhanced green-house gases emissions, lack of appropriate infrastructure, traffic congestion, and lack of basic amenities (electricity, water, and sanitation) in many localities, etc. This study shows that there has been a growth of 1028% in urban areas of Greater Bangalore across 45 years (1973 to 2017). Urban heat island phenomenon is evident from large number of localities with higher local temperatures. The study unravels the pattern of growth in Greater Bangalore and its implication on local climate (an increase of ~2 to 2.5 ºC during the last decade) and also on the natural resources (88% decline in vegetation cover and 79% decline in water bodies), necessitating appropriate strategies for the sustainable management.
Frequent flooding (since 2000, even during normal rainfall) in Bangalore is a consequence of the increase in impervious area with the high-density urban development in the catchment and loss of wetlands and vegetation. This is coupled with narrowing and concretising storm water drains, lack of appropriate drainage maintenance works with the changes in enhanced run-offs, the encroachment and filling in the floodplain on the waterways, obstruction by the sewer pipes and manholes and relevant structures, deposits of building materials and solid wastes with subsequent blockage of the system and also flow restrictions from under capacity road crossings (bridge and culverts). The lack of planning and enforcement has resulted in significant narrowing of the waterways and filling in of the floodplain by illegal developments. Causal factors and remedial measures to mitigate impacts of flooding are:
Reasons
1. Loss of interconnectivity among lakes due to encroachment of drains or dumping of solid wastes, Construction and Demolition (C & D) wastes
2. Encroachment of flood plains and wetlands (construction in valley zones, flood plains and lake bed) and de-notifying lakes (under the guise of ‘dead lakes’ – no lake can be dead as it does the job of ground water recharge)
3. Narrowing and concretising storm water drains impairing hydrological functions of the natural drains
4. Loss of pervious areas - reduction of open spaces, wetlands and vegetation cover
5. Increased paved surfaces in the city (78% paved surface and likely to be 94% by 2020) due to unplanned irresponsible urbanisation by senseless decision makers.
Solutions: Ecological Management of Storm Water Drains and Wetlands to Mitigate Frequent Flooding in Bangalore
1. Reestablish interconnectivity among lakes by removing all blockades (encroachments, solid waste dumping)
2. Protect Valley zones and Buffer regions of wetlands: protect valley zones considering ecological function and these regions are ‘NO DEVELOPMENT ZONES’ as per CDP 2005, 2015
3. Stop narrowing and concretising natural drains
• Vegetation in the drain takes the load during peak monsoon, there is no need to concretise the channel.
• Vegetation allows groundwater recharge while treating the water (bioremediation);
• Drains with vegetation without any bottlenecks (hindrances) would be the best option to mitigate floods.
• Narrowing channel and concretizing would only increase the quantum of water and velocity, which would be disastrous.
• Objective should be towards mitigation of floods and not to generate high overland flows (with increased quantum and flow velocity)
• Experts should think sensibly with holistic knowledge (considering all subject knowledge) than fragmented narrow sectorial knowledge. Advice by pseudo experts would be detrimental as the society would be deprived of ground water, frequent floods and unnecessary livelihood threats.
4. Decongest Bangalore
• Shift major installations to other cities in Karnataka,
• Stop further industriaisation and commercial establishments in bangalore.
• Protect open spaces – lakes, parks, etc.
• Stop further growth of dying city – with water and oxygen scarcity
• BWSSB should stop issuing senselessly NOC (no objection certificate) to major building projects as there is not sufficient water in the city.
• Environment clearance as per the norms of Environment Protection Act (2016), Wetlands (Conservation and Management) Rules, 2016, SWM 2016, C & D Wastes, 2016, Air act 1981, Water (prevention of Pollution) Act, 1974.