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WATER WISE
Smarter ways of managing water
S. VISHWANATH
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In many cities around the world it is mandatory on any new development project to take care of the excess run-off it generates
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BOUNTY: Manage rainwater overflow wisely
Bangalore, at least some parts of it, has been going through a traumatic time with flooding affecting day-to-day life. The visit of a Prime Minister of a nation to a leading IT institution was cancelled reportedly because the road was under water. Not the best of times for a global city aspirant. What went wrong and what can be done to set things right?
The flooding is primarily caused by rains, unlike in a city like Patna, where rain in the upper catchment of the Ganga can raise water levels and cause flooding with no rains in the city itself. In that sense, because of its elevation, Bangalore can manage its floods better. It knows the rainfall distribution and intensity in its catchment and is therefore in charge of handling the storm water generated.
Urban climate
While geography and climate have been the cause of Bangalore’s boom, they too have to be understood and managed to assure a quality of life. When a city grows and sprawls it dramatically alters the hydrological regime. Rainfall in the heart of the city and in the downwind direction can go up by 15 per cent, intensity of the rainfall can go up by 50 per cent. Bangalore now has to deal with 90 mm per hour intensity rainfalls.
Runoff rates also rise sharply. In built-up areas which are now fully paved, the runoff coefficient can go up by factors of four to even nine. Imagine an un-built area of three hectares close to Yeshwantpur on a ridge, now converted into a large wholesale mall totally built up with virtually not a square inch of grass. This space has one drain emerging from it to carry storm water.
An 80 mm rain will send nearly 22 lakh litres barrelling out of the premises to be handled by the city’s drains, whereas previously it could have been only around four lakh litres. No amount of widening and deepening storm drains will help tackle this excess runoff.
In many cities around the world it is mandatory on any new development project to take care of the excess run-off it generates through a process of retention and detention and therefore not to overload the existing system. People pay for the excess storm water they create through built-up areas. In Bangalore, bulldozers clear up encroachments on ‘Raja Kaluves.’
Created primarily for agricultural purposes, tanks have an important ecological and hydrological purpose too. Their inter-linkages drawing upon natural valley flows, if designed and maintained properly, can be excellent buffers for limiting flood waters, but they need to be regulated too. When rain is anticipated there should be a natural draw down of water levels in the tank to receive storm water and retain/detain rainwater. If the tanks are full when it rains they are not of much use.
Urban planning and land use too should respond by clearly and legally identifying our tanks and the valleys connecting them and then taking steps to prevent their encroachment. In the day and age of Google Earth when even a car can be seen from satellite, it is unconscionable that we do not identify and protect our water courses.
Institutions
Unless we have a single urban water management institution, fragmented approaches to water will prevail. Surface water bodies will remain with the Lake Development Authority, interlinking valleys with encroachers, catchments with the people, ground water with everybody and nobody, piped water with the Bangalore Water Supply and Sewerage Board, sewage water when in pipes with the BWSSB and when in drains with the Mahanagara Palike and a flood situation to be handled by the Palike. A coherent plan for managing all waters will not emerge.
By using the rainwater and storm water to recharge ground water, not only will we control floods but also have a buffer for our water requirements in times of need. A clear understanding of the hydro-geological characteristics of the city will help identify areas of recharge. A good catchment management plan will ensure that pollution of ground water is avoided when only pure rainwater is recharged.
You and me
Every citizen has a role in flood prevention. If each and every construction becomes responsible for say 60 mm of rain and takes steps to retain this rainwater in sumps for future use or recharge the aquifer through a recharge well or pit so that it does not flow into the storm drains and cause misery to everybody, Bangalore will be a better place. Otherwise Prime Ministers will have to make other plans when the rain god Varuna decides to descend on the city.
www.rainwaterclub.org
www.arghyam.org
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