Wednesday, September 30, 2009

Only if their potential is not forgotten

Only if their potential is not forgotten
A little effort and sticking to basics of engineering can help ensure that lakes are used to prevent floods...

Bangalore: The city getting flooded after every downpour only points to the insufficient capacity of choked storm water drains, and land encroachments. “How about using the existing lakes as a flood-control measure?” suggests D N Ravi Shankar, an environmental consultant.
Instead of spending crores of rupees that are likely to go down the drain, a ‘proper engineering’ of lakes can keep floods at bay, he says. According to the basic principles of drainage engineering, one of the most significant benefits of a lake is the long-term protection against floods. They modify the natural flow of water, helping to avoid the inundation of downstream areas.
Flooding in the vicinity of places where lakes once existed — Kanteerava stadium for instance — have no solution unless we introduce high discharge low-head pumps with a collection system.
Function of lakes and their monitoring should include engineering aspects like irrigation, power generation, water supply, groundwater recharge, flood control, recreation, aesthetics.
Bangalore once had more than 1,000 lakes. Many of them were designed and used for irrigation, in addition to potable water needs. These became part of the urban environment with the city’s growth. Bangalore has now grown to an area of 800 square kilometres. ‘Irrigation lakes’ have become ‘urban lakes’. Changes in land pattern, in both watershed and drainage zones, have resulted in a change of the lake ecosystems There is something common to the flooding every year. The areas that get inundated are, more often than not, close to: An existing lake A lake that existed there A storm water drain in a low-lying area
Almost all lakes in Bangalore are polluted with untreated/partially treated waste water entering them
City gets 900 MLD of potable water from different sources; 80% of it gets gets converted to waste water before entering a treatment plant; 20% wastage is supposed to be losses in sewer joints en route the treatment plant, besides other losses like evaporation More than a lakh borewells supplement potable water. Assuming 2,000 litres per borewell, this amounts to another 200 MLD All the waste water generated finds its way into lakes. This is not true of rural lakes as they are fed only with rain water Inflow of waste water into Bangalore’s lakes on non-rainy days is greater than seepage losses and loss due to evaporation When lakes are full round the year, how can they help prevent floods? Where did we go wrong in planning?
Residential layouts are formed lower than the flooding level. An example of this is RMV Extension. The basic civil engineering concept of developing a layout above this level is forgotten. Who is to be blamed? Developers of apartments also forget this rule while fixing the plinth level. There is a need to educate engineers of the utility of checking the flood level while sanctioning plans
The entry of untreated waste water into lakes causes imbalance. There are problems with groundwater pollution, vector nuisance, odour nuisance and aesthetics, among others. Prevention of lake pollution was attempted by different civic authorities, but without a holistic approach or long-term planning
Any community develops next to a water body. Going back to the history of lakes, there existed a village next to all of them. Its size was based on its location profile, catchment, flood level and drainage zone. Rapid urbanization has changed these factors. Now, the drainage zone for irrigation is not considered
The amount of run-off that enters lakes depends on the intensity of rain and characteristics of the catchment area. In Bangalore, the catchment areas around lakes are impervious as the city is a concrete jungle. Infiltration of storm water into groundwater is also decreasing. So, even with small intensity of the rainfall, there is maximum discharge within the city


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