While efforts to rejuvenate Bengaluru’s lakes are laudatory, they fall short when it comes to the design of their restoration. The latter has an implication on the lake’s socio-ecological system.
When undertaking restoration, one needs to examine the anatomy of a lake ecosystem. Most of south India’s lakes are a network of reservoirs and canals where water moves from higher to lower elevations, and ultimately into the Bay of Bengal. Depending on the region, there could be 2 to 200 connected lakes. They are not static water bodies. They are part of a water circulation system of sorts. Thus, when restoring a lake, it’s imperative to think of restoring other lakes it is connected with and the rajakaluves (canals) that connect them.
The lake’s structure is another key factor. A lake has an earthen bund. It is used to block runoff, that is, more water than the land can absorb. The lakebed is dug in a way that it is deepest near the bund and sloping towards the foreshore, where water enters the lake through several inlets. Such a design ensures the shallow end of the lake can support a wetland, and maximise the lake’s ecological diversity. This benefits several species of wading birds that require shallow water for feeding and nesting.
The N K Patil committee report on the status of Bengaluru’s lakes in 2012 emphasised the same. It recommended that a gently sloping depth profile must be followed when restoring a lake. It noted that the lake must have a ‘wet mud’ zone that is farthest from the bund, a shallow water zone in the middle, and a deep water zone adjacent to the bund.
Reality check
However, what we see in most Bengaluru lakes is the infamous ‘soup bowl’ design. A steep wall with stones is built around the lake’s edge to stop encroachment. A paved path with a neat hedge atop the wall is laid to make space for walkers and joggers. Beautifying elements like a central island, a gazebo and a variety of trees (some right on the bund that can weaken it as the roots burrow into the ground) are seen. The ‘wild’ in the lake is lost, and it no longer offers ecological benefits to humans and non-human species.
The soup bowl design is 30 to 50 feet deep and is only meant to be a water retention structure. Since the waterbody has a uniform depth, wading birds can no longer populate the lake’s edges. Smaller and more delicate semi-aquatic plants cannot grow in the swampy wetland, which reduces the food available for birds, fish, insects, and small mammals. A noticeable decrease in the biodiversity of lakes can be noticed.
The ‘soup bowl’ approach to restoration has been undertaken in many lakes in Bengaluru and there seems to be no learning from past mistakes. The Konanakunte lake off Kanakapura Road is being restored in a soup bowl design, and so is the Billapura lake in Anekal, where a central island is also being added to beautify it. Bhoganhalli and Carmelaram lakes are other examples that are being restored similarly.
The fundamental reason for the lakes’ degradation is often not addressed. There is a need to unblock ‘rajakaluves’ and not merely divert them to prevent sewage and effluents from entering the lake.
Potential
We live in a city blessed with lakes. The massive 900-acre Bellandur lake is connected to the 400-acre Varthur lake. We must press for holistic restoration of these two lakes. If these lakes can be converted into living bodies of water, we can reap benefits like flood control, recharging groundwater, increased biodiversity, more rainfall and cooler temperatures. The supply of nutrition from fishing and foraging; activities like jogging, cycling and birdwatching around lakes can also improve citizens’ health.
How to save our water bodies
Chandrashekar N P is a retired executive engineer from the Public Works Department. He says the shape of the lake doesn’t matter in lake rejuvenation. “To start with, any encroachment as per the revenue records must be removed. Correct catchment inlets must be identified and waste weir for outflow must be designed as per the gradient,” he says.
Currently, urban lakes have more sewage entering them. He feels this needs to be addressed first. “If needed, wetlands must be provided for treatment. A permanent solution would be to divert the sewage.”
Before taking up rejuvenation of any lake, it’s ideal to study the cascade system of the upper and lower lakes. “This will help in diverting the sewage flow in the correct direction. STPs must be built at appropriate locations and sewage must be treated. This will help augment the water level in the lake,” he adds.
The soup bowl design is based on an urban engineering approach that treats water bodies merely as a recreational spot. “However, if we want to increase the flora and fauna of the city, lakes should be built like a check dam (with a bund only on one side),” says sustainability activist Sandeep Anirudhan.
The Puttenahalli lake is an example of rejuvenation done right, say experts. Lake conservationist Usha Rajagopalan, who was a part of the lake’s renovation, says, “It has an undulated lake basin. The BBMP provided raised edges but also deeper and shallow parts. This increased the bird count of both shallow water birds and birds like spot billed pelicans that require deep water,” she adds. Today, around 18 bird species nest at the lake.
K G Ranga Raju is a retired professor from the civil engineering department of IIT Roorkee and a hydraulic engineering consultant. He talks about Puttenahalli lake’s makeover from a “garbage dumpyard”. “Diverting stormwater drains into the lake and ensuring inflow from an STP helped to fill the lake. Adding floating wooden platforms (with nutrient-absorbing saplings) kept harmful bacteria at bay,” he explains.
(The author is a core team member of Tanks of Anekal, which documents lakes. He is also a faculty at Azim Premji University)
(With Inputs from Tini Sara Anien)