Right way to bring a lake back to life

The lakes of Bengaluru have been in rejuvenation mode for decades. In spite of repeated spending of money and so-called “restoration efforts”, many lakes remain the same.

The reasons can be many. However, the way a lake is rejuvenated decides how long the rejuvenation can last. A major problem is prioritising cosmetic beautification and civil aspects over water which should have been the pivotal aspect of lake rejuvenation.

Originally created as irrigation tanks by erstwhile kings, Bengaluru’s lakes suffered the most during urbanisation and lost their original purpose. Currently, these lakes are even more crucial and important in maintaining water security and sustainability in the city.

They act as rainwater harvesting, groundwater recharge, flood mitigation zones, and limnological and ecological biodiversity zones. However, publicly they are seen only as recreational zones.

Many lakes are being rejuvenated without any approved Detailed Project Report (DPR). They miss out on the basic standards of lake rejuvenation. Sometimes in the name of rejuvenation, lakes are filled with concrete and steel structures, and manicured gardens where no biodiversity can thrive. In some lakes, walking and jogging paths are lit at night, repelling birds and other animals.

Careful planning

Lake rejuvenation planning should be city-wide, constituency or ward-wise, and not stand-alone. Ridge-to-valley lake rejuvenation approach is required as Bengaluru lakes are interconnected and rejuvenating a lower lake without addressing the upper lake has proved to be futile.

Inlet (feeder channel) design: With almost all the drains flowing with raw sewage across the city, it is impossible to expect the lake to receive good-quality rainwater. Diversion channels are being built to divert raw sewage during the non-rainy season. However, these have an inlet weir that allows water flow during rains which may also allow sewage into the lake. In this design flaw, the weir gets silted up gradually and raw sewage enters the lake even when there is no rain. Inlet drains should be free from garbage with screens or filters and regular maintenance.

Wetland design: Biological nutrients like nitrates and phosphates cause the maximum water pollution. Wetlands which act like the kidneys of a healthy lake removing excess nutrients are often small and cannot remove enough biomass of nitrogen-based nutrients. This needs to be designed scientifically.

Addressing water pollution: The majority of lakes receive domestic sewage. Some lakes near industrial areas see heavy metal pollutants. Unscientific methods of water quality improvement without proper scientific research give temporary relief but do not address the water pollution parameters. A sewage treatment plant with biological nutrient removal technology and real-time monitoring of pollutants is necessary to maintain water quality.

Desilting: The soup bowl design of desilting where the lake floor is of the same level throughout, meant only for commercial fishing, is detrimental to ecological biodiversity. Desilting only 1.5 meters as a norm without morphology and geotechnical studies is problematic. Sludge should be removed irrespective of its depth. Various zones corresponding to light and temperature should be created as per the scientific process. This will achieve optimal biodiversity with underwater plants and other life forms.

Bunds: Bunds should be built with silt from the lake only after a thorough geotechnical study, to avoid breach of the lake in course of time as a badly compacted bund can break quickly and cause flooding.

Following science: Strict scientific and technical monitoring of rejuvenation should be mandatory in all aspects including civil, environmental, geological, hydrogeological, ecological, limnological and toxicology.

Spending: Money should be spent on the creation of core assets, development and maintenance, desilting, functional wetlands, weirs, silt and garbage traps, feeder channels etc. Secondary funds can be used for social and recreational assets. Piecemeal approaches to core rejuvenation have only resulted in money being spent repeatedly for the same assets with no benefit to lakes.