Bengaluru study finds diversion channels improve lake water quality

Diversion channels helped lakes with complete inlet diversion reach an average Water Quality Index score of 93, classified as Clean, in a study of eight Bengaluru water bodies. Lakes without structural intervention at their inlets averaged 56, in the Polluted category.

Researchers compared lakes with complete or partial sewage diversion, lakes receiving treated and untreated wastewater, and lakes without such measures. Seven water-quality parameters, including nitrogen, phosphorus and chemical oxygen demand, were lower at lakes with complete diversion than at those without intervention.

The channels do not treat sewage. They redirect it through Bengaluru’s drainage system, and the researchers said restoration plans need to account for connected drains and catchments rather than focus only on a lake’s inlet.

Lakes receiving a mix of treated and untreated wastewater averaged 67, or Slightly Polluted. Sarrakki, Hulimavu and Jakkur were in this group. Sarrakki and Jakkur also supported fishing, with approximate weekly catches of 175kg and 75kg respectively during the study period.

Researchers collected samples three times between February and July 2022 after dry spells. The findings therefore describe pre-monsoon conditions rather than year-round lake performance.