Renaturing Bengaluru with natural-based solutions

Bengaluru, once abounded with pristine lakes and lush gardens, is now tussling with water stress and related public health hazards. Economic factors and growth dynamics throw up significant challenges to the health of the city's lakes and their rich green cover. This situation is provoked by human activities such as improper land use management, rapid groundwater extraction, industrial effluent and greywater discharge. Population growth and migration have led to an increase in water consumption and consequently increased wastewater generation in urban areas. The tank cascade system in Bangalore, designed for stormwater storage and agriculture irrigation, is now full of open sewers receiving domestic and industrial effluents. Furthermore, lakes in Bangalore receive partially treated/ untreated sewage, resulting in the ingress of nutrients in the water and hence eutrophication of urban lakes. While seeking to address the consequences of rapid and unplanned urbanisation, Bangalore Development Authority (BDA) developed Master Plan 2050 that envisioned sustainable growth and development of the city. Nature-based solution (NbS) is an impetus for city planners and developing authorities to support environmental restoration for resilient growth in cities by working with nature and setting up solutions with stakeholders. 

Natural treatment systems are nature-based solutions that mimic and represent natural treatment in a controlled environment. Strategic instream treatment systems (STRAINS) are one such engineered systems that are designed and constructed to mimic the natural process of wetlands operating with design features similar to modified horizontal flow constructed wetlands. These interventions can reduce contaminant load from dry weather flows in open drains before they flow into downstream receiving waters. A semi-controlled field experiment was conducted near the inlet of a small urban lake known as Sowlkere in Bangalore. At Sowlkere, a small-scale ‘model nallah’ condition was developed, which mimics the dimensions and materials of a typical concretized stormwater channel found throughout the city. Two different filter materials, gravel and terracotta, were tested in the setup planted with Canna lilies. Urban wastewater from a manhole, receiving nearby commercial and domestic sewage, was fed into the setup. The system was successful in removing 77% organic matter and 20–50% nutrients from the urban wastewater flow. The study opens up the possibility of using inexpensive, locally available aggregate materials (gravel and terracotta rubble) to reduce downstream water source contamination from open stormwater drains without the use of specialised or mechanical technology. To move towards the Master Plan 2050, Bengaluru needs to focus on NbS to tackle water management challenges in all sectors. Upscaling NbS in our city can accelerate by promoting research and policies, legal regulations and funding and improving cross-sectorial collaborations and knowledge base.