Anthropogenic depletion of water resources in the TG Halli catchment near Bangalore, India
University of California, Berkeley
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The TG Halli watershed outside of Bangalore, India, faces a multitude of challenges due to urbanization and intensification of agriculture. Groundwater irrigation became popular in the 1970s, followed by shifts from traditional crops to eucalyptus plantations and in-stream check dams for aquifer recharge. The river, which supplied Bangalore with all of its water through the early 1970s, now yields only a small fraction of historical flows. Bangalore and its rapidly growing population have increasingly relied on imported water.We seek to understand the links between reductions in streamflow and local anthropogenic activities (e.g., groundwater pumping, land-use change, and watershed management practices such as managed aquifer recharge). Using a series of Landsat images from the 1970s to present, we classified over 500 surface water bodies in the catchment in each image and found that streamflow depletion is present throughout the catchment, except in the vicinity and downstream of urban areas. We conducted a suite of field research analyses, which demonstrate that most present-day streamflow is generated as infiltration excess runoff. Observed land-use changes within the catchment are unlikely to cause a reduction in infiltration excess runoff. We conclude that reductions in streamflow are caused by the loss of the shallow groundwater table due to groundwater pumping, and in-stream check dams which impound streamflow for groundwater recharge.While local water managers are aware of the changes within the catchment, the details of the local water balance are not well understood. Sustainable solutions are often overlooked as the incentives favor addressing short-term water needs, both for farmers and urban water managers. Farmers continue pumping as much as possible to sustain irrigated agriculture and the city continues to look further away for its water supply, with major projects for inter-basin transfers underway. Our work is a step towards understanding the local water balance and sustainable use of water resources in the Bangalore area.