Evaluating the Impact of Rainwater Harvesting on Urban Runoff Reduction in Bengaluru

The ground surface changes from undisturbed soils with a natural plant covering to disturbed soils as urbanisation and population pressure increase, amplifying the rapid expansion of impervious surfaces in cities. Without adequate stormwater controls, these impervious surfaces alter the hydrologic cycle by lowering infiltration rates and raising runoff peak flows and volumes. Bengaluru city experiences a more temperate climate throughout the year, and the heavy destruction caused by rains is India’s IT hub. Numerous drains get submerged and saturated after only two days of excessive rain, symbolizing the necessity of harvesting techniques in collecting rainwater and reducing runoff volume. Built-up area dynamics were observed from supervised classification and rainfall data collected from the IMD. Annual collectable rainwater was calculated considering the different cumulative rainfall frequencies, i.e. (25/50/75) %. The overall volume of containers was calculated considering different return periods of (5/10/20) years along with (10/20/30) minute rainfall duration. A 45.7% and 25.8% runoff volume reduction (%) was seen in the study area by considering two cases of maximum daily rainfall and maximum average monthly precipitation, respectively. The calculations indicated a significant capacity for collecting rainwater from impervious surfaces is achievable.