Simulation of flood associated with extreme rainfall events over the urban city, Bengaluru, India

Bangalore city witnessed many flash floods associated with extreme rainfall events (EREs) in the recent past. Our analysis showed an increasing trend in the annual and monthly average rainfall over major valleys in Bengaluru Urban from 1971 to 2020 which indicated the possibility of rise in the frequency of urban flooding in recent decades. The digital elevation map (DEM) is examined to understand the topography of high elevation and low-lying areas, enabling the assessment of flood impacts of EREs in various areas of Bengaluru Urban. We have selected four flash flood events associated with EREs over one of the critically low laying Koramangala-Challaghatta watershed valley (KC valley) in the city for our simulation study. To understand the flood pattern, timing and volume during these flood events, stormwater management model (SWMM) simulations were conducted with observed rainfall from rain gauge stations. The model simulations could capture the inundation prone regions of KC valley for the flood events of different rainfall intensity. The hyetograph of the rainfall runoff with elapsed time demonstrates the model capability to calculate the runoff amount for different intensity of EREs. The bias in simulated storm water discharge range from +4 to -4 cubic meter per second (CMS) at different time scales and intensities within specific areas of stormwater drainage network system. The flood modeling systems like the one presented in this study can serve as valuable decision support system for management of urban floods associated with EREs and planning of mitigation strategies.