Flood inundation mapping for the Gwadar city

Abstract

Floods wreak havoc with human society, infrastructure and the environment. Accuracy and reliability of the forecasts concerning the resultant inundation depths and extents of these floods are primarily dependent upon the employed hydrologic modeling approach. In the present study, a more precise distributed hydrological modeling approach has been exploited with grid-based spatial discretization for the simulation of flood inundation in Akara river watershed which contains a proposed metropolitan-level developed coastal city of Gwadar in the ‘Balochistan’ province of Pakistan. Institute of Industrial Sciences Distributed Hydrological Model, a physically based distributed hydrological model, has been employed. This model, through fully implicit finite difference schemes, utilizes diffusive wave approximations of 1D and 2D Saint Venant’s governing equations for the river and over-land flow components, respectively. While the model is calibrated against the cyclonic flood event of June 2007, to earmark the potential hazardous areas inside as well as outside the Master Plan boundary the flood inundation simulation for the worst precipitation events of 50 and 100 years return periods are performed. The simulated flood inundation depths at various known locations showed good agreement with the observed ones. Moreover, the simulations depict that the simulated flood inundation depths at the same locations increase by 1.07 to 1.87 times and 1.21 to 1.89 times respectively due to 50 and 100 years return period rainfalls.