Local-inertial shallow water model on unstructured triangular grids

•The inertial formulation of the St. Venant equations is often used to simulate the slowly varying flood.•In case of structured grid based inertial models, the use of a single finer grid or the combination of finer and coarser grids (i.e., sub-grid) inevitably increases the overall computational time.•Therefore, this study proposes an unstructured grid based local-inertial model to have variable resolution mesh in the computational domain for faster simulation of a flood event. Two-dimensional shallow water models are widely used for flood risk assessment. Application of these models to large-scale urban areas significantly increases the computational cost as it requires high-resolution simulations to capture the complex hydrodynamic processes. Hence, simplified models that are based on local-inertial formulations have been proposed by different researchers. Although these models are successful in simulating floods, their applications are limited by the use of structured grids and instability issues. Structured grids do not have the flexibility of providing different mesh resolutions to model the computational domain. Importantly, in the case of structured grids, the use of a single grid or the combination of finer and coarser grids inevitably increases the overall computational time. To overcome all these problems, an unstructured grid-based local-inertial model is developed. The performance of the model is rigorously evaluated by solving analytical test cases and simulating an urban flood in Glasgow, UK. Finally, the model is applied to simulate a catastrophic flood event that occurred in Chennai, India. The simulated water depths and inundation extents are compared with observed data or full-2D model results. The investigations show that the developed model has the potential for simulating floods on a large-scale with high-resolution grids at a comparatively lower computational cost than its predecessors for a similar range of accuracy.