Verification of simplified flash flood inundation modeling using Scalgo Live and the SWMM model

The increasing frequency of short-duration, high-intensity rainfall events enhances the risk of flash floods, particularly in urbanised and low-lying areas where drainage systems are heavily loaded. In response to the need for rapid hazard assessment, simplified modeling tools are increasingly applied to provide fast estimates of flood inundation. The aim of this study is to verify whether simplified flash flood modeling performed using the Scalgo Live environment can be considered a reliable tool for preliminary flood risk analysis.

The analyses were conducted for a low-lying catchment located in southern Poland, characterized by a complex drainage system consisting of open channels and melioration ditches. Simulations were performed for intense short-duration rainfall scenarios with a probability of occurrence of p = 1%, as well as for variants including the implementation of a retention basin. Results obtained with Scalgo Live were subsequently verified using the hydrodynamic SWMM model.

The results indicate a significant increase in inundation extent and water volume with increasing rainfall duration. The flooded area increased from approximately 4.5 ha for a 15-minute rainfall event to more than 15 ha for a 24-hour event, while the volume of stagnant water rose from about 9.6 × 10³ m³ to over 4.2 × 10⁴ m³. The largest inundation extent was observed for the 24-hour rainfall scenario . Scalgo Live enabled a clear identification of critical sections of the drainage system where hydraulic capacity was exceeded. Comparison with the SWMM model showed good agreement in the location of inundated areas and hydraulic overloads. The implementation of a retention basin resulted in a clear reduction of inundation extent. The results confirm that Scalgo Live is a useful tool for rapid, preliminary flash flood risk assessments.