Time and spatial natural uncertainty integration associated with the Manning’s roughness coefficient in two-dimensional flash flood models

Abstract

Context: The natural spatial and temporal variability (uncertainty) of the inputs involved in hydrodynamic modeling for hazard assessment and delineation of potentially flood-prone areas is propagated in the output variables of the models. In normal practice, only natural temporal variability in terms of return period is usually considered, but the propagation of spatial uncertainty is unknown. Methodoly: This paper presents the analysis of uncertainty propagation using the first order second moment method of Manning’s roughness coefficient in the depth, velocity and flow intensity output variables of the numerical shallow water model implemented in HEC RAS 2D. A simulated flash flood in the municipality of Mocoa (Putumayo) and the corresponding probability of reaching a damage level for different return periods were analyzed, regarding the events occurred in March 2017. Results: A procedure applicable to flood hazard assessment is obtained where the temporal natural variability associated to hydrographs with different return periods and the spatial natural variability associated to the Manning’s roughness coefficient are integrated. Conclusions: The propagation of uncertainty was able to establish a direct relationship between the increase of flow (return periods) and the increase of uncertainty in the evaluation of the flood hazard indicator.

Keywords

• uncertainty propagation
• roughness coefficient
• flash flood
• flood hazard