Sensitivity Analysis of Simplifications in Street Cross-sections and Uncertainties in Roughness and Slopes in Designing for Exceedance Events

Designing for exceedance events has been a remediation and adaptation strategy to mitigate effects of flooding that is also being applied for new developments in an increasingly number of cities. 1D/1D modelling or simpler approaches are often applied in the design of flood flow pathways and detention areas. In this study, simple equations are obtained from the concept of the equivalent section for the estimation of street flood heights and velocities based on the results obtained for rectangular sections. Equations are discussed within a sensitivity analysis of the width and shape of street cross-section and of the roughness uncertainty in both the streets surfaces and the sewers. Results highlight that compliance with safety thresholds for the product of flood heights and velocities can be particularly sensitive to details and uncertainties on steep streets. The use of rectangular or simplified street cross-sections can significantly influence flood velocity calculations. The same applies to the uncertainty in street surface roughness and slope. Uncertainty in sewer conveyance capacity can significantly impact flood flows, heights and velocities, especially if this capacity is reduced.