Parameter Uncertainties in Flow Rate and Velocity Analysis of Heavy Rain Events

Abstract

Flooding due to intensive precipitation poses a major threat to lives and property. Information about flood-prone areas is needed in order to reduce potential risks via mitigation and adaptation measures. The flood probability of a certain point in the landscape depends, firstly, on the projected frequency and characteristics of heavy rainfall events that generate surface runoff and, secondly, on the specific properties of the terrain that determine flow and runoff, e.g. the surface morphology and the hydraulic roughness of diverse surfaces or land uses. Simulation models of surface water flow are standard tools for the assessment of flood dynamics caused by extreme precipitation events. In order to make informed decisions that take modelling uncertainties into account as well as to get an idea of the probability space, it is necessary to quantify the effects of alternative sets of model parameters by drawing on different data sources as well as spatial and temporal resolutions of the input data. For the current study, we evaluated the impact of different parameter sets on the flow rate and velocity as determined for a study area in south-eastern Germany using the hydronumeric computational fluid dynamics model HiPIMS. The considered parameters were rainfall input (time and space invariant, spatially invariant and time varying, space and time varying), hydraulic roughness and spatial resolution of the digital elevation model. We present point-based time series of flow rates and velocities to indicate the bandwidths of probable flooding dynamics. Results show that the modelled flow rates and velocities are strongly dependent on the particular form of rainfall data as well as the spatial resolution of the digital elevation model. The effects of variations in hydraulic roughness are also found to be significant while in all cases the location of data capture points in the catchment area has a strong influence.