Comparison of three bed form models to predict roughness for operational flood modelling

Jord Warmink, Suleyman Naqshband, Olav J M van Duin

Friday 3 july 2015

13:45 - 14:00h at Oceania Foyer (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Flooding along in rivers and coasts

Parallel session: 16L. Flood risk - Flooding

The hydraulic roughness of the main channel of most lowland rivers is dominated by bed forms. River bed forms act as roughness to the flow, thereby significantly influencing the water levels, which are essential for flood forecasting. We compared a time-lag model and a physically based pickup and deposition model to predict dynamic bed form evolution during a flood wave in the flume and the field. The results showed that the explicit computation of bed form and associated roughness predictions perform equally well as a calibrated model for the flume case, but slightly less for the field case. We were able to explain a large part of the roughness of the main channel that is normally calibrated and explicitly account for the hysteresis effect. Calibration will always remain necessary, but using the knowledge of bed form evolution and including this in the prediction can largely improve the accuracy of water level predictions, especially in circumstances where calibration data is scarce.