Consequences of dike breaches and dike overflow in a bifurcating river system

Abstract

Currently, the effect of dike breaches on downstream discharge partitioning and flood risk is not addressed in flood safety assessments. In a bifurcating river system, a dike breach may cause overland flows which can change downstream flood risk and discharge partitioning. This study examines how dike breaches and overflow affect overland flow patterns and discharges of the rivers of the Rhine delta. For extreme discharges, an increase in flood risk along the river branch with the smallest discharge capacity was found, while flood risk along the other river branches was reduced. Therefore, dike breaches and resulting overland flow patterns must be included in flood safety assessments.

Hydraulic modelling approaches to decrease uncertainty in flood frequency relations

“…If the simulated water levels in the 1D proles exceed the dike crest levels, water starts to ow into the storage areas corresponding with inundations of the hinterland. Bomers et al (2019b) showed that for the discharge range considered in this study, no signicant overland ows are present. The water that leaves the river system is not capable of owing back into the river at a downstream location.…”

“…This is because a low discharge with a high main channel friction results in a similar simulated water level as a high discharge with a low main channel friction. Therefore, a 1D-2D coupled model calibrated with the 1995 ood event, available from previous work (Bomers et al, 2019b), is used to determine the friction range used. The range is set equal to the minimum and maximum Manning's friction values found after calibration.…”

Historic Flood Reconstruction With the Use of an Artificial Neural Network

“…Consequently, it might be that the discharge wave shape used as boundary condition is not correct since this has a typical shape of a normal flood event generated by a precipitation event. However, the work of Bomers et al (2019d) shows that the discharge wave shape only has a little effect on downstream maximum discharges. Hence, the reconstructed discharge at Lobith represents a reliable maximum number.…”

“…This is because a low discharge with a high main channel friction results in a similar simulated water level as a high discharge with a low main channel friction. Therefore, a 1-D/2-D coupled model calibrated with the 1995 flood event, available from previous work (Bomers et al, 2019d), is used to determine the friction range used. The range is set equal to the minimum and maximum Manning's friction values found after calibration.…”

Decreasing uncertainty in flood frequency analyses by including historic flood events in an efficient bootstrap approach

“…Since the 1374 flood event was much larger than the current discharge capacity of the Lower Rhine, the maximum discharge at Lobith decreases. The reconstruction of the 1374 flood over modern topography is presented in detail in Bomers et al (2019b). On the other hand, the other 11 flood events were below this discharge capacity and hence only a slight reduction in discharges was found for some of the events as a result of dike breaches, whereas overflow did not occur.…”