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.
Highlights
Throughout Europe, flood frequency analyses are widely used to estimate discharges associated with various return periods (Benito et al 2004)
For larger upstream flood events, significant overland flow patterns start to occur. This results in a change in flood risk and in an increase in the maximum discharge along the downstream end of the IJssel river
To correctly predict flood risk and the maximum discharge during extreme flood events for this river section, overland flows must be included in the analysis
Summary
Throughout Europe, flood frequency analyses are widely used to estimate discharges associated with various return periods (Benito et al 2004). The common procedure of a flood frequency analysis is to select the annual extreme discharges of the observational data, or peak values that exceed a certain threshold (Hegnauer et al 2014). These extreme values are used to identify the parameters of a probability distribution that provides statistical data about the selected extreme values. From this fitted distribution, discharges corresponding to any return period can be derived (Hegnauer et al 2014). In the case of a single branch river system, a dike breach results in a decrease of the maximum discharge further downstream and in a reduction in the hydraulic load downstream (De Bruijn et al 2014; Schweckendiek et al 2008; Vorogushyn et al 2010) if the water does not flow back into the river at a
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