Consequences of dike breaches and dike overflow in a bifurcating river system
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Consequences of dike breaches and dike overflow in a bifurcating river system Anouk Bomers1 · Ralph M. J. Schielen1,2 · Suzanne J. M. H. Hulscher1 Received: 11 October 2018 / Accepted: 13 June 2019 / Published online: 17 June 2019 © The Author(s) 2019
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. Keywords Dike breaches · Discharge partitioning · Hydraulic flood modelling · Overland flow · Flood risk
1 Introduction 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 then 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). However, a major drawback of the flood frequency analysis is that the effects of inundations as a result of upstream overflow and dike breaches on the downstream discharge wave cannot be incorporated in the analysis unless such events have occurred during the measurement period. In the case of a single branch river system, a dike breach results in a decrease of the maximum discharge further downstream and hence 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 * Anouk Bomers [email protected] 1
University of Twente, Dienstweg 1, Enschede, The Netherlands
2
Ministry of Infrastructure and Water Management-Rijkswaterstaat, Arnhem, The Netherlands
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Vol.:(0123456789)
310
Natural Hazards (2019) 97:309–334
downstream location. For all river systems, dike breaches can result in serious flooding. However, a dike breach in a river system with multiple bifurcations can result in a change of the discharge partitioning of these bifurcations since water may flow through the embanked areas towards another river or river branch. This may specifically result in a change in flood risk if the discharge capacity of the other river is much lower than the capacity of the river in which the dike breach occurred. This situation is applicable in
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