Robust river systems: On assessing the sensitivity of embanked rivers to discharge uncertainties, exemplified for the Netherlands' main rivers

Frans Klijn,Erik Mosselman,Nathalie Asselman

doi:10.1111/jfr3.12511

Abstract

There is increasing attention for the robustness of systems, in view of more frequent and more extreme weather events. Calls to increase a system's robustness are usually motivated by the resulting reduced sensitivity to extreme events and uncertainties about their probability of occurrence. The concept has been elaborated for flood risk systems, but recently questions have arisen about whether subsystems, such as flood defences or rivers, should and could also be assessed on their robustness. Against the background of a recent debate in the Netherlands about whether to raise the embankments again or to make more room for the rivers in anticipation of increasing extreme river discharges into the future, we propose to define the robustness of embanked alluvial rivers by their sensitivity to uncertainties in flood discharge, expressed by the relationship between discharge and flood water level. We assess the Rhine River branches and Meuse River in the Netherlands and show how their planform, as defined by the location of the embankments and the presence of obstacles in the floodplains, causes remarkable differences in robustness per river and per river stretch. We finally discuss what this might entail for policy planning.

Highlights

Worldwide, rivers have been regulated and embanked in order to maximise their societal functions and to reduce the risks they pose to society
In addition to a better look at the slope itself, we focus on the relationship between flood levels (h, in metres above datum) and discharge (Q in m3/s), as this may prove the key in considerations about whether or not and to what degree we can cope with uncertainty about a river's discharge, and in the future
In this paper we have looked at the robustness of rivers from a flood risk management perspective

Summary

Introduction

Rivers have been regulated and embanked in order to maximise their societal functions and to reduce the risks they pose to society. In order to reduce flood risks, large parts of the alluvial plains are reclaimed and protected from flooding by extensive flood defence systems. Lowland rivers, running through wide alluvial plains or in deltas, are often fully embanked and constrained into narrow active floodplains along a trained main channel. In alluvial rivers any human interference inevitably triggers natural feedback processes that govern river behaviour. Disturbance of the delicate balance between erosion and deposition results in changes in morphology. Unregulated braided or meandering rivers tend to react primarily by horizontal erosion of the riverbanks and changes in the planform, whereas rivers with fixed channels tend to react by

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