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

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.

Feedback Mechanism in Bifurcating River Systems: the Effect on Water-Level Sensitivity

“…Analyses of sensitivity and uncertainty have been performed for several single-branch rivers around the world, generally agreeing that the upstream discharge [8][9][10] and the main channel roughness [3,7,9,10] influence water-level prediction the most. Discharge uncertainty for a river stretch includes the inability to accurately estimate return periods of very high discharges [8,11] and the uncertain distribution of discharge over branches [12,13]. When looking at uncertain water-level predictions at a given discharge, the most important source of uncertainty is the roughness of the main channel.…”

Human interventions in a bifurcating river system: Numerical investigation and uncertainty assessment

“…All branches are compound channels, with wide floodplains conveying significant discharge when the bank-full discharge is exceeded. The hinterland is protected by dikes, which are dimensioned to keep out water until discharges of 16,000 m 3 /s, generally associated with a return period of 1250 years (Klijn et al, 2018). More recent studies show that this discharge level is more likely associated with lower return periods, perhaps exceeding 10,000 years (Sperna Weiland et al, 2015).…”

“…On top of the mean effect of the intervention, this further reduces the flooding probabilities at these locations. In the enlarged cross-section, water levels are less sensitive to discharge (also considered by Klijn et al, 2018) and to roughness parameters, effectively flattening the depthdischarge relationship.…”

“…Creating more space in the river lowers water levels and flow velocities (Silva et al, 2004), thereby reducing flooding probabilities as well as the expected consequences if a flood occurs (Asselman & Klijn, 2016;Klijn et al, 2018). Both of these aspects are considered in the new Dutch flood risk framework (Kok et al, 2017) for which the norms are set in the Dutch Water Act.…”

Exactly Where Does the River Need Space to Move? Seeking Participatory Translation of Fluvial Geomorphology into Flood Management

“…Across the world, there are increasing calls for human development to make room for rivers to move and flood (Gonz alez et al 2017;Klijn et al 2019). One of the chief benefits of this approach to development is that when rivers flood, floodwaters can spread out and slow down without damaging infrastructure (Biron et al 2014).…”