Anthropogenic Effects on the Contemporary Sediment Budget of the Lower Rhine‐Meuse Delta Channel Network

J. R. Cox,M. G. Kleinhans,A. J. F. Hoitink,J. R. F. W. Leuven,N. E. Vellinga,M. van der Vegt,S. M. Knaake,Y. Huismans

doi:10.1029/2020ef001869

Abstract

AbstractDeltas and estuaries worldwide face the challenge of capturing sufficient sediment to keep up with relative sea‐level rise. Knowledge about sediment pathways and fluxes is crucial to combat adverse effects on channel morphology, for example, erosion which enhances bank collapse and increasing tidal penetration. Here, we construct sediment budgets which quantify annual changes for the urbanized Rhine‐Meuse Delta of the Netherlands, a typical urban delta experiences changing fluvial and coastal fluxes of sediment, engineering works and dredging and dumping activities. The delta shows a negative sediment budget (more outgoing than incoming sediment) since the 1980s, due to anthropogenic intervention. Following a large offshore port expansion, dredging in ports and harbors in the region has doubled in the past 5 years, likely due to the induced change in net sediment fluxes. In addition, the deeper navigation channels, ports, and harbors are now trapping siltier sediment, changing the sediment composition in the mouth. The removal of sediment by dredging is adverse to the necessity for sediment in heavily eroding branches. To allow for sustainable sediment management in the future and to cope with sea‐level rise, further measurements are required to properly quantify the amount of incoming sediment at the boundaries of the system and the internal mechanisms of transport. The varied response of the branches has important consequences for navigation, ecology and flood safety and management of the sediment in the system. These effects will be of pivotal importance in coming decades with similar implications for many urbanized deltas worldwide.

Highlights

Coastal regions and deltas are home to half of the world's population, and are locations for major ports and important global economic hotspots
We focus on the urbanized Rhine-Meuse Delta (RMD), which has undergone extensive human interventions of various kinds
Within the RMD system, the sediment budget shows a clear negative trend (Figure 5) in recent years linked to increased dredging of harbors areas in the mouth of the delta in recent years

Summary

Introduction

Coastal regions and deltas are home to half of the world's population, and are locations for major ports and important global economic hotspots. These regions both record and are subject to, intense global natural and anthropogenic environmental change (Bianchi & Allison, 2009). They are at the highest risk of climate change-induced sea-level rise (Giosan et al, 2014; Elliott et al, 2019). One of the key factors in determining if and how deltas will cope with sea-level rise is sediment management and in particular, actions that can increase sedimentation at desired locations (Tessler et al, 2015). A lack of sediment in a delta leads to a myriad of problems including channel deepening causing salinity intrusion (Eslami et al, 2019), increased flood risk from tidal penetration and surges and a loss of ecologically rich areas (Best, 2019)

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Conclusion