Future sediment delivery and distribution of the Rhine-Meuse Delta (Netherlands)

Abstract:

Deltas worldwide are facing sediment shortages due to anthropogenic interference. Furthermore, climate change is altering hydrological regimes whilst sea level rise is changing hydrodynamics and sediment input at the coastal boundary. These effects make sediment delivery to deltas uncertain under future climate scenarios.

Here we estimate the future sediment delivery and changing sediment distribution of the Rhine-Meuse Delta (RMD) in the Netherlands, an anthropogenically controlled system which has experienced a negative sediment budget for the last 30 years in response to human interventions. Considering current and future sea level rise it is crucial that the RMD receives sufficient sediment or it risks increased flood risk, decreased ecological area, channel bed degradation and drowning.

We estimate upstream fluvial sediment delivery using BQART, an empirical suspended load sediment model. Bedload flux is neglected as it is negligible in the RMD. We use an empirical relation to relate changing sediment import from sea-level rise to accommodation space. Projections for 2050 and 2100 are presented based on region-specific climate scenarios for discharge and sea-level rise, and include projected upstream reservoir construction. We use observed suspended sediment-discharge (QS) relations from the distributary channels to investigate resulting sediment redistribution between channels.

Suspended delivery from upstream is projected to stay constant or decrease slightly whilst sea level rise will cause tidally driven suspended sediment delivery to move further inland. Based on the QS relations, the northern branches will receive more sediment which suggests the potential for increased dredging as these branches are currently continuously dredged for navigation purposes. Meanwhile, cross cut tidal channels will experience a sediment deficit causing further bed degradation. The southern branches will receive similar amounts of sediment. These branches contain important nature areas and require sufficient sediment to maintain their ecosystems. Future sediment management concerns in the RMD are therefore channel-dependent. The severity of the changes is dependent on the climate change scenario. Sustainable sediment management is required to counteract these future negative effects.