Rivers2Morrow Project: sediment dynamics of the Benedenrivieren of the Jana Cox, Maarten G. Kleinhans, Ymkje Huismans [email protected], [email protected], [email protected]

1. Project summary Future sediment management (given future challenges e.g. The lower Rhine branches or Benedenrivieren are a complex network of Long term river channels which make up the Rhine- delta. These tidally SLR, changing discharge) influenced channels provide access to multiple ports and harbours such as . The decline in sediment availability over the past 50 years has caused the erosion of many of the branches, whilst dredging activity Current sediment budgets further removes sediment from the system. As sea levels rise and Medium term discharge varies due to climate change, understanding how the Rhine- Meuse delta will respond and how the sediment availability and delivery will vary is a key issue. To predict how the sediment dynamics and Clear understanding of availability will change, first a complete sediment budget for the recent process controlling the budgets past and present is needed (figure 1). & tidal motion Short term

Figure 1: Workflow for the research

2. Study area & recent branch elevation trends 3. Methodology for calculating the sediment budget

Figure 1 shows the cumulative change in bed elevation for the Benedenrivieren Figure 2 shows the method used to calculate the sediment budget for the between 2000-2017. Some branches have large changes due to dredging whilst other region. To create a sediment budget at scale of the entire Rhine-Meuse delta un-dredged channels also show high levels of erosion. Conversely, some branches dredging and dumping activity and fluxes of sediment in and out of the have a net sedimentation trend. sediment are the key parameters required.

Hollandse IJssel Legend +10 to +15cm Human influence Sea level rise +5 to +10cm +1 to +5cm -1 to +1cm -1 to -5cm Fluxes in and -5 to -10cm Dredging & Overall out of the -10 to -15cm dumping sediment flux -15 to -20cm system Delta -20 to -25cm scale -25 to -30cm Bed -30 to -35cm Boven level ± -35 to -40cm change -40 to -45cm -45 to -50cm Suspended Branch Bedload Changing sediment scale Dordtsche flux discharge Kil flux

Beneden Maas Bergsche Maas Hollandse Diep Changing sediment supply Grain Sediment erodibility scale

Kilometers Sediment composition 0 5 10 20

Figure 2: Branches of the lower Rhine and the cumulative change to bed elevation(cm) between 2000-2017 Figure 3: Equation for creating sediment budgets and processes which affect the different components and their relative spatial scales 4. Creating a sediment budget: dredging and dumping 5. Creating a sediment budget: fluxes in and out

Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community Dredging in the Rhine Meuse delta is a combination of dredging of branches and North Sea

dredging of the ports and harbours. Dredged sediment is dumped either off the coast 95% sediment out <1% sediment in Hollandse IJssel (90%) or in specifically designed dumpsites called slufters (10%). Thus dumping sediment in 43% does not influence the sediment budget.

8% sediment in Lek

Haringvliet

5% sediment out 35% sediment in

Bergsche 15% sediment in Maas

Figure 5: Map showing the relative percentage per location in the Rhine Meuse delta of the total sediment coming in and out of the system.

7.Sediment budget vs bed level change The sediment budget of the Rhine-Meuse delta is decreasing over time, rapidly in recent years due to increased dredging. Since 2000 the area loses on average 1.6 megatonnes of sediment per year. Figure 4: Dredging amounts for the branches of the Benedenrivieren and the ports and harbours in the area over time. Data for the branches since 2012 is in the process of being secured.

6. Relative importance of components in the sediment budget Most dredging occurs in the ports and harbours near the Maasmond, which removes nearly the entire volume of sediment that is coming in from the North Sea. Then, the delta is reliant solely on sediment input from upstream which is decreasing due to use of dams and will become increasingly variable with variable discharge. Figure 6: Percentage contribution of dredging, flux in and fluxes out to the Figure 7: The sediment budget for the Rhine-Meuse delta as calculated using multibeam survey data and measured dredging and overall sediment budget. flux data. Note the DEM data is often missing the influence of the dredging of the ports and harbours.

The sediment budget of the Benedenrivieren is decreasing over time which is exacerbated by increased dredging activity in recent years. Sustainable sediment management in the future is therefore crucial to combat the negative effects caused by this lack of sediment.