ALBERT

Description: 〈div data-abstract-type="normal"〉 〈p〉Climate change is very likely to cause a global acceleration in sea-level rise (SLR). The projected acceleration of SLR will also affect the Wadden Sea. In addition to an accelerated SLR, gas and salt extraction will cause subsidence that adds to an increase in water depth in the tidal basins. This will have consequences for the sediment budget of the Wadden Sea and especially for the intertidal flats that have a high ecological value. This synthesis presents projections of the future state of the Dutch Wadden Sea for the years 2030, 2050 and 2100.〈/p〉 〈p〉The projected changes in mean sea level by 2100 for Den Helder and Delfzijl are above the global mean projections, mainly due to the above-average ocean dynamics and glacio-isostatic adjustment contributions in the regional projections. The projected rise in mean sea level for 2100 with relation to 2018 in these locations is 0.41m, 0.52m and 0.76m for, respectively, the RCP2.6, RCP 4.5 and RCP8.5 climate scenarios.〈/p〉 〈p〉When we combine the presented SLR scenarios with the subsidence estimates and compare these rates to the critical rates for ‘drowning’ of intertidal flats that were calculated for the individual tidal basins, we can determine the moment that the maximum imported sediment volume can no longer compensate the increase in accommodation space in a basin and the intertidal flats will start to diminish in surface area and/or height. In the RCP2.6 scenario, the projected rates of relative SLR will be below the critical rate for drowning of the inlet systems in the Dutch Wadden Sea. For the RCP4.5 scenario, the critical SLR rate will be exceeded for Vlie Inlet in 2030, and for the RCP8.5 scenario the critical SLR rate will be exceeded for Vlie Inlet in 2030, Texel Inlet in 2050 and Ameland Inlet in 2100. For the other basins the critical rate will not be exceeded until 2100 or later.〈/p〉 〈p〉The way the intertidal flats in a basin will react to ‘drowning’ is not clear beforehand. It is highly possible that erosion of flats in one place will produce the sediment to maintain flats in other places. Tidal flats close to the sediment-delivering tidal inlet are not likely to disappear, because there the balance between supply and erosion is not likely to change.〈/p〉 〈/div〉

Description: 〈div data-abstract-type="normal"〉 〈p〉The Wadden Sea is a unique coastal wetland containing an uninterrupted stretch of tidal flats that span a distance of nearly 500km along the North Sea coast from the Netherlands to Denmark. The development of this system is under pressure of climate change and especially the associated acceleration in sea-level rise (SLR). Sustainable management of the system to ensure safety against flooding of the hinterland, to protect the environmental value and to optimise the economic activities in the area requires predictions of the future morphological development.〈/p〉 〈p〉The Dutch Wadden Sea has been accreting by importing sediment from the ebb-tidal deltas and the North Sea coasts of the barrier islands. The average accretion rate since 1926 has been higher than that of the local relative SLR. The large sediment imports are predominantly caused by the damming of the Zuiderzee and Lauwerszee rather than due to response to this rise in sea level. The intertidal flats in all tidal basins increased in height to compensate for SLR.〈/p〉 〈p〉The barrier islands, the ebb-tidal deltas and the tidal basins that comprise tidal channels and flats together form a sediment-sharing system. The residual sediment transport between a tidal basin and its ebb-tidal delta through the tidal inlet is influenced by different processes and mechanisms. In the Dutch Wadden Sea, residual flow, tidal asymmetry and dispersion are dominant. The interaction between tidal channels and tidal flats is governed by both tides and waves. The height of the tidal flats is the result of the balance between sand supply by the tide and resuspension by waves.〈/p〉 〈p〉At present, long-term modelling for evaluating the effects of accelerated SLR mainly relies on aggregated models. These models are used to evaluate the maximum rates of sediment import into the tidal basins in the Dutch Wadden Sea. These maximum rates are compared to the combined scenarios of SLR and extraction-induced subsidence, in order to explore the future state of the Dutch Wadden Sea.〈/p〉 〈p〉For the near future, up to 2030, the effect of accelerated SLR will be limited and hardly noticeable. Over the long term, by the year 2100, the effect depends on the SLR scenarios. According to the low-end scenario, there will be hardly any effect due to SLR until 2100, whereas according to the high-end scenario the effect will be noticeable already in 2050.〈/p〉 〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉The Wadden Sea region spans a distance of nearly 500km along the North Sea coast from the Netherlands to Denmark. It consists of a chain of barrier islands which shelter an area of extensive intertidal flats and salt marshes that are dissected by tidal channels and creeks. Moreover, several estuaries are part of this area which is known for its intriguing morphodynamics. The natural process of continuous erosion, transport and deposition of sediment shapes the morphology of the area, which has a high ecological value, especially the intertidal morphology that supports a wide range of wildlife.〈/p〉〈/div〉

Description: The Wadden Sea region spans a distance of nearly 500km along the North Sea coast from the Netherlands to Denmark. It consists of a chain of barrier islands which shelter an area of extensive intertidal flats and salt marshes that are dissected by tidal channels and creeks. Moreover, several estuaries are part of this area which is known for its intriguing morphodynamics. The natural process of continuous erosion, transport and deposition of sediment shapes the morphology of the area, which has a high ecological value, especially the intertidal morphology that supports a wide range of wildlife.

Description: The estuaries in the SW Netherlands, a series of distributaries of the rivers Rhine, Meuse and Scheldt known as the Dutch Delta, have been engineered to a large extent as part of the Delta Project. The Voordelta, a coalescing system of the ebb-tidal deltas of these estuaries, extendsc.10 km offshore and coversc.90 km of the coast. The complete or partial damming of the estuaries had an enormous impact on the ebb-tidal deltas. The strong reduction of the cross-shore directed tidal flow triggered a series of morphological changes that continue until today. This paper aims to give a concise overview of half a century of morphological changes and a sediment budget, both for the individual ebb-tidal deltas and the Voordelta as a whole, based on the analysis of a unique series of frequent bathymetric surveys. The well-monitored changes in the Voordelta, showing the differences in responses of the ebb-tidal deltas, provide clear insight into the underlying processes. Despite anthropogenic dominance, knowledge based on natural inlets can still explain the observed developments. Complete damming of the three northern estuaries Brielse Maas, Haringvliet and Grevelingen resulted in a regime shift, from mixed-energy to wave-dominated, and sediments are transported in landward and downdrift direction. This results in large morphodynamic changes – sediments are redistributed from the delta front landward – but small net volume changes – a 0.1–0.2 × 106m3a−1increase in volume over the period 1965–2010 – since the dams block sediment transport into the estuaries. Sediment volume losses of 106m3a−1are observed on the ebb-tidal delta of the partially closed Eastern Scheldt and still open Western Scheldt estuary. As a result of a reduction of the estuarine tide in the mouth of the Eastern Scheldt, the north–south-running North Sea tidal wave has gained impact on its ebb-tidal delta, which causes morphological adjustments and erosion of the Banjaard shoal area. Moreover, the Eastern Scheldt ebb-tidal delta delivers sediment to its neighbours. The stable ebb-tidal delta configuration in the Western Scheldt, despite major dredging activities, illustrates that these large inlet systems are robust and resilient to significant anthropogenic change, as long as the balance between the dominant hydrodynamic processes (tides and waves) does not alter significantly.

Description: Climate change is very likely to cause a global acceleration in sea-level rise (SLR). The projected acceleration of SLR will also affect the Wadden Sea. In addition to an accelerated SLR, gas and salt extraction will cause subsidence that adds to an increase in water depth in the tidal basins. This will have consequences for the sediment budget of the Wadden Sea and especially for the intertidal flats that have a high ecological value. This synthesis presents projections of the future state of the Dutch Wadden Sea for the years 2030, 2050 and 2100.The projected changes in mean sea level by 2100 for Den Helder and Delfzijl are above the global mean projections, mainly due to the above-average ocean dynamics and glacio-isostatic adjustment contributions in the regional projections. The projected rise in mean sea level for 2100 with relation to 2018 in these locations is 0.41m, 0.52m and 0.76m for, respectively, the RCP2.6, RCP 4.5 and RCP8.5 climate scenarios.When we combine the presented SLR scenarios with the subsidence estimates and compare these rates to the critical rates for ‘drowning’ of intertidal flats that were calculated for the individual tidal basins, we can determine the moment that the maximum imported sediment volume can no longer compensate the increase in accommodation space in a basin and the intertidal flats will start to diminish in surface area and/or height. In the RCP2.6 scenario, the projected rates of relative SLR will be below the critical rate for drowning of the inlet systems in the Dutch Wadden Sea. For the RCP4.5 scenario, the critical SLR rate will be exceeded for Vlie Inlet in 2030, and for the RCP8.5 scenario the critical SLR rate will be exceeded for Vlie Inlet in 2030, Texel Inlet in 2050 and Ameland Inlet in 2100. For the other basins the critical rate will not be exceeded until 2100 or later.The way the intertidal flats in a basin will react to ‘drowning’ is not clear beforehand. It is highly possible that erosion of flats in one place will produce the sediment to maintain flats in other places. Tidal flats close to the sediment-delivering tidal inlet are not likely to disappear, because there the balance between supply and erosion is not likely to change.

Description: The Wadden Sea is a unique coastal wetland containing an uninterrupted stretch of tidal flats that span a distance of nearly 500km along the North Sea coast from the Netherlands to Denmark. The development of this system is under pressure of climate change and especially the associated acceleration in sea-level rise (SLR). Sustainable management of the system to ensure safety against flooding of the hinterland, to protect the environmental value and to optimise the economic activities in the area requires predictions of the future morphological development.The Dutch Wadden Sea has been accreting by importing sediment from the ebb-tidal deltas and the North Sea coasts of the barrier islands. The average accretion rate since 1926 has been higher than that of the local relative SLR. The large sediment imports are predominantly caused by the damming of the Zuiderzee and Lauwerszee rather than due to response to this rise in sea level. The intertidal flats in all tidal basins increased in height to compensate for SLR.The barrier islands, the ebb-tidal deltas and the tidal basins that comprise tidal channels and flats together form a sediment-sharing system. The residual sediment transport between a tidal basin and its ebb-tidal delta through the tidal inlet is influenced by different processes and mechanisms. In the Dutch Wadden Sea, residual flow, tidal asymmetry and dispersion are dominant. The interaction between tidal channels and tidal flats is governed by both tides and waves. The height of the tidal flats is the result of the balance between sand supply by the tide and resuspension by waves.At present, long-term modelling for evaluating the effects of accelerated SLR mainly relies on aggregated models. These models are used to evaluate the maximum rates of sediment import into the tidal basins in the Dutch Wadden Sea. These maximum rates are compared to the combined scenarios of SLR and extraction-induced subsidence, in order to explore the future state of the Dutch Wadden Sea.For the near future, up to 2030, the effect of accelerated SLR will be limited and hardly noticeable. Over the long term, by the year 2100, the effect depends on the SLR scenarios. According to the low-end scenario, there will be hardly any effect due to SLR until 2100, whereas according to the high-end scenario the effect will be noticeable already in 2050.