Patrick Kiden

Rising sea levels due to climate change can have severe consequences for coastal populations and ecosystems all around the world. Understanding and projecting sea-level rise is especially important for low-lying countries such as the Netherlands. It is of specific interest for vulnerable ecological and morphodynamic regions, such as the Wadden Sea UNESCO World Heritage region.
Here we provide an overview of sea-level projections for the 21st century for the Wadden Sea region and a condensed review of the scientific data, understanding and uncertainties underpinning the projections. The sea-level projections are formulated in the framework of the geological history of the Wadden Sea region and are based on the regional sea-level projections published in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5). These IPCC AR5 projections are compared against updates derived from more recent literature and evaluated for the Wadden Sea region. The projections are further put into perspective by including interannual variability based on long-term tide-gauge records from observing stations at Den Helder and Delfzijl.
We consider three climate scenarios, following the Representative Concentration Pathways (RCPs), as defined in IPCC AR5: the RCP2.6 scenario assumes that greenhouse gas (GHG) emissions decline after 2020; the RCP4.5 scenario assumes that GHG emissions peak at 2040 and decline thereafter; and the RCP8.5 scenario represents a continued rise of GHG emissions throughout the 21st century. For RCP8.5, we also evaluate several scenarios from recent literature where the mass loss in Antarctica accelerates at rates exceeding those presented in IPCC AR5.
For the Dutch Wadden Sea, the IPCC AR5-based projected sea-level rise is 0.07 ± 0.06 m for the RCP4.5 scenario for the period 2018–30 (uncertainties representing 5–95%), with the RCP2.6 and RCP8.5 scenarios projecting 0.01 m less and more, respectively. The projected rates of sea-level change in 2030 range between 2.6 mm a−1 for the 5th percentile of the RCP2.6 scenario to 9.1 mm a−1 for the 95th percentile of the RCP8.5 scenario. For the period 2018–50, the differences between the scenarios increase, with projected changes of 0.16 ± 0.12 m for RCP2.6, 0.19 ± 0.11 m for RCP4.5 and 0.23 ± 0.12 m for RCP8.5. The accompanying rates of change range between 2.3 and 12.4 mm a−1 in 2050. The differences between the scenarios amplify for the 2018–2100 period, with projected total changes of 0.41 ± 0.25 m for RCP2.6, 0.52 ± 0.27 m for RCP4.5 and 0.76 ± 0.36 m for RCP8.5. The projections for the RCP8.5 scenario are larger than the high-end projections presented in the 2008 Delta Commission Report (0.74 m for 1990–2100) when the differences in time period are considered. The sea-level change rates range from 2.2 to 18.3 mm a−1 for the year 2100.
We also assess the effect of accelerated ice mass loss on the sea-level projections under the RCP8.5 scenario, as recent literature suggests that there may be a larger contribution from Antarctica than presented in IPCC AR5 (potentially exceeding 1 m in 2100). Changes in episodic extreme events, such as storm surges, and periodic (tidal) contributions on (sub-)daily timescales, have not been included in these sea-level projections. However, the potential impacts of these processes on sea-level change rates have been assessed in the report.

Although the Netherlands has a long tradition of sea-level research, no Holocene relative sea-level curve is available for the north of the country. Previous studies hypothesized that the relative sea-level reconstruction for the western Netherlands is also valid for the northern part of the country. However, glacial isostatic adjustment (GIA) models predict a lower and steeper relative sea-level curve because of greater postglacial isostatic subsidence. Long-term data of relative sea-level change are important to inform GIA models and understand postglacial vertical land motion related to the rebound of Fennoscandia and neotectonic activity.
We compiled and evaluated a set of basal peat radiocarbon dates to reconstruct the Holocene relative mean sea-level rise in the Dutch Wadden Sea area. For the early Holocene, this reconstruction is lower than the western Netherlands curve. After 6400 cal a BP, the curve for the Wadden Sea is statistically indistinguishable from that for the western Netherlands, a result that conflicts with GIA model results. It remains to be investigated whether the problem lies with the GIA model predictions or with the quality of the available data. Additional basal peat radiocarbon dates from suitable sites should be collected to further resolve this problem.

... start of E5 (Mostaert and De Moor, 1989), whereas in The Netherlands this happened at ... However, according to Zagwijn (1996), who correlates the Eemian pollen zonation with a time ... The deglaciation history of the Late Pleistocene ice sheets over Fennoscandia, the British Isles ...

Early and middle Holocene sea-level data from Belgium plot ca. 2 m above data from the western Netherlands, reflecting differential tectonic and isostatic movements. The total uplift rate of Belgium relative to the western Netherlands decays gradually from 0.66 m kyr^−1 at 7500 cal. yr BP to less than 0.25 m kyr^−1 since 5000 cal. yr BP. The tectonic component of this relative movement, inferred from Eemian sea-level data, is in the order of 0.06 to 0.16 m kyr^−1. The isostatic component of the uplift is related to the last phase of the collapse of a peripheral bulge under The Netherlands and the Dutch and German sectors of the North Sea, and to hydroisostatic subsidence of the North Sea basin caused by water loading as sea-level rose. Comparisons with isostatic rebound models show that they predict well the Holocene isostatic movement between Belgium and the western Netherlands, and that the predictions are improved when the tectonic component is removed from the observations. Preliminary evaluation of sea-level data from the Dutch sector of the North Sea shows that glacio-hydroisostatic subsidence relative to Belgium was significantly greater than for the western Netherlands coastal area, and spatially highly variable.

Macroscopic opal-A concretions were observed in lake marl deposited in a small Flemish lake (Belgium) during the Allerød biozone of the Weichselian Late-glacial (ca. 12–11 ka BP). The silica from these concretions was derived within the profile, by the leaching of siliceous microfossils – mainly diatom frustules. Formation of the concretions probably resulted from pH- and/or evaporation related precipitation of the silica at a lower stratigraphic level, presumably corresponding more or less to a former low position of the groundwater table. The presence of these concretions is probably related to alternatingly wet and dry local conditions during the middle and later part of the Allerød.

ABSTRACT Over the last ten to twenty years, geological surveys all over the world have been entangled in a process of digitisation. Their paper archives, built over many decades, have largely been replaced by electronic databases. The systematic production of geological map sheets is being replaced by 3D subsurface modelling, the results of which are distributed electronically. In the Netherlands, this transition is both being accelerated and concluded by a new law that will govern management and utilisation of subsurface information. Under this law, the Geological Survey of the Netherlands has been commissioned to build a key register for the subsurface: a single national database for subsurface data and information, which Dutch government bodies are obliged to use when making policies or decisions that pertain to, or can be affected by the subsurface. This requires the Survey to rethink and redesign a substantial part of its operation: from data acquisition and interpretation to delivery. It has also helped shape our view on geological surveying in the future. The key register, which is expected to start becoming operational in 2015, will contain vast quantities of subsurface data, as well as their interpretation into 3D models. The obligatory consultation of the register will raise user expectations of the reliability of all information it contains, and requires a strong focus on confidence issues. Building the necessary systems and meeting quality requirements is our biggest challenge in the upcoming years. The next step change will be towards building 4D models, which represent not only geological conditions in space, but also processes in time such as subsidence, anthropogenic effects, and those associated with global change.

Detailed characterisation and 3D-modelling of the shallow subsurface was carried out for the construction of a Radial Collector Well (RCW) at the drinking water pumping station of Brabant Water at Macharen (near ‘s Hertogenbosch, province of Noord-Brabant, southern Netherlands). The objective was to assess the lithological and hydraulic properties of the uppermost 30 m of the subsoil in order to find the optimal depth and orientation of the 4 horizontal collector arms of the RCW.

The Geological Survey of the Netherlands maps its country systematically in 3D, putting out four models
that each correspond with a particular application domain. Rather than the models themselves, we discuss
the meaning and implementation of working systematically, focusing on quality assurance and model
versioning and maintenance. Our aims for quality assurance are to put a system in place that arranges for
independent and documented checks of all model output, according to well-defined quality standards,
finding a balance between rigorousness on the one hand, and user demands to deliver information faster
on the other. Regarding model versioning and maintenance, we aim to significantly shorten our release
cycles, publishing models after making specific improvements rather than full updates. These two aspects
of working systematically are particularly important in helping us to be accountable in terms of the value
and quality of our modeling work, which in its turn is vital to the continuity of our Survey.