Late-Holocene sea-level reconstruction (1200 BC–AD 100) in the Westergo terp region of the northern Netherlands

Abstract In the early 20th century, archaeological research in the terp (artificial dwelling-mound) region of the northern Netherlands focused, besides settlement history, on natural salt-marsh dynamics and sea-level rise. In particular Van Giffen used salt-marsh deposits under dated terp layers to reconstruct the rate of sedimentation of the developing salt marsh and relative sea-level rise. This line of research in archaeology was rekindled during excavations in the terp of Wijnaldum-Tjitsma between 1991 and 1993. Since then, geology has become an integral part of archaeological research in the terp region. This paper focuses on the northwestern part of the province of Friesland (Westergo), where most archaeological terp research during the past three decades has been carried out, owing to several research programmes by the Province of Friesland. The primary aim of the geoarchaeological research is to better understand the interaction between human inhabitants and the salt-marsh landscape. The sedimentary record exposed in the excavation trenches makes it possible to collect data on the development of the coastal environments of the Wadden Sea prior to habitation, including data on sea-level rise. The sea-level data collected in the geoarchaeological studies in Westergo are the topic of this paper. The measured levels of the tidal-flat/salt-marsh boundary underneath the terps make it possible to reconstruct palaeo-Mean High Water (palaeo-MHW) levels. Such sea-level index points (SLIPs), based on marine shell data points from 12 locations, now make it possible to establish a palaeo-MHW diagram for this part of the Wadden Sea, for the period between 1200 BC and AD 100. In this period the palaeo-MHW in the Westergo region rose from c.1.8 m to 0.3 m −NAP: a mean sea-level rise of c.0.12 m per century. We discuss the fact that elevation of the palaeo-MHW SLIP is not only determined by relative sea level (RSL), but also by the magnitude of the tidal amplitude. The tidal range, and therefore the MHW elevations in a tidal basin, can change from place to place and also in time. Also in a single tidal basin the tidal range is variable, due to the distortion of the tidal wave as a result of the morphology of the tidal system. Such local tidal range fluctuations – not related to sea-level rise – influence the palaeo-MHW curve of Westergo and other tidal basins in the Wadden Sea and need to be taken into account when interpreting the curve. In this paper, we will go into the causes of changes in palaeotidal ranges in meso- and macrotidal systems, analyse the tidal range variations in recent and subrecent basins and estuaries and discuss the implications of these changes on the sea-level curve of the Westergo region in NW Friesland.

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Exposure to Coastal Hazards in a Rapidly Expanding Northern Urban Centre, Iqaluit, Nunavut

ARCTIC ◽

10.14430/arctic4526 ◽

2015 ◽

Vol 68 (4) ◽

pp. 453 ◽

Cited By ~ 6

Author(s):

Scott V. Hatcher ◽

Donald L. Forbes

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Critical Infrastructure ◽

High Water ◽

Water Levels ◽

Coastal Hazards ◽

Tidal Range ◽

Urban Centre ◽

Relative Sea Level ◽

Run Up

The City of Iqaluit, Nunavut, is an expanding urban centre with important infrastructure located in the coastal zone. This study investigates the exposure of this infrastructure to coastal hazards (rising mean sea level, extreme water levels, wave run-up, and sea ice). Using a coastal digital elevation model, we evaluate the inundation and flooding that may result from projected sea level rise. Some public and private infrastructure is already subject to flooding during extreme high water events. Using a near upper-limit scenario of 0.7 m for relative sea level rise from 2010 to 2100, we estimate that critical infrastructure will have a remaining freeboard of 0.3–0.8 m above high spring tide, and some subsistence infrastructure will be inundated. The large tidal range, limited over-water fetch, and wide intertidal flats reduce the risk of wave impacts. When present, the shorefast ice foot provides protection for coastal infrastructure. The ice-free season has expanded by 1.0–1.5 days per year since 1979, increasing the opportunity for storm-wave generation and thus exposure to wave run-up. Overtopping of critical infrastructure and displacement by flooding of subsistence infrastructure are potential issues requiring better projections of relative sea level change and extreme high water levels. These results can inform decisions on adaptation, providing measurable limits for safe development.

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Future Response of the Wadden Sea Tidal Basins to Relative Sea-Level rise—An Aggregated Modelling Approach

Water ◽

10.3390/w11102198 ◽

2019 ◽

Vol 11 (10) ◽

pp. 2198 ◽

Cited By ~ 2

Author(s):

Lodder ◽

Wang ◽

Elias ◽

van der Spek ◽

de Looff ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Wadden Sea ◽

Dynamic Equilibrium ◽

Tidal Inlet ◽

Scale Model ◽

Tidal Basin ◽

Critical Limit ◽

Tidal Basins ◽

Rise Rate

Climate change, and especially the associated acceleration of sea-level rise, forms a serious threat to the Wadden Sea. The Wadden Sea contains the world’s largest coherent intertidal flat area and it is known that these flats can drown when the rate of sea-level rise exceeds a critical limit. As a result, the intertidal flats would then be permanently inundated, seriously affecting the ecological functioning of the system. The determination of this critical limit and the modelling of the transient process of how a tidal basin responds to accelerated sea-level rise is of critical importance. In this contribution we revisit the modelling of the response of the Wadden Sea tidal basins to sea-level rise using a basin scale morphological model (aggregated scale morphological interaction between tidal basin and adjacent coast, ASMITA). Analysis using this aggregated scale model shows that the critical rate of sea-level rise is not merely influenced by the morphological equilibrium and the morphological time scale, but also depends on the grain size distribution of sediment in the tidal inlet system. As sea-level rises, there is a lag in the morphological response, which means that the basin will be deeper than the systems morphological equilibrium. However, so long as the rate of sea-level rise is constant and below a critical limit, this offset becomes constant and a dynamic equilibrium is established. This equilibrium deviation as well as the time needed to achieve the dynamic equilibrium increase non-linearly with increasing rates of sea-level rise. As a result, the response of a tidal basin to relatively fast sea-level rise is similar, no matter if the sea-level rise rate is just below, equal or above the critical limit. A tidal basin will experience a long process of ‘drowning’ when sea-level rise rate exceeds about 80% of the critical limit. The insights from the present study can be used to improve morphodynamic modelling of tidal basin response to accelerating sea-level rise and are useful for sustainable management of tidal inlet systems.

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New data from terp excavations on sea-level index points and salt marsh sedimentation rates in the eastern part of the Dutch Wadden Sea

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/njg.2018.2 ◽

2018 ◽

Vol 97 (1-2) ◽

pp. 31-43 ◽

Cited By ~ 1

Author(s):

Annet Nieuwhof ◽

Peter C. Vos

Keyword(s):

Salt Marsh ◽

Sea Level ◽

Tidal Flat ◽

Wadden Sea ◽

High Water ◽

Sedimentation Rates ◽

Similar Data ◽

Geological Data ◽

Rate Of Development ◽

Upper Limit

AbstractThis paper presents new geological data from two terp excavations at Englum and Ezinge, in the Dutch province of Groningen, and compares them to similar data from the western part of Friesland, in particular from the terp of Wijnaldum-Tjitsma. This terp is situated at a salt marsh ridge of the same height and thickness as Englum and Ezinge, although habitation started 650 years later at Wijnaldum. The measured levels of the tidal-flat/salt-marsh boundary underneath these terps make it possible to reconstruct palaeo-Mean High Water (MHW) levels. These sea-level index points show that palaeo-MHW in the Groningen part of the Wadden Sea was at the upper limit of the range of palaeo-MHW that has been reconstructed for the Dutch Wadden Sea on the basis of data from its western part. The deviating levels indicate that there are differences between regions of the Wadden Sea; this has earlier been established for the German section of the Wadden Sea. In the eastern part of the Dutch Wadden Sea, MHW nowadays is considerably higher than in the western part of the Wadden Sea; the data suggest that this may have been the case already in the 1st millennium BC. Salt marsh levels under dated terp layers make it possible to establish the rate of sedimentation of the developing salt marsh, at 23–91 cm per century for the pioneer zone and low marsh. This rate of development slowed to 4–5 cm per century for the middle marsh and 3–4 cm per century for the high salt marsh.

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Assessment of the sensitivity of the southern coast of the Gulf of Corinth (Peloponnese, Greece) to sea-level rise

Open Geosciences ◽

10.2478/s13533-012-0101-3 ◽

2012 ◽

Vol 4 (4) ◽

Cited By ~ 14

Author(s):

Efthimios Karymbalis ◽

Christos Chalkias ◽

George Chalkias ◽

Eleni Grigoropoulou ◽

George Manthos ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Tidal Range ◽

Sensitivity Index ◽

Southern Coast ◽

Gis Technology ◽

Relative Sea Level ◽

Gulf Of Corinth ◽

Rise Rate ◽

Relative Sea Level Rise

AbstractThe eustatic sea-level rise due to global warming is predicted to reach approximately 18–59 cm by the year 2100, which necessitates the identification and protection of sensitive sections of coastline. In this study, the classification of the southern coast of the Gulf of Corinth according to the sensitivity to the anticipated future sealevel rise is attempted by applying the Coastal Sensitivity Index (CSI), with variable ranges specifically modified for the coastal environment of Greece, utilizing GIS technology. The studied coastline has a length of 148 km and is oriented along the WNW-ESE direction. CSI calculation involves the relation of the following physical variables, associated with the sensitivity to long-term sea-level rise, in a quantifiable manner: geomorphology, coastal slope, relative sea-level rise rate, shoreline erosion or accretion rate, mean tidal range and mean wave height. For each variable, a relative risk value is assigned according to the potential magnitude of its contribution to physical changes on the coast as the sea-level rises. Every section of the coastline is assigned a risk ranking based on each variable, and the CSI is calculated as the square root of the product of the ranked variables divided by the total number of variables. Subsequently, a CSI map is produced for the studied coastline. This map showed that an extensive length of the coast (57.0 km, corresponding to 38.7% of the entire coastline) is characterized as highly and very highly sensitive primarily due to the low topography, the presence of erosionsusceptible geological formations and landforms and fast relative sea-level rise rates. Areas of high and very high CSI values host socio-economically important land uses and activities.

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Morphodynamic development and sediment budget of the Dutch Wadden Sea over the last century

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/s0016774600000457 ◽

2012 ◽

Vol 91 (3) ◽

pp. 293-310 ◽

Cited By ~ 36

Author(s):

E.P.L. Elias ◽

A.J.F. van der Spek ◽

Z.B. Wang ◽

J. de Ronde

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Wadden Sea ◽

Control Measures ◽

Tidal Basin ◽

Sediment Volume ◽

Tidal Basins ◽

Present Rate ◽

Continuous Sedimentation ◽

Equilibrium Morphology

AbstractThe availability of nearly 100 years of bathymetric measurements allows the analysis of the morphodynamic evolution of the Dutch Wadden Sea under rising sea level and increasing human constraint. The historically observed roll-over mechanisms of landward barrier and coastline retreat cannot be sustained naturally due to numerous erosion control measures that have fixed the tidal basin and barrier dimensions. Nevertheless, the large continuous sedimentation in the tidal basins (nearly 600 million m3), the retained inlets and the similar channel-shoal characteristics of the basins during the observation period indicate that the Wadden Sea is resilient to anthropogenic influence, and can import sediment volumes even larger than those needed to compensate the present rate of sea-level rise. The largest sedimentation occurs in the Western Wadden Sea, where the influence of human intervention is dominant. The large infilling rates in closed-off channels, and along the basin shoreline, rather than a gradual increase in channel flat heights, render it likely that this sedimentation is primarily a response to the closure of the Zuiderzee and not an adaptation to sea-level rise. Most of the sediments were supplied by the ebb-tidal deltas. It is, however, unlikely that the sediment volume needed to reach a new equilibrium morphology in the Western Wadden Sea can be delivered by the remaining ebb-tidal deltas alone.

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Are Wadden Sea tidal systems with a higher tidal range more resilient against sea level rise?

Journal of Coastal Conservation ◽

10.1007/s11852-016-0469-1 ◽

2016 ◽

Vol 22 (1) ◽

pp. 71-78 ◽

Cited By ~ 8

Author(s):

Jacobus L.A. Hofstede ◽

Johannes Becherer ◽

Hans Burchard

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Wadden Sea ◽

Tidal Range

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Buying Time with Runnels: a Climate Adaptation Tool for Salt Marshes

Estuaries and Coasts ◽

10.1007/s12237-021-01028-8 ◽

2022 ◽

Author(s):

Alice F. Besterman ◽

Rachel W. Jakuba ◽

Wenley Ferguson ◽

Diana Brennan ◽

Joseph E. Costa ◽

...

Keyword(s):

Salt Marsh ◽

Sea Level Rise ◽

Sea Level ◽

Salt Marshes ◽

Climate Adaptation ◽

Open Water ◽

Tidal Range ◽

Management Interventions

AbstractA prominent form of salt marsh loss is interior conversion to open water, driven by sea level rise in interaction with human activity and other stressors. Persistent inundation drowns vegetation and contributes to open water conversion in salt marsh interiors. Runnels are shallow channels originally developed in Australia to control mosquitoes by draining standing water, but recently used to restore marsh vegetation in the USA. Documentation on runnel efficacy is not widely available; yet over the past 10 years dozens of coastal adaptation projects in the northeastern USA have incorporated runnels. To better understand the efficacy of runnels used for restoration, we organized a workshop of 70 experts and stakeholders in coastal resource management. Through the workshop we developed a collective understanding of how runnels might be used to slow or reverse open water conversion, and identified unresolved questions. In this paper we present a synthesis of workshop discussions and results from a promising case study in which vegetation was restored at a degraded marsh within a few years of runnel construction. Despite case study outcomes, key questions remain on long-term runnel efficacy in marshes differing in elevation, tidal range, and management history. Runnel construction is unlikely to improve long-term marsh resilience alone, as it cannot address underlying causes of open water conversion. As a part of holistic climate planning that includes other management interventions, runnels may “buy time” for salt marshes to respond to management action, or adapt to sea level rise.

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ASSESSMENT OF THE EFFECTS OF THE ZUIDER SEA CLOSURE ON THE HYDRODYNAMICS OF THE WADDEN SEA INLETS

Coastal Engineering Proceedings ◽

10.9753/icce.v33.management.47 ◽

2012 ◽

Vol 1 (33) ◽

pp. 47

Author(s):

Julia Vroom ◽

Edwin Elias ◽

Jamie Lescinski ◽

Zheng Bing Wang

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Wadden Sea ◽

Tidal Range ◽

Hydrodynamic Simulations ◽

Drift Direction ◽

And Sea Level

Large hydrodynamic and morphodynamic changes have taken place in the western Dutch Wadden Sea due to the closure of the Zuider Sea in the early 1930s. Hydrodynamic simulations for three situations, viz. just before the closure, just after the closure and at present, have been carried out in order to investigate the hydrodynamic changes since the closure and to improve our understanding of the observed morphodynamic changes. The model results show a large increase in tidal range after the closure of the Zuider Sea. This increase continued to grow after the closure due to bathymetric change and sea level rise. The morphodynamic analysis focuses on the changed behavior of the ebb-tidal deltas of the Texel Inlet and the Vlie Inlet. Both ebb-tidal deltas have undergone a re-orientation in up-drift direction. Two possible explanations based on the literature for this change are discussed with the help of the hydrodynamic simulations.

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Late Holocene salt marsh development under a regime of rapid relative-sea-level rise: Chezzetcook Inlet, Nova Scotia. Implications for the interpretation of palaeomarsh sequences

Canadian Journal of Earth Sciences ◽

10.1139/e93-118 ◽

1993 ◽

Vol 30 (7) ◽

pp. 1374-1384 ◽

Cited By ~ 25

Author(s):

S. C. Jennings ◽

R. W. G. Carter ◽

J. D. Orford

Keyword(s):

Nova Scotia ◽

Salt Marsh ◽

Sea Level Rise ◽

Sea Level ◽

Late Holocene ◽

Environmental Gradients ◽

Relative Sea Level ◽

Spatial Changes ◽

Relative Sea Level Rise ◽

Outer Estuary

Pollen data illustrating a 2000-year record of salt marsh development have been obtained from a variety of outer-estuarine settings in close proximity to the present gravel-dominated coastal barriers at Chezzetcook Inlet, Nova Scotia. The relationship between the biostratigraphic and lithostratigraphic data and relative-sea-level movement is complex. In the outer estuary, temporal and spatial changes to the floral and sedimentological composition of the salt marsh reflect principally processes of estuarine and back-barrier sedimentation that resulted in steep environmental gradients and the development of regressive marsh–sediment complexes, despite a relative-sea-level rise of up to 3.8 mm/a during the late Holocene. Our results contrast with those from the inner estuary at Chezzetcook Inlet, where salt marsh has developed only over the last 200 years as a result of sediment inwash due to European land use, and followed a prolonged episode (approx. 5000 years) of tidal flat conditions. This contrast highlights differences in sediment input and distribution between the outer and inner estuary.

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