All lectures

Dr Friederike Bungenstock, Head of research of the Department of Coastal and Quaternary Geology at the Lower Saxony Institute for Historical Coastal Research.

Wadden Sea archives of changes in past sea-level and landscapes

Read the abstract of Dr Friederike Bungenstock

The response of coasts to global sea-level rise is highly variable even on a regional scale. Knowledge of driving coastal processes alongside the regional sea-level history is therefore indispensable when the response to global sea-level rise is to be assessed.

Sea level data for the tidal basin of the East Frisian Island Langeoog have been collected and evaluated by profile sections and seismic tracks in order to create a Holocene sea level curve representative for this area. Combined with an existing model of the base of Holocene deposits (NIBIS map server, official portal to the Geodata of the Lower Saxony Soil Information System NIBIS), assumptions of paleo tidal ranges and the lithostratigraphical data of more than 5000 cores, archived at the LBEG (Geological Survey of Lower Saxony), palaeogeographical maps from 9000 BP onwards could be reconstructed. Although there is a lack of absolute chronology, these maps deliver a general picture of the depositional history and change of lithological units over time.

Due to the lack of datings and further landscape information mainly on vegetation history and ecological parameters these maps initiated the WASA (Wadden Sea Archive) project. The interdisciplinary research project integrates sedimentology, hydroacoustics, geochemistry, palaeoecology and archaeology in a multiproxy approach involving exploration, analysis and predictive modelling. The focus of the project is to identify and investigate coastal archives in order to reconstruct the development of the Quaternary palaeo-landscapes and to model the environmental conditions for site location preferences of former human societies.

Dr Aimée Slangen, NIOZ Royal Netherlands Institute for Sea Research, Department of Estuarine & Delta Systems, and Utrecht University.

Past, present and future sea-level rise in the Netherlands

Read the abstract of Dr Aimee Slangen

Sea-level change is an important topic in the area of climate research. Changes in sea level are the result of changes in many different components of the climate system: the ocean, the land, the atmosphere and the cryosphere. Studying sea-level change and its consequences for coastal systems and communities therefore requires a complete and integrative view of the climate system on a range of spatial and temporal scales.

In this presentation, we will discuss the different processes that contribute to sea-level change and come to understand why global and regional sea-level change are different. We will look at observed and modelled sea-level change along the Dutch coast for the 20th and 21st century, and discuss the main uncertainties in sea-level projections for the coming centuries. Finally, we will look at examples of coastal impacts of sea-level change, such as changing sea-level extremes and geomorphology.

Dr Marjolijn Haasnoot, water resources management and environmental modelling at Deltares and Utrecht University

Adaptation pathways to uncertain sea-level rise.

Read the abstract of Dr Marjolijn Haasnoot

Rising sea-levels increase the risk of coastal flooding, erosion of the coastal environment, and reduce fresh water availability for drinking water and agriculture through salt water intrusion. In many coastal regions sea-level rise scenarios are used for coastal management decisions. Uncertainty about amount and rate of sea-level rise complicates decision making on adaptation. Exploring alternative sequences of adaptation pathways can support decision making despite the uncertainties about future sea levels.

In this presentation, we will present adaptation pathways to uncertain sea level rise for different coastal archetypes. For the Dutch delta, we show different pathways to maintain the coast, reduce flood risk and supply fresh water. Finally, we will discuss how potential high-end and accelerated sea-level rise could be a game-changer for coastal adaptation.

Dr. Andrea D'Alpaos, Associate Professor at the Department of Geosciences, University of Padova.

Morphodynamics of Tidal Meanders and Related Sedimentary Products.

Read the abstract of Dr. Andrea D'Alpaos

Tidal landscapes are commonly dissected by networks of branching and meandering channels that control the flux water, sediments, nutrients and biota across these landscapes, ultimately impacting the ecomorphodynamic evolution and the stratigraphy of the platforms they incise. Although tidal channeled patterns have been extensively studied in the last decades, through field observations, mathematical modeling, and laboratory experiments, just a few studies on tidal meanders exist. Indeed, despite their prominence and wide occurrence, the characteristics and dynamics of tidal meanders lack the detailed investigation that has been devoted to their fluvial counterparts, so that questions remain on whether tidal meander dynamics are similar to (or rather unlike) those of fluvial meanders. Key differences suggest otherwise, such as, among others, the periodic reversal of tidal flows, the occurrence and magnitude of the landscape forming discharges and their spatial variations, the different behavior of the stage-discharge relationship, and the different mutual role of bend lateral migration and platform vertical aggradation.

Recent analyses of tidal meander dynamics carried out within the Venice Lagoon suggest that tidal meanders, traditionally viewed as quite stable landscape features, display migration rates per unit width and modes of migration quite similar to those characterizing their fluvial fellows. However, statistical analyses of relevant morphological features for about 10’000 meander bends belonging to about 100 tidal and fluvial channels worldwide suggest that tidal meanders display less complex planar configurations than their fluvial relatives, both at the single-meander and at the reach scale. In addition, field observations and modelling for both modern (in the Venice Lagoon) and ancient (Cretaceous Tremp Basin) meander deposits, show that tidal asymmetries may significantly influence erosion and deposition patterns together with sediment sorting along tidal meandering channels, thus providing appropriate proxies to detect tidal influence and the dominance of either ebb or flood flows also in the fossil record.

Interestingly, although the signatures of the different governing processes can hardly be unraveled by the analysis of tidal meander planform configurations and dynamics, detailed analyses of the internal architecture and sedimentary features of modern and ancient tidal point bars emphasize the existence of relevant differences that might be imprinted in the sedimentary record.

Results emerging from the analysis of modern and ancient tidal meanders, carried out for different systems worldwide on the basis of a multidisciplinary approach coupling field observations and numerical modeling, can improve current knowledge of tidal meander dynamics and of the related stratal architecture, a key issue for the evolution and restoration of coastal landscapes, exposed as they are to natural and anthropogenic environmental change.

Bas van Maren

Dr Bas van Maren, Expert on fine sediment transport and morphology at Deltares.

Impact of human interventions on the tidal channels of the Ems Estuary

Read the abstract of Dr Bas van Maren

Alluvial estuaries form an intricate pattern of tidal channels, shoals and tidal flats, often characterized by alternating, mutually evasive ebb and flood channels connected by shoals or sills. Such estuarine systems are dynamic, with channels and meanders migrating laterally in response to tidal forcing, but over longer timescales they are in dynamic equilibrium. In past centuries, and especially in recent decades, many estuaries worldwide have been modified in order to reclaim land and to allow ever larger ship access to inland waterways. These interventions include the deepening, straightening and narrowing of tidal channels, resulting in modified tidal dynamics and as a result, complex morphodynamic feedback. With ever increasing pressure resulting from human interventions and Sea Level Rise, there is a rising need to predict the effect of present-day and future human interventions. Unfortunately, understanding the impact of historic human interventions on tidal dynamics and morphodynamics, for which observational data is available, is already challenging. Still, a thorough understanding of the pas is crucial before attempts are made to predict the effect of present-day (or future) interventions. Mathematical models are becoming increasingly more accurate tools to hindcast and predict estuarine. However, despite their mathematical simplicity, the impact of human interventions was already surprisingly accurately described using classical descriptive geomorphology.

The pioneering work of van Veen (1950) on estuarine morphodynamics meant a breakthrough on unravelling the impact of human interventions on tidal basins in general, and the Ems Estuary in particular. At that time, the existing main channel of the Ems Estuary was degenerating while a new channel took over its role. Van Veen hypothesized that the degenerating channel was the ebb channel, losing its flow capacity because to a flood channel because the sill separating two flood chutes was removed. As described nearly simultaneously by Gerritsen (1952), this deterioration of the ebb channel was enhanced by the reclamation works in the Dollard, further reducing the channel capacity. Estuarine science has greatly progressed since then, both in physical understanding and in development of analytical and numerical tools. These modelling tools allow us to hindcast estuarine evolution, and thereby investigate the relative importance of historic changes, but also predict the effect of present-day human interventions. Current research activities in the Ems estuary are strongly driven by the observed increase in suspended sediment concentration (and its adverse ecological consequences), which is largely attributed to the range of human interventions that occurred in the past decades to centuries.

This lecture will address the progress in understanding the morphologic effect of human interventions, from the descriptive geomorphology practised by van Veen and Gerritsen, to the more quantitative model-based approaches used today. We will show recent progress in modelling the dynamics of tidal channels in the Ems Estuary on timescales of centuries. A comparison with old maps shows that such model simulations can reproduce the large-scale development of the estuary, but also reveals that the present-day morphology is strongly influenced by human interventions which took place centuries ago. Also on shorter timescales there is a strong link between human interventions and the suspended sediment concentration, as will be quantified and explained using numerical model approaches.

Dr Sergio Fagherazzi, Geomorphology, hydrology, and coastal and marine geology, Boston University

Non-Linear dynamics determine the fate of salt marshes 

Read the abstract of dr SERGIO FAGHERAZZI

The potential of salt marshes to serve as natural buffers against violent storms seems even more important in view of significant threats imposed by climate change, such as increased storminess and higher hurricane activity registered in the past decades. Unfortunately, Salt marsh losses have been documented worldwide because of land use change, wave erosion, and sea-level rise. Sea level rise is often viewed as the main driver of salt marsh deterioration. 

However, while salt marshes can reach equilibrium in the vertical direction, they are inherently unstable in the horizontal direction. Marsh expansion driven by sediment supply rarely matches lateral erosion by waves, creating a dynamic landscape. Recent results show that marsh collapse can occur in the absence of sea level rise if the rate at which sediment is eroded at marsh boundaries is higher than the input of sediment from nearby rivers or from the continental shelf.

We propose that the horizontal dynamics and related sediment fluxes are key factors determining the survival of salt marshes. Only a complete sediment budget between salt marshes and nearby tidal flats can determine the fate of marshes at any given location, with sea level rise being only one among many external drivers. Moreover, salt marshes seem more susceptible to variations in mean wave energy rather than changes in the extremes. The intrinsic resistance of salt marshes to violent storms and their predictable erosion rates during moderate events should be taken into account by coastal managers in restoration projects and risk management plans.

Dr. Tjeerd J. Bouma, Estuarine and Delta Systems, Royal NIOZ

Small-scale process as driver of large-scale dynamics in coastal vegetation

Read the abstract of Dr Tjeerd Bouma

There is a growing desire to manage (and even create) coastal vegetation such as e.g. salt marshes, mangroves and seagrasses for coastal defense. Such application however requires in depth understanding of the dynamic horizontal extent (i.e., width) of these ecosystems. Especially understanding the factors affecting the minimum vegetation width is important.

This presentation will highlight how process-based studies can help to provide insight in which factors affect the long-term large-scale development of salt marsh and other coastal vegetation. Recently it was found that vegetation establishment can be described by the Windows of Opportunity theory. Having this mechanistic understanding enables us to develop means to restore coastal ecosystems. Moreover, it allows us to gain a basic insight in which factors determine the minimum-width of a salt marsh, and how dredging material may potential be used to initiate marsh growth.

Recent insights explaining that the short-term vertical sediment dynamics on the bare tidal flat is a key driver of the lateral vegetation dynamics, emphasizes that we should start with continuous monitoring of such sediment-dynamics. The vegetation response to the short-term vertical sediment dynamics can however be highly species specific, resulting in species-specific large-scale ecosystem dynamics. Experimental process-based studies remain of key importance for understanding ecosystem dynamics in addition to the rapidly developing earth observation techniques and modelling capabilities.

Prof James Best

Prof James Best, Department of Geology, Geography & GIS, University of Illinois

Sedimentology of the fluvial-tidal transition: insights from the lower Columbia River, USA, and some simple laboratory experiments

Read the abstract of Prof James Best

The fluvial-tidal transition labels a major part of the Netherlands. Over centuries society has taken advantage of the possibilities that rivers and estuaries offer and the areas have been adapted to our needs. Emphasis has shifted from land reclamation, via safety against flooding to the ecological values and at the same the nautical use of the waterways has continued. Balancing the different functions of and along the fluvial-tidal transition is a challenge for estuarine management. A thorough understanding of the fluvial-tidal transitions promotes sensible management decisions.  Two developments from the Western Scheldt – the seaward part of the Scheldt estuary- will be shown, that still present challenges for our understanding of the fluvial transition.

In the Western Scheldt the large-scale pattern of inter-tidal flats has changed. In the beginning of the twentieth century the flats consisted of complexes with several smaller flats with complex and long waterlines, intersected by channels. Today’s pattern shows large flats with smooth circumferences and very few intersecting channels. The transition towards larger and smoother flats is ongoing. The origins of this development under debate, with likely relations to the autonomous development of the channel pattern and to the embankments. The implications of these morphological changes for the hydrodynamics of the estuary are not yet fully understood.

The distribution of mega-ripple beds over the inter-tidal flats (for the distribution in the sub-tidal realm the number of observations is limited) has changed over the recorded period of ’70 years and the spatial extent of the mega-ripple beds has decreased. Fields with mega-ripples typically occur along the fringes of the inter-tidal flats, where ebb and flood chutes protrude in to the flats. Along with the decrease of the mega-ripple fields the areas with flats beds have increased. These flat flats are interpreted as upper-stage plane bed areas. The transition from mega ripples to upper-stage plane bed is a function of several factors (current velocity, depth, grain size, etc.) and the key factor has not yet been identified.

Things have changed in the hydrodynamics and the sediment dynamics of the tidal flats. The two developments presented here appear on very different spatial scales, but are likely related. The presence of mega-ripples is associated with the small-tidal channels that used to dissect the inter-tidal flats and both are decreasing. Getting grip on these developments- and many others- requires fundamental knowledge, both on the large spatial scale of pattern formation and development in the estuary and on the much smaller scale of bedform generation and dynamic. In order to retain the values of the Scheldt estuary for society insight in its dynamics is imperative.

Jelmer Cleveringa

Dr. Jelmer Cleveringa, Arcadis Nederland

Ripples in the Scheldt

Read the abstract of Dr Jelmer Cleveringa

The fluvial-tidal transition labels a major part of the Netherlands. Over centuries society has taken advantage of the possibilities that rivers and estuaries offer and the areas have been adapted to our needs. Emphasis has shifted from land reclamation, via safety against flooding to the ecological values and at the same the nautical use of the waterways has continued. Balancing the different functions of and along the fluvial-tidal transition is a challenge for estuarine management. A thorough understanding of the fluvial-tidal transitions promotes sensible management decisions.  Two developments from the Western Scheldt – the seaward part of the Scheldt estuary- will be shown, that still present challenges for our understanding of the fluvial transition.

In the Western Scheldt the large-scale pattern of inter-tidal flats has changed. In the beginning of the twentieth century the flats consisted of complexes with several smaller flats with complex and long waterlines, intersected by channels. Today’s pattern shows large flats with smooth circumferences and very few intersecting channels. The transition towards larger and smoother flats is ongoing. The origins of this development under debate, with likely relations to the autonomous development of the channel pattern and to the embankments. The implications of these morphological changes for the hydrodynamics of the estuary are not yet fully understood.

The distribution of mega-ripple beds over the inter-tidal flats (for the distribution in the sub-tidal realm the number of observations is limited) has changed over the recorded period of ’70 years and the spatial extent of the mega-ripple beds has decreased. Fields with mega-ripples typically occur along the fringes of the inter-tidal flats, where ebb and flood chutes protrude in to the flats. Along with the decrease of the mega-ripple fields the areas with flats beds have increased. These flat flats are interpreted as upper-stage plane bed areas. The transition from mega ripples to upper-stage plane bed is a function of several factors (current velocity, depth, grain size, etc.) and the key factor has not yet been identified.

Things have changed in the hydrodynamics and the sediment dynamics of the tidal flats. The two developments presented here appear on very different spatial scales, but are likely related. The presence of mega-ripples is associated with the small-tidal channels that used to dissect the inter-tidal flats and both are decreasing. Getting grip on these developments- and many others- requires fundamental knowledge, both on the large spatial scale of pattern formation and development in the estuary and on the much smaller scale of bedform generation and dynamic. In order to retain the values of the Scheldt estuary for society insight in its dynamics is imperative.