sediment pathways – Coastally Curious

Veni!

Large populations near the sea are vulnerable to coastal floods, making coastal safety and sustainability an urgent societal priority. This is especially true in the Netherlands, where over a quarter of the country lies below sea level, and the main protection from deadly coastal floods is a barrier of wide, high sandy beaches and dunes. However, this sandy buffer is constantly moving and chronically eroding. To plan effective future coastal adaptations, we need to know where that sand is coming from, going to, and which paths it takes to get there. I am delighted to share that I have just received a Veni grant from the Dutch Research Council (NWO) to investigate this!

Where is the sand on beaches going, and how does it get there?

My overarching goal is to enable effective sediment-based climate adaptation strategies for vulnerable coasts. To approach this, I consider coasts as an interconnected network of sediment pathways, like a subway map showing how stations are linked. This connectivity reveals the hidden structure underlying chaotic sediment pathways through coastal systems. These pathways are immensely difficult to identify on real coasts due to the challenge of tracking individual sand grains from multiple sources in such a dynamic environment.

Proof-of-concept connectivity analysis of a beach and harbour.
(a) Map of tracer particles in example SedTRAILS model from 7 different source patches at a snapshot in time. (b) The number of particles (n_p) from a given source in each receptor is counted to yield a connectivity matrix, graphically represented by a connectivity network diagram (c).

To deal with this challenge, this grant will enable me to develop both a scale model in a physical laboratory and a numerical model in a digital laboratory. In a wave tank the size of an Olympic swimming pool, I will construct a beach from multi-coloured sand. As waves disperse the sand, the resulting rainbow of sediment will reveal their pathways, which I will then quantify as a network in the digital laboratory. The resulting open datasets and numerical models will serve as a benchmark for the coastal research community, generating new theories and improved tools. My collaborators in the Netherlands, US, and New Zealand will help me to implement these findings in research, engineering practice, and coastal management policy. In this way I hope to enable more effective management of sediment for coastal adaptation and a more holistic understanding of our coastal systems.

Stay tuned for more updates once the project begins!

PhD Opportunity: Nourishment Hydrodynamics and Sediment Transport (SOURCE)

My colleague Matthieu de Schipper and I are looking for a new PhD candidate as part of the large SOURCE research project! SOURCE stands for Sand nourishment strategies for sustainable Coastal Ecosystems. The SOURCE philosophy is that carefully planned sand nourishments now will create the required and desired resilient and dynamic multifunctional coastal landscapes of the future.

Sand nourishment has been essential in the Dutch government’s strategy to sustainably maintain flood protection levels along the Dutch coast for more than 30 years. Nourishment volumes are projected to increase to keep up with the expected acceleration in sea level rise. However, we currently lack fundamental knowledge on how the nourished sand finds its way through the coastal system, and what the long-term, cumulative effects are for the coast as an ecosystem. For instance, we know that beaches that are nourished with sand in the nearshore are eroding less, but which sediment is accumulating on the landward beach is still unknown. Likewise it is still unknown which hydrodynamic and sediment transport processes dominate in the vicinity of a nourishment.

In its entirety, the SOURCE research team will deliver the scientific knowledge, models and design tools to develop and evaluate nourishment strategies in a multi-stakeholder co-creation process. Our Living Labs are two sand nourishments along the Dutch coast. These will be co-designed, monitored and evaluated by the SOURCE consortium (in particular the 12 PhD and postdoc researchers at 8 academic institutes in total) in collaboration with 25 partners from government organizations, research institutes, nature organizations and industry.

As part of the SOURCE project, the PhD candidate at Delft University of Technology will examine the morphological development of shoreface nourishments. Understanding the hydrodynamics and sediment transport are key in this research. You will therefore use state-of-the-art field equipment and strategic numerical modelling to unravel the physical processes shaping nourishments. This will ultimately contribute to the robustness of (Dutch) sandy coasts to climate change and the safety of its people against flood hazards.

You will:

Plan, execute and analyse field observations at a nourished beach to better understand the impact of nourishments on the hydrodynamics, sediment transport, and morphological evolution.
Use strategic modelling to predict coastal sediment pathways at recently nourished beaches and the origin of sediment accumulated in the lee side.
Combine data and findings of multiple nourishment projects to show the link between engineering design and coastal settings on the nourishment performance. This step will require you to collaborate with government and industry partners (abroad).
Collaborate with academic partners in the SOURCE project to translate quantitative metrics of physical beach response to ecological and socio-economic impacts.

At TU Delft, you will be part of the Coastal Engineering section where we combine research on hydrodynamics, morphodynamics, and human interventions to the coast using numerical modelling and field measurements. You will primarily work with Matthieu de Schipper and myself (Stuart Pearson), embedded within a larger ecosystem of research partners.

More information about the topic and the application process can be found here.

Come join our team! Feel free to get in touch with us (s.g.pearson@tudelft.nl) if you have any questions. Applications close July 21st, 2024!

Saving the Mangroves, One Fence at a Time

Mangrove forests provide valuable coastal habitats but also provide a natural form of coastal flood protection and a host of other services. However, many of these mangrove forests are threatened by coastal development and groundwater pumping-induced subsidence, among other natural and human changes. Part of the challenge is that mangroves are extremely choosy about their habitat, and need just the right combination of tidal submergence and mud to take root. If these habitats are thrown out of balance by people or natural causes, it becomes hard for new mangrove seedlings to grow there and sustain the forest.

To make happier places for the mangroves to develop, different kinds of coastal fences/dams have been proposed. The general principle is that waves and currents are attenuated or blocked by the fences, which makes a nice quiet area behind them for mud to accumulate and mangrove propagules to take root. What impact do these structures have on the coastal “conveyor belt” transporting mud and propagules? Enter Nirubha Raghavi Thillaigovindarasu!

Just before Christmas, Raghavi successfully defended her thesis, “Mangrove-Sediment Connectivity in the Presence of Structures Used to Aid Restoration“. Beginning with a numerical model of a site in Indonesia to simulate the motion of rivers and tides, she then applied the SedTRAILS model to visualize and interpret the pathways of sediment and mangrove propagules as they journeyed along the coast. By adding structures to her model, she was able to demonstrate how this trapping behaviour has an influence in the vicinity of a structure but also up to a kilometer away.

Example of bamboo fence constructed near Demak, Indonesia, for the purposes of restoring mangrove forests to the coastal region there. Photo: BioManCo project (Alejandra Gijon Mancheno, Silke Tas, Celine van Bijsterveldt).

PhD Opportunity: Coastal Sediment Connectivity

How can we ensure that vulnerable coasts and deltas remain robust to the effects of climate change? We need to better understand how sediment moves along our coasts and deltas, and plan to do so by treating coastal systems as networks of interconnected sediment pathways.

We are looking for a curious and motivated PhD candidate to work with us on an exciting project here at TU Delft in the Netherlands. The main goal of this position is to develop novel approaches to quantify sediment pathways and connectivity, and to use these approaches to inform coastal sediment management.

Our main strategy for ensuring the climate-robustness of the Dutch coast is to nourish or place sand to widen its beaches and dunes. However, the fate of sand placed on the coast is still poorly understood in the context of the full coastal system. Understanding where nourished sand goes is necessarily rooted in understanding the natural sediment transport pathways and connectivity of the system. To take advantage of advances in the field of network analysis and extend these concepts to analyzing sediment transport pathways in coastal systems, we established the framework of coastal sediment connectivity (Pearson et al., 2020).

In this project, you will advance coastal engineering by introducing established techniques from other fields (e.g., network analysis) in a novel way to understand and predict sediment transport. These techniques will yield a new and useful toolbox of methods for predicting and understanding sediment pathways, and enable more efficient and effective nourishment design and execution. This will ultimately contribute to the robustness of the Dutch coast to climate change and the safety of its people against flood hazards.

In this PhD, you will:

Apply network analysis techniques to better understand how sediment pathways are connected at small/short and large/long space/time scales.
Use coastal sediment connectivity networks to probabilistically model sediment pathways via Markov chains or machine learning approaches.
Quantify (a)synchronization of coastal sediment networks and relate to hydrodynamic forcing.
Relate quantitative metrics of network structure to practical coastal management goals (eg, identifying resilience or tipping points).

At TU Delft, you will be part of the Coastal Engineering section where we combine research on hydrodynamics, morphodynamics, and human interventions to the coast using numerical modeling and field measurements. You will primarily work with me (Stuart Pearson) and Ad Reniers, embedded within a larger ecosystem of research partners.

More information about the topic and the application process can be found here: https://www.tudelft.nl/over-tu-delft/werken-bij-tu-delft/vacatures/details?jobId=14744

Come join our team! Feel free to get in touch with us (s.g.pearson@tudelft.nl) if you have any questions. Applications close November 30th, 2023!

The Cappuccino Effect

Do you ever think about the swirling patterns in your cappuccino as you stir your spoon around, the brown coffee folding in past the white foam? And do you ever think about sediment transport as you do it? Just me? Ok, never mind…

I had the great privilege of hanging out in New Orleans this past week, being a sand nerd with four hundred of my fellow sand nerds at the Coastal Sediments conference. In between jazz sets at the Spotted Cat, we shared our latest ideas about coastal dynamics, built new collaborations, and rekindled old pre-pandemic friendships. My contribution this year was an attempt to bring the science behind cappuccino coffee swirls to coastal sediment transport.

Postdoc Job Opportunity

What is the fate of nourished sand? What are the pathways of sediment on an ebb-tidal delta or in a tidal basin? What role does sediment play in the UNESCO-world heritage area of the Wadden Sea? We are looking for a curious and motivated postdoc to work with us on an exciting project here at TU Delft in the Netherlands. The main goal of this position is to develop and test novel simulation approaches to trace pathways of different sediment types, and to predict sediment dispersal and morphodynamic responses to different nourishment strategies.

More information about the topic and the application process can be found here: https://www.tudelft.nl/over-tu-delft/werken-bij-tu-delft/vacatures/details/?nPostingId=3875&nPostingTargetId=10801&id=QEZFK026203F3VBQBLO6G68W9&LG=UK&mask=external

I also worked on this project as a postdoc until recently starting a new position, and I really enjoyed both the topic and teammates. Now you have the opportunity to join our team and continue developing this research! A summary of previous work on the project can be found here:
https://coastallycurious.com/2022/12/15/tracking-sand-that-hides-from-the-sun/

Come join our TRAILS team! Feel free to get in touch with us if you have any questions. Applications close March 12th, 2023!

Stuart Pearson (S.G.Pearson@tudelft.nl)
Bram van Prooijen (B.C.vanProoijen@TUDelft.nl)

Of Sediment and Seedlings

Mangrove forests protect tropical coastlines around the world from the effects of waves, in addition to providing valuable habitat for countless species. As such, their preservation and restoration is a key element of many plans for improving coastal resilience against flooding and erosion in the face of climate change. However, you can’t *just plant* a mangrove forest anywhere – mangroves are extremely picky, dancing on the edge of the intertidal zone where they get just wet enough but never too wet for too long. They also need safe, stable shorelines for their seedlings to take root and grow stronger, without too many waves and with just the right sort of muddy conditions to make a comfortable home.

Mangroves drop their seeds (called propagules) in the water, which then float around with the currents for days to weeks until they find a suitable home. But which pathways do these mangrove seedlings take as they float along the coast? Are those the same pathways that sand and mud take? These are questions that we need to answer in order to make better decisions about mangrove restoration. To get to the bottom of this, we recruited Femke Bisschop.

Last Friday, Femke successfully defended her thesis, “Modelling sediment and propagule pathways to improve mangrove rehabilitation: A case study of the pilot project in Demak, Indonesia“. She developed a numerical model of a site in Indonesia to simulate the motion of rivers and tides there, and then used the SedTRAILS model to visualize and interpret the pathways of sediment and mangrove propagules.

Tracking Sand that Hides from the Sun

Keeping Dutch feet dry is mainly done by placing piles of sand along the coast as “nourishments”. These nourishments build out the beaches and dunes to act as a protective buffer against storms. However, as was recently pointed out by an official at Rijkswaterstaat, the Dutch water ministry, the Hamvraag or “bacon question” is still “where the heck does all that sand actually go?”

Knowing where nourished sand goes is important for understanding the ecological impact of nourishments, as well as their effectiveness. If you want your sand to reach a certain destination, how much of it actually gets there and how quickly?

Sediment Pathways on Ebb-Tidal Deltas

After 5 years of blood, sweat, and tears, I present to you my PhD thesis: Sediment Pathways on Ebb-Tidal Deltas: New Tools and Techniques for Analysis! I will defend my PhD on March 8th.

How do sand and mud move around on our coasts? This is a question that we need to answer in order to sustainably manage coastlines in the face of sea level rise and climate change. To do so, we use a combination of field measurements and computer simulations at Ameland Inlet in the Netherlands. In the course of my PhD we developed several new methods, including morphodynamic mapping techniques, a sediment composition index (SCI) derived from optical and acoustic measurements, techniques for sediment tracing, the sediment connectivity framework, and a Lagrangian sediment transport model (SedTRAILS). Together, these approaches reveal new knowledge about our coasts which can be used for managing these complex natural systems.

That’s a bit of a mouthful, so let’s break it down and try to explain what I have been doing with sand for the last half-decade…

Keeping it Connected Around the World

It has been a crazy year, but work-wise I am on the final stretch, at least. Tonight at the ungodly hour of 12am CET, I will present my poster at the American Geophysical Union conference. It is at a much more reasonable 3pm PST in California where the conference organizers are located. If you have registered for the conference, you can see the poster via this link. Otherwise, I will try to put you in the loop here.

Estuaries are complex environments shaped by the interaction of waves, tides, rivers, and humans. Understanding how sand and mud move through estuaries is essential for their effective management. In an approach known as connectivity, the pathways taken by sand and mud through estuaries can be represented as a connected network of nodes and links, similarly to a subway map. Connectivity provides numerous mathematical techniques and metrics that are well-suited to describing and comparing these pathways in estuaries.

Network diagrams depict the sediment transport pathways of each estuary as a series of nodes and connecting links. The Mouth of the Columbia River (1) and San Francisco Bay (2) are on the west coast of the United States, while Ameland Inlet (3) and the Western Scheldt (4) are in the Netherlands. Red arrows indicate the 90th percentile of all connections in terms of sediment fluxes, superimposed on greyscale bathymetry of each estuary.

We use connectivity to map out and analyze sand and mud pathways in four estuaries around the world: the Wadden Sea (the Netherlands), Western Scheldt (NL), San Francisco Bay (US), and Columbia River (US). Our analysis is based on the outcome of numerical simulations, and we explore the benefits of different simulation techniques. We conclude that connectivity is a useful approach for visualizing and comparing the pathways that sand and mud takes through different estuaries. We can use this method to plan and predict the impact of human interventions in these environments, such as dredging.

However, a comparison of connectivity metrics suggests a dependency not just on sediment transport processes, but also on the choices made in schematizing networks from underlying models. Essentially, we’re not comparing apples to apples yet, so if we are going to make comparisons between different estuaries, we need to make sure that we set up our models in an equivalent way. Our ongoing research will focus on optimizing these numerical models to make more meaningful quantitative comparisons of different estuaries.