Biological activity in shallow tidal environments significantly influence sediment dynamics and morphology. Here, a bio-morphodynamic model is developed that accounts for hydro-climate variations in biofilm development to estimate the effect of biostabilisation on the bed. Results reveal that key parameters such as growth rate and temperature strongly influence the development of biofilm under a range of disturbance periodicities and intensities, shaping the channel equilibrium profile.

Climate change is causing mountain lakes behind glacier barriers to drain through ice tunnels as catastrophe floods, threatening people and infrastructure downstream. Understanding of how process works can mitigate the impacts by providing advanced warnings. A laboratory study of ice tunnel development improved understanding of how floods evolve. The principles of ice tunnel development were defined numerically and can be used to better model natural floods leading to improved prediction.

Floodplain formation in estuaries limit the ebb and flood flow, reducing channel migration and shortening the tidally influenced reach. Vegetation establishment on bars reduces local flow velocity and concentrates flow into channels, while mudflats fill accommodation space and reduce channel migration. These results are based on experimental estuaries in the Metronome facility supported by numerical flow modelling.

Unsustainable sand mining poses a threat to the stability of river channels. We use satellite imagery to estimate volumes of material removed from the Mekong River, Cambodia, over the period 2016–2020. We demonstrate that current rates of extraction now exceed previous estimates for the entire Mekong Basin and significantly exceed the volume of sand naturally transported by the river. Our work highlights the importance of satellite imagery in monitoring sand mining activity over large areas.

Numerical models can be used to understand how coastal systems evolve over time, including likely responses to climate change. However, many existing models are aimed at simulating 10- to 100-year time periods do not represent a vertical dimension and are thus unable to include the effect of sea-level rise. The Coastline Evolution Model 2D (CEM2D) presented in this paper is an advance in this field, with the inclusion of the vertical coastal profile against which the water level can be altered.

Increased salt intrusion jeopardizes freshwater supply to the Mekong Delta, and the current trends are often inaccurately associated with sea level rise. Using observations and models, we show that salinity is highly sensitive to ocean surge, tides, water demand, and upstream discharge. We show that anthropogenic riverbed incision has significantly amplified salt intrusion, exemplifying the importance of preserving sediment budget and riverbed levels to protect deltas against salt intrusion.

Accurate and continuous data collection is challenging in physical scale experiments. A novel means to augment measurements is to numerically model flow over the experimental digital elevation maps. We tested this modelling approach for one tidal and two river scale experiments and showed that modelled water depth and flow velocity closely resemble the measurements. The implication is that conducting experiments requires fewer measurements and results in flow data of better overall quality.

We investigated the effect of tides on the morphodynamic evolution of bifurcations in tide-influenced deltas. Using results from a numerical morphodynamic model (Delft3D), we found that tides cause less asymmetric bifurcations and thereby keep both downstream channels open. Our results explain why avulsion rarely occurs in tide-influenced deltas, whereas it occurs more often in river-dominated deltas.

Climate adaptation of deltas is a hot topic given their high population density in many countries. We quantified trade-offs between hydraulics, potential biodiversity, implementation costs, and the number of land owners involved, using a newly developed tool called RiverScape. With our approach, we move towards finding integrated solutions at the scale of a large river in a delta to support the negotiations among stakeholders in the decision-making process.

The challenge to measure three-dimensional bank irregularities in a mid-sized river reach can be quickly solved in the field flying a drone with ground-control points and later applying structure from motion photogrammetry. We tested a simple approach that achieved sufficient resolution and accuracy to identify the full bank erosion cycle, including undermining. This is an easy-to-use and quickly deployed survey alternative to measure bank erosion processes along extended distances.

In estuaries, mud sedimentation enhances salt marsh accretion. Here we explore system-scale effects of plants and mud on planform shape and size of estuaries. We coupled Delft3D for hydromorphodynamics with our vegetation model and ran controls for comparison. Effects are greatest at the fluvial–tidal transition, where for the first time in a model, a bedload convergence zone formed. Regardless of local vegetation effects, mud and vegetation cause gradual filling of estuaries over time.

This paper reports the along-channel variability in occurring bed levels as described by hypsometry in natural estuaries. We found a novel relation between the estuary planform shape and the hypsometric function shape, which implies that it is possible to characterise and predict subwater estuarine morphology and bed levels in data-poor environments.

In this study we show how the Overijsselse Vecht river changed from a laterally stable to a meandering river ca. 500 years ago. We developed a methodology to reconstruct the historical discharge and found that the change in river style was caused by an increase in peak discharges. This increase was likely caused by the Little Ice Age and land use changes in the catchment (peat reclamation and exploitation). This study shows how river style changes as a result of discharge regime changes.

Sticky sediments are an important component of many rivers and coasts. Stickiness depends on many factors including the presence of micro-organisms, also known as biofilms. We performed a laboratory study to better understand the role of biofilms in controlling sediment transport and dynamics. We find that sand with biofilms requires significantly higher flow velocities to be mobilised compared to uncolonised sand. This will help improve predictions of sediment in response to currents and waves.

A 20-year data record from the Bayelva site at Ny-Ålesund, Svalbard, is presented on meteorology, energy balance components, surface and subsurface observations. This paper presents the data set, instrumentation, calibration, processing and data quality control. The data show that mean annual, summer and winter soil temperature data from shallow to deeper depths have been warming over the period of record, indicating the degradation and loss of permafrost at this site.

Creating estuaries in the laboratory has been challenging. When the ebb and flood currents are driven by ebb and flood in the sea, they are too weak to move sand. Here we describe how the periodic tilting of an entire experimental set-up leads to ebb and flood currents with similar behaviour as in nature and with enough strength to move sand. This means that this novel set-up now allows for the creation of estuarine landscapes in experiments.

Mud raises concern in the short-term management of estuaries, but it is not known whether cohesive mud affects the long-term development of estuaries. We discovered that a small supply of mud from the river confines the estuary by forming stable mudflats on the sides in centuries, whereas estuaries with only sand continue to grow. Mudflats also reduce the shifting of channels and bars. This implies that changes in mud supply in estuaries may have led to changes in shape and dynamics in the past.

We studied the propagation of natural and human-induced perturbations in large braided sand-bed rivers using a physics-based 3-D model. The results show that the perturbations not only affect the local morphology but their effects amplify while propagating through the braided network. This occurs by destabilization of bifurcations in combination with reshaping of bars and branches. These results could have a major impact on the assessment of engineering measures in large braided sand-bed rivers.