Periodic Reporting for period 2 - DUNAMICS (Analysis and prediction of submarine dune dynamics)
Periodo di rendicontazione: 2024-04-01 al 2025-03-31
Sand dunes pose a significant risk for offshore activities in coastal areas and for navigation along the most frequented maritime routes. The presence of sand dunes leads to a significant increase of the flow resistance, which needs to be carefully described for predicting flow velocities and water levels in forecast models. Understanding dune evolution is therefore an important issue to predict the flow circulation, sediment fluxes and bathymetric variations in sandy subaqueous environments. Nevertheless, their evolution is still poorly understood due to their complex behavior. The Marie Curie GF-DUNAMICS solved fundamental issues in our comprehension of submarine dunes and improved their predictability. First, dune equilibrium mechanisms were analyzed by integrating flume measurements and numerical modeling techniques. Then, an investigation of deep-water dune dynamics in the Queen Charlotte Sounds of New Zealand was performed. Finally, an operational model was improved to simulate dune evolution.
The work carried out during the project allowed the following objectives to be achieved : to study experimentally and theoretically the equilibrium conditions of dunes; to study large submarine dunes through numerical modeling; and to improve a numerical model. The work also went beyond the objectives by investigating machine-learning algorithms to successfully predict dune dimensions at equilibrium.
The work carried out during the project allowed the following objectives to be achieved : to study experimentally and theoretically the equilibrium conditions of dunes; to study large submarine dunes through numerical modeling; and to improve a numerical model. The work also went beyond the objectives by investigating machine-learning algorithms to successfully predict dune dimensions at equilibrium.
During the duration of the project, the conducted research aimed at understanding dune stability mechanisms, dune equilibrium prediction, an investigation of in-situ deep water dune dynamics in the Queen Charlotte Sounds in New Zealand along with improving a numerical model. The tasks that were carried out during the Marie Curie GF-DUNAMICS project were as follows : 1) Setup and preparation of the flume experimentations (sieve analysis, flume calibration, instrumentation, testing), 2) PIV experimentation for five scenarios : observation of dune growth, equilibrium, acquisition of series of images at high frequency & resolution with the PIV camera, 3) Numerical modelling study with DUNE2D of dune saturation for seven configurations and explanation of dune saturation mechanisms, 4) Machine learning study using genetic programming and derivation of prediction equations for dune dimensions at equilibrium, 5) Environmental data analysis for the deep water dune fields in the Queen Charlotte Sounds, 6) Implementation of the tidal numerical model and simulations across several tidal cycles for analysis of in situ dune migration and saturation, 7)Testing the MIKE numerical model and implementing morphological solvers.
A detailed analysis of the physical mechanisms setting the position of the maximum of the bed shear stress over the dune profile was carried out. The findings gave a deeper insight into mechanisms controlling finite amplitude dune saturation for several flow conditions. It showed that four modes of dune saturation existed depending on the rescaled mean grain diameter, gravity, and the sediment flux inertia length. These findings were published in the journal Earth Surface Processes and Landforms (Doré and Coco, 2025). Machine Learning, particularly genetic programming, was utilized to develop highly accurate dune predictors that outperform current models (Doré and Coco, 2025b).
The flume study spanned over several months enabling the collection of valuable data essential for future analysis. A comprehensive sediment grain size analysis was conducted that served as the basis for the implementation of various experimental scenarios designed to replicate the formation of hydraulic dunes. However, the laboratory did not have a powerful enough LED system. An original methodology was therefore implemented using a powerful LED projector and lens system to focus beams for data acquisition on dune evolution. Five scenarios were successfully captured following the methodology.
The study of tidal sand dunes in the Queen Charlotte Sounds included the numerical modeling of representative dune profiles. The results showed a high frequency oscillation of dune crests during tides. For the first time, the results revealed the mechanisms of saturation of submarine dunes during tidal cycles. The analysis was carried out based on the previous findings that served to interpret the results. An article has been authored and is currently undergoing peer review at Marine Geology journal (Doré, Mac Donald and Coco, 2025).
The MIKE numerical model has undergone extensive testing, revealing that the existing morphological scheme struggles to accurately predict dune profiles, particularly at the crests where significant flux divergences occur. To address this issue, two new numerical schemes have been implemented within MIKE, designed to enhance stability and accuracy.
Doré A ., G. Coco, 2025. Numerical modelling investigation of finite amplitude subaqueous dune saturation, Earth Surface and Planetary Landforms , doi : 10.1002/esp.70046
Doré A ., G. Coco, 2025b. A hybrid, genetic programming and physically-based predictor of dune geometry, Geomorphology , doi : 10.1016/j.geomorph.2024.109495
Doré, A., MacDonald, H., Coco, G., 2025. Morphodynamics of Eddy-Driven Submarine Dunes in the Queen Charlotte Sound/Totaranui, New Zealand, Marine Geology, Under review.
A detailed analysis of the physical mechanisms setting the position of the maximum of the bed shear stress over the dune profile was carried out. The findings gave a deeper insight into mechanisms controlling finite amplitude dune saturation for several flow conditions. It showed that four modes of dune saturation existed depending on the rescaled mean grain diameter, gravity, and the sediment flux inertia length. These findings were published in the journal Earth Surface Processes and Landforms (Doré and Coco, 2025). Machine Learning, particularly genetic programming, was utilized to develop highly accurate dune predictors that outperform current models (Doré and Coco, 2025b).
The flume study spanned over several months enabling the collection of valuable data essential for future analysis. A comprehensive sediment grain size analysis was conducted that served as the basis for the implementation of various experimental scenarios designed to replicate the formation of hydraulic dunes. However, the laboratory did not have a powerful enough LED system. An original methodology was therefore implemented using a powerful LED projector and lens system to focus beams for data acquisition on dune evolution. Five scenarios were successfully captured following the methodology.
The study of tidal sand dunes in the Queen Charlotte Sounds included the numerical modeling of representative dune profiles. The results showed a high frequency oscillation of dune crests during tides. For the first time, the results revealed the mechanisms of saturation of submarine dunes during tidal cycles. The analysis was carried out based on the previous findings that served to interpret the results. An article has been authored and is currently undergoing peer review at Marine Geology journal (Doré, Mac Donald and Coco, 2025).
The MIKE numerical model has undergone extensive testing, revealing that the existing morphological scheme struggles to accurately predict dune profiles, particularly at the crests where significant flux divergences occur. To address this issue, two new numerical schemes have been implemented within MIKE, designed to enhance stability and accuracy.
Doré A ., G. Coco, 2025. Numerical modelling investigation of finite amplitude subaqueous dune saturation, Earth Surface and Planetary Landforms , doi : 10.1002/esp.70046
Doré A ., G. Coco, 2025b. A hybrid, genetic programming and physically-based predictor of dune geometry, Geomorphology , doi : 10.1016/j.geomorph.2024.109495
Doré, A., MacDonald, H., Coco, G., 2025. Morphodynamics of Eddy-Driven Submarine Dunes in the Queen Charlotte Sound/Totaranui, New Zealand, Marine Geology, Under review.
During the study on dune saturation, it appeared that deriving prediction equations was more suitable by using machine learning. Based on a published database that reports most laboratory experiments known to date, a genetic program (GP) was implemented that generates dune prediction equations. An analytical approach was further applied to develop two novel 'hybrid' predictors. These hybrid predictors provide robust approaches for predicting sand dune characteristics, and outperform classic estimators. It is anticipated that the model will be widely utilized by engineers and scientists, to accurately forecast dune dimensions for both operational and research applications.
The study of dune saturation revealed for the first time how subaqueous dunes stabilize with the flow. The findings give a deeper insight into mechanisms controlling dune saturation and reveal four possible modes of saturation depending on four dimensionless numbers. This work opens new perspectives for deriving dune stability diagrams, and for numerical models in achieving a good description of the phenomenology controlling dune stabilization.
Detailed in-situ simulations of dunes fields in the Queen Charlotte Sounds revealed how dune shapes could be explained based on local environmental parameters, opening new perspectives for the interpretation of bedforms in deep water. The analysis of flow and sediment transport fields above dune profiles showed how dunes oscillate at a high frequency during tidal phases while steadily migrating towards a preferred direction. Results offered deeper insights into the complex dynamics of in situ dunes and circumscribed important physical processes that need to be described in an operational model.
The ability of the numerical model MIKE3, developed at DHI, has been tested to reproduce dune evolution. Based on previous findings, MIKE3 was adapted by updating the numerical scheme, to retrieve bedform shapes and migration rates. The potential is huge in terms of applicability of such a model in coastal areas for navigation, for the marine industry and offshore renewable energies.
The study of dune saturation revealed for the first time how subaqueous dunes stabilize with the flow. The findings give a deeper insight into mechanisms controlling dune saturation and reveal four possible modes of saturation depending on four dimensionless numbers. This work opens new perspectives for deriving dune stability diagrams, and for numerical models in achieving a good description of the phenomenology controlling dune stabilization.
Detailed in-situ simulations of dunes fields in the Queen Charlotte Sounds revealed how dune shapes could be explained based on local environmental parameters, opening new perspectives for the interpretation of bedforms in deep water. The analysis of flow and sediment transport fields above dune profiles showed how dunes oscillate at a high frequency during tidal phases while steadily migrating towards a preferred direction. Results offered deeper insights into the complex dynamics of in situ dunes and circumscribed important physical processes that need to be described in an operational model.
The ability of the numerical model MIKE3, developed at DHI, has been tested to reproduce dune evolution. Based on previous findings, MIKE3 was adapted by updating the numerical scheme, to retrieve bedform shapes and migration rates. The potential is huge in terms of applicability of such a model in coastal areas for navigation, for the marine industry and offshore renewable energies.