Estuaries and tidal basins form the transition zones between land and sea. They contain important habitats for flora and fauna and are extensively used by people, like for navigation. For ecological and navigational purposes, it is important to understand and predict the evolution of channels and shoals, including sedimentation rates and the composition of the bed sediments. The bed material of large estuaries and tidal basins largely consists of mixtures of mud and sand, with predominantly sandy channels and mainly muddy intertidal areas. The interaction between sand and mud, in combination with currents and waves, leads to complex dynamics in these areas, with migrating channels and shoals
Much is known about the behaviour of the individual sediment fractions, but the knowledge and understanding of sand-mud interaction remains limited, as do the available tools and models to accurately predict the bed evolution and sediment transport rates in sand-mud areas. Existing models, like the ones by Van Ledden (2003), Soulsby & Clarke (2005) or Van Rijn (2007) have only limitedly been verified with observations due to a lack of good quality observational data. Also, none of the available approaches cover the complete spectrum of sand-mud interaction, which includes settling, erosion processes, and bed shear stresses due to waves and currents. Therefore, in practice, sand- and mud fractions are often treated separately. This decoupled approach limits the predictive capacity of numerical models, and therefore the understanding of impact of human intervention such as deepening of channels and port construction on maintenance dredging volumes and other morphological changes.
In the MUSA-research project, a consortium* of contractors, consultants and research organizations join forces to increase the understanding of the dynamics of sand-mud mixtures through flume tests and field measurements. The developed knowledge, insights and data will be incorporated in engineering tools and in numerical modelling software. The four-year project (2020-2023) consists of the following activities:
▪ Literature analysis
▪ Laboratory experiments
▪ Field measurements
▪ Development and improvement of formulations on sand-mud dynamics
▪ Development of engineering tools
▪ Implementation of formulations in numerical software
The project started in May 2020 and will end at the end of 2023. In the current stage of the project (Summer 2022), multiple activities are going on: the laboratory experiments are being processed and reported by WaterProof and HR Wallingford, field experiments are carried out in de Wadden Sea and the first analyses by Leo van Rijn and Deltares are starting up.
* the TKI-MUSA consortium consists of WaterProof, Leo van Rijn Sediment Consultancy (LVRS), Jan de Nul, DEME, Boskalis, HR Wallingford, DHI, Royal HaskoningDHV, Arcadis and Deltares.
