Project Investigators
- Dr Jaco Baas
- Dr Michael Roberts
- Dr Katrien Van Landeghem
- Mr. Connor McCarron
The impact of seabed dredging
Collaborations with National Oceanography Centre, Liverpool and Llanelli Sand Dredging Ltd.
When analysing shelf seabed morphological behaviour, it is largely ignored that this seabed commonly consists of sand and gravel mixtures - often palaeo-glacial deposits. Advances in predicting sediment transport in such mixtures focus on rivers, despite the fact that the following cannot be explained using conventional bedload transport predictors:
- variations in net offshore bedload transport directions
- many unusual bedforms on our mixed seabeds
Bedload transport needs quantifying when assessing the sustainability of e.g.
- aggregate extraction via seabed recovery rates
- emplacement of offshore turbines, platforms, pipes and cables.
- coastal erosion
- benthic habitat potential.
- turbulence variation (through changing bed roughness) and thus changing fluxes of particles and dissolved matter (e.g. sediments, nutrients, carbon, pollutants),
- palaeo-environmental reconstruction of shelf sea sequences in geological outcrops
- high-resolution glacio-isostatic modelling, hence local relative sea level changes.
Sand and gravel in a mixture leaves larger grains "exposed" and smaller grains "hidden", changing the efficiency of the flow to mobilise different grain size fractions ("hiding-exposure" effect). As the flow entrains sediments and redistributes them, the mixture changes, as will the "hiding-exposure" effect, depending on flow asymmetry and strength. This leads to varying depths of the "active layer", from fully armoured to fully mobile. These changes are known to significantly affect bedload transport and morphodynamics, but at present remain to be quantified in shelf sea environments. We thus focus on
- Analyses of seafloor evolution at various sites
- Experimentally parameterising changes in bedload transport for various mixtures of sands and gravels
- Modify existing bedload transport formulae to reflect complexity in mixed beds and test model outputs with offshore data.