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Oceans 2025 Theme 3, Work Package 3.3: Bottom Boundary Layer, Optics and Suspended Sediments Processes

This Work Package (WP) is a combination of Work Package 3.3 and 3.4 as proposed in the original Oceans 2025 proposal. It continues and expands the research undertaken in the Proudman Oceanographic Laboratory Dee Experiment project.

Sediment transport process models underpin scientific ability to predict the entrainment of sediments into the water column and the transport of sediments for forecasting seabed and coastal morphodynamic evolution. The difficulty in achieving accurate process models lies with the complex inter-dependence of sediment processes in the bottom boundary layer. Near the bed, the fundamentals of sediment transport are governed by interactions between the sediment transport triad; the bed, the hydrodynamics and the mobile sediments. These three components interrelate, being mutually interactive and interdependent.

POL aim to use a combination of high-frequency underwater acoustics and laser optical measurements to make co-located simultaneous measurements of the triad. These measurements provide an observational framework capable of assessing and advancing the latest sediment transport models available. These measurements will be made in a range of environments, with the objective of achieving significant advances in understanding and modelling capability in coastal sediment transport. POL will also address the dynamics of suspended sediment behaviour in the context of sediment supply to the coastal zone from estuaries, and of coastal water column optical properties. Ths will allow improvement of the modelling accuracy of coastal suspended sediment transport and enable development of a new description of sediment suspension and water opacity that will improve simulation of coastal primary productivity.

The specific objectives are:

  • Assess process-based models over different sediment types, cohesive to non-cohesive
  • Investigate intra-wave and turbulence processes over flat and rippled beds to improve process based sediment transport models; parameterisation of the process modelling output for input into large-scale area models
  • Advance the description and parameterisation of the impact benthic biota has on sediment transport processes (jointly with the Plymouth Marine Laboratory (PML))
  • Acquire new knowledge of the dynamics of sediment flocculation and its impact on suspended particulate material (SPM) in shelf seas and estuaries
  • Provide preliminary formulations for aggregation-disaggregation and test these formulations using shelf sea models of the Eastern Irish Sea
  • Develop understanding of the processes that affect the sediment fluxes between estuaries and the adjacent shelf sea.
  • Derive and apply formulations of the effects of SPM on optical attenuation and absorption and assess their potential impact on primary productivity using existing models


The study site chosen by POL for this research was the Dee Estuary, Liverpool Bay. POL performed fieldwork in the Hilbre Channel on the eastern side of the Estuary and the Welsh Channel on the western exit of the Estuary, with emphasis placed on two repeat stations, HC and WC . The fieldwork under Work Package 3.3 commenced in April 2007 and has been summarised below:

Cruise Dates Hilbre Channel Welsh Channel
PD06_07 2007-04-16 to 2007-04-19 18 hour CTD station
Mooring recovery
15 hour CTD station
Mooring recovery
PD04_08 2008-02-12 to 2008-02-15 25 hour CTD station
2 x mooring deployment
19 hour CTD station
1 x mooring deployment
PD02_09A 2009-02-02 to 2009-02-04 25 hour CTD station
1 x mooring deployment
22 hour CTD station
1 mooring deployment
PD06_09 2009-03-03 to 2009-03-05 25 hour CTD station
Mooring recovery
18 hour CTD station
Mooring recovery

More detailed information on this Work Package is available at pages 8 - 9 and 9-10 of the official Oceans 2025 Theme 3 document: Oceans 2025 Theme 3