Coastal morphodynamics and bathymetric evolution

Oceans 2025 Theme 3, work package 3.5

Much of the work at POL is aimed at development and improvement of ocean models, primarily focussing on the hydrodynamics. In recent years we have started applying these models to coastal regions and we have focussed on dealing with the extra problems that this introduces.

At the same time we have a strong track record in measuring small scale sediment transport processes, and are looking towards using this knowledge to improve the prediction of sediment movement within the models. However, between these large scale models and the small scale process studies, there lies the intermediate scale of beaches, sand banks and estuaries.

The evolution of such features is the result of small scale sediment transport processes, but is far more obvious to the casual observer and consequently of direct relevance to a great many people.

Our ability to study coastal features has advanced considerably in recent years with the development of remote sensing techniques such as airborne Laser surveying (LIDAR) and ground based radar systems.

These measurement techniques are allowing subtle (and not so subtle) changes in beaches, sandbanks and channels to be measured regularly, remotely and safely. Progress in this work package will be underpinned by several ongoing field studies:

The Hilbre Island Observatory - A marine X-band radar was installed on Hilbre Island in 2004 and started continuous recording in early 2006. This records 10 minute sequences of radar images of the sea surface every hour. Wave patterns can be seen within these image sequences which allow us to map the underlying water depth, hence allowing bathymetric evolution to be monitored. In addition, LIDAR flights have been performed at 1-2 year intervals since 2003, allowing changes to be identified over the entire Dee Estuary.

The results of an MSc project investigating the migration of intertidal sand dunes on West Kirby sand flats are expected soon, based on radar derived dune locations.

LEACOAST2 - Study of shore parallel breakwaters in East Anglia. – This collaborative project is studying the hydrodynamics and sediment transport around a series of shore parallel breakwaters using a variety of methods. One of POL’s contributions is a radar overlooking the study area. The data from this deployment have already led to the identification of a (previously unobserved) migrating field of offshore sand waves which could be a significant sand transport pathway. It is also hoped that detailed bathymetric inversions (mapping) of the embayments will show the beach response to storm events on an hourly basis – something previously impossible to achieve.

Other Data - The project also has access to the data from a number of prior radar deployments in a variety of locations.

Figures: The figures show a radar derived bathymetric map of a 4km radius area around Hilbre island based on three radar records taken around high water on the 6th October 2006. The other figure shows the combined 2003 LIDAR, multibeam sonar and chart derived survey of the same area as currently used by our modelling group. The two plots can be seen to agree reasonably well, especially in the southern half of the images where the area where the survey data are most reliable.

Figure 1

Figure 2