Researcher develops method to predict movement of marine sand waves.

28 August 2009 

The seabed consists of sand waves, that is underwater dunes that can move at speeds of up to 100 meters per year. To ensure that ships do not become trapped in sand waves, the Royal Navy constantly observes the location of sand waves on the North Sea seabed and then updates charts accordingly.

Navy thankful for less expensive measurement method.

The seabed consists of sand waves, that is underwater dunes that can move at speeds of up to 100 meters per year. To ensure that ships do not become trapped in sand waves, the Royal Navy constantly observes the location of sand waves on the North Sea seabed and then updates charts accordingly. Leendert Dorst has now developed a way to interpret and predict the movement of sand waves. With these predictions, less measurements of the seabed are required, which drastically reduces the costs involved. Dorst's PhD graduation ceremony is on Friday, September 4 at the Faculty of Technical Sciences at the University of Twente.

Two Royal Navy ships almost constantly sail over the North Sea and with sonar equipment they map the seabed. They track, among other things, the sand waves, which can be up to five meters high. From these constant measurements the ships create reliable charts of the North Sea Dutch Continental Shelf.

It is not possible to create a permanently lasting chart because parts of sand waves gradually move. This movement occurs at a maximum speed of 100 meters per year and is affected by the ocean's depth, the seabed itself, the amount of shipping, and other human intervention like mining. Each area is surveyed anything from once a year to once every fifteen years by two Naval ships.

Leendert Dorst has developed a new method to predict the movement of sand waves. It is based on a statistical model that compares different depth measurements of the same place at different times. From this information, an estimate can be made about the direction and speed of the sand waves' movement. It is essential that a series of measurements of the seabed over time are available.

When using this model, less of the expensive seabed measurements are needed. In some areas, the frequency of measurements required has already halved. However it will be sometime before this method can be applied to the complete Dutch Continental Shelf, because in areas where fewer measurements were required, there is currently insufficient data.

Note for the press

Leendert Dorst completed his doctoral research within the Department of Water Management (WEM) at the University of Twente, and was supervised by Professor Suzanne Hulscher (UT) and Captain Floor de Haan (Chief of the Royal Navy Hydrographic Service). During his doctoral research Dorst worked as Head of Geodesy and Tides in the Hydrographic Service of the Royal Navy. The thesis "Estimating sea floor dynamics in the Southern North Sea bathymetric survey to improve planning" is available digitally on request. Press Contact: Joost Bruysters (053 489 2773).