Caught in the Drift: Laying a Submarine Cable in a Moving Sand Bank

A new submarine cable is to be installed, routed to the north of the mobile sandbank Long Sand in the Thames Estuary, UK. Cables can be anthropogenically threatened when uncovered as a result of seabed mobility.

Analysis of the seabed change was performed to confirm and forecast the migration dynamics of Long Sand Head (LSH, the northeastern face of Long Sand) with respect to the cable route. 3D bathymetric difference and boundary change analyses were conducted to determine the historical seabed changes during a 15 year survey period. In addition, based on the bathymetric contours of LSH, the movement of the morphology was forecasted in relation to the cable route.

The migration pattern of LSH’s boundary showed an average displacement rate of 20 m/yr towards the cable. Changes in depths over 15 years showed that an increase in sediment accumulation caused shoaling by more than 5 m. The sediment thickness was predicted to increase at the cable route with a 50% probability by 10 m by the year 2037.

The method reported here represents a novel approach to estimating sandbank mobility over a timescale of years to decades allowing a more cost-effective burial depth for submarine cables.