Mapping of seabed and bathymetry in Alssund, Sønderborg. Seismic and acoustic mapping for The Green Water Research Project

The Green Water Research Project (GWRP) has asked GEUS to perform a combined geological and bathymetrical survey using high-resolution and high-accuracy multibeam bathymetry, side scan sonar and sub-bottom profiler data in Alssund in Sønderborg. The combination of information on the seabed sediment types and thickness and a detailed bathymetry has shown that at suitable locations for siting the prototype of heat exchange installation are available. There are extensive areas where the water depth exceeds 18 m with sandy or gravelly sediments present. However, the seismic data shows evidences of the presence of gas in large areas of the sub-surface, indicating the presence of fine grained, muddy sediments.

A basin adjacent to the SDU Sønderborg campus seems to be one of the most suitable locations, with water depths reaching 23.6 m and sandy sediments appearing. Steep gradients encountered on the channel margin and the risk of slope failure during or after pipeline installation could be a concern here. An alternative potential area for the project an infilled channel has been designated in Alssund west of Odden.

It is strongly recommended to perform a sediment sampling programme to verify the seismic and acoustic
interpretations.