Volume of disposed sediments in the deep water confined disposal facility at Malmøykalven, inner Oslofjord

Abstract

Acoustic methods including GeoSwath 250 kHz interferometric sonar and TOPAS parametric sub-bottom profiler have been used to determine the volume of dredged sediments disposed in the natural submarine depression at Malmøykalven in the inner Oslofjord since the beginning of the Oslo harbor remediation project in 2006. This natural depression that has a threshold at 66 m towards the north-east, and which had a maximum water depth of 72 m before the start of the remediation project, is used as a deep water confined disposal facility (CDF). Calculation of the volume of disposed sediments in the CDF is based on elevation change, derived from two high-resolution bathymetric datasets obtained in 2004, i.e. before the onset of the remediation project, and on April 1-7, 2008. Seismic profiles through the CDF have been used to estimate the settling of the original seabed, caused by loading-induced dewatering and compaction of the seabed sediments below the disposed masses.