Acoustic characterisation of the seabottom in the Southern shelf of İstanbul (Avcılar–Büyükçekmece)

In this thesis, which focuses on determining the seabed acoustic characteristics between the Avcılar-Büyükçekmece in the southern shelf of İstanbul, the seafloor sediment types and their distributions are defined by the reflection characters by using various acoustic based marine geophysical data. In addition, the seabed morphology of the study area was also presented by means of acoustic data sets. Although the sediment distribution are quite complex in general, the current condition and dominant waves in the region, the amount of material transported from the land in the control the hydrodynamic forces and the depth of the seabed are main factors. The sea floor has affected by highly human sourced damage like; anchor deformation and associated seabed deformations; disturbing traces of trawl fishing net at the bottom, structures built on nearby shore and sea floor (such as natural gas pipelines, fishing shelters and piles of harbors) and related dune accumulations that cause shallowing . Acoustic reflections related as evidences of a possible old harbor and some wrecks were determined in the Side Scan Sonar data. 60 m-70 m length long blocks situated at average water depth of 7-10 m. Although these blocks are oriented towards east and west, their settled structure is well preserved. However, shorter blocks are observed to spread out of the normal trend. It is possible that fishing nets are stuck on and caused displacement, or the effect of big earthquake that causes mass movement. The sand bar, which is an east-west oriented, morphological structure starting from the immediate vicinity of the blocks, probably that the material transported by the system starts to settle and formed sandbar parallel to the structure because of the historical port structures cause decreasing on the current system velocity and therefore lose their energy in these areas.