Improving Maritime Operations Through High-Resolution Bathymetric and Geophysical Survey of Cawthrone Channel

Abstract

Bathymetric survey is very important for every marine based operation, from navigation to pipe lay and cable lay operation to dredging and every other engineering endeavour within the maritime space. The demand for geophysical information is equally high as decision makers and stake holders in the maritime sector depend highly on this for project planning and implementation. Hence, the lack of these information presents a fundamental problem in policy making and administration within the maritime environment. The aim of the study to conduct a high resolution bathymetric and geophysical survey of a section of Cawthorne Channel 2 to enhance navigation and other maritime based operations. The objectives were to: ascertain the tidal range of Cawthrone Channel; determine the depth variation within Cawthrone Channel and to carry out a sub-bottom profiling of Cawthrone Channel. The data acquired for the purposes of this study included position and depth information across the study area using the C-Nav 3050 GNSS receiver and South SDE-28 echo sounder. Sound velocity information within the immediate vicinity of the study area was collected using the Veleport CTD probe. Seabed imagery, Sub-bottom profiles and magnetic anomaly across the study area was also acquired using the Tri-tech Starfish Seabed Imaging system, Edge Tech SB-216s Sub-Bottom Profiler and Sea Spy Marine Magnetometer respectively. The Hypack premium and SonarWiz software package was used to process, interpret and analyse all the acquired data to produce the desired outcome. The result showed that the study area has a depth range of 3 to 23 meters with an average sound velocity of 1537.67 m/s. The tidal gauge data also indicated high water level variations of up to 1.5 meters. Hence, the study area can be inferred to be highly tidal. The Side Scan Sonar imagery also showed the presence of some seabed features within the study area as reflective discrete returns observed along the route studied were interpreted either as sand ridges, scars, debris and depressions. The shallow geology profile analysis shows between 1 and 3 layers within the study area. The seabed was mostly composed of very soft silty clay and silty sand with no significant change in the formation.  Several magnetic anomalies were equally observed within the study area. These magnetic anomalies observed can be attributed to the existing pipelines and other metallic elements across the study area. The study recommends the use of the multi-beam echo-sounder for an improved bathymetric data collection and seabed imaging using the more accurate back scatter technology. Also, further studies to be designed to cover the entire Cawthorne Channel 2 using a multi-beam echo-sounder and including discharge measurement, water flow direction and sediment sampling was also recommended to produce a more holistic bathymetric and geophysical database.