Multibeam surveys - Ulithi Atoll and Yap Harbour, Yap State Federated States of Micronesia

Seabed mapping was completed using a Reson 8101 multibeam system to delineate the seabed morphology in the vicinity of the wreck USS Mississinewa located in water depths of around 40 m in Ulithi Atoll. A second area was mapped in Ulithi Atoll along the NE eastern margin of the lagoon from Masu to Asor island. Results of this mapping did not delineate any extraordinary feature other than the existing morphology of the seabed. The most interesting feature seen were elliptical-shaped mounds which may imply bi-directional bottom currents of similar magnitudes. The mapping of Yap harbour was also completed. These results have been presented in map form as contours and as soundings. The results of the mapping for Yap and Ulithi are available in GIS format. Digital side-scan imagery for all surveyed lines for both Ulithi and Yap harbour were collected and is presently only archived for processing should this facility become available. Conclusions are: The dataset for Ulithi lagoon provides excellent baseline information for long-term assessment of the impacts of the wrecks on the environment. Detailed maps and visualisation of seabed wrecks provides an opportunity for tourism e.g. a potential dive sites. The completion of the multibeam survey of Yap harbour and approaches provides for excellent baseline data for future infrastructure development. Recommendations are: Updating of the existing topographic map for Yap to account for expanding infrastructure in Colonia harbour should be completed. The use of IKONOS imagery in GIS provides an immediate solution for new and up-to-date maps for development planning