How fast does the bathymetry change on the Swedish west coast? Modeling how fast the bathymetry change, to know where to prioritize new hydrographic surveys

Abstract: The Swedish Maritime Administration is responsible for the passability and availability of vessels on the Swedish coast. They are doing hydrographical surveys to ensure the safety of the maritime transportation corridors on the coast. The surveys are classified after precision in the classification systems FSIS-44 and Category Zones of confidence (CATZOC). To know how long data can be classified with the highest standard, it is essential to know how fast the bathymetry change and how often you need to remeasure the seafloor. Two different GIS models were built, one to see how bathymetry has changed over the years and one that can predict risk for future changes. Different factors that can affect the bathymetry are the type of bottom (sediments or bedrock), currents, slope, maritime transportation corridors, sedimentation rates, sea level rise, and land uplift, to name a few. Previous studies that have been made on how safe nautical charts are have mainly focused on the risks according to how much traffic operates in the area. One study made in the US has focused on more different factors, this included many years of remeasuring the bathymetry in the Chesapeake Bay and the Delmarva Peninsula area. This study has been focused on the Swedish west coast (Skagerrak and Kattegat), and the factors used in this model were slope, maritime transportation corridors, seabed type, and currents. The model was at first tested on smaller areas where the result could be compared to actual changes. The result showed that slope has the most significant effect, seabed type comes second, and maritime transportation corridors have the least impact on the bathymetry (currents could not be included in the small-scale model). These conditions were then used for the large-scale model over the coast. The result gave a map that shows where it might be good to resurvey the bathymetry. Since much of the data is confidential (seabed type and slope), data in the largescale model is very generalized. This must be considered when studying the results. The outcasts made in this report need to be improved with more precise data and more factors that have not yet been included. To ensure that the model is correct more areas need to be remeasured regularly during a period.