Developing a Seabed Resurvey Strategy: A GIS approach to modelling seabed changes and resurvey risk A. M. Bakare, J. G. Morley, R. R. Simons Department of Geomatic Engineering, University College London, Gower Street, London WC1E 6BT, United Kingdom Telephone: +44 (0)20 7679 2741 Fax: +44 (0)20 7380 0453 Email: a.bakare@ge.ucl.ac.uk 1. Introduction The application of GIS systems to environmental contexts is well established with a multitude of examples (see Goodchild et al, 1993). It has only recently been applied in coastal and marine environments, which present challenges due to the dynamic nature of the spatial and temporal environment, the lack of data and issues of accuracy and scale (Wright and Bartlett, 2000). It still has not been utilised to evaluate the forces that determine sediment transport in connection with the volume moved, the resulting changes in the seabed morphology and relevant application factors. Examples of potential applications include maintaining navigation safety and evaluating risk to offshore cables and pipelines. Sediment on the seabed is in a constant state of flux as a direct response to the forces exerted by hydrodynamic, meteorological and physical conditions in the form of tides, storm surges and waves. The amount of sediment material that is moved is further influenced by the physical characteristics of the sediment and water column. Therefore an understanding of the transport characteristics, seabed morphological response and interaction with factors specific to an application (such as coastal population density) is frequently required for planning and management decisions in the marine environment. The problem directly addressed by this project is that faced by bodies responsible for resurveying areas of seabed to maintain navigation safety in British territorial waters. Survey areas and re-survey frequencies are currently determined from qualitative knowledge of sediment movement and navigation intensity (IHMC, 2004) and there is a need to quantify this approach so the information can be ascertained more easily by an end-user. 2. System Development A survey decision tool has been developed which dynamically couples a GIS (ESRI ArcGIS) to a numerical sediment transport model (SEDTRANS05), a current model (POLPRED) and a wave dataset for the West Gabbard wave buoy (obtained from the WaveNET service). The methodology employed utilises the GIS as the principle mechanism to undertake the morphological modelling and navigation risk assessment to enable a re-survey decision. The GIS is used to acquire the modelling inputs, initiate the sediment transport calculations, distribute the calculated sediment flux to predict bed height changes, analyse the risk posed to navigation and visually display the results. In order to evaluate the functionality of the tool it has been applied to a study region off the east coast of Norfolk between Caister-On-Sea and Orford Ness, within a