Towards a high resolution cellular model for coastal simulation (CEMCOS)

The proposed research was designed to enhance the UK capability to simulate the complex behaviour of coastline environments in the face of climate change and human activities. Prediction of the response of complex systems to human actions and climate change is difficult because it is now generally acknowledged that information gained through reductionism alone is rarely applicable to the understanding of the behaviour of the whole system. Overcoming this deficiency can be attempted by allowing bottom-up interactions of processes, at the microscale, to simulate the emergence of macroscale phenomena. In this respect, recent attempts to use high-resolution process-based cellular automata (CA) models to simulate geomorphological phenomena within terrestrial catchment systems show great promise (e.g. Coulthard et al., 2000). The present pilot project extended these studies to the coastline using the best available geomorphic, coastal and oceanographic information to derive transitional rules for water flow (tides and waves), sediment transport, erosion and deposition. The one-year project successfully compiled rules for tidal, wave and sediment processes and produced an effective cellular modelling environment for simulating estuary response through integration of these rules. The High Resolution Cellular Model for Coastal Simulation (CEMCOS) incorporates relationships between water depth, flow velocity, tideand wave-induced shear stress and sediment transport, and models ‘sedimentary outcome’ as a function of erosion and deposition thresholds determined by flow velocity and physical properties of the bed (e.g. critical shear stress for non-cohesive particles, consolidation, bed roughness and ‘bioarmouring’). The model is now sufficiently well developed to be run from an initial condition in order to capture emergent and other nonlinear properties in the Blackwater Estuary, Essex, and to validate the outputs with reference to Admiralty Charts, Ordnance Survey maps and sedimentary records. Once validated, it is intended that this CA-type model will provide the opportunity to run simulations into the future in order to evaluate the potential impacts of climate change, sea-level change and coastal defence options, and to identify suitable adaptive responses for decision-makers. Objectives • To develop and partially validate a new high resolution cellular model that can simulate nonlinear and complex behaviour in tideand wave-dominated coastal environments; • To identify modelling rules and input datasets of crucial significance for estuary and open coastal simulation; • To apply the model to the Blackwater Estuary and its adjacent coastline, and to test its skill through comparison with historical information; • To assess the practicalities of developing a fully integrated cellular model for the East Anglian coastline and its drainage area. Work undertaken A large majority of the modelling work was undertaken directly by the post-doctoral researcher Dr Nicola Richmond in conjunction with colleagues at the University of Liverpool, University of Wales Aberystwyth, and Proudman Oceanographic Laboratory. The initial tasks were to identify the complete list of relevant parameters and processes (Appendix 1); generate mathematical rules for three estuarine components: tides, waves and sediment dynamics; and to incorporate them within a PC-based interactive cellular environment. Development of an early 1-D estuary length model offered a simple platform on which to couple together mathematical expressions within and between cells. Each cell was defined as a cubic component of the estuary and its bed with properties of mean water depth, bed elevation, sediment cohesion etc. Existing models for tides were used to simulate tidal current in each cell (in conjunction with Prof D. Prandle), and