ESTEEM - a New 'Hybrid Complexity' Model for Prediction of Estuary Morphological Evolution at Decadal to Centennial Scales

Despite the wealth of historical and geological insights into coastal and estuarine landform behaviour, models capable of generating quantitative predictions at decadal to centennial scales are required if we are to meet the management challenges of the 21st century. Despite an emerging consensus that progress on this front is more likely to be made through models that are essentially synthesist in approach, the nature of marine forcing, especially in estuaries, means that it is frequently necessary to retain a degree of hydrodynamic complexity that can only be obtained via more reductionist models. We see great potential, therefore, in fusing these approaches rather than deploying them separately as end members of a modelling spectrum. This paper thus presents a novel approach to mesoscale estuary morphological evolution that combines physically complete 1-D simulation of tidal hydrodynamics, highly parameterised 2-D mechanistic representation of wave-driven tidal flat morphodynamics, and a largely empirical representation of 2-D variation in salt marsh deposition. This approach is embodied in the Estuary SpaTial LandscapE Evolution Model (ESTEEM) code, being developed in the UK as part of the NERC-funded iCOASST project. ESTEEM classifies an estuary into the distinct landform types (subtidal channel, tidal flat, etc), which are then simulated appropriately via one of the approaches highlighted above. Other notable aspects of the model architecture include use of a composite raster and vector data model and compatibility with the OpenMI external coupling standard. The paper describes the contrasting algorithmic approaches and presents illustrative 100-year simulations for a test case estuary.