Abstract
Coastal and shoreline management increasingly needs to consider morphological change occurring at decadal to centennial timescales, especially that related to climate change and sea-level rise. This requires the development of morphological models operating at a mesoscale, defined by time and length scales of the order 101 to 102years and 101 to 102km. So-called ‘reduced complexity’ models that represent critical processes at scales not much smaller than the primary scale of interest, and are regulated by capturing the critical feedbacks that govern landform behaviour, are proving effective as a means of exploring emergent coastal behaviour at a landscape scale. Such models tend to be computationally efficient and are thus easily applied within a probabilistic framework. At the same time, reductionist models, built upon a more detailed description of hydrodynamic and sediment transport processes, are capable of application at increasingly broad spatial and temporal scales. More qualitative modelling approaches are also emerging that can guide the development and deployment of quantitative models, and these can be supplemented by varied data-driven modelling approaches that can achieve new explanatory insights from observational datasets. Such disparate approaches have hitherto been pursued largely in isolation by mutually exclusive modelling communities. Brought together, they have the potential to facilitate a step change in our ability to simulate the evolution of coastal morphology at scales that are most relevant to managing erosion and flood risk. Here, we advocate and outline a new integrated modelling framework that deploys coupled mesoscale reduced complexity models, reductionist coastal area models, data-driven approaches, and qualitative conceptual models. Integration of these heterogeneous approaches gives rise to model compositions that can potentially resolve decadal- to centennial-scale behaviour of diverse coupled open coast, estuary and inner shelf settings. This vision is illustrated through an idealised composition of models for a ~70km stretch of the Suffolk coast, eastern England. A key advantage of model linking is that it allows a wide range of real-world situations to be simulated from a small set of model components. However, this process involves more than just the development of software that allows for flexible model coupling. The compatibility of radically different modelling assumptions remains to be carefully assessed and testing as well as evaluating uncertainties of models in composition are areas that require further attention.
Highlights
The increasing concentration of human populations close to open coast and estuarine shores places great pressure on the living and nonliving resources of these coastal environments (Vitousek et al, 1997; Turner, 2000)
Since reduced complexity models have already been successfully applied to real coastal management issues, and this type of model has proven to be effective in simulating realistic emergent behaviours and geomorphic change over larger spatial and temporal scales (Walkden and Hall, 2005; Dawson et al, 2009), it is worth further exploring the full potential of this modelling strategy in generating quantitative predictions of mesoscale coastal evolution
Coastal and Estuarine System Mapping (CESM) captures a system state averaged over a time interval that is long enough to exclude extraneous variability, but short enough to exclude trends that lead to gross changes in configuration (though localised state changes, such as barrier breakdown, can be included if these are persistent and relevant to the mesoscale; French et al)
Summary
The increasing concentration of human populations close to open coast and estuarine shores places great pressure on the living and nonliving resources of these coastal environments (Vitousek et al, 1997; Turner, 2000). Following French et al (this issue — a), this scale is referred to as the mesoscale, and is characterised by time horizons of the order 101 to 102 years and less rigorously imposed spatial dimensions of the order 101 to 102 km Such predictions of coastal change should be delivered within an uncertainty framework that is robust enough to inform management and policy thinking. In this paper we present an overall vision for a hierarchical modelling framework for mesoscale coastal change that is intended to help facilitate the overall integration process It considers the open coast, estuaries and the inner shelf and their interactions as a coupled system, including all phases of sediment, from fine-grained transport of silts and clays potentially at the scale of shelf seas, to non-cohesive sediment transported at the scale of littoral cells and sub-cells.
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