Coastal erosion was widespread during the 20th Century and is expected to accelerate and become even more pervasive through the 21st Century due to sea-level rise and climate change. Erosion is a direct hazard for coastal residents and it also makes it more likely that natural and artificial defences will fail during storms, increasing the risk of coastal flooding. The risk of tidal flooding is widespread along open coasts and especially in estuaries, where extreme water levels are partly controlled by interactions between tide, surge and morphology and there are extensive flood plains. We can predict erosion and flooding during a specified extreme storm with some skill, but as we look further into the future, our ability to predict possible changes in risk diminishes. Much of this difficulty stems from our inability to quantitatively predict coastal and estuarine morphological changes over time scales of decades to centuries (the mesoscale).
The NERC-funded iCOASST (integrating COAstal Sediment SysTems) project comprises a consortium of UK Universities, Research Laboratories and Engineering Consultants. The Environment Agency are an embedded partner who actively supported the development of the project and its application throughout the project life. Collectively, they are considering how best to address this challenge and predict coastal morphological change at the mesoscale to inform shoreline management, strategy studies and other long-term coastal decision-making. As we have already noted, this is a difficult problem, not least because the erosion and/or accretion of a coastal landform such as a beach is influenced by interaction with adjacent coastal landforms, be they cliffs, saltmarshes, tidal deltas, etc. The problem is further complicated by the role of soft and hard human interventions, which also exert a pervasive control on coastal evolution.
Accordingly, the iCOASST approach is founded on a set of linked components, outlined below and illustrated in the Figure. The key components are:
- A new Coastal and Estuarine System Mapping (CESM) framework, supported by a GIS-based software tool (CESMapper), for describing and mapping the interactions between coast, estuary and inner shelf landforms and the extent to which these are constrained by human interventions. CESM provides a basis for developing a shared understanding between scientists, stakeholders and policy makers concerning the most important processes, sediment pathways and human interventions that govern landform behaviour.
- Well-validated hydrodynamic and sediment transport shelf models, applied at the scale of UK territorial waters, to calculate currents, waves and net sediment movement for representative years. These model outputs define broad-scale sediment pathways and identify locations where there is likely to be active inner shelf-coast interaction in terms of sediment exchange.
- New and improved landform behaviour models for open coasts (SCAPE+), inlets (MESO_i) and estuaries (ESTEEM) that are appropriate for mesoscale simulations and are linked to coastal state indicators of importance to stakeholders.
- Groups, or 'compositions', of coupled coastal and estuarine landform models, informed by CESM outputs, which exchange information as they run. Linking models in runtime is a difficult task that has hardly ever been achieved before now for quantitative predictions of coastal morphological change. The iCOASST project is using the Open Model Interface (or OpenMI) standard for this purpose. As a proof of concept, we are also demonstrating an alternative way of linking models at the conceptual stage (CoastalME).
Data are also fundamental to the validation and effective application of models. Coastal monitoring data are increasingly available in the public domain (e.g. at http://www.channelcoast.org) and this is stimulating the development of a new generation of models and data-driven analyses.
The iCOASST project framework links these components to achieve a system-level understanding of coastal change. The ultimate goal is multiple simulations of coastal evolution to explore sensitivity and uncertainties in future decadal-scale coastal response, including the effects of climate change and management choices.
The project is developing demonstration case studies in Liverpool Bay and on the Suffolk coast, including an active and ongoing engagement with local stakeholders to explore the realism and utility of our results. This has identified the importance of defining appropriate coastal state indicators and other results that link to activities such as shoreline management planning.
iCOASST is also taking a participatory modelling approach, which includes all interested stakeholders, including the public. Stakeholders bring valuable knowledge and contribute to structuring the problem and the formulation of an agreed modelling approach, rather than merely being 'consulted' on simplified outputs from a modelling process led purely by 'experts'.
Beyond iCOASST, the joint Defra/EA Flood and Coastal Erosion Risk Management R & D programme has funded a package of work to encourage uptake of the iCOASST deliverables and lessons into practice. The main output from this work is a package of end user focused reporting and guidance that clearly sets out the work of the iCOASST consortium and how its deliverables can be used to deliver operational shoreline management benefits to the Environment Agency, Natural Resources Wales and coastal risk management authorities. General lessons and advice about modelling coastal morphological evolution over decades or longer are also included. This reporting includes guidance on:
- The generation and use of the Coastal and Estuarine Systems Mapping (CESM) approach and products;
- The selection and use of Coastal State Indicators to improve coastal management decision making;
- The set up and running of the mesoscale modelling software;
- Guidance on mesoscale model selection, applicability, strengths and weaknesses, benefits over existing approaches in shoreline management planning and coastal / estuarine strategy studies.
The ambition is for the guidance to serve three levels of user:
- The generally interested member of the coastal management community including local stakeholders and coastal risk management authority managers;
- Coastal engineers who are not experts in modelling and may not use the models ;themselves but need to understand the concepts, methodology, pilot site and outputs and how they might be used to improve decision making; and
- The coastal modelling community who want a user guide on how to run the models and generate outputs.