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Coastal and estuarine systems mapping


Coastal and Estuarine System Mapping (CESM) has been developed at University College London as an approach to the conceptualisation of connected estuary-coast-inner shelf sediment systems. Coastal and estuarine systems are 'mapped' conceptually as a set of interconnected components that includes various scales of landform (e.g. beaches, cliffs, tidal flats, estuaries etc.), exchanges of sediment and other interactions (e.g. wave sheltering by offshore sand banks), and human interventions (e.g. defensive structures, beach nourishment). The process of creating these 'concept maps' is extremely useful as a means of bringing together scientific and stakeholder knowledge and achieving a shared understanding of how a given coastal region is believed to operate. The maps also constitute a useful data and knowledge product that can be used to inform the development and application of quantitative models (e.g. to simulate morphological change) as well as management decision-making.

A key advantage of the CESM approach is that it integrates our understanding of open coast, estuary and the offshore zone - environments that have often been separated for management purposes. Although CESM is presented as a generic process, the resulting maps are more useful if they are produced within a geospatial framework. We have therefore developed a CESM software tool that operates within a free and open-source Geographical Information System (GIS), namely QGIS ( Use of a GIS allows a system to be mapped out conceptually over map and other data layers containing information such as bathymetry, geology, habitat type etc. They can then be made available for viewing online or distributed as editable products that can evolve with our understanding or changing management needs.

Earlier approaches to the conceptualisation of coastal systems

Conceptualisation of coastal systems in terms of their sediment budgets and by the segmentation of open coasts into hierarchies of nested sediment cells has provided a geomorphological basis for shoreline management that has endured for several decades now. This is particularly effective for open coasts dominated by beach-grade sediments (sands, gravels). However, cell mapping does not extend readily to include estuaries, and long-range transfers of fine sediment (mud) that link cliff erosion to deposition within estuarine tidal flats and marshes are harder to capture.

A need for a greater degree of integration between the management of coastal, estuarine and offshore zones has prompted the development of more sophisticated conceptual schemes capable of broader application at multiple scales. One such advance was the FutureCoast project (Burgess et al., 2002), which embedded littoral cells within a spatial hierarchy of geomorphological units (effectively individual landforms), shoreline behaviour units (sub-systems, such as embayments and estuaries) and regional coastal behaviour systems. These were defined for the entire coast of England and Wales to inform a new generation of Shoreline Management Plans. A different approach was taken by Cowell et al. (2003) with their concept of the 'coastal tract'. This is based on the idea of a broad-scale sediment-sharing system that encompasses not only the shoreline of the open coast but also estuarine (or backbarrier) environments as well as the inner shelf. Their hierarchy is primarily one of nested timescales, with the aim of separating progressive changes (such as chronic erosion) from short-term variability.
CESM aims to combine the integration of estuary, open coast and inner shelf found in the 'coastal tract' concept with the spatial hierarchy of interactions identified by the FutureCoast work. The work done in iCOASST draws upon earlier coastal system 'concept mapping' undertaken by French and Burningham (2009) as part of an Environment Agency-funded project on large-scale coastal geomorphological behaviour (Whitehouse et al., 2009). This has been generalised, extended and implemented within an open source GIS software environment.

Role of CESM within iCOASST

CESM fulfils two key roles within the iCOASST vision. First, it provides an initial qualitative conceptualisation of the configuration of a coastal system of interest in a way that maps out not only the natural system components (landforms, sediment feeds) but also the multitude of human interventions and constraints. This can then be used to specify the most important components and interactions to include in quantitative predictive models. Further insights into the behaviour of the system can be gained by supplementing CESM with other qualitative modelling approaches, especially the application of Causal Loop Analysis, which has also been advanced within iCOASST (Payo et al., 2014, 2016).

Second, CESM provides a platform on which to build a more participatory approach to both model-building and management. Participatory modelling has emerged as an important means of achieving meaningful engagement between scientists, policy makers and stakeholders (e.g. Voinov and Bousquet 2010). This requires that the knowledge and perceptions of scientists and stakeholders be brought into alignment to achieve a shared understanding of the system being studied and the nature of the problems that need to be addressed. CESM as a process can be an effective catalyst for achieving this.

High level summary of the CESM methodology

CESM is based on a spatial 'ontology' (Figure 1) insert and link to CESM-ontology-diagram1.jpg (put simply, a classification + some rules governing the interaction between components) that couple together estuary, coast and inner shelf and nest individual landforms within larger landform complexes and within broader-scale coastal regions. It generates a 'snapshot' of how a system is configured in terms of morphology, sediment pathways and other interactions, as constrained and influenced by human intervention.

(Figure 1)

The method is defined more fully in French et al. (2016a) but can be summarised by a simple workflow diagram (Figure 2).

The key stages involve:

  1. Scoping of the problem, including the region of interest, and assembly of supporting datasets within a GIS.

  2. Mapping of main landform complexes for the open coast, estuaries and inner shelf.

  3. Mapping of component landforms within these complexes.

  4. Mapping of structures and any non-structural interventions such as beach nourishment.

  5. Mapping of interactions, including sediment pathways and other linkages such as the effect of a jetty on the stability of a channel.

  6. Rationalisation to remove redundant linkages and represent the system using a minimal set of interactions.

  7. Optional annotation with data (e.g. quantitative sediment fluxes where known), meta-data (e.g. sources of information) and/or reports and images.

(Figure 2)

The CESMqgis software tool (Figure 3) provides an easy interface for accomplishing this process within QGIS, an open-source Geographical Information System.

(Figure 3)

Application of CESM to the iCOASST case study regions and lessons learnt

CESM layers have been produced for the Liverpool Bay and Suffolk case study regions within the iCOASST project. These have provided an initial high-level conceptual framework within which to synthesise scientific understanding of the processes driving coastal behaviour and to provide a basis for stakeholder engagement. The system maps have also been used to inform the development of the iCOASST model compositions.

System mapping has also been undertaken outside the iCOASST project areas (e.g. in The Solent). We are currently working to extend the system mapping around other areas of the coast and to develop further the capabilities of the software to create a geospatial database and also implement various analytical functions.