Goal: Developing techniques to identify and assess the influence of geologic and geomorphic frameworks on coastal dynamics, with a focus on applications to coastal management for Western Australia.
Western Australian Sediment Cells & Coastal Compartments:
Application of geomorphic frameworks to Western Australian (WA) government coastal management has been more of an ‘objective’ than a ‘project’. Project studies and components have been funded on an ad hoc basis, opportunistically based on short-term needs of several different agencies. The strategic vision behind development and use of geomorphic frameworks has been led by Dr Ian Eliot.
Several of the team members have been involved in development and implementation of coastal planning policy through the 1980s to early 2000s. Although the incredibly diverse morphology along the enormous WA coast was acknowledged, only one simple method was presented for determining coastal setback allowances. This involved use of a beach profile storm-erosion model and local rates of coastal vegetation line change. Progressive application by bureaucrats and interpretation by consultants became increasingly convergent, largely resulting in limited consideration of either changes in morphology or the influence of the wider coastal setting.
The need for improved integration of locally-relevant coastal science with policy was identified by the State Government. Three pathways for improvement were undertaken:
Refinement of numerical modelling techniques to provide improved simulation of locally-relevant processes, co-ordinated through the Western Australian Marine Science Institute;
Improved description and classification of Western Australian coastal morphology;
Revision of the State Coastal Planning Policy to incorporate greater consideration of the morphologic range.
Almost simultaneous to this process, refinement of marine planning in Western Australia had acknowledged the relationship of geologic and geomorphic settings to the spatial distribution of marine habitats. Mapping of regional and sub-regional geomorphology (i.e. large-scale) was used to support definition of marine planning precincts.
Parallel classification of coastal geomorphology at a range of scales supported synthesis of scale-relationships. Consideration of how geomorphic information is used at different scales highlighted the need for a multi-disciplinary approach between planners, coastal engineers, geomorphologists, ecologists and environmental geologists. This provided a scientific challenge to meaningfully transfer between the modes of thinking used by coastal engineers, geomorphologists and geologists to explain coastal dynamics. The knowledge and intense collaboration of Dr Ian Eliot and Dr Bob Gozzard (Geological Survey WA) were essential to develop of a meaningful approach.
A hierarchical framework based on geomorphology and geology was developed, built around the main applications of planning at different scales. In this regard, the framework deliberately differs from solely spatial-based hierarchies.
Several applications of the geomorphic hierarchy have subsequently been undertaken:
Coastal information has been collated for a number of sub-regions along the Western Australian coast to support strategic planning. Geomorphic classifications within the framework were used to develop large-scale evaluations of coastal vulnerability. The relative sensitivity of each morphologic classification to active drivers (e.g. meteorology and oceanography) was combined with a measure of the relative susceptibility to change (e.g. sea level rise or human coastal interventions), to develop a vulnerability index.
Analysis of physical coastal parameters including geology, sediments, morphology, geometry and energetics was used to define two-dimensional sediment cells along extended parts of the Western Australian coast. The sediment cells provide indication of areas within which sediment exchange may be strongly related, and therefore provide an important contextual basis for evaluation of observed or anticipated coastal change. A three-level hierarchy has been used, broadly related to time scales from years to centuries, within which coherent behaviour is expected to occur.
The geomorphic framework at the scale of tertiary sediment cells has been used to structure a regional coastal monitoring program for the Peron-Naturaliste coast in southwest WA, along a length of approximately 300km. Identified coastal behaviour within sediment cells supports the integration of high resolution monitoring techniques in areas of high development density with more cost-effective use of indicator monitoring in areas of low development density
Regional differences in pathways for coastal response to sea level rise have been presented in the context of geomorphic frameworks. Consideration of existing morphology in the Vlamingh (southwest WA) and Pilbara (north WA) regions has demonstrated the need for improved understanding of sediment dynamics and controls when evaluating sensitivity to change.
The considerable body of work developed to support use of geomorphic frameworks on the Western Australian coast has helped to stimulate national interest and activity. Most States have experienced a similar pathway of coastal policy and science divergence over the last 30 years.
Organisations who have funded studies that contributed to the identification and application of geomorphic frameworks for coastal management include the Western Australian Departments of Planning, Transport and Parks & Wildlife, along with Geoscience Australia and the nine local government bodies who form the Peron-Naturaliste Partnership. Within each of these agencies, we have had in-industry champions, too numerous to list. The contribution of the Geological Survey of Western Australia, through the ongoing involvement of Dr Bob Gozzard, has been immeasurable.
WA Sediment Cells Summary:
The aim of these studies was to identify a hierarchy of sediment cells for planning, management, engineering, science and governance of the WA coast.
Sediment cells are natural management units with a physical basis, identifying sections of the coast within which sediment transport processes are strongly related. They provide an elegant format for summarising coastal data and can be used to:
Conceptualise the spatial context for coastal evaluations;
Provide a visual framework for communicating about the coast;
Support coastal management decision-making;
Support a range of technical uses largely relating to coastal stability assessment; and
Reduce problems caused by selection of arbitrary or jurisdictional boundaries.
Each sediment cell is a collection of marine and terrestrial landforms, inter-related by sediment transport between them. They include areas of sediment supply (sources), sediment loss (sinks) and areas through which sediment is moved between sources and sinks (pathways). Sediment transport pathways include both alongshore and cross-shore processes and therefore cells are best represented in two-dimensions.
Sediment Cells Mapping
Sediment cells have been mapped as a hierarchy of primary, secondary and tertiary levels to incorporate three spatio-temporal scales. The hierarchical nature of the cells gives a basis for comparison of planning and management at a number of scales, from small-scale engineering works, through to large-scale natural resource management.
Sediment cells have been defined in three steps through selection of:
Points along the shoreline (beachface);
Offshore and onshore boundaries; and
Alongshore boundaries through the points to the offshore and onshore boundaries.
An example at the secondary cell scale for the Mid-West Region is shown here.
Sediment cells have been mapped and reported individually for:
Vlamingh Region [2015: Coastal Sediment Cells for the Vlamingh Coast, Between Cape Naturaliste and Moore River, Western Australia]
Mid-West Region [2014: Coastal Sediment Cells for the Mid-West Region between the Moore River and Glenfield Beach, Western Australia]
Northampton Region [2014: Coastal Sediment Cells for the Northampton Region between Glenfield Beach and the Murchison River, Western Australia]
Pilbara Region [2014: Coastal Sediment Cells for the Pilbara Region between Giralia and Beebingarra Creek, Western Australia]
The cell information is provided for download for each region as a report and a dataset of boundaries and beachface points in ESRI Shapefile format and as Google Earth KMZ files.
For other regions, sediment cells were mapped as part of the national mapping process.
National Sediment Compartment Framework for Australian Coastal Management
Presentation of the Western Australian compartment and cells framework (Eliot et al. 2011) at a national forum provided an opportunity to discuss the relative merits of large scale geomorphic frameworks. It was identified that for most States, geomorphic frameworks have been used for coastal management, to one degree or another. Led by Professor Bruce Thom, a pathway towards national application of geomorphic frameworks was established:
Step 1 of the National Coastal Compartments Project involved developing a consensus on a practical geomorphic hierarchy. This defined several different spatial scales, including three 'coastal compartment' scales, which define segments of coast within which there are characteristic geomorphic relationships. The most widely applied characteristic is that of sediment exchange, therefore bringing strong parallels between 'coastal compartments' and the concepts of 'sediment cells' used for the UK and US.
Identification of primary and secondary compartments was determined by a panel of geomorphologists with experience around Australia. Mapping of the coastal compartments was undertaken by Geoscience Australia (McPherson et al. 2013).
Step 2 of the National Coastal Compartments Project involved evaluation of the compartments approach, particularly with respect to its value for climate change impact assessment.
This included two 'case studies', looking at aspects of how to apply compartments. The 'east coast' study examined the viability of using uncertainty based methods for describing future change in compartments with different degrees of sediment closure (Mariani et al. 2013). The 'west coast' study examined how a hierarchical geomorphic framework may guide refined assessment of coastal dynamics (Eliot 2013). Application to the different settings of the southwest and Pilbara demonstrated that generic coastal frameworks are likely to substantially miss spatial variation of behaviour.
Step 3 of the National Coastal Compartments Project has included dissemination of expert knowledge regarding coastal processes through NCCARF's CoastAdapt website.
Development of this knowledge base was led by Professor Bruce Thom, and involved input form a number of coastal geomorphologists around Australia.
BG Thom, I Eliot, M Eliot, N Harvey, D Rissik, C Sharples, AD Short & CD Woodroffe. National Sediment Compartment Framework for Australian Coastal Management.
Some Misunderstandings relevant to Geomorphic Frameworks (for discussion)
A regular failing of coastal practitioners is reliance on the notional concept of littoral transport, supplemented by assumption of direct relationships between environmental forcing (often solely waves) and alongshore sediment transfer. This ignores the capacity for morphology to alter pathways and rates of sediment transport. On a compartmentalised coast, such as southwest Australia, the capacity for sediment to transfer between compartments (mainly through headland bypassing) is related to the volume and distribution of sediment. Consequently, the simplified representation of wave-driven littoral transport, on its own, has limited capacity to represent regional-scale coastal sediment dynamics.
Illustration of how geomorphic frameworks affects regional sediment dynamics is available over both short and long time scales, with spatial scales around 20-30km for Cockburn Sound (Stul et al. 2008) and southern Geographe Bay (Eliot 2011), through to 300km (Searle & Semeniuk 1985). Within the Mandurah region, alongshore sediment supply has been measured as part of sand bypassing works, showing year-to-year variability that is not solely associated with wave conditions, including a substantial lag in supply following the protracted la Nina conditions from 2011-2013. Longer-term patterns of sediment dynamics are illustrated by the distribution of sedimentary coastal landforms (Gozzard 2009).
A partial explanation of observed variability in sediment supply can be developed through the concept of the beach as a sedimentary storage unit. Observed relationships between beach volume and environmental parameters have been demonstrated (Eliot & Clarke 1983; Masselink et al. 2001; Eliot & Travers 2011), including responses to sea level and anomalistic alongshore wind conditions. For other parts of Australia, relationships to wave conditions have been demonstrated (Turner et al. 2016). Variation of environmental parameters can therefore change the effective beach storage, increasing or reducing the available sediment supply.
Misunderstanding of geomorphic frameworks has been demonstrated in design and interpretation of impacts associated with coastal facilities. Near-field responses, typically involving updrift accretion and downdrift erosion, commonly provide the most rapid response. However, far-field responses, particularly those developed through changes to alongshore sediment supply, are accumulative and may involve more substantial volumes. A valuable demonstration of this process was provided by Guerin St groyne at Busselton, including its subsequent removal. Progressive shoreline erosion or accretion responses may occur along much longer sections of coast, in the order of kilometres, but are often obscured by natural coastal variability.
Other Documents & Presentations:
2010: Interpreting Estuarine Change in Northern Australia: Physical Responses to Changing Conditions
Landform analysis provides an opportunity to more effectively use the broad array of available coastal modelling techniques. In the absence of detailed observations and monitoring, landform analysis provides indication of what coastal sensitivities need to be considered when undertaking modelling or choosing management indicators.
Presentation: Eliot et al (2013) Revisiting Landforms Presentation
This document describes potential application of geomorphic frameworks to the improved assessment of sea‐level rise impacts. Assessment of coastal response to sea‐level rise has demonstrated diversity that is beyond the capacity of widely used simple models to represent successfully. Use of increasingly conservative climate change scenarios to extend the use of these models to more complex coasts is ultimately an impractical solution, as the methods cannot distinguish relative sensitivity along the coast. This potentially leads to a breakdown of the principle of intelligent siting to avoid coastal hazards. Geomorphic frameworks are proposed as a robust means to facilitate an appropriate level of complexity in sea‐level rise impact assessment.
2015: Sediment Compartments and Landform Frameworks for Coastal Management and Planning (Presentation)
2017: Geomorphic Frameworks for Coastal Management and Planning (Presentation)
The concept of coastal sediment compartments was first used in the 1960s in the United States. It has since been recognised as appropriate for defining sections of the Australian coast, but had not been uniformly adopted around the nation in the way that has underpinned management, as in other countries. In 2012, the Australian Government supported a project to better understand coastal sediment dynamics using the sediment compartment approach as a framework within which to consider future shoreline behaviour and the impacts of climate change, including rising sea level, changing wave climates and sediment budgets. This paper outlines the sediment compartment project and uses case studies to demonstrate its application. The project consisted of three steps. The first step involved delineation of a hierarchy of coastal sediment compartments following a nationally agreed set of criteria, integrating the onshore/offshore geologic framework with known patterns of sediment movement and those inferred from surface landforms. This identified more than 100 primary compartments bounded by major structural features such as headlands or changes of shoreline orientation. At a finer scale, approximately 350 secondary compartments were identified, many of which encompass smaller scale structural features that define tertiary scale compartments or cells. For verification of this sediment compartments approach to coastal planning and management, the second step of the study comprised case studies of contrasting compartments with different patterns of sediment supply, transport and deposition. The third step, involved embedding all secondary compartments around the continental coast into the Shoreline Explorer, within the CoastAdapt toolbox (National Climate Change Adaption Research Facility). Information regarding the sensitivity of shorelines to change was compiled at the compartment scale, based upon evidence such as substrate, sediment transport attributes and oceanographic forcing, including waves, tides and storm processes. Presentation of information through CoastAdapt within the compartments framework provides a resource to facilitate improved coastal planning and management over different implementation levels, from national strategy scale down to local policy scale. Case studies from several contrasting settings around the Australian coast demonstrated the potential and feasible application of the sediment compartment approach at different spatial and temporal scales.
This presentation collates information describing regional factors that may contribute to variation of coastal dynamics along the Vietnam coast. Using this information, a preliminary basis for classification of regional-scale geomorphic segments was identified. Within each segment, the range of morphotypes should also be acknowledged.
Part of a short course introduction to coastal engineering in Western Australia, covering: - Coastal Morphology - Coastal Management - Geomorphic Frameworks - Coastal Engineering Pressures & Some Interventions in WA
2021: Opportunities for Mangrove-based NBS to address Coastal Flooding and Erosion Hazard in Panamá City
This summarises a nature based solutions assessment for Panama City, focusing on use of mangroves to mitigate coastal hazards.
2022: Coastal Dune Management (Poster)
Present-day dune management substantially focuses on instabilities due to human disturbance or local-scale dune-wind interactions such as blowouts. Under conditions of rising sea levels, increased flooding episodes or reduced sand-supply from narrowed beaches will modify existing cycles of rapid storm erosion and gradual wind-driven recovery. This will potentially prompt widespread instability, beyond our effective capacity using existing approaches. To maintain the ability of coastal dunes to protect against waves and inundation, it is anticipated that a coastal management paradigm shift will be required, with increased focus on enhancing dune recovery processes, and greater tolerance of dune evolution.
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