Dr David Wainwright

Water surface level exceedances and extreme flooding for Australia's most exposed estuary, Swansea Channel, was estimated using sea level rise epistemic uncertainty with symmetric and asymmetric shapes. Flood estimates were obtained using a simple hydraulic model what was applied within a statistical simulation, included atmospheric and oceanic forcing and their aleatory uncertainties. These predictions are then used to discuss vertical allowances for coastal planning. There are different allowance approaches to include sea level rise epistemic uncertainty ranging from asset independent (allowance includes a particular degree of sea level rise uncertainty) to asset specific approaches (allowance that ensures frequency of inundation does not increase). Regardless of the allowance approach, the sea level rise uncertainty distribution and its shape are expected to influence these allowances. The impact on flood estimates and derived allowances from symmetric and asymmetric uncertainties includes expected features of increasing water level variations and allowances in both time and in space (Swansea Channel becomes more hydraulically efficient as its depth increases). Using asymmetrical shaped uncertainty for coastal planning constrained by low risk tolerance would, for example, increase the 1% annual exceedance probability flood elevation that includes 99% of sea level rise uncertainty by ca 0.8 m along Swansea Channel when compared to symmetric uncertainties. If the future sea level rise uncertainty is indeed asymmetric then application of allowances based on the symmetrically shaped distributions underestimate possibilities of future extreme water levels and may be exceeded earlier than anticipated. Annual exceedance duration estimates indicate that in 2120, epistemic (sea level rise) uncertainty is greater than aleatory (weather related flooding) variational along Swansea Channel.

Local government organisations in coastal Australia have historically commissioned studies aimed at understanding risks in their locality to future sea level rise as a starting point for developing adaptation strategies to climate change. Therefore, the success of the overall adaptation activities of local government are strongly influenced by the way those initial risk studies are scoped and conducted, and how the outputs of those studies underpin subsequent adaptation planning activities within the organization. Mainstreaming of adaptation planning activities within local government is critical in terms of getting stakeholder support and required resources for its implementation. This paper analyses a sample of these coastal risk assessment studies across seven states and territories in Australia, with an aim to critically investigate the current state of practice among coastal local governments. First, we develop a typology of studies that have been undertaken by or for practitioners to understand coastal climate change risks, and discuss the applicability of the studies within the policy-making context of local government. Second, we identify a set of sample studies from the ¿grey literature¿ through a systematic process and investigate to what extent they adhere to best practice risk management guidelines and principles, such as ISO31000. Third, we interview stakeholders from top performing studies to identify how/if the risk studies helped their organization in progressing their adaptation planning. We find that there is a significant inconsistency among terminologies in the coastal climate change risk assessment unpublished literature as studies use ¿risk¿, vulnerability¿ and ¿hazard¿ concepts interchangeably despite their separate objectives and aims. Most studies perform poorly in evaluating risk against broader organizational criteria. Subsequently, it is difficult to integrate the findings of such studies into a broader organizational risk register, limiting opportunities for identified coastal climate change risks to be integrated into councils¿ long-term strategic decision making. Conversely, the follow up interviews of studies that performed well in scoping and consultation in our assessment demonstrate that these aspects were beneficial to stakeholders in terms of informing adaptation planning. Importantly, the findings presented in this paper confirm the need for a consistent risk assessment approach for local councils in the coastal zone to underpin successful adaptation planning. This is a critical issue, not only for Australia, but for local government organisations globally given that sea level rise is a projected threat for all populated coastal regions worldwide.

A field data set of the artificial breaching of a coastal lagoon berm is presented, and includes a detailed analysis of the breach evolution in plan and elevation, together with water levels and flow velocities. A semi-coupled two-dimensional (depth averaged) numerical model describing both the shallow water hydrodynamics and morphodynamics is developed and tested against the field data. Key hydrodynamic and morphodynamic processes are discussed, and strategies to model these processes are presented and evaluated, such as accounting for modified roughness under transcritical flows and testing an improved algorithm for widening of the breach channel through side wall erosion. While further research is warranted, the processes relating to the erosion of the breach side walls and sediment transport under transcritical flow regimes were found to be essential to developing a realistic model of the overall breach process. A new channel bank erosion model is developed and implemented, which shows improved performance.