Field measurements of beach-dune dynamic profiles to assess erosion hazard on the coast of NSW, Australia

The coast of New South Wales (NSW), Australia is about 2000 km long and consists of 721 sandy beaches (68%), rock coastline (32%), and more than 185 estuaries. It is most populated in Australia and one of the NSW greatest assets with significant economic, social and environmental values. The NSW coast has epsodically been ravaged by severe storms together with large ocean waves and high water levels, resulting in severe dune-beach erosion/recession, damaging coastal infrastructure and properties and degrading coastal ecosystems. With potential changes to storm-wave climate and rising sea level, coastal erosion hazards on the NSW coast are likely to worsen in the future. This study was undertaken to collect essential field data on beachdune profiles and sediment grain-size distributions over more than 200 sandy beaches to assess NSW coastal erosion hazard. For each of the selected beaches, three beach-dune profiles of shore-normal transects at 50m apart were surveyed by RTK-GPS, and three sediment samples only on the first transect line were also colleced from the dune, dry beach/berm and swash zone by using a simple hand grabbing method. A sediment grain size analyzer, Malvern Mastersizer 2000E, was used to obtain sediment grain size distributions. It is found that the 618 sediment samples analysed consist of fine sand (10%), medium sand (82%) and coarse sand (8%), and that the dune sand d50 correlates well with the dry-beach sand d50 and is about 8% smaller, but less well correlates with the swash sand d50 and is about 15% smaller. The beach orientation was estimated from the direction of the shore-normal transect lines and generally ranges from 90o to 150o. The beaches surveyed are found to have erosion problems when they weredirectly exposed to predominant waves in the south-east direction and also when the dune toe elevations were lower than 3~3.5m (AHD). A conceptual model is also developed to assess likelihood storm erosion of a beach-dune system

Ocean driven flooding of a coastal lake

Analysis of Lake Conjola flooding in April 2006, provided in this paper, attributes it to waves pumping water over a 300 m long beach berm and into Lake Conjola. This overwash, generated by the medium wave height swell occurring during this flooding, was able to lift the lake levels near the entrance, persistently over several tidal cycles, to well above the ocean water levels . The wave pump model was used to model this flooding. Lake Conjola water storage and dynamics were modelled by using a two-node continuity based model that a change in storage in time is driven by the net inflow to a node and these nodes and the ocean are linked by log-law. The extents of these two nodes were established from previous water surface measurements. While the qualitative flood behavior was reproduced by this remarkably simple model, the peak flood level was not satisfactorily predicted when using literature values for model turning parameters. One reason for this mismatch was that the waves pumped against a head including critical flow on the beach berm. Based on recent images of Lake Conjola wave overwash events, it may be concluded that pumping against critical flow is too harsh. Removing this from the model has halved the gap between the measurements and predictions. However, more research is definitely required to establish what components should be included in the hydraulic head pumped against

Practitioner needs to adapt to Sea-Level Rise: Distilling information from global workshops

Climate-induced sea-level rise threatens the world’s coastal populations, critical infrastructure, and ecosystems. The science of sea-level rise (SLR) has developed to inform understanding of global climate mitigation and adaptation challenges, but there is much less engagement with practitioners to discern their climate services needs and support the development of adaptation planning and action on the ground. In addition, adaptation planning and implementation processes for SLR are relatively new and practitioners developing leading practices are seeking interaction with their peers and the SLR science community. To address these gaps, we co-produced online global workshops with sixty-nine practitioners from twenty-six countries. These workshops aimed to increase understanding of the state of SLR adaptation planning practice worldwide, gather information on practitioners' existing knowledge and service needs to advance their adaptation efforts, and facilitate exchange between practitioners engaged with coastal adaptation and the SLR science community. The workshops uncovered commonalities across contexts and identified consistent needs from scientists and other technical experts amongst the practitioner community. These needs include generating more localized SLR impact data, understanding of compound risk, creating data timelines for decision making, and developing clarity about uncertainties and probabilities. We also observed important differences between urban and rural locations and between places with different economic resources. To meet their needs, practitioners identified three crucial next steps: 1) Develop more online engagement opportunities, 2) Establish a global practitioner community of practice, and 3) Scale and improve the provision of climate services

Consideration of uncertainty in sea level rise in Australia's most exposed estuary: a discussion on allowances under different epistemic uncertainties

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

Timescales of inlet morphodynamic forced by tides and waves

The time scale at which an inlet responds to changes of wave height, freshwater inflow or sediment supply is called the morphological timescale, T. To determine the morphological time scale, one usually analyses survey data of the inlet throat area or the volume of flood/ebb tidal deltas, but such data are costly and therefore rare. This paper analyses tidal records using a 24.5 hour moving window approach to find Tand provides relationships between Tand the external forcing from waves and tides for different coastal inlets in New South Wales, Australia. Response to extreme changes in forcing depends strongly on bay/inlet size; from small inlets which open and close several times every year to larger systems where the effect of even the most severe weather events is not- or is barely measurable via changes to the inlets hydraulic performance. Outcome can be used in coastal inlet management without extensive river flow and bathymetry data

Second-Pass Assessment of Potential Exposure to Shoreline Change in New South Wales, Australia, Using a Sediment Compartments Framework

The impacts of coastal erosion are expected to increase through the present century, and beyond, as accelerating global mean sea-level rise begins to enhance or dominate local shoreline dynamics. In many cases, beach (and shoreline) response to sea-level rise will not be limited to passive inundation, but may be amplified or moderated by sediment redistribution between the beach and the broader coastal sedimentary system. We describe a simple and scalable approach for estimating the potential for beach erosion and shoreline change on wave-dominated sandy beaches, using a coastal sediment compartments framework to parameterise the geomorphology and connectivity of sediment-sharing coastal systems. We apply the approach at regional and local scales in order to demonstrate the sensitivity of forecasts to the available data. The regional-scale application estimates potential present and future asset exposure to coastal erosion in New South Wales, Australia. The assessment suggests that shoreline recession due to sea-level rise could drive a steep increase in the number and distribution of asset exposure in the present century. The local-scale example demonstrates the potential sensitivity of erosion impacts to the distinctive coastal geomorphology of individual compartments. Our findings highlight that the benefits of applying a coastal sediment compartments framework increase with the coverage and detail of geomorphic data that is available to parameterise sediment-sharing systems and sediment budget principles. Such data is crucial to reducing uncertainty in forecasts by understanding the potential response of key sediment sources and sinks (e.g., the shoreface, estuaries) to sea-level rise in different settings