Elevated water levels at trained river entrances on the east coast of Australia

The south-east coast of Australia has many low-lying areas at river entrances that are vulnerable to coastal inundation due to high water levels elevated by ocean tides, coastal storms, ocean waves and other drivers. The penetration of elevated entrance water levels into rivers can further intensify river flooding associated with high rainfall events. In this study, historical water level data, which were collected continuously at 17 inshore and 5 offshore permanent tide stations along the East Coast of Australia, are used to study effects of tides and waves on water levels at trained river entrances and also to estimate extreme entrance water levels without major entrance rainfall-related flooding

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

Statistical simulations of Swansea Channel flooding under uncertain sea level rise

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

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

Economic impacts of climate change on the Australian dairy sector

We analyse the economic implications of climate-driven pressures on the pasturebased dairy sector in Australia. We use an integrated assessment model that includes a climate scenario generator, a climate-biophysical response framework and an economywide analytical framework. For the climate scenario generator, we use data from the OzClim database of the Commonwealth Scientific and Industrial Research Organisation. For the climate-biophysical response framework, we use the DairyMod model with inputs of changes in climate variables from OzClim to quantify climate change effects on pasture growth and productivity. For the economywide analytical framework, we use the National Integrated Assessment Model to quantify the economic implications of these effects on the dairy sector. The simulated pattern of regional changes in dairy output is not a simple function of the changes in dairy productivity. Our results show that the relative size of productivity changes across regions affects the relative competitive advantage of dairy-producing regions. Several factors affect the regional distribution of simulated dairy-output changes, including substitution among sources of dairy output and competition for inputs like supplementary feed. An increased output in regions with moderate reductions in dairy productivity may occur because the severely climate-affected regions absorb the greatest loss in output

Wave setup and other tidal anomalies in coastal rivers

The tailwater level is together with rainfall the most important input to flood modeling in coastal rivers. Thus, the need for an ocean-river interface which can provide tailwater levels for numerical models is obvious. The state of the art is however not very advanced. Detailed waterlevel profiles through the Brunswick River entrance from 500m inside the breakwaters to 150m outside during a wide range of weather conditions revealed that the wave setup through the zone of wave breaking is much smaller than what is being used by practicing modelers in Australia. Barometric effects of the order 1cm per hPa is only a minor part of the tidal anomalies, which range up to 0.8m 500m inside the breakwaters, and wind effects, although not modeled in detail, are estimated to be small on the fairly narrow continental shelf of South East Australia. Tidal anomalies of the order 0.5 to 0.7 metres have been observed in the absence of rainfall and strong local winds during Cyclone Roger in 1993. An offshore record indicated that a substantial fraction of this tidal anomaly (of the order 0.25m) also occurred in 25m of water offshore from the Tweed River on the border between New South Wales and Queensland. This indicates the presence of weather related oceanic forcing of a nature which is not understood in detail