Modelling tsunami inundation on coastlines with characteristic form

This paper provides an indication of the likely difference in tsunami amplification and dissipation between different characteristic coastal embayments, coastal entrances and estuaries. Numerical modeling is performed with the ANU/Geoscience Australia tsunami inundation model. Characteristic coastal morphology is represented by simpler generic morphological shapes which can be applied easily in the ANUGA model, such that key non-dimensional parameters (e.g. embayment depth/bay width) can be varied. Modeling is performed with a range of bay shapes, seabed gradient and different incident tsunami wave shapes and wave angles, including sine waves, solitary waves and leading depression Nwaves. The results show a complex pattern for both large and small embayments, with wave breaking an important control on the amplification of the wave between the 20m contour and the shore. For large embayments, the wave run-up can be amplified by a factor six in comparison to the amplitude at the model boundary. For small embayments, the amplification is dependent on the location of the ocean water line, or tidal stage

NSW tsunami risk – an overview of the NSW risk assessment scoping study

The NSW Department of Environment and Climate Change and the State Emergency Service with support from Geoscience Australia and the Bureau of Meteorology have recently managed a tsunami risk assessment scoping study for the NSW coastline. The study comprised the following components: • Identification of tsunami sources, including an assessment of their relative tsunamigenicity; • Summary of NSW tsunami history, including paleotsunami studies; • Estimation of travel times for each credible tsunami source; • Estimation of maximum nearshore wave heights along the entire NSW coast for regional and distant tsunami sources; • Assessment of the influence of typical coastal configurations on tsunami runup; • Broad based assessment of coastal vulnerability; Funding for the study was successfully obtained through the Natural Disaster Mitigation Program. Individual sections of the project were performed by Risk Frontiers, University of Queensland, Manly Hydraulics Laboratory and URS Corporation. The outcomes of the study which are discussed in this paper provide a general assessment of tsunami risk and provide information for the prioritisation of communities for future detailed tsunami inundation modelling.11 page(s

Application of the wave pump concept to simulate tidal anomalies in Lake Conjola, NSW

The present paper applies the wave pump concept to a flooding event at Lake Conjola, Australia. We explain how the raised water level in the lake was caused by waves with large height and very long period pumping water into the lagoon across a berm separating the lagoon from the ocean with the nominal wave set up effects. Outflow through the entrance channel, modeled as critical flow over a weir, results in less agreement with measurements compared to that of approximating it as a channel with finite length. An inverse analysis indicates that the entrance scoured out to become more efficient during the wave event, returning to normal cross section after the event. This insight was utilized to adjust the entrance area in a forward model to get optimal fit with measured water levels. Finally, the wave pump concept was confirmed using a two node model that reflected the actual surface areas of two lakes in series

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

Identifying sediment compartment dynamics on the Illawarra Coast

This project aims to produce a framework for assessing compartment dynamics within two sediment compartments in the Illawarra region to assist in assessing coastal hazards. Sediment sources, pathways and sinks will be examined for the Wollongong and Illawarra Coast - South compartments, defined by Geoscience Australia and CoastAdapt. A compartment based approach allows for more holistic coastal planning and management which considers sediment transport at differing scales, and interconnectivity of beaches. This type of approach underpins national guidance on open coast risk assessment and has been incorporated within the NSW Coastal Reforms and the Draft Coastal Management Manual. The adjacent sectors of the Wollongong Coast and Illawarra Coast-South compartments extend for approximately 30 km from Bellambi Point to Bass Point. The rock platform of Red Point marks the shoreline division between these two contrasting compartments. The Wollongong Coast is an urbanized relatively little studied leaky compartment, whereas the Illawarra Coast-South is a well-defined and confined compartment whose main sedimentary characteristics are represented by the infilling of the Lake Illawarra barrier estuary and the erosionprone Warilla Beach. This detailed examination of sediment resources brings together the state-wide coastal seabed mapping program being undertaken by the NSW Office of Environment and Heritage (OEH), and coastal geomorphological investigations being undertaken along the southern NSW coast by the University of Wollongong (UOW). These initiatives involve collation of historical data, sediment sampling, and the use of recently available sophisticated remote sensing technologies, such as terrestrial airborne LiDAR, single and multibeam bathymetry, sidescan sonar imagery, and underwater video and still camera

Observations of beach recovery in SE Australia following the June 2016 east coast low

In June 2016 a severe east coast low storm impacted the coastline of southeast Australia and resulted in substantial beach erosion extending from southern Queensland to Tasmania. With extreme conditionsforecast six days in advance of the storm, a rapid response coastal monitoring team was able to capture unique regional-scale pre- and post-storm measurements using Airborne Lidar and other technologies. In theensuing six months, observations of the subsequent beach recovery have been undertaken, providing a rare insight as to the rates and magnitude of beach recovery following an extreme storm at the regional scale.Beach recovery observations at six representative embayed beaches along the NSW coastline (Trial Bay, North Haven, Elizabeth, Boomerang, Terrigal-Wamberal and Narrabeen-Collaroy) indicate that the six monthpost-storm period reported here was characterised by substantial recovery of the subaerial beach. This recovery was initially rapid (35% of eroded sand returning in the first three months) but gradually decreasedin rate (51% in the first six months). Recovery of dune systems eroded during the storm on the other hand was initially minor (6% of eroded dune volume returning in three months), but gradually increased in rate(19% in six months). Significant spatial variability in the rate of beach recovery was observed, revealing that embayed beach orientation to the prevailing southerly swell waves is a major control determining beachrecovery rates

Penetration of tides and tidal anomalies in new south wales estuaries

Flooding in the coastal waterways of New South Wales is rarely a function of just one source variable, therefore understanding the risk posed by the combined effect of two or more environmental variables such as waves, tide, storm surge, river flow, rainfall, swell and wind is important. This study aims to investigate the penetration behaviour of tides and tidal anomalies into estuaries in NSW. NSW Public Works' Manly Hydraulics Laboratory (MHL) and the University of Queensland (UQ), with input from the Office of Environment and Heritage (OEH), employed a number of different analysis techniques to investigate tides and tidal anomalies in NSW estuaries including harmonic analysis and HiLo analysis. The analysis techniques were used to investigate in detail the behaviour of tides and anomalies for a number of identified anomaly events at six key estuaries in NSW: Brunswick River, Hunter River, Lake Macquarie, Hawkesbury River, Lake Illawarra and Lake Conjola. These key estuaries were chosen due to their relative spread along the NSW coast and as typical representatives of the river, bay, lake and ICOLL estuary types

Techniques for Classifying Seabed Morphology and Composition on a Subtropical-Temperate Continental Shelf

In 2017, the New South Wales (NSW) Office of Environment and Heritage (OEH) initiated a state-wide mapping program, SeaBed NSW, which systematically acquires high-resolution (2–5 m cell size) multibeam echosounder (MBES) and marine LiDAR data along more than 2000 km of the subtropical-to-temperate southeast Australian continental shelf. This program considerably expands upon existing efforts by OEH to date, which have mapped approximately 15% of NSW waters with these technologies. The delivery of high volumes of new data, together with the vast repository of existing data, highlights the need for a standardised, automated approach to classify seabed data. Here we present a methodological approach with new procedures to semi-automate the classification of high-resolution bathymetry and intensity (backscatter and reflectivity) data into a suite of data products including classifications of seabed morphology (landforms) and composition (substrates, habitats, geomorphology). These methodologies are applied to two case study areas representing newer (Wollongong, NSW) and older (South Solitary Islands, NSW) MBES datasets to assess the transferability of classification techniques across input data of varied quality. The suite of seabed classifications produced by this study provide fundamental baseline data on seabed shape, complexity, and composition which will inform regional risk assessments and provide insights into biodiversity and geodiversity