Darrell Strauss

Assessment of Post-Storm Recovery of Beaches Using Video Imaging Techniques: A Case Study at Gold Coast, Australia

Ever-expanding networks of surf cameras offer a unique opportunity to monitor the coastline over large expanses at very little cost compared to traditional in situ survey methods. Here, we describe and test a new coastal monitoring system maintained by CoastalCOMS Pty Ltd. at their test site at Gold Coast, Australia. The two-camera system monitors two highly sensitive 4-km stretches of sandy coastline adjacent to high-value assets. The traditional static multi-camera setup has been replaced by a single rotational camera. A 14-month data set, encompassing one major storm, a recovery period, and a seasonal cycle, was analyzed. Positive shoreline detections using the new camera system were available 64% of the time (roughly 145 days of the available 226, where daily offshore significant wave heights Hs ≤ 1 m). Comparison of the CoastalCOMS-derived shorelines and in situ survey data showed a mean shoreward bias of 25.5 m. Daily shoreline estimates were used to calculate weekly and five-week running mean beach widths at both sites. Analysis showed that both sites eroded between 15-22 m during the May 2009 storm and then recovered during the proceeding five-month calm period. Distinct intersite variability was observed between the more exposed Northern Beaches that displayed an annual shoreline cycle and very little intrasite variability and the more sheltered southern Palm Beach site that displayed large intrasite spatial variability and sensitivity to changes to both wave direction and wave height.

Empirical Estimation of Nearshore Waves From a Global Deep-Water Wave Model

Global wind-wave models such as the National Oceanic and Atmospheric Administration WaveWatch 3 (NWW3) play an important role in monitoring the worlds oceans. However, untransformed data at grid points in deep water provide a poor estimate of swell characteristics at nearshore locations, which are often of significant scientific, engineering, and public interest. Explicit wave modeling, such as the Simulating Waves Nearshore (SWAN), is one method for resolving the complex wave transformations affected by bathymetry, winds, and other local factors. However, obtaining accurate bathymetry and determining parameters for such models is often difficult. When target data is available (i.e., from in situ buoys or human observers), empirical alternatives such as artificial neural networks (ANNs) and linear regression may be considered for inferring nearshore conditions from offshore model output. Using a sixfold cross-validation scheme, significant wave height Hs and period were estimated at one onshore and two nearshore locations. In estimating Hs at the shoreline, the validation performance of the best ANN was r=0.91, as compared to those of linear regression (0.82), SWAN (0.78), and the NWW3 Hs baseline (0.54)

Using generalized additive modelling to understand the drivers of long-term nutrient dynamics in the Broadwater Estuary (a subtropical estuary), Gold Coast, Australia

ABSTRACT Richards, R.; Chaloupka, M.; Strauss, D., and Tomlinson, R., 2014. Using generalized additive modelling to understand the drivers of long-term nutrient dynamics in the Broadwater Estuary (a subtropical estuary), Gold Coast, Australia. Conclusions drawn from comparing short-term monitoring data with a baseline data set and water-quality guidelines need to be viewed in the context of numerous physical and biogeochemical mechanisms controlling nutrient concentrations within a system over long timescales. This paper highlights the use of generalized additive models (GAMs) to explore the functional relationships between four commonly used water-quality indicators (total nitrogen, total phosphorous, ammonia, nitrate) and a range of drivers including catchment inflow, wind speed, and tidal current. The results of this GAM assessment highlighted that nutrient concentrations within a subtropical estuary (Broadwater, Australia) is most dependent on catchment inflow. In particular, this assessment indicated the apparent importance of the Nerang River as a determinant of the nutrient concentrations observed in the Broadwater compared with the role of other tributaries, even though these other rivers provide the bulk of the freshwater flow into the system. This assessment also highlighted that the potential effects of monitoring location, tides, wind, and monitoring year need to be accounted for when framing the results of short-term data.

A new system for breakzone location and the measurement of breaking wave heights and periods.

This paper presents a new system for measuring breakzone locations, breaking wave height and wave periods across the surfzone from a digital video sequence. The system (Wave Pack) aims to provide real-time measurement of breaking and re-breaking wave heights and wave periods using low mounted video camera installations. Following on site data collection and analysis it was found that the Wave Pack system provides a low cost, robust, reliable and accurate system for measuring continuous wave height and period from a low elevation video camera aimed at the target beach under a wide range of wave conditions. These tests have verified the accuracy of Wave Pack in comparison to existing systems.

Modelling Transitions Between Barred Beach States on a Straight Coast

The utility of numerical models of beach morphodynamics is constrained by our ability to establish that the theoretical dynamics match reality. The inherent difficulty in collecting suitable validation data for spatial and temporal bathymetric models of beach evolution has resulted in relatively few studies which perform empirical validation of nearshore morphological models. The present study addresses the validity of morphological modelling of an exposed beach by qualitatively comparing the evolution of a numerically modelled beach state transition with data observed using remote imaging. The application of the numerical model was broadly validated, in that, when forced with parameterised wave conditions, the morphological development is consistent with that observed via optical sensing.

Beach nourishment and coastal protection along the Gold Coast, Australia: a case study at Palm Beach

Effectively managing coastal beaches in areas exposed to high wave climate variability requires an appraisal of all the stakeholder interests and consideration of the above into a decision making framework. The popularity of the Gold Coast beaches as a national and international tourist destination as well as the increasing residential population ensures that the care of beaches maintains a high priority for the local government. Lessons learned from past management strategies are reviewed and a new methodology for assessment of beach condition is presented here which integrates the primary descriptors of beach health for the Gold Coast region of Australias East Coast.

Effect of environmental conditions on cetacean entanglements: a case study from the Gold Coast, Australia

Entanglement of marine mammals in fishing gear is recognised worldwide and is a continuous management concern. Gill-net entanglement data from the Queensland Shark Control Program (QSCP) on the Gold Coast, Australia, from 1990 to 2012 were analysed in the present study. Environmental drivers that may affect entanglements of humpback whales (Megaptera novaeangliae) and common dolphins (Delphinus delphis) were selected. M. novaeangliae entanglements coincided with their annual migration, with the greatest occurrences in September. D. delphis were mostly entangled from March to November, with the greatest occurrences in June. For both species, entanglements primarily occurred when the wave height was between 0.5 and 1.25m, the wave power was between 0 and 5kWm–1 and the wind speed was between 12 and 19kmh–1. M. novaeangliae entanglements were significantly more likely to occur in low rainfall (<6mmh–1), and D. delphis entanglements were more likely to occur during spring tides. There was a correlation between entanglements and the position of the East Australian Current’s (EAC) maximum velocity, with 73% of M. novaeangliae entanglements and 79% of D. delphis entanglements occurring when the EAC’s maximum velocity was west (shoreward) of its average position at 154°E. The present study provides the first set of possible management intervention targets associated with environmental conditions.

Hydrosedimentological Modelling of a Small, Trained Tidal Inlet System, Currumbin Creek, Southeast Queensland, Australia

ABSTRACT Shaeri, S.; Strauss, D.; Etemad-Shahidi, A., and Tomlinson, R., 2018. Hydrosedimentological modelling of a small, trained tidal inlet system, Currumbin Creek, southeast Queensland, Australia. Small tidal inlets with an entrance width of less than 50 m or a cross-sectional area of less than 100 m2 have not been investigated as often as their larger counterparts. To discern the major processes responsible for entrance infilling in a small inlet system, the hydrosedimentological processes in the annually dredged Currumbin Creek (Australia) inlet system were investigated. Delft3D was applied and validated using local field measurements and regional data. A standalone regional hydrodynamic model and three nested standalone wave models provided detailed data for the offshore boundary of the more detailed creek entrance model, which was a coupled, local flow–wave–sediment transport model. The noncohesive sediment transport module was calibrated based on the volume of dredging and the net annual volume of longshore transport. The results of this hindcast model provided insight into the dominant processes responsible for the inlets current configuration (i.e. significant refraction of incident waves to a nearly shore normal direction; a noteworthy onshore-offshore transfer of sediments; channel infilling induced by wave-induced currents; very limited sediment transport within the back-barrier lagoon because of an absence of wave-induced currents, as well as weak tide-induced currents; and infilling of the dredged area because of immersed slope stability, rather than hydrodynamic processes). Overall, the adopted modelling approach and the selected model setups proved to be a suitable combination of the available resources and tools to forecast the influence of any alteration to the current maintenance strategy. Accordingly, the identified physical processes and findings can be applied to similar cases with narrow inlet entrance widths and small back barriers with limited circulation.