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An understanding of suspended particulate matter (SPM) dynamics is of great importance to design awareness and management strategies of estuaries. Using a Laser In Situ Scattering and Transmissiometry (LISST) instrument, variations in suspended particle size volumetric concentrations (VC) and particle size distributions (PSD) were measured at six sites within Port Curtis estuary (Australia). The port is a macrotidal estuary with significant economic and environmental importance. Observed VC and SPM sizes demonstrated spatial and temporal trends strongly controlled by the variable energy conditions operating on the neap and spring cycle timescale, with a clear trend towards increasing concentrations and decreasing SPM sizes with increasing tidal ranges. Mid-estuary sites were characterized by the greatest depth-averaged VC under transitional and spring conditions. Estuary-wide mean spring tide total water profile concentrations revealed a near 300% increase in comparison to neap tide condition concentrations. In the upper-estuary sites the mean contribution of the combined 2.5–35 µm size classes to the total profile PSDs was greatest during all tidal conditions, whilst within the lower-estuary site the combined 35–130 µm size classes were greatest. Mean contributions of the largest size class (300–500 µm) dominated surface-waters throughout the estuary during the neap tide period, which when compared with the transitional and spring tide conditions, demonstrated changes of −82% to −48% and −82% to −40%, respectively. Overall, the results from this case study provides further evidence of the important influence of neap and spring tidal regimes on SPM dynamics within estuarine settings and the need to observe parameter dynamics on such timescales. [ABSTRACT FROM AUTHOR]

Banks Strait, Tasmania, Australia, has been identified as a potential site for the deployment of tidal turbines. In this study, the characterization of sediment transport and large sand waves for this site is performed. Observations of bed level change collected from surveys in 2018 showed a migration of large sand waves over a period of nine months. Migration rates in an excess of one hundred meters for nine months were found, which are large compared to the rate reported at other coastal sites, by several meters per year. A validated hydrodynamic model is coupled with a morphodynamic model to perform sensitivity tests and identify what parameters influence migration to better understand sediment dynamic in the Banks Strait. Numerical analysis showed a constant shift of the sand waves profile in an eastward direction, consistent with the observations. This migration was strongly linked with tidal asymmetry, with a residual current flowing towards the east. The principal parameters driving the migration of sand waves in the Banks Strait were found to be sediment sorting, bed friction and residual current. This study gives new insights for the seabed of Banks Strait and provides an assessment of the natural variability of sediment for futures tidal farms deployments. [ABSTRACT FROM AUTHOR]

The development of tidal energy in Australia is still a challenge with few studies performed on the characterisation of the resource, due to the difficulty to acquire data and uncertainties about the influence of this anthropogenic activity on the marine environment. Changes in flow could lead to alterations in sediment transport and have further influence on the marine habitat. A case study in a promising area, Banks Strait (Australia), was created using high resolution 2D and 3D models validated against in situ data to investigate changes to hydrodynamic conditions with two scenarios of tidal farms (100 and 300 turbines). Comparison between 2D and 3D is performed to find the best compromise between model accuracy and computational time for preliminary assessment. Changes to current speed and bed shear stress over a 35 day period were found to be localised around the tidal farms and did not extent more than 7 km from the farm (300 turbines) for both 2D and 3D. The results showed that for near field and far field, 2D models are sufficient to give a first approximation of the hydrodynamic influence of tidal farm deployment on its environment. [ABSTRACT FROM AUTHOR]

Modelling investigations into the local changes in the shoreline resulting from enhanced atmospheric greenhouse gas concentrations and global climate change are important for supporting the planning of coastal mitigation measures. Analysis of Global Climate Model (GCM) and Regional Climate Model (RCM) simulations has shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in south-eastern Australia, is situated in a region that may experience noticeable future changes in longshore winds, waves and coastal currents, which could alter the supply of sediments to the shoreline. This paper will demonstrate a downscaling procedure for using the data from GCM and RCM simulations to force a local climate model (LCM) at the beach scale to simulate additional nearshore wind-wave, hydrodynamic and sediment transport processes to estimate future changes. Two types of sediment transport models were used in this study, the simple empirical coastline-type model (CERC equation), and a detailed numerical coastal area-type model (TELEMAC). The two models resolved transport in very different ways, but nevertheless came to similar conclusions on the annual net longshore sediment transport rate. The TELEMAC model, with the Soulsby-Van Rijn formulation, showed the importance of the contribution of storm events to transport. The CERC equation estimates more transport during the period between storms than TELEMAC. The TELEMAC modelled waves, hydrodynamics and bed-evolutions are shown to agree well with the available observations. A new method is introduced to downscale GCM longshore sediment transport projections using wave-transport-directional change parameter to modify directional wave spectra. We developed a semi-empirical equation (NMB-LM) to extrapolate the ~3.7-year TELEMAC, storm dominated transport estimates, to the longer ~30-year hindcast climate. It shows that the shorter TELEMAC modelled period had twice as large annual net longshore sediment transport of the ~30 year hindcast. The CERC equation does not pick up this difference for the two climate periods. Modelled changes to the wave transport are shown to be an order of magnitude larger than changes from storm-tide current and mean sea level changes (0.1 to 0.2 m). Discussion is provided on the limitations of the models and how the projected changes could indicate sediment transport changes in the nearshore zone, which could impact the coastline position. [ABSTRACT FROM AUTHOR]