Tidal flow can generate unsteady wakes, large eddies, and recirculation zones in the lee or around complex natural and artificial obstructions, such as islands, headlands, or harbours. It is essential to understand the flow patterns around such structures given the potential impacts they can have on sedimentation, the marine environment, ecology, and anthropogenic activities. In this paper, the wake around an island in a macro-tidal environment has been studied using a widely used hydro-environmental model, Telemac-2D. Current data collected using moored acoustic Doppler current profilers (ADCPs) were used to validate and refine the Telemac-2D model. Four different turbulence models and several different solver options for the k- ε model were tested in this study to assess which representation could best replicate the hydrodynamics. The classic k- ε model with the solver of conjugate residual was the most suitable method to simulate the wake in the lee of the island. The model results showed good correlation with measured data. The island wake parameter used to predict the wake behaviour and its predictions matched the model results for different tidal conditions, suggesting that the island wake parameter could be used to predict the wake behind obstacles in macro-tidal environments. The model predictions showed the development of a wake is similar between ebb and flood tides in the neap tide while showing more difference in spring tide. With the increase of velocity in the neap tide, two side-by-side vortices will appear and then changing to stable Karman Vortex Street. During the ebb phase of spring tide, the wake will develop from a stable vortex to an unstable Karman Vortex Street, while the wake remained stable with two vortices during an flood tide.

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<div> <div> <p>The Bristol Channel and Severn Estuary comprise the area most thoroughly investigated for tidal lagoons development, due to its second largest tidal range in the world and the high demand for clean electricity in the surrounding area. Accurate hydrodynamic modelling of tidal lagoons is a solid foundation for predicting potential electricity generation and environmental impact assessment. However, it is reported that in correct selection of an open boundary may amplify any disturbance associated with the tidal lagoons by affecting the resonant modes. Thus a model that simply held the identical open boundary condition for pre- and post-lagoons conditions may contain inaccuracies in the electricity generation and the impacts on the hydrodynamics of the region.</p> <p>To investigate the influence of open boundary location on tidal lagoon modelling, the West Somerset Lagoon (WSL) was simulated using different hydrodynamic models with different open boundary locations. Two hydrodynamic models were established using the TELEMAC system, one of which covers the whole Bristol Channel and Severn Estuary (SEBC) as the most prior research used. Another one is a Continental Shelf (CS) model, which was centred on the Bristol Channel, and has its open boundary extended beyond the Continental Shelf. Both SEBC and CS models were run for pre- and post-WSL, to achieve the power output of WSL and the hydrodynamic impact in each model. The WSL was introduced into both hydrodynamic models using the domain decomposition method, and full momentum conservation was achieved by refining the momentum source terms at the turbine locations.</p> <p>Although the hydrodynamic influences were generally similar between CS and SEBC models, results showed the influence of WSL on water level extended to the outer Bristol Chanel in the CS model, with over 10 cm decrease of tidal range on the location of the open boundary of SEBC model. However, there was a minor difference in far-field velocities prediction between the two models. The annual energy generation of WSL using the different models showed slight differences, i.e. less than 6%. However, this could also be exacerbated by the fact that similar operation was used in both scenarios.. This study concludes that  SEBC could be considered as a suitable model for early-stage studies and preliminary environmental impact modelling due to lower computational and set up time requirements. However, for later stages of the TRS design, such as power prediction for accurate revenue assessment and business case development, then a more precise open boundary condition is expected to be needed, either by extending the model domain to the Continental Shelf or theoretically modifying the open boundary characteristics.</p> </div> </div>

<p>The ocean tides are a key driver of a range of Earth system processes. Tidal energy drives vertical mixing with consequences for ocean circulation, climate, and biological production, and the tidal stream transport sediments, pollutants, and other matter through the ocean. On long time-scales tidal drag acts to slow down Earth’s spin, which means the Moon must move away from Earth to conserve angular momentum. The problem here is that the age of the moon doesn’t fit today’s recessions rate and it has been suggested that the tides must have been much weaker for prolonged periods of Earth’s history. Numerical modelling efforts over the past decade have shown that the tides today are very large and a poor representation of past tides, and that for the past 1.5 Gyr, tidal dissipation rates have been around 45% of present-day values. Here, we present a new series of high-resolution simulations of Phanerozoic tides and discuss sensitivity to topography, forcing, and ocean stratification. The results confirm previous results about dissipation rates obtained at lower resolution. Furthermore, we apply proxies for tides collated from the geological literature for three selected periods (the Devonian, Jurassic, and Cretaceous) and show that our simulations mostly conform well with the proposed tidal characteristics from the proxies. The simulations also show that the most important controller of tides on long scales is tectonics: the locations of the continents set the size of ocean basins, and basins of the right size can host very large tides due to tidal resonance. Consequently, the supercontinent cycle generates a corresponding supertidal cycle with weak tides during supercontinent stages and a series of tidal maxima during the dispersion and assembly of the supercontinent.</p>