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Tidal range energy comprises a vast theoretical resource of 9,220 TWh per year, globally, with advantageous characteristics of predictability, generation flexibility and reliability. Approximately 13% of this resource lies within the United Kingdom's (UK) coastal waters, where it could supply up to 12% of annual electricity demand. Tidal range energy conversion traditionally involves constructing and operating large-scale coastal or offshore impoundments (O 10-100 km 2), which will redefine near and far-field water levels and flow patterns. The relationship between the scale of the impoundment area and hydrodynamic impact has not been investigated for UK sites. To address this, we develop a two-dimensional (depth-averaged) TELEMAC model of the Irish Sea, and simulate six scenarios involving tidal range schemes of increasing basin area, from 25 to 150 km 2 , located on the North Wales coast in an open coastal basin setting. Results indicate that far-field (30 − 150 km) changes to the amplitude of the semi-diurnal (M 2) tidal constituent exhibit a linear relationship with impoundment area and volume (correlation coefficient R = 0. 95 and R = 0. 96 , respectively). The largest impoundment (150 km 2) caused far-field changes in maximum surface elevation (2 < η m a x < 3 cm); near-field surface elevation was reduced ( η m a x > 3 cm). • The UK has a vast and untapped tidal range energy resource. • Uncertainty regarding hydrodynamic impacts are a key barrier to tidal range energy conversion. • Tidal range impoundment size is linearly correlated with changes in tidal amplitudes. • Tidal amplitudes are reduced near the impoundment (< 50 km), and increased in the far-field (> 50 km). [ABSTRACT FROM AUTHOR]

In some shelf sea regions of the world, the tidal range is sufficient to convert the potential energy of the tides into electricity via tidal range power plants. As an island continent, Australia is one such region – a previous study estimated that Australia hosts up to 30% of the world's resource. Here, we make use of a gridded tidal dataset (TPXO9) to characterize the tidal range resource of Australia. We examine the theoretical resource, and we also investigate the technical resource through 0D modelling with tidal range power plant operation. We find that the tidal range resource of Australia is 2004 TWh/yr, or about 22% of the global resource. This exceeds Australia's total energy consumption for 2018/2019 (1721 TWh/yr), suggesting tidal range energy has the potential to make a substantial contribution to Australia's electricity generation (265 TWh/yr in 2018/2019). Due to local resonance, the resource is concentrated in the sparsely populated Kimberley region of Western Australia. However, the tidal range resource in this region presents a renewable energy export opportunity, connecting to markets in southeast Asia. Combining the electricity from two complementary sites, with some degree of optimization tidal range schemes in this region can produce electricity for 45% of the year. ● The tidal range resource of Australia is 2004 TWh/yr – around 22% of the global resource. ● The resource is primarily concentrated in the Kimberley region of Western Australia. ● Although this region is remote, it represents an export opportunity to SE Asia. ● We optimize the operation of two complementary sites in this region. ● Variability is reduced at both diurnal and semi-diurnal scales. [ABSTRACT FROM AUTHOR]

Tidal energy is one of the most predictable forms of renewable energy. Although there has been much commercial and R&D progress in tidal stream energy, tidal range is a more mature technology, with tidal range power plants having a history that extends back over 50 years. With the 2017 publication of the “Hendry Review” that examined the feasibility of tidal lagoon power plants in the UK, it is timely to review tidal range power plants. Here, we explain the main principles of tidal range power plants, and review two main research areas: the present and future tidal range resource, and the optimization of tidal range power plants. We also discuss how variability in the electricity generated from tidal range power plants could be partially offset by the development of multiple power plants (e.g. lagoons) that are complementary in phase, and by the provision of energy storage. Finally, we discuss the implications of the Hendry Review, and what this means for the future of tidal range power plants in the UK and internationally. [ABSTRACT FROM AUTHOR]

Bahia Magdalena (BM), known for its high primary productivity, is one of the largest tidal lagoons on the Mexican Pacific coast of the Baja California Peninsula. BM is located in an area of active coastal upwelling and significant tides with a maximum range of about 2.4 m. Dissolved inorganic nutrients upwelled from the depths are transported by tidal water exchange into the lagoon, contributing to its fertilisation. To estimate the magnitude and mechanisms driving the tidal exchange of water and nutrients, field observations of the nutrient content were made in the inlet area and on the adjacent shelf during March 2003, December 2004 and June, August and November 2005. In March 2003, the research vessel El Puma carried out a complete hydrological study of the area using Seabird-19 CTD profiler. At the same time, a current meter with a tide gauge was installed in the BM inlet, and multiple measurements of currents were made on a section across the inlet with a SonTek hull-mounted Acoustic Doppler Current Profiler (ADCP). Field studies were complemented by numerical experiments with the hydrodynamic model ECOM 3D. Analysis of the currents in the inlet area, deriving from both the ADCP data and the numerical simulation, indicates that the water volume transported during a semidiurnal tidal cycle through the inlet varied from 0.3 km 3 for neap tide to 0.82 km 3 for spring tide. Net nitrate mass intakes to the lagoon deriving from currents in the mouth can be estimated as 7.0 × 10 3  kg for neap tides and 20.0 × 10 3  kg for spring tides, and the maximum phosphate contribution was estimated at 2.5 × 10 3  kg and 8.5 × 10 3  kg, respectively. Taking into account that fluvial contribution in the lagoon is practically absent, unexpanded mangroves are distributed mainly at its northern part, and organic sediment decomposition is potentially evaluated as low, we can thus conclude that the coupled effect of upwelling and tidal currents play an important role in fertilising the BM. Naturally, this mechanism works only in periods of upwelling activity, namely, from March to June, and to a lesser extent from September to October. [ABSTRACT FROM AUTHOR]

Tidal lagoons are an attractive renewable energy option that could aid the UK in meeting its ambitious renewable energy targets. One of the main barriers to tidal range development in the UK to date has been regulatory environmental concern. In order for the nascent lagoon industry to move forward into development, the views of the developers and other influential stakeholders such as government bodies, regulators, conservationists and practitioners (herein referred to as ‘influencing stakeholders’ or ‘influencers’) need to be aligned. This study is the first of its kind using online questionnaires and semi-structured interviews to present and compare the views of both developers and influencing stakeholders on the environmental interactions of tidal lagoons. We find that, whilst both influencers and developers are working towards the common goal of a good environmental outcome for tidal lagoons, there are mismatches in their views in terms of the priorities given to the key environmental impacts, benefits and potential solution options. The work provides insight into what is at the forefront of developers' and influencers' minds, highlighting the key themes within their views and transforming this information into policy recommendations that will help the industry's development move forward. [ABSTRACT FROM AUTHOR]

Marine renewable energy (MRE) developments often coincide with sites frequented by small cetaceans. To understand habitat use and assess potential impact from development, echolocation clicks were recorded with acoustic click loggers (C-PODs) in Swansea Bay, Wales (UK). General Additive Models (GAMs) were applied to assess the effects of covariates including month, hour, tidal range and temperature. Analysis of inter-click intervals allowed the identification of potential foraging events as well as patterns of presence and absence. Data revealed year-round presence of porpoise, with distinct seasonal and diel patterns. Occasional acoustic encounters of dolphins were also recorded. This study provides further evidence of the need for assessing temporal trends in cetacean presence and habitat use in areas considered for development. These findings could assist MRE companies to monitor and mitigate against disturbance from construction, operation and decommissioning activities by avoiding times when porpoise presence and foraging activity is highest in the area. [ABSTRACT FROM AUTHOR]

Tidal range power plants represent an attractive approach for the large-scale generation of electricity from the marine environment. Even though the tides and by extension the available energy resource are predictable, they are also variable in time. This variability poses a challenge regarding the optimal transient control of power plants. We consider simulation methods which include the main modes of operation of tidal power plants, along with algorithms to regulate the timing of these. This paper proposes a framework where simplified power plant operation models are coupled with gradient-based optimisation techniques to determine the optimal control strategy over multiple tidal cycles. The optimisation results inform coastal ocean simulations that include tidal power plants to gauge whether the benefits of an adaptive operation are preserved once their hydrodynamic impacts are also taken into consideration. The combined operation of two prospective tidal lagoon projects within the Bristol Channel and the Severn Estuary is used as an example to demonstrate the potential benefits of an energy maximisation optimisation approach. For the case studies considered, the inclusion of pumping and an adaptive operation is shown to deliver an overall increase in energy output of 20–40% compared to a conventional two-way uniform operation. The findings also demonstrate that smaller schemes stand to gain more from operational optimisation compared to designs of a larger scale. [ABSTRACT FROM AUTHOR]

Tidal range technology has seen much development and interest in recent years. The times when a barrage scheme would be rejected due to environmental and cost concerns is coming to an end. A large variety of new lower cost and less invasive methods have since emerged in the forms of tidal lagoons, reefs and fences. Since the construction of La Rance in 1967, advancements in turbine technologies and design has since resulted in a plethora of new, exciting turbine designs for tidal energy. A selection of new turbines with possible tidal range applications includes the modified bulb turbine with two sets of guide vanes, a counter-rotating turbine, Archimedes screw and a gyro device. However, the same design is continuously being chosen – the Kaplan bulb turbine. Through the use of a marking criterion covering key aspects that should be considered when choosing a turbine a variety of the new designs available are investigated. The key aspects researched include, environmental effects, the two-way efficiency, initial costs and maintenance costs/difficulty. [ABSTRACT FROM AUTHOR]

Global energy focus is turning more and more towards renewable energy. With legally binding agreements requiring a drastic increase in the percentage of national energy demand created with renewable sources, tidal energy holds an important advantage – predictability. The UK is fortunate, having the greatest potential for this energy in the world, which if exploited, would be able to provide approximately 20% of the national energy demand. The most discussed tidal energy site has been the Severn estuary barrage, with repeated proposals outlined and rejected throughout the last 100 years. The reasons for this refusal were due to both high costs and environmental concerns. However, a new proposal for a tidal lagoon in Swansea Bay has been able to circumnavigate both of these downfalls by reducing both the investment needed and effects to the surrounding environment. Subject to a tidal range of 10.5 m and situated next to a largely populated city with excellent grid connections, Swansea bay is a perfect location. If the lagoon project goes ahead, it would be able to produce a rated output of 320 MW using bulb turbines, powering 155,000 homes. Being the first tidal lagoon project, what is certain is: the UK and Wales in particular are sending out a strong message regarding renewable energy and it has the whole worlds attention. This paper sets out to bring together current literature regarding the planned Swansea Bay tidal lagoon into one concise document. [ABSTRACT FROM AUTHOR]

The number of distributed resources for renewable energy installed worldwide has been increasing rapidly in the last decade, and the great majority of these installations consist of solar panels and wind turbines. Other renewable sources of energy are not exploited to the same level: for instance, tidal energy is still a minute portion of the global energy capacity, in spite of the large amount of potential energy stored in tidal waves, and of the successful experience of the few existing plants. The world’s second largest tidal range occurs in the UK but at the moment tidal installations in this country are limited to a few prototypes. More recently, there has been a renewed interest in harnessing tidal energy in the UK, and a few tidal lagoon projects have been evaluated by the UK government. This paper provides an overview of the historical and current developments of tidal plants, a description of operation of tidal lagoons, challenges and opportunities for their integration within the UK energy systems and solutions to improve the dispatchability of tidal energy. The concepts described in the paper are applied to a tidal project proposed for South Wales.

UK Energy policy is focused on the challenges posed by energy security and climate change, however, efforts to develop a low-carbon economy have overlooked tidal energy a vast and unexploited worldwide resource. Since 1981, UK tidal lagoon schemes have been recommended as an economically and environmentally attractive alternative to tidal barrages. More recently, two proposals for tidal lagoons in Swansea Bay have emerged and there have been several reports documenting the potential to harness significant tidal energy from Swansea Bay using a tidal lagoon. This paper assists in determining a realistic approximation of the energy generation potential in Swansea Bay, a numerical estimation is obtained from a zero dimension, 0D, ‘backwards difference’ computational model, utilising the latest turbine data available and high-resolution bathymetric data. This paper models the behaviour of the tidal lagoon in dual mode generation, in line with the above proposals. The results of model testing using a variety of fixed and variable parameters are displayed. The ebb mode model with provision for pumping at high tide is then explored further by carrying out optimisations of the starting head, number of turbines and turbine diameter in order to determine the maximum annual energy output from the tidal lagoon. [ABSTRACT FROM AUTHOR]

Beach Profiles surveys and gale climate data were utilised to assess medium timescale beach rotation at four beaches located along the shores of a crenulated embayment within Swansea Bay, Southwest Wales. The proposed Tidal Lagoon is located within this Bay. Results identified a 7 year (1998–2005) record of cyclic summer/winter rotation and a 14 year (1999–2013) record of annual rotation within the subaerial zone on all four assessed beaches. In the absence of headlands to trap sediment it is asserted that the driving force for beach rotation is the presence of Swansea Dockland/Tawe dredged channel complex, Port Talbot Harbour and the Neath dredged channel which form surrogate headlands essentially creating four separate beach systems through restricting sediment by-pass. Seasonal averaged wind and wave variables showed differing correlation with volume changes and cross-correlation results showed that volume variation lagged behind forcing variables by up to six months (i.e. the resolution of the data). This was confirmed by the annually averaged results which showed only subtle correlation. Here volume change in most cases lagged forcing variables by less than one year. Based on correlations, wind direction variability follows closely with volume changes but wind speed, wave period and height are generally opposite. Initial results suggest that the proposed Swansea Bay Tidal Lagoon, located between sediment cells and surrogate headlands, would have little negative effect on subaerial coastal processes. These datasets will be used as a benchmark for monitoring prior to, during and post construction, with results being used to update and inform subsequent strategies. [ABSTRACT FROM AUTHOR]

Despite its relatively small amplitude, the nodal tide can play a relevant role in several environmental processes, spanning from ecology to morphodynamics; in particular, field studies and numerical investigations indicate the nodal tide as the dominant factor in long-term and large-scale net sediment transport in some estuaries. Nevertheless, while some important results have been obtained about its morphological effect on estuary channels, the response of tidal flats and salt marshes is still to be investigated. In the present work, a two-dimensional (2D), vertically averaged, long-term morphodynamic model based on the concepts of intertidal dispersion and transport concentration has been applied to the case of a schematic lagoon forced by a nodally-modulated tidal range. The effect of such a periodic oscillation has been studied in terms of sediment fluxes, suspended sediment concentration, and morphology. The results of simulations, carried out starting from different equilibrium conditions in which a nodal perturbation was introduced in the tidal signal, were postprocessed via Fourier analysis to detect the characteristics of the nodal perturbation within the domain and to draw some considerations about the spatial differentiation, in terms of both amplitude and phase, of the morphodynamic response throughout the domain. Although taking into account the nodal contribution has little influence in a long-term (several decades to centuries) analysis, as shown in the current study, such a small oscillation in tidal range (approximately 4%) can locally result in bathymetric oscillations of relevant relative amplitude. [ABSTRACT FROM AUTHOR]

Abstract: This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide. The long-term deposition (or erosion) rate in a given location is expressed as proportional to the difference between the local transport concentration and the local equilibrium concentration, depending in turn on the local stirring action by waves and currents. The two-dimensional model is able to reproduce the ontogeny of a tidal lagoon as a consequence of a breaching of the littoral dune line. During the ontogenetic phase, the system tends rapidly toward a quasi-equilibrium condition apparently characterized by a stable planimetric configuration of the channel network. The structure of the channels and their watersheds is qualitatively similar to the Venice Lagoon''s ones. After the relatively fast ontogenetic phase, the subsequent morphological evolution of the bottom continues at a slower pace until a stable bathymetric configuration of the lagoon is reached. The model is able to reproduce the morphological effects of subsequent perturbations of natural or anthropogenic origin. [Copyright &y& Elsevier]

Abstract: The design and operation of mathematical models of solute mixing and sediment transport in estuaries rely heavily on the provision of good-quality field data. We present some observations of salinity, suspended sediment concentration and velocity at one of the tidal limits of a semi-enclosed tidal lagoon in Southern England (Pagham Harbour, West Sussex, UK) where the natural processes of tidal incursion and solute mixing have been heavily modified as a result of the construction of sea walls dating back to the 18th Century. These observations, made immediately downstream of two parallel tidal flap gates by conductivity-temperature-depth (CTD) profiler, and also using bed-mounted sensor frames to measure velocity at 2 fixed depths, have yielded a set of results covering 11 tidal cycles over the period 2002–04. It is clear from the results obtained that over a typical tidal cycle, the greatest vertical salinity gradients occur in the 1–2h immediately after the onset of the flood tide, and that subsequently, energetic mixing acts to rapidly break down this stratification. Under moderate-to-high fresh water flows (>0.5m3/s), the break-down in vertical salinity gradient is more gradual, while under low fresh water flows (<0.2m3/s), the vertical salinity gradient is generally less pronounced. Estimates of Richardson number during the early flood-tide period reveal values that vary rapidly between <1 and about 20, with lower values occurring after around 1.5–2h after low water. Observations of suspended sediment concentration vary widely even for similar tidal and fresh water flow conditions, revealing the possible influence of wind speed, the storage effects of the water in the lagoon downstream of the observation site, and the complexity of the hydrodynamics downstream of tidal flap gates. The data also show that most of the sediment transport is landward, and occurs during flood tides, with estimated total tidal landward flood tide flux of fine sediment of the order of 50–120kg under low fresh water flow conditions. These observations, which reinforce the results presented in Warner et al. (2004) and elsewhere, can help to provide information about the appropriate techniques for managing sediments and pollutants, including nutrients from sewage effluent waters, in estuaries where hydraulic flap gates are used to control the entry of fresh water over the tidal cycle. [Copyright &y& Elsevier]

Tidal energy has a significant advantage over many other forms of renewable energy because of the predictability of tides. Tidal Range Structures (TRSs) are one of the main forms of tidal renewable energy. Designing the operation of TRSs is one of the challenging aspects in early stages due to the large variety of scenarios. Traditionally this has been done using a grid search. However, grid search can be very elaborate and time consuming during the design of TRSs. This paper proposes a novel and more efficient method to optimise the design of the operation of TRSs by maximising their electricity generation using a Genetic Algorithm. This GA model is coupled with a 0-D model which breaks the tides into small units and considers flexible operation. This approach delivered more than a 10% increase in electricity generation when compared to non-flexible operation, i.e. using fixed heads for all tides, just by optimising the operation. The GA model was able to achieve the same amount of electricity compared to the best grid search method with flexible operation more efficiently, i.e. with about a 50% reduction in simulation time. The feasibility of the elite operational scheme is validated through a developed 2-D model. • GA model coupled with an enhanced 0-D model to optimise Tidal Range Schemes. • The GA model considers flexible operation for each half tide and includes pumping. • The GA model achieved the same amount of electricity in less than 50% of time. • Operation designed by the GA model was validated with a 2-D model. [ABSTRACT FROM AUTHOR]