Tidal Barrages Research Papers - Academia.edu (original) (raw)

As tidal turbine farms grow they interact with the larger scale flow along a channel by increasing the channel's drag coefficient. This interaction limits a channel's potential to produce power. A 1D model for a tidal channel is combined with a theory for turbines in a channel to show that the tuning of the flow through the turbines and the density of turbines in a channel's cross-section also interact with the larger scale flow, via the drag coefficient, to determine the power available for production. To maximise turbine efficiency, i.e. the power available per turbine, farms must occupy the largest fraction of a channel's cross-section permitted by navigational and environmental constraints. Maximising of power available with these necessarily densely packed farms requires turbines to be tuned for a particular channel and turbine density. The optimal through-flow tuning fraction varies from near 1/3 for small farms occupying a small fraction of the cross-section, to near 1 for large farms occupying most of the cross-section. Consequently, tunings are higher than the optimal through-flow tuning of 1/3 for an isolated turbine from the classic turbine theory. Large optimally tuned farms can realise most of a channel's potential. Optimal tunings are dependent on the number of turbines per row, the number of rows, as well as the channel geometry, the background bottom friction coefficient and the tidal forcing.

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- Marine Renewable Energy, Tidal Stream Energy, Tidal Stream Turbine Modelling, Tidal turbine

Stilling basins are in common use when designing heading-up hydraulic structures such as barrages, dams, weirs, …etc. Careful investigation of the flow characteristics and associated flow phenomena should be conducted before constructing such important and costly structures. During this phase, many scenarios are tested to conclude the basic features of the safe design and to suggest and test proposed solutions of the observed harmful flow-associated problems. Generally, the investigated flow characteristics may include the main parameters of the submerged hydraulic jump, the vertical velocity distribution along the bed, the velocity decay, and the stability of bed protection downstream the apron of the stilling basin. In the present research paper, these characteristics will be tested in a pool-type stilling basin with multi-end steps downstream (DS) Naga Hammadi Barrages physical model. The used flume had 1.0 m wide, 26.0 m long and 1.20 m deep. The results of the tested models were compared to conclude the optimal hydraulic design criterion. Each model was tested under 36 different flow conditions. This extensive investigation revealed that the optimal design should satisfy the criteria e/H u =0.14 and k 2 /H u =0.14 where e is the height of the pool at the inlet and k2 is the height of the pool at the outlet. The design will be optimal if it produces the shortest length of submerged hydraulic jump, faster decay of near-bed-velocity, shortest length from the gate to the section where the velocity distribution is fully developed, minimum scour dimensions DS of basin and hence the highest stability of bed protection.

- by Mohamed Elgamal and +1
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- Engineering, Traffic Flow Characteristics, Tidal Barrages, Velocity Distribution in Open Channel

We discuss certain design aspects of tidal lagoons to inform future proposals. We demonstrate the tidal lagoon representation within a 0-D and 2-D hydrodynamic modelling framework. We examine the potential of simplified 0-D modelling techniques for operation optimisation. We highlight the extent where 2-D hydrodynamic model power predictions can deviate from 0-D modelling.

Abstract
The renewable energy route map for Wales outlines ambitious targets for 50% renewables by 2025. The Welsh coast, subject to tidal ranges of the order of 13m and tidal flows in excess of 3 m/s, is thus in an ideal position to
significantly contribute to these targets. Tidal stream energy is an emerging energy sector and a relatively small number of devices are at various stages of development in Wales. However, before such demonstration devices or
arrays can be applied at a larger scale, a number of consents and permissions must be obtained to ensure safe and environmentally responsible deployment. This paper describes the multidisciplinary work that has been undertaken on an area of ocean that could be used for the
deployment of a tidal stream turbine. The paper aims to put the scientific work undertaken into the context of device deployment in a complex marine environment and to provide an overview of the surveying and modelling
required for the deployment of a single demonstration device off the Welsh coast. The Bristol Channel was chosen as a case study because of its high tidal flows and proximity to national grid connections and support
infrastructure. This paper provides an overview of the research carried out during the project; the details of each discipline will be provided in individual papers by the respective subject authors

- by Roger A Falconer
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- Tidal Stream Turbine Modelling, Tidal turbine, Tidal Barrages

The feasibility and sustainable operation of tidal lagoons and barrages has been under scrutiny over uncertainties with regards to their environmental impacts, potential interactions and energy output. A numerical modelling methodology that evaluates their effects on the hydro-environment has been refined to consider technical constraints and specifications associated with variable turbine designs and operational sequences. The method has been employed to assess a number of proposals and their combinations within the Bristol Channel and Severn Estuary in the UK. Operational challenges associated with tidal range power plants are highlighted, while also presenting the capabilities of modelling tools tailored to their assessment. Results indicate that as the project scale increases so does its relative hydrodynamic impact, which may compromise annual energy output expectations if not accounted for. However, the manner in which such projects are operated can also have a significant impact on changing the local hydro-environment, including the ecology and morphology. Therefore, it is imperative that tidal range power plants are designed in such a way that they efficiently tap into the renewable energy sources, with minimal interference to the regional hydro-environment through their operation.

- by Athanasios Angeloudis
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- Tidal Barrages, Coastal Ocean Modeling, Tidal energy, Severn Barrage

The present paper aims to analyze and develop theoretical equations for submerged Hydraulic Jump (H.J) characteristics created downstream of Barrages. An extensive experimental program has been conducted on a model simulating Assuit barrages in HRI. A sharp discontinuous current deflector has been used to control the hydraulic jump. The basic hydraulic flow equations have been used to develop theoretical equations for the relative depth and energy loss of the jump. The characteristics of the jump formed without the current deflector are compared to that of the jump formulated under the presence of the current deflector. Empirical model is proposed to compute the length of the submerged hydraulic jump based on the result of the dimensional analysis using multiple linear regression analysis. The derived theoretical models are in good agreement with the experimental results. So, the developed equations can be used in the design field. The derived statistical model is in a good agreement with the experimental results.

- by Abdelazim Negm
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- Tidal Barrages

Abstract
The Bristol Channel and Severn Estuary constitute a large, semi-enclosed body of water in the southwest part of the UK. Communities have settled in the coastal lowlands of this estuary for hundreds of years, and many of these lowlands and settlements have been subject to sea floods and have relied on the protection of artificial sea defences. In England and Wales alone it is estimated that 5 million people and 2 million properties are currently at risk of flooding, and many of these are located in coastal floodplains. Because of the future sea level rise and the occurrence of extreme tides due to climate change, the probability of coastal flooding risk in the Severn Estuary will increase accordingly. Therefore, it is significant to predict the future status of coastal flooding in the Severn Estuary using the scenarios with the effect of climate change. In this study, an existing two-dimensional hydrodynamic model is outlined, which is based on an unstructured triangular mesh and a finite volume algorithm, and can simulate the processes associated with the operation of a barrage. Three scenarios at the open seaward boundary were then proposed, including the observed water level hydrograph as the baseline (scenario I), the current hydrograph plus a sea level rise of 1.0 m (scenarios II) and the current hydrograph in Scenario I with a surge height of 1.0 m (scenarios III). Finally, the numerical model was used to simulate the hydrodynamic processes in the Severn Estuary using three seaward boundary scenarios for the conditions without and with the Severn Barrage. Simulated results show that: (i) without the barrage, the mean maximum water level could rise by 1.0-1.2 m due to sea level rise, and the effect of extreme tides on the distribution of maximum water levels will be noticeable only in the outer estuary reach; and (ii) with the barrage, the mean value of maximum water levels could reduce by 1.0 m upstream of the barrage even if a sea level rise of 1.0 m will occur, and extreme tides could not influence the distribution of maximum water levels upstream of the barrage.

- by Roger A Falconer
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- Flood Risk Management, Tidal Stream Energy, Tidal Barrages

The renewable energy route map for Wales outlines ambitious targets for 50% renewables by 2025. The Welsh coast, subject to tidal ranges of the order of 13 m and tidal flows in excess of 3 m/s, is thus in an ideal position to significantly contribute to these targets. Tidal stream energy is an emerging energy sector and a relatively small number of devices are at various stages of development in Wales. However, before such demonstration devices or arrays can be applied at a larger scale, a number of consents and permissions must be obtained to ensure safe and environmentally responsible deployment. This paper describes the multidisciplinary work that has been undertaken on an area of ocean that could be used for the deployment of a tidal stream turbine. The paper aims to put the scientific work undertaken into the context of device deployment in a complex marine environment and to provide an overview of the surveying and modelling required for the deployment of a single demonstration device off the Welsh coast. The Bristol Channel was chosen as a case study because of its high tidal flows and proximity to national grid connections and support infrastructure. This paper provides an overview of the research carried out during the project; the details of each discipline will be provided in individual papers by the respective subject authors.

- by Reza Ahmadian and +6
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- Civil Engineering, Renewable Energy, Marine Renewable Energy, Tidal Stream Energy

This paper presents an investigation of the impacts of a Severn Barrage on the hydro-environment of the Bristol Channel and Severn Estuary using the Environmental Fluid Dynamics Code (EFDC) model with a recently developed Barrage module (EFDC_B). Details are given of a barrage module being implemented into the EFDC model to represent the various hydraulic structures, such as turbines and sluice gates, as deployed along the barrage line. Several cases, both with and without the barrage, have been simulated to investigate the potential changes on the peak water levels, minimum water depths and peak tidal currents arising from a barrage. The impacts of a barrage on the salinity concentration distribution have also been simulated in both 2D and 3D modes. The predicted results showed that the maximum water levels could be significantly reduced, especially downstream of the barrage and for much of the region in the Severn Estuary and that the minimum water depths would be changed so much that there would be 80.5 km2 loss of intertidal habitats due to the sitting of a barrage across the estuary. Likewise, the peak tidal currents would be considerably reduced, and by as much as a half in the middle of the main channel. The predicted salinity concentrations results indicated that at high water, the salinity concentrations would be reduced by 1–2 ppt downstream and upstream of the barrage and salinity concentrations in the region near Beachley would be reduced by up to 5 ppt, and that at low water, salinity concentrations would be reduced by 0.5–1 ppt in the middle of the Bristol Channel and by typically 0.5 ppt and 1 ppt downstream and upstream of the barrage, respectively. The predicted results also indicated that salinity concentrations downstream and upstream of the barrage would be under a stable state with slight oscillations all the time due to the effects of the barrage. A comparison between the salinity concentration distributions predicted by the 2D and 3D models indicated that the two models produced similar salinity distributions, especially in the Severn Estuary and in the region between the middle of the Bristol Channel and the seaward open boundary.

- by Roger A Falconer
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- Hydrodynamics (Physics), Numerical Modelling, Salinity, Tidal Barrages

This paper describes an exercise completed by sixth form college students to compare the power output from a local coal fired power station with the potential power output from renewable sources including wind farms, solar farms, and the... more

- by Pam Dugdale
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- Renewable Energy, Tidal Stream Energy, Sustainable Energy, Physics Education

Tidal turbines in strong flows have the potential to produce significant power. However, not all of this potential can be realized when gaps between turbines are required to allow navigation along a channel. A review of recent works is used to estimate the scale of farm required to realize a significant fraction of a channel's potential. These works provide the first physically coherent approach to estimating the maximum power output from a given number of turbines in a channel. The fraction of the potential realisable from a number of turbines, a farm's fluid dynamic efficiency, is constrained by how much of the channel's cross-section the turbines are permitted to occupy and an environmentally acceptable flow speed reduction. Farm efficiency increases as optimally tuned turbines are added to its cross-section, while output per turbine increases in tidal straits and decreases in shallow channels. Adding rows of optimally tuned turbines also increases farm efficiency, but with a diminishing return on additional rows. The diminishing return and flow reduction are strongly influenced by how much of the cross-section can be occupied and the dynamical balance of the undisturbed channel. Estimates for two example channels show that realizing much of the MWatt potential of shallow channels may well be possible with existing turbines. However unless high blockage ratios are possible, it will be more difficult to realize the proportionately larger potential of tidal straits until larger turbines with a lower optimum operating velocity are developed.

Stilling basins are in common use when designing heading-up hydraulic structures such as barrages, dams, weirs, …etc. Careful investigation of the flow characteristics and associated flow phenomena should be conducted before constructing such important and costly structures. During this phase, many scenarios are tested to conclude the basic features of the safe design and to suggest and test proposed solutions of the observed harmful flow-associated problems. Generally, the investigated flow characteristics may include the main parameters of the submerged hydraulic jump, the vertical velocity distribution along the bed, the velocity decay, and the stability of bed protection downstream the apron of the stilling basin. In this paper, these characteristics will be tested in a pool-type stilling basin with multi-end steps downstream (DS) of Naga Hammadi barrages physical model. The used flume has 1.0 m wide, 26.0 m long and 1.20 m deep. The results of the tested models were compared to conclude the optimal hydraulic design criterion. Each model was tested under 36 different flow conditions. This extensive investigation revealed that the optimal design should satisfy the criteria e/H u =0.14 and k 2 /H u =0.14 where e is the height of the pool at the inlet and k2 is the height of the pool at the outlet. The design will be optimal if it produces the shortest length of submerged hydraulic jump, faster decay of near-bed-velocity, shortest length from the gate to the section where the velocity distribution is fully developed, minimum scour dimensions DS of basin and hence the highest stability of bed protection.

Marine renewable energy is playing an increasing significant role in many parts of the world, mainly due to a rise in the awareness of climate change, and its detrimental effects, and the increasing cost of natural resources. The Severn Estuary, located between South West England and South Wales, has a tidal range of up to 14 m which makes it the second highest tidal range in the world. There are a number of barrage proposals amongst various marine renewable energy schemes proposed to be built in the estuary. The Cardiff-Weston STPG (Severn Tidal Power Group) Barrage, which would be one of the world's largest tidal renewable energy schemes if built, is one of the most publicised schemes to-date. This barrage would generate about 17 TWhr/annum of power, which is approximately 5% of the UK's electricity consumption, whilst causing significant hydro-environmental and ecological impact on the estuary. This study mainly focuses on investigating the hydro-environmental impacts of the STPG barrage for the option of two-way generation, and compares this with the commonly investigated option of ebb-only generation. The impacts of the barrage were modelled by implementing a linked 1-D/2-D hydro-environmental model, with the capability of modelling several key environmental processes. The model predictions show that the hydroenvironmental impacts of the barrage on the Severn Estuary and Bristol Channel, such as changes in the maximum velocity and reduction in suspended sediment and bacteria levels,

The potential impacts of ebb-only (one-way) and flood-ebb (two-way) modes of operation of a tidal barrage on the eutrophication potential of the Severn Estuary were investigated in this study using the simple modelling approach adopted by the UK’s Comprehensive Studies Task Team (CSTT). The model predictions were compared against CSTT thresholds for assessing eutrophication in estuaries and coastal waters. For the no barrage scenario, as well as the ebb-only and flood-ebb operating modes, the estuary was found to be potentially eutrophic as the predicted equilibrium nutrient concentrations and potential maximum phytoplankton biomass chlorophyll concentrations exceeded the threshold limits. Potential maximum phytoplankton primary productivity under both ebb-only and flood-ebb operating modes were found to be noticeably higher than that for the no barrage scenario. This is believed to be due to a combination of increased water residence time and greater light availability behind the barrage. However, the conditions for phytoplankton production are likely to be more favourable under ebb-only operating mode as the potential for maximum phytoplankton primary production was found to be significantly increased under ebb-only operating mode, with largely decreased suspended particulate matter concentration compared to flood-ebb operating mode where only a small reduction in suspended particulate matter concentration is predicted.

- by Roger A Falconer
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- Marine Renewable Energy, Eutrophication, Tidal Barrages, Primary Production

- by Margaret Kadiri
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- Marine Renewable Energy, Water quality, Phytoplankton, Eutrophication

Stilling basins are in common use when designing heading-up hydraulic structures such as barrages, dams, weirs, …etc. Careful investigation of the flow characteristics and associated flow phenomena should be conducted before constructing such important and costly structures. During this phase, many scenarios are tested to conclude the basic features of the safe design and to suggest and test proposed solutions of the observed harmful flow-associated problems. Generally, the investigated flow characteristics may include the main parameters of the submerged hydraulic jump, the vertical velocity distribution along the bed, the velocity decay, and the stability of bed protection downstream the apron of the stilling basin. In this paper, these characteristics will be tested in a pool-type stilling basin with multi-end steps downstream (DS) of Naga Hammadi barrages physical model. The used flume has 1.0 m wide, 26.0 m long and 1.20 m deep. The results of the tested models were compared to conclude the optimal hydraulic design criterion. Each model was tested under 36 different flow conditions. This extensive investigation revealed that the optimal design should satisfy the criteria e/H u =0.14 and k 2 /H u =0.14 where e is the height of the pool at the inlet and k2 is the height of the pool at the outlet. The design will be optimal if it produces the shortest length of submerged hydraulic jump, faster decay of near-bed-velocity, shortest length from the gate to the section where the velocity distribution is fully developed, minimum scour dimensions DS of basin and hence the highest stability of bed protection.

The potential impacts of two different modes of operation of a tidal barrage (i.e. ebb-only and flood-ebb operating modes) on the eutrophication potential of the Severn Estuary were assessed in this study using a simple modelling approach adopted by the UK’s Comprehensive Studies Task Team (CSTT). The model predictions were compared against CSTT thresholds for assessing eutrophication in estuaries and coastal waters. The estuary was found to be potentially eutrophic under no barrage conditions as well as under the ebb-only and the flood-ebb operating modes. Potential maximum primary production was found to be significantly higher under the ebb-only and the flood-ebb operating modes compared to the no barrage condition. This is believed to be a direct consequence of increased water residence time and greater light availability behind the barrage. However, the conditions for phytoplankton growth are likely to be more favorable under ebb-only operating mode as the potential maximum primary production was found to be significantly greater under ebb-only operating mode with largely decreased turbidity compared to flood-ebb operating mode with only a small reduction in turbidity.

- by Margaret Kadiri
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- Marine Renewable Energy, Water quality, Eutrophication, Nutrient Cycling

Tuning is essential to maximise the output of turbines extracting power from tidal currents. To realise a large fraction of a narrow channel's potential, rows of turbines not only have to be tuned for a particular tidal channel, they must also be tuned in the presence of all the other rows, i.e. tuned in-concert. The necessity for in-concert tuning to maximise farm efficiency occurs because the tuning of any one row affects a channel's total drag coefficient and hence the flow through all other rows. Surprisingly, in several circumstances the optimal in-concert tunings are the same or almost the same for all rows. Firstly, in both constricted and unconstricted channels, rows with the same turbine density have the same optimal tuning. Secondly, turbine rows in channels with a quasi-steady dynamical balance typically have almost the same optimal in-concert tunings, irrespective of their turbine density or any channel constrictions. Channel constrictions, occupying a large fraction of the cross-section or adding more rows of turbines, also make optimal tunings more uniform between rows. Adding turbines to a cross-section increases a farm's efficiency. However, in a law of diminishing returns for quasi-steady channels, turbine efficiency (the output per turbine) decreases as turbines are added to a cross-section. In contrast, for inertial channels with only moderate constrictions, turbine efficiency increases as turbines are added to a cross-section.

A simple method for estimating the potential of currents in tidal channels to produce power is presented. The method only requires measurement of the peak tidal volume transport through the channel without turbines, along with a bottom drag coefficient and the channel's dimensions. A recent existing method for estimating potential requires measurements of the undisturbed transport as well as water levels at both ends of the channel to give the head loss. The adaptation of the existing method presented here exploits analytic solutions for the transport and optimal farm drag coefficient and does not require measurement of the head loss. The equations presented allow both the channel's potential and the flow reduction due to power extraction to be estimated using a calculator. Thus the presented method has much of the ease of use of the older KE flux method, but is more reliable as it includes retardation of the flow by the turbines. The presented method can be used for the initial assessment of channels to determine if the additional measurements required to use the existing method are warranted. It can also be used where the headloss in the channel is too small to measure reliably. The presented equations enable the maximum power available to be simply traded off against environmentally acceptable flow speed reduction. The presented method is applied to two example channels. Cook Strait NZ has an estimated potential of 15. GW, while the entrance channel to Kaipara Harbour has a potential between 110. MW and 240. MW

- by Bettina Bockelmann-Evans
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- Engineering, Economics, Coastal Engineering, Renewable Energy

http://dx.doi.org/10.1680/ener.2010.163.3.93 The renewable energy route map for Wales outlines ambitious targets for 50% renewables by 2025. The Welsh coast, subject to tidal ranges of the order of 13 m and tidal flows in excess of 3 m/s, is thus in an ideal position to significantly contribute to these targets. Tidal stream energy is an emerging energy sector and a relatively small number of devices are at various stages of development in Wales. However, before such demonstration devices or arrays can be applied at a larger scale, a number of consents and permissions must be obtained to ensure safe and environmentally responsible deployment. This paper describes the multidisciplinary work that has been undertaken on an area of ocean that could be used for the deployment of a tidal stream turbine. The paper aims to put the scientific work undertaken into the context of device deployment in a complex marine environment and to provide an overview of the surveying and modelling required for the deployment of a single demonstration device off the Welsh coast. The Bristol Channel was chosen as a case study because of its high tidal flows and proximity to national grid connections and support infrastructure. This paper provides an overview of the research carried out during the project; the details of each discipline will be provided in individual papers by the respective subject authors.

- by Ian Masters and +4
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- Marine Renewable Energy, Tidal Stream Energy, Tidal Barrages, Ocean Energy

Tidal turbine deployment in the Bristol Channel: a case study Willis et al.

- by Guanghai Gao
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- Civil Engineering, Marine Renewable Energy, Tidal Stream Energy, Energy

- by Yousry Ghazaw
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- Environmental Engineering, Civil Engineering, Tidal Barrages, Computer Program

A subsidiary weir is proposed to be constructed downstream of each of the existing barrages on the Nile river in Egypt to secure its stability, which might have been affected after the construction of the Aswan High Dam. The present paper is intended to investigate the characteristics of seepage flow beneath two structures with an intermediate filter. The downstream structure (the proposed weir) has a slopping middle apron and two flat aprons in the upstream and downstream sides and is also provided with upstream and downstream cutoffs. The upstream structure (the existing barrage) has upstream and downstream cutoffs. A conformal mapping technique is used to solve the problem. Equations to calculate the uplift pressure distribution acting on both the existing barrage and the suggested weir are obtained; also equations to calculate the values of exit gradient along the intermediate filter and the downstream bed are derived. The seepage flows which seep into and/or drained from the intermediate filter are estimated. The analytical results are verified using experimental measurements performed on electrical analogue model and a very good agreement is noticed. A computer program is designed to compute the seepage flow, the uplift pressure and the exit gradients.

- by Yousry Ghazaw
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- Tidal Barrages, Conformal Mapping, Seepage, Weirs