06. Physical presence – Effects on hydrodynamics and sediment transport processes

Issues

From DCCEEW’s Environmental Factors Document page 25 – Physical presence of OWF infrastructure can change natural patterns of ocean water movement (e.g. currents, waves and mixing dynamics) and the transport of sediments in marine systems. The extent and severity of these effects will be influenced by the natural metocean conditions and how they interact with the scale, complexity, design and layout of proposed infrastructure. Changes in ocean water movement have the potential to result in the alteration to the spatial distribution of biological productivity in the water column, which may have knock-on implications for marine fauna that feed on plankton or, the distribution and settlement of planktonic larvae of commercially and ecologically important species. This can result in cascading effects at an ecosystem level… it is important that proponents consider site selection carefully and design OWFs in a manner that minimise modification to hydrodynamic processes and flow on ecological effects.

This can be significant if an OWF is located near to a RAMSAR wetland. Measures are suggested to Minimise, Monitor and Mitigate these effects. Also the impacts can vary depending on the different foundation types eg fixed vs floating – USA BOEM report. So it is important to use care in applying findings fixed foundation turbines to floating offshore wind farms.

In the Illawarra the upwelling effects at the edge of the continental shelf are very attractive to foraging seabirds, and so it would be desirable to be assured that this upwelling effect would not be impacted by any hydrodynamic changes from an  arrary(s) of offshore wind turbine.

  • “Continental shelves, the area where the relatively shallow coastal seabed plunges to the ocean depths, can be “hot” places for pelagic birds where upwelling of water from the deep can create a rich food chain“.
  • Upwelling is a process in which currents bring deep, cold water to the surface of the ocean. Upwelling is a result of winds and the rotation of the Earth. Because the deep water brought to the surface is often rich in nutrients, coastal upwelling supports the growth of seaweed and plankton. These, in turn, provide food for fish, marine mammals, and birds. Upwelling generates some of the world’s most fertile ecosystems
  • Nature & Frontiers – 2022 – In California there were concerns the development of large-scale offshore wind farms can reduce the wind stress at the sea surface, which could affect wind-driven upwelling, nutrient delivery, and ecosystem dynamics. Modelling was carried out and additional studies planned – a more definitive and quantitative characterization of effects of wind turbine arrays on upwelling will require application of an ocean circulation model.
  • Wikipedia

How Waves And Mixing Drive Coastal Upwelling Systems – 1,

Note – Hydrodynamic issues may also impact Waves and Surfing – see SAS UK

Resources

There are a number of papers on hydrodynamic impacts of offshore wind farms – often these state that the impacts are not well understood. Some of these papers cover seas that are not as open, nor as deep, as the waters off the Illawarra coastline. Not all papers cover biological species issues in relation to hydrodynamic matters. Some papers do cover surfing as impacted by hydrodynamic factors.

  • Potential Hydrodynamic Impacts of Offshore Wind on Nantucket Shoals Regional Ecology – 2023 – see my comments in a separate document
    • This paper is focused on potential hydrodynamic impacts of offshore wind on zooplankton supply, which is a key prey for critically endangered North Atlantic Right whales
    • Issues include the Gulf Stream and also column & seasonal stratification which influence phytoplankton upon which zooplankton forage; zooplankton in turn provide prey for critically endangered North Atlantic Right whales; there is a lack of knowledge about how these whales forage in this area; a single turbine can interrupt circulation processes through a wake effect and induce turbulence downstream and surrounding the turbine – this becomes more complex with an array of turbines;
    • Studies were recommended on the impact of the disrupted circulation processes on North Atlantic Right whale foraging.
    • Studies needed on zooplankton supply, life history and behaviour, abundance and aggregation
    • Conclusion – Significant uncertainties in hydrodynamic responses of wind and ocean wakes and of hydrodynamic effects of turbines – so more studies/observations needed through all phases of wind farm development, operation and decommissioning
    • Conclusion – modelling has been done on hydrodynamic aspects – however validation studies of the various models are needed
    • Observational assessment of the impacts of wind turbines, including wake effects on local zooplankton assemblages, production and aggregation are limited
    • Uncertainties regarding impacts of hydrodynamics on zooplankton supply, also how the turbines will impact hydrodynamics,  and so it is unclear how wind power will impact North Atlantic Right whale prey availability in the region – more observations, monitoring and studies are needed
    • Applicability to the proposed Illawarra Wind Zone: comparative depths of Nantucket Shoals with the Illawarra coastline; phytoplankton supply and role as prey for marine life along the Illawarra coast; any whale foraging activities along the Illawarra coastline
  • The seasonal hydrography and circulation over Nantucket Shoals – 1982 study of circulation & stratification effects when oil and gas exploration was under consideration; biological impacts such as phytoplankton and zooplankton were not considered;  depths in the area vary from a few metres to 60 metres to less than 100 metres to 200 metres
  • Could federal wind farms influence continental shelf oceanography and alter
    associated ecological processes? A literature review – US Atlantic Continental Shelf – noting that past European experience may not have application due to different stratification and tidal regimes.

  • Validation of a Hydrodynamics and Sediment Transport Modeling Framework for the Evaluation of Offshore Wind Farms

  • Western Australia Offshore Windfarm Pty Ltd: Preliminary Marine Environment Assessment – WA Offshore Windfarm Pty Ltd is planning to develop offshore wind energy within Western Australia coastal waters, offshore of Myalup.
    • Hydrodynamic impacts – High value seagrass, coastal shoreline – Possible Likelihood – High Consequence – Medium Risk Rating – Potential for localised
      impacts to any nearby benthic habitats (to be assessed by modelling) or
      changes to coastal processes if launching areas required.  – suggested mitigation measures to reduce Likelihood to Unlike;u
  • Robbins Island – Appendix T Marine Hydrodynamics Assessment (Phase 1) – METOCEAN DATA ANALYSIS REPORT – A report prepared for GHD Australia by Macquarie University and Risk Frontiers – – does not cover biological issues.  “The climate at Robbins Island is dominated by the seasonal shift in the position of the subtropical ridge (STR) and, to the south, the passage of fronts driven by the band of strong westerly winds encircling Antarctica. The hydrodynamic regime is highly complex and results from a mixture of tidal, wind and wave forcing. Winddriven wave energy is generally low, leaving tidal variations as the main driver of hydrodynamic flow.
  • Pentland Floating Offshore Wind Farm EIA Scoping Report – Changes to local sediment transportation processes and seabed features within the operation and
    maintenance phases due to altered hydrodynamics related to interactions between mooring cables, anchors and cables with action of water currents and waves may occur. Any effects are likely to be limited to localised areas of scouring and accretion (within a few metres) around seabed anchors, mooring lines and export cable protection from either physical abrasion or due to increased water turbulence. Furthermore, sediment changes related to open cut trenching and cable armouring may lead to sediment disturbance and water clouding. Sensitive location across medium sandy bottom could mitigate this since the sands over much of the eastern side of the Export Cable Corridor appear to be of sufficient size to settle rapidly after disturbance – Benthic and geophysical surveys undertaken in 2021 – A geophysical survey will be undertaken, the results of which will be used to inform the scope of a benthic survey campaign and the production of a habitat map which will include grab sampling, video and/or photography will take place in the Offshore Study Area to characterise the benthic environment and to identify any species or features of conservation importance. These findings will be presented in the relevant receptor chapters of the EIA report e.g. Water and Sediment Quality, Fish and Shellfish – Indirect physical disturbance to marine and coastal archaeological features – Indirect changes to the hydrodynamic and sedimentary regimes could occur, resulting in disturbance to archaeological features through sediment transport, scouring or deposition.- considered to be minor
    Ecology, Marine Mammals and other Megafauna, and Commercial Fisheries

  • Identifying sediment compartment dynamics on the Illawarra Coast – 2017 – outline a framework for assessing sediment dynamics within the adjacent Wollongong Coast and Illawarra Coast-South sectors, a 30-km stretch of the NSW coast between Bellambi Point (north) and Bass Point (south), marked by two contrasting compartments. The objective of the project is to develop an improved understanding of the sediment budgets within these compartments and to apply a sediment compartments approach to assessing the risk of coastal erosion and shoreline change
  • Mapping the Shoreface of Coastal Sediment Compartments to Improve Shoreline Change Forecasts in New South Wales, Australia – 2020 – We present high-resolution mapping of the shoreface-inner shelf in southeastern Australia from airborne lidar and vessel-based multibeam echosounder surveys, which reveals a more complex seabed than was previously known. 
  • Shellharbour – Tharawal (Illawarra South) multi-beam data now available on AusSeabed -2020 – With a full digital elevation model stretching from 200m inland to a depth of ~60m, the data have already been used in a case study to examine data utility toward improving shoreline change forecasting.
  • The Atmospheric and Oceanic Wakes of Offshore Wind Turbines and Their Effects on Local Marine Environments – Planned Future Study – “Offshore turbines create atmospheric wakes that excite surface waves, which in turn generate flow below the water’s surface. Observational evidence has shown that subsurface flow can produce underwater sediment plumes that stretch for miles downstream of offshore turbines. Thick clouds of sediment can prevent sunlight from reaching subsurface depths and disrupt the distribution of nutrients, potentially starving marine animals and plants, as well as harming breeding areas for the fish on which many coastal communities rely. The researchers will simulate and study the interaction of the turbulent boundary layers between the atmospheric wake from wind turbines and the sea surface, and between the sea surface and subsurface flow, to understand the mechanism by which sediment is trapped. They will validate their data with experimental work related to the development of wind turbine wakes over rough surfaces.”
  • Sediment Plumes  – deals with shallower seas than Illawarra coastline – “For at least the past decade, satellites have spotted white dots cropping up in the North Sea. If viewed from Earth’s surface, you would see that these dots are actually wind turbines—huge arrays of towers rising from the sea and topped with electricity-generating rotors. But they’re doing more than harvesting the wind. They appear to also be giving rise to sediment plumes.
  • North Sea – . “The wind wake effect of offshore wind farms affects the hydrodynamical conditions in the ocean, which has been hypothesized to impact marine primary production. So far only little is known about the ecosystem response to wind wakes under the premisses of large offshore wind farm clusters. The model also projects an increase in sediment carbon in deeper areas of the southern North Sea due to reduced current velocities, and decreased dissolved oxygen inside an area with already low oxygen concentration. Our results provide evidence that the ongoing offshore wind farm developments can have a substantial impact on the structuring of coastal marine ecosystems on basin scales. Atmospheric wakes appearing in the lee of wind farms extend on scales up to 65 km and beyond, depending on atmospheric stability, with a wind” –  As this covers shallower depths of the North Sea, I am not fully convinced that this would be significantly relevant to the Illawarra context, however it is interesting 
  • Undark- As Offshore Wind Ramps Up, Scientists Flag Potential Impacts –  “A 2023 study led by oceanographer Kaustubha Raghukumar, for example, found that turbine-driven alterations in wind speed could produce changes in ocean upwelling — a natural process where cold water from the deeper parts of the ocean rises to the surface — “outside the bounds of natural variability.” Those cold waters contain nutrients that support phytoplankton, the single-celled plants and other tiny organisms that form the basis of the oceanic food chain. Shifts in upwelling could have an impact on phytoplankton — although those impacts are still in question, particularly as climate change alters the equation… A 2022 paper modeled the effect that planned wind farms might have in the North Sea, off the coasts of the U.K. and Norway, and concluded that they could influence phytoplankton, which could alter the food web.
  • Projected cross-shore changes in upwelling induced by offshore wind farm development along the California coast – the development of large-scale offshore wind farms can reduce the wind stress at the sea surface, which could affect wind-driven upwelling, nutrient delivery, and ecosystem dynamics.. the key finding of this study is that while wind farm wakes result in a local diminishment and enhancement in upwelling on either side of the wake, there is little net change in upwelling when integrated over a larger area that fully encompasses the wind energy areas of interest. However, changes in the spatial structure of upwelling due to wind turbines can be greater than the interannual changes that occur due to natural variability.
  • Offshore wind farms are projected to impact primary production and bottom water deoxygenation in the North Sea – this paper refers to the Doggerbank Wind Farm, so it will be interesting to review any future studies in regard to the impact of wind wake and hydrodynamics. “The wind wake effect of offshore wind farms affects the hydrodynamical conditions in the ocean, which has been hypothesized to impact marine primary production. So far only little is known about the ecosystem response to wind wakes under the premisses of large offshore wind farm clusters. Here we show, via numerical modeling, that the associated wind wakes in the North Sea provoke large-scale changes in annual primary production with local changes of up to ±10% not only at the offshore wind farm clusters, but also distributed over a wider region. The model also projects an increase in sediment carbon in deeper areas of the southern North Sea due to reduced current velocities, and decreased dissolved oxygen inside an area with already low oxygen concentration. Our results provide evidence that the ongoing offshore wind farm developments can have a substantial impact on the structuring of coastal marine ecosystems on basin scales.
  • The Effects of Offshore Wind Farms on Hydrodynamics and Implications for Fishes
  • The large-scale impact of anthropogenic mixing by offshore wind turbine foundations in the shallow North Sea
  • Horns Rev 3 Offshore Wind Farm Technical report no. 3 HYDROGRAPHY, SEDIMENT SPILL, WATER QUALITY, GEOMORPHOLOGY AND COASTAL MORPHOLOGY – does not cover biological impacts
  • Worldwide Synthesis and Analysis of Existing Information Regarding Environmental Effects of Alternative Energy Uses on the Outer Continental Shelf – Farfield effects of a modified wave climate include impacts to coastal zone hydrodynamics and sediment transport, altered recreational capabilities such as surfing, and limits on the capability
    of neighboring areas to generate power using wave energy conversion facilities. Nearfield effects of a modified wave climate include changes in navigational conditions, wave loads on adjacent structures, and sediment transport under waves.
  • Assessment of system effects of large-scale implementation of offshore wind in southern North Sea – a brief mention of biological impacts –  These ambitious (inter)national scenarios for more and larger wind farms in the North Sea are likely to have consequences for the ecosystem in the North Sea at scales and in ways that are currently not well understood. The large-scale impacts of such an extensive construction of offshore wind power on the hydrodynamic climate (waves, currents and surge), suspended matter and morphodynamics and thereby the ecological functioning of the southern North Sea is poorly known .. The large-scale construction of offshore wind farms can impact the hydrodynamic processes in the North Sea (Clark et al. 2014). Large-scale wind farms can act on both the near- and farfield through different processes. The North Sea is a semi-enclosed shelf sea where tides and currents are important processes for vertical and horizontal mixing (e.g. Otto et al., 1990; Huthnance, 1991; Ducrotoy et al., 2000). Tidal currents may reach a speed of tens of cm.s−1 and generally dominate over flows driven by density or wind. Residual currents contribute to the cyclonic circulation pattern of the North Sea. These residual currents are driven by tidal residual currents together with wind-driven circulation and baroclinic effects … In a study by Carpenter et al. (2016) the wind turbines near the tidal mixing front changed the hydrodynamics sufficiently to decrease stratification by 5–15%. Furthermore, despite the limited horizontal extent of these changes in flows at the foundations (less than 20 m) their impact on stratification is felt much more widely. Using an idealized modelling approach, Carpenter et al. (2016) showed that widespread construction of wind farms could impact the large-scale stratification. For present wind farms with a spatial scale of 10 km, the effect is limited, but it could become very significant when the farms are scaled up to ~100 km… Generally, the larger the number of offshore wind turbines the more tidal energy will be dissipated and hence the larger the impact on hydrodynamics … As such, there is sufficient understanding of how a single wind farm foundation may affect local currents, but there is a lack of knowledge of cascading effects and cumulative impacts of large-scale construction of offshore wind farms on hydrodynamics in the North Sea… 
  • Rapid Marine Environmental Impact Assessment of the proposed Offshore Wind Farm in Gulf of Khambhat – off Jafrabad, Gujarat – high hydrodynamic action in the region that makes the sediment unstable and nonconducive habitat for megabenthic species – The hydrodynamics of the region is mostly controlled by the tides and reversing
    monsoonal winds. .. Considering the baseline conditions, it can be presumed that exceptionally few organisms will be able to colonies these structures because of high turbidity, sedimentary load in the water column, and strong hydrodynamic region in the area
  • Academia – Wind Farms and Hydrodynamic
    • Hydrodynamic Regimes in Offshore Wind Farms – seems to be focused on wave regimes  “The majority of offshore wind farms installed are located intransitional waters, and their presence has a relevant influenceon the coastal processes due to the associated changes in thehydrodynamic regime.“
  • Academia – Wind Farms and Stratification
  •  Academia  – Wind  Turbines  and Ocean Stratification

    • Large-Eddy Simulation of Wind-Turbine Wakes: Evaluation of Turbine Parametrisations– With the fast growing number of wind farms being installed worldwide, the interaction between wind-turbine wakes and atmospheric boundary-layer (ABL) turbulence, and its effects on energy production as well as dynamic loading on downwind turbines,have become important issues in both the wind energy and the atmospheric science communities.

  • Turbulence Effects of Wind Towers on Oceans Study
  • Sediment Plumes
  • North Sea – . “The wind wake effect of offshore wind farms affects the hydrodynamical conditions in the ocean, which has been hypothesized to impact marine primary production. So far only little is known about the ecosystem response to wind wakes under the premisses of large offshore wind farm clusters. The model also projects an increase in sediment carbon in deeper areas of the southern North Sea due to reduced current velocities, and decreased dissolved oxygen inside an area with already low oxygen concentration. Our results provide evidence that the ongoing offshore wind farm developments can have a substantial impact on the structuring of coastal marine ecosystems on basin scales. Atmospheric wakes appearing in the lee of wind farms extend on scales up to 65 km and beyond, depending on atmospheric stability, with a wind” – I am not convinced that this would be relevant to the Illawarra context, however it is interesting

Surfing & Hydrodynamic Impacts

  • Guidance on environmental impact assessment of offshore renewable energy development on surfing resources and recreation – Changes to the wave climate are associated with wave energy modification due to the interruption of wave propagation and the resulting hydrodynamic effects such as refraction and diffraction. If they are of sufficient magnitude, wave climate changes can affect the sedimentary environment of the seabed.

  • Surfing Resources and Offshore Wind Farm – “Although studies discussed in this report have found negligible impacts on wave regimes, they have also proved that the presence of renewable energy structures offshore interferes with wave energy transmission. The predicted outlook of offshore wind energy brings up important issues such as wave impacts from larger-scale projects in future developments associated with increased electricity demand from renewable energy. Developers need to consider the cumulative impacts of multiple projects and the geographical extent of impacts with the development of larger wind farms. As technology advances to meet cost-effective, high-performance standards of offshore wind energy, through expanding the size of turbines and the installation of floating devices, more research studies are necessary to address the potential impacts on surfing resources.

2024 – RWE Continues Taking Part in Wake Effect Research Projects in Anticipation of Increasingly Densely Built Offshore Wind Farms – In planning new wind farms, developers calculate various factors affecting their performance. One important factor is the wake effect, where the wind slows down and swirls once it encounters a turbine, reducing the yield of the wind turbines positioned behind. To make sure offshore wind farms produce as much power as possible, this effect needs to be taken into account during the planning of a project. Currently, standard computer models are used for these calculations, but as offshore wind farms become more tightly packed, especially in places like the North Sea, highly precise calculations are needed, meaning that the existing models will need to be refined, according to RWE. In 2023, the offshore wind developer joined a project called C2-Wakes (Controlled Cluster Wakes), which will involve studies at three adjacent RWE offshore wind sites in the North Sea. Supported by the BMWK, the project aims to help gain a better understanding of the effects of offshore wind generation on wind patterns…The focus of Fraunhofer IWES’s work is also on deriving recommendations for action to reduce large-scale wind farm effects for the planning of future very large offshore wind farm clusters. RWE’s part of the project, which was granted nearly EUR 295,000, involves a LiDAR measurement campaign within an offshore wind farm that the company operates in the German North Sea… The X-Wakes project will allow for more accurate predictions of changes in wind conditions resulting from the planned large-scale expansion of offshore wind farms in the North Sea… A second project RWE completed last year, named Global Blockage Effect in Offshore Wind (OWA GloBE), was related to the ‘blockage effect’, the phenomenon of wind dropping in speed just before it hits the turbine…At the beginning of 2023, RWE also teamed up with DNV to validate the implications of long-distance wake effects from large offshore wind clusters. RWE said its models predicted that large clusters of offshore wind farms could have far-reaching wind-shadowing effects, impacting the yield of future offshore wind farms. The company’s preliminary model outlined that these effects can have an impact up to 200 kilometres or more and cause the energy yield in the wake areas to be reduced – in certain cases by over ten per cent.

2023 – Study: RWE and DNV to validate implications of long-distance “wake effects” from large offshore wind clusters .. RWE and DNV have now agreed on a scope to conduct a large study assessing the impact of far wakes in offshore wind. The scope of the study asks DNV to validate the effects that RWE experts have identified. RWE models predict that large clusters of offshore wind farms could have far-reaching wind-shadowing effects, impacting wind yield of future offshore farms… RWE reviews its methodology and approaches to wind energy yield modelling on an ongoing basis. Based on this the company has developed a good understanding of these long-distance “cluster wake effects”. The preliminary model from RWE forecasts that these can have an impact up to 200 kilometres or more and cause the energy yield in the wake areas to be reduced – in certain cases by over 10 percent. This could have possible implications on future offshore development projects in Europe, for example in the German North Sea.

2020 – Cluster wakes impact on a far-distant offshore wind farm’s power …With a rising offshore wind energy utilization, cluster wake shadowing effects will occur to an increasing degree, leading to power losses and uncertainties in offshore wind resource assessment. Wind turbine wakes were subject of intensive research in the last decade. .. Wind farm cluster wakes in the far field of more than 20 km downstream have not been measured over longer periods.. We find that long-distance wake effects of a wind farm cluster exist at least 55 km downstream in stable and weakly unstable stratification. They persist for more than 2.5 h… This contribution proves the existence of steady power reductions in a far downstream wind farm caused by cluster wakes. We encourage further investigations on far-reaching wake shadowing effects for optimized areal planning at sea and reduced uncertainties in offshore wind power resource assessment.

2023 – Do you know what the ‘wake effect’ is in a wind farm? – Just as a ship can be placed upwind of another and leave it without wind, wind turbines located in a certain way can affect others in the production of energy…The ‘wake effect’ is the trail left by each turbine where wind speeds are reduced. The wind regime generates additional turbulence to that already produced by the terrain, affecting nearby wind turbines and even neighboring wind farms. This is an important factor that must be taken into account in the design and construction phase of a wind farm to avoid possible deviations in production, both for each individual generator and for the wind farm as a whole. The regions where the ‘wake effect’ is observed are normally two.

  • The first refers to the air flow in the area immediately upstream of the rotor of a wind turbine.
  • The second is in a ‘downstream’ region far from the location of the turbine, where the wind speed is reduced, causing the turbines located in that space, a decrease in energy production.

.. taking into account the predominant wind directions, turbines should be spaced between 5-8 rotor diameters apart. While, for non-predominant wind directions, the distance should be between 2-4 rotor diameters. Understanding the type of air that the turbine is confronted with is decisive when talking about production. 

2018 – First in situ evidence of wakes in the far field behind offshore wind farms ..  To optimise the use of the marine areas, wind farms are typically clustered in units of several hundred turbines. Understanding wakes of wind farms, which is the region of momentum and energy deficit downwind, is important for optimising the wind farm layouts and operation to minimize costs. While in most weather situations (unstable atmospheric stratification), the wakes of wind turbines are only a local effect within the wind farm, satellite imagery reveals wind-farm wakes to be several tens of kilometres in length under certain conditions (stable atmospheric stratification), which is also predicted by numerical models. The first direct in situ measurements of the existence and shape of large wind farm wakes by a specially equipped research aircraft in 2016 and 2017 confirm wake lengths of more than tens of kilometres under stable atmospheric conditions, with maximum wind speed deficits of 40%, and enhanced turbulence … For wind farms located several tens of kilometres downwind of neighbouring wind farms along the main wind direction, the productivity of the downwind farms may be reduced during periods with stable stratification… Our airborne observations provide the first in situ confirmation of the existence of far wakes extending at least 45 km downwind from wind farms, confirming the ability of numerical simulations and SAR satellite images in capturing the spatial structure of wind-farm wakes.

Wikipedia – Stable Stratification and Unstable Stratification  – Stable stratification of fluids occurs when each layer is less dense than the one below it. Unstable stratification is when each layer is denser than the one below it.