A review of benthic ecological surveying for marine renewable developments in Scottish waters

2 Scope of marine renewable energy developments (MREDs)

2.1 Current status of Marine Renewable Energy Developments in Scottish waters

Most of the activity related to MREDs in Scottish waters has been from offshore wind developments, starting with the Robin Rigg offshore wind farm in the Solway Firth, followed by a progressive build-out of offshore wind capacity in the Moray Firth and off the Aberdeenshire and Angus coasts. Existing offshore wind lease options will lead to further growth of the sector around eastern and northern Scotland as well as the Northern Isles and Outer Hebrides. There are generally two scales of offshore wind development: smaller scale demonstration projects of up to and around 100 Megawatt (MW) and large commercial scale Gigawatt (GW) projects. An Environmental Impact Assessment (EIA), backed by appropriate baseline characterisation, is required to accompany a licence application for all types of offshore wind development (Scottish Government, 2015, 2018, 2020, 2021).

In comparison to offshore wind, there has been less activity associated with wave and tidal energy, however, there has been extensive testing of technology in Orkney with European Marine Energy Centre (EMEC) test sites at Billia Croo, Scapa Flow, The String and the Fall of Warness. Demonstration scale deployments have been established in Bluemull Sound, Shetland, and south of Stroma in the Pentland Firth. Individual technologies have been installed for short term testing at a variety of other locations in Shetland, off Orkney, in the inner Moray Firth and down the west coast at the Falls of Lora, Islay and in the Corran Narrows. Tidal energy generation currently is most likely with small-scale projects (<10MW; 5-20 turbines) but there may be larger scale (~100 MW; 50-200 turbines) developments as operational confidence grows. The next technology deployment steps for wave energy will probably be single devices and small array deployments (<10 MW; 20 devices) associated with established test sites, or for specific niche markets such as powering remote offshore facilities.

Each form of renewable energy generation, outlined above, will also need to export the energy generated. This may involve an offshore substation and/or an energy conversion plant (e.g., electricity to hydrogen) and the export of energy is most likely to be achieved as electricity through an export cable. This may be alternating current (AC) electricity over shorter distances and direct current (DC) electricity where distances to the nearest onshore sub-station and associated grid connection point are greater. There may also be circumstances where the energy generated offshore is converted offshore into a liquid or gaseous energy carrier, such as hydrogen or ammonia, and then shipped by pipeline to shore.

Where cables or pipelines are used there are also seabed protection mechanisms that may need to be applied. These include covering with concrete mattresses, covering with placed rock materials, trenching with or without backfill, or direct slit burial into the seabed.

At the coastal landfall site, another set of protection mechanisms can be used such as beach burial on sandy and muddy shores through trenching and backfill, shoreline crossing with clam shell steel covers or concrete cover protection, or directional drilling under the shore.

The purpose of any MRED proposal, whether it be testing, demonstration or full commercial activity, will influence the scale and duration of development activity and therefore the extent, duration and intensity of any potential impacts arising. The novelty of the development in terms of technology or location will also influence the likelihood of there being existing data and understanding about possible impacts. These factors will collectively influence the type and intensity of seabed ecology survey needed.

2.2 Stages of MRE project development, locations and impact extent

A key consideration when developing a suitable surveying strategy is the specific stage of development and how surveying needs may alter through the lifetime of a project. The key stages of a project relevant to benthic surveying are site characterisation, pre-construction, post-construction/operational and decommissioning. Further detail on the aims and considerations at each stage are provided in section 4.5.1.

Wind, wave, and tidal energy developments and their associated energy export infrastructure can spread from a few kilometres (km) to over 100 km and can extend from the intertidal, to the nearshore (<12 nautical miles (NM)) and offshore (>12 NM) areas out to the continental shelf edge. Across these areas, MREDs are likely to intersect a diverse array of seabed habitats and associated communities of species so that any surveying strategy approach may require an appropriate variety of sampling and analysis tools.

Potential direct effects on intertidal and seabed habitats could manifest within a few metres to tens of metres from the devices and infrastructure with indirect effects going beyond this. To be able to examine such issues, close proximity and high accuracy of benthic ecology sampling methods are likely to be key factors underpinning survey success.