Most of the environmental issues to be considered are identified in guidance received from the Environment Agency (EA). Whilst there are a number of issues to be considered and mitigated where appropriate, in particular marine and migratory fish, nothing which is likely to be a “show stopper” has been identified so far. The scheme has been discussed with the RSPB who raised no immediate objections.
There are no designated Special Areas of Conservation or Special Protection Areas within the basin and the nearest is about 10km up channel. However it is possible that the scheme might have some limited impact on those SACs. Data would need to be collected and it may be necessary to provide a Habitat Risk Assessment.
An extensive preliminary desk study has been carried out to identify the available data, both published and unpublished, on the potential environmental issues that will need to be studied in detail for an Environmental Impact Assessment. The main environmental issues are summarised below.
The Bristol Channel is an area of high water velocity at spring tides and this results in a high suspended sediment load. Whilst there will be wakes both into and out of the basin during operation, the general basin water velocities will be much reduced. Thus, it is likely that there will be significant sediment deposition within the basin. However much of this would likely to be in the sub-tidal deeper water parts of the basin away from the inlet wakes.
Whilst this is not expected to have a significant impact on energy output, it would need careful study utilising computer modelling.
Change in Water Levels and Velocities
The scheme will result in slightly changed water levels outside the basin. Initial modelling show this as being generally a reduction in high water of between 0.1 and 0.2m depending on location. This might have a minor effect on up-channel ports and inter-tidal habitat. However, this would be significantly less than the predicted sea level rise due to climate change of around 0.7m by the year 2100.
Outside the lagoon, apart from the ebb wakes, velocities will be similar. For instance initial 2-D studies show a change in velocity at the Hinkley C cooling water system intake of less than 0.1m/sec.
All of these effects will need detailed hydrodynamic modelling to provide reliable predictions.
Water Quality in the Lagoon
The tidal currents within the basin will reduce in strength and change in direction; hence dispersion of effluent plumes will be slower. There are sewage treatment works at Minehead and Watchet, and possibly some combined sewer overflow discharges. No significant industrial discharges have been identified within the basin. There are designated Bathing Waters at Minehead, excellent quality, Dunster and Blue Anchor, both good. An initial discussion with Wessex Water showed that they do not expect there to be a significant problem of water quality resulting from the lagoon. However, it is expected that a water quality dispersion modelling study will be required.
Fish impinged on the cooling water inlet screens at Hinkley Point B power station, about 10km to the east, have been recorded from 1981 to 2017, some 37 years. The records show many marine fish impinged on the screens over the 37 year data period. There were also smaller numbers of bass and ray. The numbers of migratory fish recorded were small, with only 9 salmon recorded in total. It is believed that the main runs of salmon In the Bristol Channel are at, or near, the surface in the deeper and faster currents in the deep-water channel off the welsh coast.
Whilst Hinkley B is some 10 km up-channel from the WSL turbines, it is on the same side of the estuary so should be indicative of what might be found. Data on fish will need to be collected and modelling will be needed of the impact of turbine passage on migrating fish species.
Triple regulated turbines, as proposed for WSL, have the advantage over the traditional double regulated turbines as they have fewer turbine blades and, not being grid synchronous, can have slower rotation when the flow is less, thus being more fish friendly.
Whilst there are techniques to deter fish entry to the turbines, such as lights or acoustic deterrence, it will be important to manage all fish species, some of which may use the basin area as a feeding, spawning, or nursery ground. Having the large sluiceways separate from the turbines should help in this.
There are four streams that discharge within the lagoon. These streams discharge onto the foreshore at most states of the tide; thus access for migratory fish can only occur during high water. The streams have a non-return flap valve, sluices, pipes, and blocked fish passes. Thus from the electro fishing studies, and the Hinkley B fish screens it is believed that the only stream based migratory fish are eels. It is believed that elvers can pass the turbines and it is proposed that the emigrating eels be trapped and released outside the lagoon. Mitigation measures such as improvements on the streams and the provision of eel and fish passes would be considered.
The map of areas from which commercial fish landings are taken shows all are well down channel and none are within about 10km of the lagoon.
Study of the annual Somerset Birds reports by the Somerset Ornithological Society shows limited numbers of sea birds, mostly on passage. In a number of places the beach area is a dog walkers’ area, and in some places the coast path runs along the beach; thus there is existing potential for bird disturbance. These factors are believed to limit bird numbers.
The method of operation of the tidal range scheme – namely generation on both ebb and flood tides with some pumping – will result in a tide range within the lagoon which will be broadly similar to the tide range now. Thus the feeding opportunities for birds in the inter-tidal areas are expected to be broadly similar to those existing.
Artificial island bird refuges within the lagoon could perhaps be provided by the scheme to protect against the dog disturbance and also provide roosting sites.
Most of the lagoon wall structure will be below water level. Much of the above water structures would be well out to sea and will have limited height above sea level and most of the scheme will be viewed from a significant distance. Further, due to the topography and high hedges along many of the local roads, there are limited places from which the scheme could be seen. The lagoon wall would be visible from the Welsh coast but even further away. Thus landscape seems unlikely to be a significant issue.
Whilst there are a number of environmental issues to be considered and mitigated where appropriate, nothing which is likely to be a “show stopper” has been identified so far.
As part of the DCO Scoping study an Evidence Plan will be agreed with the Regulators and other stakeholders, setting out what evidence needs to be collected for input to the EIA.