Mostyn SeaPower, a subsidiary of The Port of Mostyn, has developed proposals for a tidal lagoon in the outer Dee Estuary, North Wales.

Building the 6.7 kilometre long lagoon, stretching from the breakwater at Mostyn to Point of Ayr in Flintshire, would create 300 jobs during the construction phase and up to 30 high-skilled permanent posts.

Mostyn SeaPower say the Dee Estuary is an ideal location because it has one of the highest tidal movements in the UK, as much as 10.2 metres during high spring tides, as well as having natural deep water for the installation of the turbines.

The lagoon wall will be two metres above sea level and another major benefit is that it will provide much-needed flood protection for the low-lying land along the coast which includes homes and businesses, the A548 Coast Road and the strategically important North Wales coast railway line which has suffered significant storm damage in recent years.

It will have two sets of turbine houses with three sluice gates to control the volume of water over the tidal cycle, along with lock gates allowing small vessels in and out of the sheltered lagoon.

In total there will be eight 16 megawatt turbines which will generate 298 gigawatt hours of electricity annually from the lagoon which will enclose an area of 12.2 square kilometres and has a design life of more than 100 years.

The lagoon wall will have a road running along the top and a path that will be accessible to the public.

Preparatory work, including environmental and ecological studies, has been taking place for four years and the lagoon will be designed to maintain navigational access for shipping.

Mostyn SeaPower has been working with engineering consultants Ban Nuttall from Camberley and environmental experts ABPMer, from Southampton and the company has already negotiated with the National Grid for the electricity to be used by the nearby Connah’s Quay Power Station.

It is planned to submit an application to the UK Government for a Development Consent Order by the end of 2022 and get the green light a year later.

According to APP Mer, ‘The Dee is an area of high nature conservation value. It is important therefore, that detailed information is obtained to describe the baseline ecological conditions and understand the changes that will occur as a result of constructing the proposed lagoon’.

ABPmer has been commissioned to lead a range of ecological surveys in the Estuary to inform the associated impact assessment supported by Hull Marine Laboratory and Sea Watch Foundation.

A two-year programme of fish surveys will be undertaken to understand population stock in the outer estuary, and migratory patterns of salmon and eel which could be affected by the proposed lagoon turbines. This will be underpinned by Environmental DNA (eDNA) sampling, taking advantage of major advances in the use of DNA in ecological sampling, as opposed to direct samples from individual organisms.

Marine mammal surveys will take place over a similar timeline. This work will gauge the frequency of occurrence of whales, dolphins, porpoises and seals in the proposed lagoon area. These surveys will inform understanding of the potential effects during construction and operation. Passive acoustic monitoring instruments will be used to monitor porpoise and dolphin activity.

Bird population surveys will take place over two winters, to place the populations at Mostyn in the context of the whole estuary and designated area.

The surveys started in Autumn 2020, and are expected to be completed by late 2022.

By Jake Frith