Creating a new islet is one of the biggest challenges facing designers of the proposed 22km cable tunnel beneath Morecambe Bay for the National Grid, according to a leading member of the project.
The Morecambe Bay islet’s main purpose is to house a ventilation shaft for two 400kV cable circuits in the tunnel below, which will connect the proposed 3.4GW Moorside nuclear power plant near Sellafield to the National Grid in a project worth £2.8bn.
The islet will be covered with rock armour and could be anywhere from 50m to 100m in diameter at the seabed. It will also act as a safe access point in case of an emergency in the 5m inner diameter tunnel.
But the 10m tidal range in Morecambe Bay will present a major challenge to the islet’s designers.
Morgan Sindall Professional Services (MSPS) and its sister business Underground Professional Services (UnPS) have nearly completed the front end engineering design for the tunnel. It says it is one of the most technically challenging projects of its type ever proposed. Together, MSPS and UnPS are finalising designs for the tunnel and shaft, islet, and head houses together with associated mechanical, electrical, civil and structural infrastructure works.
”Back in the day there were Chinese cockle pickers in the bay. People weren’t aware of the tide and they were killed,” said Morgan Sindall Professional Services (MSPS) director of power Alwyn Hanekom.
“It’s extremely dangerous just to get machinery to that location. This has meant we’ve had to look very carefully at the logistics of getting plant and special equipment to the islet in order to work safely with the tide timescales.”
Aesthetic considerations mean that tunnelling through complex geology and creating a technically challening islet is the preferred option.
“The reason why we are constructing the tunnel under Morecambe Bay is to avoid building 60km of overhead lines 23km of which is within the Lake District National Park,” said a National Grid spokesperson.
“Once constructed the only visible features will be the headhouses at either end, which will be located within the substation boundary, and the islet within Morecombe Bay. The islet will be approximately 12km from Roosecote and 9km from Heysham and so it would not be easily visible from the shore.”
Five different construction options are being explored to minimise the environmental impact. The area is covered by at least five environmental and scientific protections – an unusually high number.
The project – part of the North West Coast Connection – has just completed a public consultation. The energy supplier will apply for a Development Consent Order before issuing an invitation to tender for the construction work.