Corallina Mitigation Project
Client:
Costain LtdPrimary Client:
Nuclear New Build Generation CoLocation:
Hinkley Point, West SomersetTimeline:
July 2017; continuingKey Facts:
- Environmental risk management
- Ecological purpose
- Tidal zone working
- Collaborative approach
- Nuclear new build project environment
- Early contractor engagement
Description:
Costain Ltd is one of the primary contractors working at Hinkley Point C, the almost £20 billion project to build two new nuclear reactors in west Somerset. Costain was selected for one of the first major contracts, to build a jetty to receive seaborne construction materials over a period of ten years, itself an environmentally beneficial initiative. The jetty was built using the Fugro WaveWalker, a giant eight legged ‘walking’ mobile jack up barge capable of operating in rough seas and intertidal locations.
An environmental risk was identified as part of planning the work. Due to its sheer scale, the WaveWalker’s ‘feet’ could damage channels which feed Corallina Algae, growing naturally in two colonies (“waterfalls”) on the beach which the jetty crosses. Any disruption to the flow of water to the Corallina may result in it dying in a short period of time. Costain designed a water supply mitigation system to provide sea water to the channels feeding the Corallina. This involved securing two pumps at the foreshore and pumping sea water at high tide to fill two 300m3 tanks located on shore but within the normal tidal range. The tanks are used to feed the Corallina at low tide.
Costain appointed Hydroline Solutions to undertake the work. Hydroline Solutions uses Argocat 8x8 vehicles to access the works, attending 20 hours every calendar day in gangs of six, which is now rationalised to four. The measures require monitoring of minimum flowrates to each waterfall which are maintained at all times and under all tidal cycle conditions. The Bristol Channel has the second highest tidal range in the world.
The Centre for Environment, Fisheries and Aquaculture Science ('Cefas' - an executive agency of DEFRA) monitors the Corallina to make sure it receives water at the rate it needs for the duration of the low tide. As well as employing sensors to measure bund performance, Cefas uses drones to to survey the foreshore, checking the maintenance of the tank bunds and the health of the Corallina.
The work commenced in the summer of 2017 and continues.
