One, in front of The Rockmount, has led to the closure of the road between Route de Cobo and Route de Carteret. The other is on the seaside pavement about 150 yards past Cobo Post Office going towards Grandes Rocques.
Agriculture, Countryside & Land Management Services were made aware of the holes on Thursday and investigatory works began the next day.
Given the risk to the seawall and the utilities within the road, the work has been authorised as essential.
Social distancing and hygiene measures will be maintained by all personnel and efforts made to reduce the movement of vehicles and people involved to a minimum.
Castel deputy Barry Paint has lived in the area for nearly 30 years and is familiar with its history.
‘The whole road along here was built on a sand dune,’ he said. ‘I’m no engineer, but it seems that water has got behind the sea wall somehow. That could be from the sea getting in or water draining from the land or maybe both.’
Some of the wall at Cobo had a granite plinth at the foot but the two areas in question did not which Deputy Paint said could present a weakness.
People using the beach opposite The Rockmount are being advised that they might notice red dye on the sand in the vicinity of the investigation. This is ecologically friendly and will be run through the hole in the road to mark the exit points of any air spaces on the seaward side of the wall. Any staining on the sand or wall will disappear with the tides very quickly.
Signs have been placed in the area to warn pedestrians.
Aclms is apologising for any inconvenience caused during the essential work.