A short section of the road, just south of Seaford College, has been closed since Saturday afternoon (October 2) for safety reasons.
Sussex Police said officers were made aware of the incident at around 4.40pm. They supported with a road closure ‘before the matter was passed to Highways’.
West Sussex County Council’s highways department said it followed a slippage of earth over a culvert, that spans beneath the carriageway.
A council spokesman added: “The movement, possibly caused by exceptional rainfall, led to the carriageway subsiding and this section of road has been closed for safety reasons.”
In an update on Wednesday morning, the council said industry experts were on site the day before to ‘consider potential solutions’.
The spokesman added: “Further specialist support will be brought in during the coming days to establish the extent of the issues and confirm a long-term fix.
“This includes a diver and detailed geotechnical analysis to investigate the culvert that spans beneath the carriageway.
“Timescales will only be known once a solution has been identified.”
The council warned that the road closure ‘unfortunately, could be in place for some time’, adding: “We apologise for any inconvenience.
“Signed diversions are in place and will be improved during the coming days to include electronic messaging at key locations for road users.
“Businesses have been able to open as usual and we are working with Seaford College to minimise the impact where possible.”
West Sussex Highways revealed that, in the first five days of October, we had 67 per cent (53.6mm) of our long-term average monthly rainfall (79.9mm).
These figures were calculated by the weather station at the Drayton Highways depot.
On Friday, there was 12.2mm of rain, with a further 19.2mm on Saturday. Only 0.8mm of rain fell on Sunday but this increased to 5.2mm on Monday and then 16.4mm on Tuesday.
The road remained closed as of Monday, October 11.
West Sussex Highways said nearby businesses remained open and signs were still in place to aid with the diversion.