drainage

Sinkholes can be formed by gradual dissolution happening underground, but they can also be caused by heavy rain or surface flooding, construction work, leaking drainage pipes, burst water mains and groundwater abstraction, the BGS said.

Even then, the Department of Building and Safety warned that the spot widenings would lead to irregular street alignments, “thus hindering maintenance, drainage, and traffic flow,” Manville wrote in his analysis.

But city officials are hopeful that extensive “winterization efforts,” which include improving drainage, filling in cracks and lining canyon walls, can help minimize the effect of any new rain.

The Welsh government said its permission included land drainage works to be submitted to the council, and it was the authority's job to enforce planning conditions.

Structural maintenance includes resurfacing and reconstruction of roads and footways, as well as investment in both drainage infrastructure and in the structural stability of embankments.