Volunteers are lining up to help the Deep Cove Hostel (DCH) after a "wall of water" from a flooded Wanganella Stream cut the facility's water supply and wrecked a 3-bay workshop on Thursday night (31st May).

DCH Trust chair Mike McManus said the area had experienced a good lightning storm on Thursday following the departure of a school group.

The hostel had secured funding and was in the process of doing some upgrading work, McManus said.

Debris cleared from around the workshop shed. Photo: Supplied

The manager and his friend had been working in the workshop, and had just stopped for dinner when they heard an almighty rumble which they mistook for more thunder, McManus said.

"They walked outside and could smell the dirt coming down the hill, and didn't know where to go."

"This almighty tree slide came in above our hydro power plant and slid into the water catchment area."

It built up pressure, gathering more trees on the way down the hill, before spilling out on the river bends, McManus said.

"Some of [the trees] went through our shed [while] the rest carried on down the hill and blocked the culvert and subsequently washed out the road."

The hostel's dam and water supply were damaged. Pipes were subsequently reconnected. Photo: Supplied

McManus said while the hostel building was unaffected, trees had blown out two of the three workshop shed bays.

"We lost a lot of building materials down the side, and quite a bit of equipment stored in the workshop."

McManus said the facility's dam and piping had also been damaged, cutting the Cove's water supply.

Volunteers that were redeployed to clean up after Thursday's flood. Photo: Supplied

McManus said a group of volunteers who had arrived at King's Birthday Weekend to build a new deck and carry out maintenance had been redeployed on the initial clean-up and to reconnect the water supply.

Up to 70 volunteers had since offered to help out, with the first group due this weekend to tidy up the trees and paths around the hostel, ahead of the next scheduled school group, he said.

The Deep Cove Hostel has a full time manager and caters to around 2,500 children every year, with most coming from Southland and Otago.