Fire resistant shelters made of rammed earth are being built along the Bibbulmun track to replace the timber campsites destroyed by bushfires in the state’s Southwest last year.
Department of Parks and Wildlife trails coordinator Kerstin Stender said the bushfires in February 2015 completely destroyed four campsites valued at $160,000 each and caused about $1 million in damages.
“From a cost perspective if you have to rebuild from scratch it takes a lot longer to get that organised,” Ms Stender said.
“We looked around to see what materials would be good in a fire and also retain the rustic image of the Bibbulmun track.
“We got independent advice from a fire building expert to see which structures would be suitable and certainly rammed earth walls are very good.”
The new shelter design has a raw steel frame, Colorbond cladded roof and 30cm thick rammed earth walls.
Rammed earth is commonly made from a damp mixture of gravel, sand, silt, clay and cement, which is then compressed between formwork to make a solid wall.
Ms Stender said the presence of the Dieback disease in some areas meant that uninfected soil needed to be found and transported to the site from elsewhere.
Dieback damages the root systems of infected plants and can affect more than 40 per cent of native plant species in Western Australia.
There is an urgency to finish construction ahead of winter rainfall, which can reduce safe access and increase the quarantine risks associated with vehicle movement.
“We have nearly completed the Possum Springs campsite north of Collie and we are about to start on the two southern campsites: Gardener and Dog Pool,” Ms Stender said.
“In the very unfortunate event somebody was out there during a bushfire they would have a higher chance of survival behind a rammed earth wall than they would have behind a timber wall.”
According to the Australian government’s guide for sustainable homes, rammed earth has a high thermal mass, which means heat is slow to penetrate through the material.
Earth Building Association of Australia vice president Stephen Dobson spoke about the thermal properties of rammed earth in more detail.
“Thermal lag is the time delay taken for hot temperature outside in a bushfire to make it through to the inside face of the wall,” Mr Dobson said.
“That is measured in hours, and the typical lag for a mudbrick house or a rammed earth house would probably be six to eight hours.”
He said unenclosed rammed earth shelters would stop flying embers and not collapse in a bushfire, but the beneficial effects of thermal lag would be limited by an open window and doorway.
Shire of Collie executive manager of development services Keith Williams said the Bibbulmun track was very important to the town of Collie and the loss of its infrastructure has been a significant issue.
“Absolutely we would support the efforts by DPAW and the Bibbulmun track foundation to build huts that are more fire proof,” Mr Williams said.
“With the drying climate we have noticed some indications that the severity of fires are going to increase, because of more dry material on the ground.”
Mr Williams said Collie had aimed to diversify its economy, and the trails represented a significant asset and opportunity for tourism.
The Bibbulmun Track Foundation lead guide and events coordinator Steve Sertis said track diversions were still in place to prevent bushwalkers traveling through unsafe areas left by bushfires in the Shire of Harvey earlier this year.
“When we say it’s not safe, we mean trees, really big trees, come down six months after a fire,” Mr Sertis said.
He has worked on the track for 18 years, and has noticed conditions becoming much drier over the years, with streams and creeks he had known to flow regularly now stopping completely.
“The walking season as such has shrunk somewhat,” he said.
“Usually by late March and certainly April people are out walking, but various shires have extended campfire bans right through until May.
“So, yes, absolutely it is a challenge that we need to be aware of and prepared for.”