4WD Impacts on Fraser Island
During the first term of Queensland's Beattie Government (1998-2001) a million people visited Fraser Island. During that period a conservative estimate of over 1 million tonnes of sand was sluiced along the roads of Fraser Island. That amounts to an average of one tonne of sand relocated for every visitor. The biggest impact of 4WDs on Fraser Island is not on the beach or the foredunes but along its network of tracks where every heavy downpour relocates thousands of tonnes of sand thus degrading Fraser Island's World Heritage values. Other 4WD impacts include bird kills, disturbance of bird breeding, social impacts (including shrinking of wilderness, noise and safety to humans), damage to the foredunes, increased erosion on tracks and roads and the spread of litter, weeds, pathogens and other injurious agencies.
This Education Supplement prepared by the Fraser Island Defenders Organization attempts to summarise the impacts of 4WDs and suggest ways to reduce the impacts.
On the beach below the high water mark the physical impacts of 4WDs are obliterated at each change of the tide and they have a significant impact on the bird population. There has not yet been lasting evidence of any enduring impact on beach worms and molluscs as a result of 4WDs although there has certainly been a very significant decline in the ghost crab populations.
On the foredunes, just above the high water mark, 4WDs destroy vegetation and increase vulnerability to wind erosion as well as disturbing the nesting sites.
However the greatest impact of 4WDs on Fraser Island is out of sight and not readily observed. It occurs along the roads and interior of Fraser Island. Here every heavy downpour moves thousands of tonnes of sand along the roads to fill hollows, fill lake basins and smother old soil surfaces. To understand the process which is where the greatest 4WD impact on Fraser Island is one needs to understand water repellence in sand.
Water repellence: CSIRO Soil Studies in Cooloola noted the nexus between vehicle disturbance water repellence qualities of sand. Any disturbance of surface sand increases its water repellence. (Although water is expected to pass as easily through sand as through a sieve, water splashed onto dry disturbed road surface will roll up into balls with grains of sand on the outside). Once the surface it wet, the capacity of the sand to absorb the water will slowly increase. This repellence means that heavy downpours canít be absorbed before the water starts rushing down slopes carrying surface sediments.
Downcutting of road (and even walking track) surfaces is cumulative so that many roads on Fraser Island are now metres below their original elevation. The relocated sand settles at the bottom of the slope as the water velocity decreases. Too frequently this happens to be in Lake basins. There is evidence of sand being move from roads and tracks into McKenzie, Boomanjin, Allom, Garawongera, Boomerang, Birrabeen and Jennings Lakes. Elsewhere the sand moves off the road to smother old soil profiles. Given that one of the outstanding natural values of Fraser Island
The amount of downcutting is a direct function of the degree of disturbance to the road surface. The major causes of disturbance to the road surface are wheel slip, the volume of traffic, road widening and consequent desiccation and, (ironically) road maintenance.
Deposition: Sand sluiced from roads have resulted in Yidney Lake converted from a shallow but water filled lagoon to a dry surface with hundreds of tall blackbutts growing in it in less than 30 years. In places above the lake, the road has down-cut more than two metres, exposing the B horizon. There is prima facie evidence that this road sand has filled in the lake. Alluvial plumes are spreading into other lakes as a result of adjacent roads. At Lake McKenzie where the sediment contains tonnes of woodchips washed off the adjacent road. Other lakes affected include Allom, Birabeen, Boomanjin Garawongera and Jennings.
Most of the sand washed off the Central Station Eurong Road into Wanggoolba Creek is carried downstream by the fast-flowing creek, but many formerly waterlogged areas are now filled with silt.
The biggest impact from the sand movement has not been fully evaluated. Downpours regularly result in the deposition of more than 30 centimetres of sand. This is smothering the old soil surface and changing the soil profile. The impact on the flora and fauna has not been evaluated. The impact is ongoing and cumulative.
Desiccation results from the opening up of the canopy to create the roads. This in a change in the microclimate which is part of the forest ecosystem. Drying out of road surfaces reduces 4WD traction and accelerates disturbance which in turn increases water repellence and then water run-off and sediment flow. Thus desiccation causes roads to have a major physical impact on the landforms.
Desiccation results in a considerable change to some epiphytic flora near roads. Recent studies of epiphytic fern along roads near Central Station showed there was a significant variation in the distribution of ferns as a result of the opening up of the forest. During the past two decades there has been a loss of epiphytic orchids and ferns along Fraser Island's roads.
Wheel slip is influenced by the moisture on the road surface, driver competence and the power:weight:tyre-surface ratio of the vehicle (including trailers). Drier roads have much greater wheel slip. Tyre pressure also significantly influences the impact of vehicles. Vehicles towing trailers have much more wheel .
The competency of drivers is yet another variable which continues to be overlooked. The same vehicle driven by a more competent driver may have a significantly lower environmental impact because of better adjustment of load, tyre pressure and better control of power. Currently many drivers who visit Fraser Island have had no previous experience with four wheel driving let alone driving off road and in sand. These are mainly overseas backpackers who constitute over 40% of the island traffic.
Size of Vehicles: Not all vehicles have the same impact on roads. Larger vehicles erode roads more than smaller vehicles. 40-50 seat buses have more impact than smaller vehicles. It is well established that axle loading impacts heavily on conventional main roads. Despite this common knowledge, the impact of axle loading restrictions havenít yet been considered for Fraser Island. This is despite the obvious conclusion that the roads with the greatest amount of erosion/sedimentation are those used by heavy vehicles.
Seismic Impact: Vibrations from large travel considerable distance through the sand. Just as the impact of heavy vehicles can destabilise and cause cracking in large urban buildings, so the shock waves transmitted through the sand can affect vegetation some distance away. Wanggoolba Creek bank vegetation is showing already shows evidence of a slow but on-going landslip. This is exacerbated by heavy vehicles using the road parallel to it.
Road maintenance: There is increasing evidence that grading the road surfaces is exacerbating the amount of sediment run-off. More comfortable ride are achieved at an enormous environmental cost to a World Heritage site.
Vegetation: Roads can become wind tunnels especially the cross island roads which mainly follow the valleys shaped by prevailing winds. This wind tunnel exacerbates desiccation.
Changes to the substrate can leave surface and subsurface roots are exposed thus weakening or killing plants, even relatively large plants. At the mouth of Bogimbah Creek substrate rapid accretions changes resulting from road sediments caused mangroves to die. The smothering of original soil profiles is burying seeds and spores vital for the forest regeneration. The nutrient status of soils will inevitably change as a result of sediment movement. The precise impact is unknown but of concern.
Significant secondary impacts of 4WDs on Fraser Island include removing fuel woods from the forests, the increase in litter, the cause of removal of protected plants. 4WDs have been used to illegally remove ferns from Fraser Island.
Impacts on Fauna: There is an established impact on some of the very specialised fauna of the Great Sandy Region. CSIRO studies in Cooloola showed the distribution of ant were affected by tracks. Some ant species will not exist within a certain distance of roads or other significant disturbance. Others are opportunistic. Thus roads will change very markedly the species composition. Other researchers have identified the impact of roads on acid frogs. The more disturbance there is the more likely it is that non-acid frogs will invade the territory of acid frogs. Roads also affect the distribution of small birds and mammals which are vulnerable to predation in crossing open spaces. The wider the road clearing the fewer species which will cross it.
There has been a very heavy impact on beach and foredune fauna both through "road kills" and through the impact of constant disturbance. Fraser Island populations of Pied Oyster catchers, red-capped dotterels and Beach Thickknees have been decimated since the beach had become a highways for 4WDs. Terns are weakened by having to continually move to allow 4WDs passage. Dingos have also been affected by 4WDs and have now hunt less and scavenge more.
Roads as Vectors for Injurious Agencies: Off-road vehicles are a potential vectors for spreading injurious agencies around Fraser island. Fraser Island has been remarkably free of feral animals most notably Rattus rattus and brown mice. These plus weeds, soil pathogens, weed seeds and a whole range of injurious agencies can accidentally be spread through vehicle movements. Vehicles also allow access which can be used to spread fire and litter. The impact of these should not be understated.
Shrinking of wilderness: The impact of vehicles on the wilderness values is a difficult concept for many utilitarians to accept. People who only see value in something which is being physically used or which has investment /speculative potential (such as a rare painting) cannot accept the concept of wilderness. The concept is that people can get value from wilderness without actually physically visiting it and exploring it is an incomprehensible anathema. Utilitarians can only see value in natural areas as long as it is generating perceived economic activity. Such soul-less people don't appear to understand that religion has no perceived economic value, that many of the memorabilia which people most enthusiastically cherish and which mean so much to them have no perceived economic value.
Wilderness nourishes the soul and inspires people at least as much as parochialism, patriotism, religion or the arts. People don't have to go to wilderness to be inspired by it. Most Australians will not visit Antarctica yet 93% of Australians want that remote wild continent free from mining and commercial exploitation. Since wilderness is a function of being remote from roads, roads erode wilderness.
Noise: The aesthetic impact of noise is well known and understood. While we are not talking of the volume of noise to cause pain or nervous disorders, we are talking about the intrusiveness of noise in a natural area. For example anyone walking along Wanggoolba Creek would have found the sound of vehicles roaring and clanking out of sight along the road above them will understand the intrusiveness of noise.
There are many potential remedies to ameliorate the very serious degradation of Fraser IslandĎs World Heritage values resulting from the present widespread use of 4WDs. The main principle to reduce the impact is to reduce the amount of surface disturbance by 4WDs. Just as the impact of pedestrians can be minimised by using boardwalks, so lifting vehicles travelling on the interior of Fraser Island onto rails would minimise impacts.
- Buses should be scaled down in size. Commercial tour operators should be encouraged to use much smaller vehicles. Current visitor numbers could be carried in more environmentally friendly sized vehicles.
- Instead of making the roads to fit the vehicles of tour operators, tour operators should be required to get vehicles to fit a better road standard.
- Axle loading limits must be enforced on Fraser Island sooner rather than later.
- High priority should be given to exploring the feasibility of introducing a light rail people mover to reduce the surface disturbance resulting from using so many and such large 4WDs.
- There should be a restriction on trailers there travelling on many Fraser Island tracks, particularly inland tracks.
If the impact of roads is one of the most critical issues for the management of Fraser Island it needs more urgent discussion both by the CAC and SAC and the QPWS. The QPWS should be listening instead of proceeding on their own agenda.
This educational supplement is published by
the Fraser Island Defenders Organization
as a supplement to its newsletter, MOONBI 99 1 May 2001.