When soils ain’t soils in Guanaba

When parts of your neighbour’s backyard disappear downhill after a major rain event, you realise good soil structure is a critical Tamborine Mountain issue.

The Tamborine Mountain’s escarpment protection precinct relies heavily on its vegetation to ensure soil integrity remains in check, especially during wet weather, and especially during the storm events with which this region is so familiar.

The eastern escarpment precinct has seen significant landslides occur over time (and in very recent history), which have permanently changed the landscape.

One of the most notable eastern escarpment landslides occurred in the famous 1974 floods, where part of the escarpment slipped, taking with it soil, vegetation, rock and more. The instability of the eastern escarpment is well known to experts and to local residents, who often sight regular landslips after rain. There are a number of graphic pictures taken after the 1974 floods that show what happens when soil structure gives way in the escarpment.

Tamborine Mountain Landslip 1974 eastern escarpment

1974 – this major landslide occurred on the land around Kaiser Road.

Recent landslides

People who live next to the 500 acres of escarpment protection precinct have recorded landslides in very recent times (such as after the floods in January 2013). But, it doesn’t take this kind of major rain event to bring on landslides (they can occur after Summer rains synonymous with the Scenic Rim region).

Landslide after Cyclone Oswald where a whole bank gave way

Landslide after Cyclone Oswald – a whole bank gave way.

Landslide after Cyclone Oswald

Another perspective of the landslide.

Preventing landslides

It’s more effective to try and mitigate the risk of landslides by retaining essential vegetation.

“Prevention of landslides is far preferable to subsequent rehabilitation, which is expensive, long term and possibly only partly effective.”

“No further clearing should occur on susceptible locations at risk.”

Ref. Warwick Willmott; Rocks and landscapes of the Gold Coast Hinterland: Expanded third edition; Geological Society of Australia, Queensland Division; 2010.

Potential risks with certain developments on the Tamborine Mountain escarpment protection precinct

1. Any geotechnical report providing information on proposed developments within the escarpment precinct should identify critical slopes, faults, colluvium, slip zones etc.

2. Proposed developments within the escarpment must take into account the 4 rainforest gullies and water catchments – Guanaba Creek and Coomera River – and provide a solution to ensure catchments won’t be negatively impacted on.

3. Proposed developments must consider surface water runoff treatments, which may lead to the concentration of water and, potentially, initiate erosion, super saturation and slips.

4. Proposed developments should outline impacts of vegetation clearing, construction and sediment travel and surface water runoff downstream into National Park, Guanaba Creek and the Coomera River.

5. And, proposed developments should fit within the Tamborine Mountain escarpment protection precinct.

Tamborine Mountain’s escarpment is precious, delicate and in need of protection. Soil structure in the escarpment is fragile (just ask the people who live there). Out-of-place developments, that rely on the clearing vegetation to enable the frequent movement of human traffic (the likes of which the 500 acres of escarpment has never seen) will threaten soil integrity.

And when soil integrity is under stress, there is an increased risk of soil runoff, which affects the region’s water catchments and can increase the risk of landslides.

It’s vital we fight to protect the Tamborine Mountain escarpment protection precinct against developments unsuited to its very specific and special characteristics.

For more images of the 500 acres in question, see our Save Guanaba Facebook page.

(Note: Many residents near the 500 acres have spent years planting indigenous and native flora to rehabilitate their properties – formerly old farms – and extend the rich vegetation within the 500 acres into their own backyards.)