7 August 2019
Deviot, Tasmania: the impact of a slow moving landslide on home owners
Posted by Dave Petley
Deviot, Tasmania: the impact of a slow moving landslide on home owners
In Australia today, news agencies are reporting a dispute between the government and home-owners over the impact of a reactivated, slow-moving landslide. The location is Deviot in Tasmania, where a landslide is slowly destroying five properties. It is a common, and extremely sad story of the impact that a landslide has had on everyday lives.
The location is -41.226, 146.924 – there is good Google Earth imagery of the site, taken in early 2016:-
The site of the landslide at Deviot in Tasmania. Imagre via google Earth, collected in January 2016.
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In 2013, during a period of heavy winter rainfall, the landslide at this site in Deviot reactivated, causing structural damage to a house. Further significant damage occurred in 2016, with the movement affecting five houses. At least one has had to be demolished. Such an event is usually a disaster for the property owners, as in most jurisdictions domestic insurance does not cover landslide damage. The level of impact of the landslide is dramatic:-
Structural damage caused by the Deviot landslide in 2016. Image by Nick Daking (the property owner) via ABC News.
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This story, which is far from unique, has come to prominence because the property owners allege that the local authority were fully aware of the landslides at this site, but failed to inform the property owners of the hazard. The situation is being considered in the Upper House of the Tasmania Government.
Interestingly, there is a detailed geotechnical report on the site online (NB PDF), written this year by a geotechnical consultant, Dr Derek Pennington. This includes a map, from 2011, which shows the extent of the relict (historic) landslide and the portion that has reactivated, causing the property damage:-
The 2011 MRT geomorphological map showing the Deviot landslide. Extracted from the report by Dr Derek Pennington.
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The report also demonstrates that the landslide reactivated during unusually wet periods:
The rainfall record showing periods in which the Deviot landslide reactivated. Figure extracted from the report by Dr Derek Pennington.
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This situation is a tragedy for the householders, who will have suffered huge financial loss and enormous stress. It is simply the case that an ordinary property owner cannot possibly anticipate this sort of hazard. Whilst I cannot really comment on the rights or wrongs of the case going before the parliament, we have to recognise that the system is not working correctly when potential property owners have no way to know that their site is at risk, and that there is no mechanism to insure against the risk. This needs to be addressed as it is occurs again and again around the world.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
There are detailed land stability maps available for the Tamar Valley region (and other susceptible areas in Tasmania).
http://www.mrt.tas.gov.au/portal/earlier-landslide-maps
Not that it helps those recently affected, but this is the latest geohazard map of the Deviot area.
http://www.mrt.tas.gov.au/mrtdoc/map_catalogue/map_public/335853_1/slide.pdf
Hi Dave,
Many thanks for this post, as you say, such slow moving events impacting developed areas cause severe losses and stress for homeowners. May I point your readership to the following: ‘Living with Ground Instability and Landslides: an international good practice guide’ which covers many of the issues involved from a statutory planning and management, and homeowner perspectives. The guide is free to download via this link: https://www.researchgate.net/publication/325467184_Living_with_Ground_Instability_and_Landslides_an_International_Good_Practice_Guide
I am living this situation right now. We purchased a river lot on which we build a family home. The developer was aware of potential landslide risks and had a geotechnical report recommending re-sloping, but the work was only done on the furthest portion of the bend in the river. A slump developed behind our homes – exactly where the geotechnical report had anticipated. We are spending tens of thousands of dollars on remediation with no guarantee of halting the slump. The developers are pretty much broke and lawyers would cost too much, so suing isn’t an option. Fortunately, our foundation is on piles that appear to reach below the failure and our house hasn’t moved – yet. I wish we could at least purchase insurance (we don’t care about price at this point) instead of hoping the best…
It there any way to stabilise the ground by installing pillars deep into solid ground. Similar to when they cut roads into mountains and retain the hill face