I’ve recently posted news items about the Tasmanian Landslide Code, the On-site Wastewater Management Code, and the Coastal Erosion Hazard Code. I’ve produced flowcharts to help people navigate through each of these.

Many people I am sure are unaware of these Codes, and 20 or more others, which form part of Tasmania’s state-wide 2015 Interim Planning Scheme. Potentially, they affect if and how you develop your land. If you are planning a development – it might be building a new house, or extending an existing one – you should check them out beforehand.

If you are contemplating buying land to build on, I would also strongly suggest that the contract for purchase should include a clause which says that settlement is subject to a satisfactory geotechnical report.

Here’s the full list of Codes in the 2015 Interim Planning Scheme, labelled E1.0 though to E24.0. Not all of them apply to each Local Council. The ones I can help you with are linked to pages in this website.

E1.0

Bushfire-Prone Areas Code

E2.0

Potentially Contaminated Lands Code

E3.0

Landslide Code

E4.0

This code number not used

E5.0

Road and Railways Assets Code

E6.0

Parking and Access Code

E7.0

Stormwater Management Code

E8.0

Electricity Transmission Infrastructure Protection Code

E9.0

Attenuation Code

E10.0

Biodiversity Code

E11.0

Waterway and Coastal Protection Code

E12.0

This code number not used

E13.0

Historic Heritage Code

E14.0

Scenic Landscapes Code

E15.0

Inundation Prone Areas Code

E16.0

Coastal Erosion Hazard Code

E17.0

Signs Code

E18.0

Wind and Solar Energy Code

E19.0

Telecommunications Code

E20.0

Acid Sulphate Soils Code

E21.0

Dispersive Soils Code

E22.0

This code number not used

E23.0

On-site Wastewater Management Code

E24.0

Significant Trees Code

You can also see the Codes listed, and in detail, on the state government website www.iplan.tas.gov.au.

(Click on “Planning Schemes”, then select your Local Council, and, at left, “Part E Codes”.)

I’ve produced a PDF flowchart to help people navigate through the Tasmanian Acid Sulphate Soils Code.

The Code is one of many in the 2015 Interim Planning Scheme used by all Tasmanian Local Councils. See the list of Codes including the ones for which I offer professional services.

Potentially acid sulphate soils or sediments are naturally-occurring materials which contain microscopic particles of dark-coloured (mainly iron) sulphides. The sulphides were formed by sulphate-reducing bacteria acting on original sulphate in sea water.

Environments favourable for their formation are oxygen-poor (reducing) conditions in former or present day mud flats and other low-lying or shallow submarine coastal areas. Some potentially acid sulphate soils occur at higher elevations.

When disturbed and exposed to the atmosphere, the sulphides in these soils or sediments re-oxidise to sulphates and produce sulphuric acid solutions. The acid mobilises metals in the soil which in turn can cause environmental or infrastructure issues at the disturbed site, or elsewhere if seepages flow into adjacent waterways.

Importantly, if these materials are left undisturbed, sulphate is not generated. This is the key to their management.

Undisturbed soils with the potential to form acid sulphate are called PASS. Once disturbed, they are Actual Acid Sulphate Soils (AASS). Collectively these materials are called Acid Sulphate Soils (ASS).

The Tasmanian Department of Primary Industry, Parks, Water and Environment (DPIPWE) has plenty of information on where ASS occur in Tasmania, and how to manage them (PDF document). You can also check online to see if land you are interested in is in an ASS zone.

Go to the state government website www.thelist.tas.gov.au. On the home page, click “LISTmap”; double click on the location of interest and continue to double click (or use the mouse wheel) to zoom in; click “Layers” at top right, then click “Add Layer +”. In the menu box that opens, scroll down to “Geology and Soils”, click on “Soils” and click on one of the four Acid Sulphate Soils (the circular green + icons”. You may need to zoom in further until the bands are visible. Drag the menu box out of the way (or close it). At top right of the screen, click on the tiny arrow in the Acid Sulphate Soils box to see the Legend and change the transparency.

The published 1:25,000 scale digital geological map of the Hobart metropolitan area shows the OAK Tasmania’s Walkabout Industries site in Clydesdale Street, Glenorchy, and the neighbourhood, to be underlain by Jurassic-age dolerite.

New field evidence suggests the map needs to be amended.

In 2011 bulk excavations at OAK provided excellent exposures of weakly-consolidated, orange-brown boulder beds (see photo). The clasts in the material are almost entirely angular to rounded dolerite cobbles and boulders up to about 0.5m in size, with a few percent of smaller clasts of chert, and Parmeener Supergroup siltstone and sandstone.

In July 2013, a 9.6m deep auger-and-diamond drill hole sited adjacent to the excavation encountered 5.6m of similar doleritic boulder beds, overlying conglomerate composed entirely of Parmeener Supergroup sandstone and siltstone clasts to 50mm in a non-plastic silt/sand/gravel matrix. A band of pink/orange silty clay occurred in the conglomerate over the 5.90-6.05m depth interval. See the photo of the core, and the log of the hole.

I interpret the deposits in the excavation and drill hole to be Tertiary in age and of similar fault-scarp related origin to other boulder beds in the Hobart district. I think the thin horizon of silty clay in the drill hole could be volcanic ash. It is not clear how far the Tertiary deposits extend laterally from the OAK Tasmania site.

On 8 July, Hobart City Council asked me to assess the risk posed to road users and track walkers from a large dolerite boulder (50t) which had toppled off a small cliff section on steep (40+degree) slopes on Mt Wellington. Despite the millions of already-toppled boulders on the adjacent talus slopes, geological time is immense and rockfalls are rare enough to be noteworthy.  This boulder was also larger than most, and since it did not break up, its travel path was longer than most. It came to rest in a muddy bouldery watercourse 170m downslope, about 20m across the Pinnacle Track.

I arrived at the site a few hours after the fall. With daylight hours fading, and uncertain about the boulder’s stability, I though we ought to close the Pinnacle Road to the summit of the mountain. Council organised this immediately.

Next morning, after a Council crew cleared scrub from around our rock, it was clear that the boulder had come to rest against other smaller ones. I thought the potential for it to remobilise was “unlikely’, and the risk to life to a road user 300m downslope was “tolerable”.  Pinnacle Road was reopened, and we instigated a set of monitoring points around the boulder to further assess its stability.

A scramble uphill by me and Matt Lindus (Council’s Acting Manager of Bushland & Reserves) found the source – an empty 2.5m wide space between two smaller but similarly leaning boulders. We temporarily closed Pinnacle Track while I reviewed slope stability issues, runout distances and hillside slopes. Overnight, I satisfied myself that the risk to track users was also “tolerable”, and recommended that the track be reopened. We’ll be looking to see what measures (if any) are needed to reduce the likelihood of the two remaining boulders toppling. Monitoring shows that the fallen boulder seems to have stabilised.

My risk assessments included reference to the Australian Geomechanics Society series of volumes on Landslide Risk Management (2007), and to the good work being done by Colin Mazengarb and Michael Stevenson at our local Mineral Resources Tasmania. They’ve produced a series of Landslide Hazard Maps for major population centres in Tasmania. (The Potential Rockfall Hazard Map for Hobart not surprisingly identifies the steep slopes of Mt Wellington as at risk of rockfalls, but it also shows that Pinnacle Track, and most others, are at risk of runout of boulders across them.) I also had valuable discussions with Victorian geotechnical engineer Tony Miner, my erudite sounding board for more than a handful of landslide issues.

I suspect that if a detailed assessment was done of walking tracks on the mountain, the risks to walkers would range from “acceptable” through “tolerable” to “unacceptable”. But closing high risk tracks would no doubt be a very unpopular move. Maybe we should redefine what we mean by acceptable and unacceptable risk for activities which are inherently riskier than others, but in which we willingly and knowingly engage.

People (like me) who conduct geotechnical (including landslide) investigations and write geotechnical reports ought to be qualified to do so. At the very least, in Tasmania, we must have a university degree in Engineering, Geotechnical Engineering or Geology, and have Professional Indemnity Insurance (Certificates of Specialists or Other Persons).

In Tasmania, twenty or so firms or individuals advertise in this important field, but only a handful are active. Like professionals everywhere, we exhibit a range of geotechnical expertise, from poor, to OK, to good.

So there is room for improvement. But how?

It’s not easy. Under the current situation, most of us are already “suitably qualified”, yet some are clearly out of our depth and continue to churn out poor work. We have lots of help – ready access to excellent guidance from the Australian Geomechanics Society (AGS), one of the leading geotechnical organisations in the country. (Most local Councils demand that geotechnical reports are done in accordance with AGS Guidelines.)

But some of us pay only lip service to the guidelines. Local Councils are continually frustrated recipients of substandard geotechnical reports, and ask for peer reviews.

In this competitive consulting world, some of us charge cheaply to attract work. Low prices restrict our ability to do extra work if the job requires it, and in turn beget more substandard work. We should never underquote, or even quote, for geotechnical work.

Through long experience I can guarantee that these wise words will fall mostly on deaf ears.

So. Should we be accredited?

I am currently working on AS2870 site classification reports for more than 50 separate lots in a residential subdivision in Launceston.  The job involves about three weeks of field work, and a similar time in the office.  The subdivision is Eastmans Green in Newstead, and the developer is Ecoast Homes Pty Ltd from St. Helens.

I did the original geotechnical investigations for the subdivision in two stages in 2009 and 2011, and in what I believe may be a first in property development in Tasmania, Ecoast Homes has made my reports (and one of my sample AS2870 reports) available online for interested parties. Each of the AS2870 reports will also be available free of charge to stakeholders.

I was asked to produce the site classification reports when a local practitioner did a substandard job on one of the lots offered for sale.  The sale fell through. The issue, I think, was that the practitioner’s (brief) report wrongly stated that the lot was in a “known declared landslide zone”, when in fact it was in the Medium landslide planning hazard band. Not the same thing at all. The report provided a Class P classification but also stated that more information (from others) was needed before a founding depth could be provided.

Clause 2.1.3 of AS2870:2011 allows a practitioner to classify a site as Class P and call for more geotechnical information, but it hardly facilitates land development if the practitioner walks away from providing the extra geotechnical work.  My point is that if a practitioner offers a professional site classification service, and clearly feels capable of classifying a site, he or she also ought to be able to provide (or arrange to provide) all the input needed to complete the job.

I have been invited to collaborate with the Tasmanian Department of Premier and Cabinet (DPAC) and Mineral Resources Tasmania (MRT) to prepare landslide guidelines for geotechnical practitioners and regulators in this state. Both government entities have been working hard to address geotechnical hazards in Tasmania.

The players in this game are State Government, Planning Authorities (local Councils), people who write geotechnical reports, and clients.

It’s a challenging opportunity for me. Some of the issues arising from this approach might be:

• what guidelines should be adopted for landslide reports?
• what people should be authorised to write landslide reports?
• what level of investigation should the reports address? and
• how should this be incorporated in planning regulations?

A platform to discuss and contribute to these issues is available to interested parties – at MRT’s launch of the Northern Tamar Valley Landslide Zoning Map in Launceston on 25-26 March 2014. The 2-day workshop is co-sponsored by the Australian Geomechanics Society.

At the workshop, I will be presenting some initial thoughts on how we practitioners currently handle landslide assessments and reports, how we might do it better, and how regulators and planners might get involved. If you are working in this field, you should attend.

Contact Colin.Mazengarb@dier.tas.gov.au.

Some useful background links…

Our shack at Spring Beach in eastern Tasmania is on a coastal cliff of Triassic-age sandstone. We’ve been holidaying there for 35 years, and though sand and silt and small pieces of stone fall every day from the cliff, I’ve never seen a bigger rock fall than this one. And I wasn’t there when it happened (!) – sometime between April and June 2013. Lucky no-one else was there either (if you were, and you’re still alive, let me know!).

The boulder is a cube of sandstone at least two metres on a side. With a density of about 2.5 tonnes per cubic metre, that’s about 20 tonnes in all. A few extra tonnes fell as a swag of smaller pieces.

The cliffs at Spring Beach recede slowly this way, and so do most cliffs, coastal or otherwise. Rockfalls (“geohazards”) are natural.

It was a nice fall – worthy of attention. The other reason I mention it is that it helps people like me try and work out how often falls like this happen. Then we can estimate risk to people. In itself, the single rock fall is not much help, but when added to other rock falls from the other end of Spring Beach, a picture starts to build up. At this other end, holidaymakers carved their names in the sandstone shore platform at the base of 30m sandstone cliffs back in the 1950s (where are they now?). Since our family noticed these back in the 1970s, when the names were half their age, they have been partly covered by boulders fallen from the cliff. (Smaller stuff gets quickly washed away by waves, but the 2 – 3 tonne boulders here are harder to shift.)

So, in 50 years or so, half a dozen boulders big enough to kill people have fallen from the Spring Beach cliffs — say, one a decade on average. The chances of a person being hit by one of these missiles is very low — we would have to say acceptably low — so I’m not about to suggest we close Spring Beach to the holidaying public just yet. Or ever.

Almost 10 years ago, at an Australian Geomechanics Society meeting, I lamented how bad some Tasmanian “expert practitioners” were at doing soil testing and classification for houses. Mostly, like bad doctors, their work goes unchallenged – until something goes wrong.

Recently, when providing a second opinion about a house site to a client, I was reminded that people are still receiving bad geotechnical advice. The property in question was not in a declared landslide zone, but nearby, serious slope instability issues were reported on 15 years ago by Mineral Resources Tasmania, and house-threatening landslides are still occurring in the area. This situation ought to have been recognised by the classifier, but not only did his advice fail to refer to potential instability, it recommended on-site wastewater discharge on steep, hummocky, probably unstable ground immediately adjacent to mapped “old landslides”. Not a good idea.

How do you know when you have received bad or inadequate geotechnical advice? My thoughts on soil tests for house sites (PDF download) might help.