South Sister St. Marys, Tasmania

South Sister

proof of evidence

GEOLOGICAL STUDIES NEAR SOUTH SISTERS, TASMANIA
David Stapledon

SUMMARY AND RECOMMENDATIONS

Investigations in the South Sister have involved examinations of air photos, contour plans and maps of MRT, followed by less than 3 days traversing the area within and around the proposed coupe. During the traversing we found:

two landslides on the northeast-facing slope above Dublin Town Road, each showing some leaning trees. These appear to extend into the Triassic bedrock and may be bounded by bedding, and joints or faults in the rock. They may well extend below the road. The other parts of this slope, to the north and south, were not inspected on the ground, but are also steep and must be suspect for past and possible first-time sliding.
the scarps of three smaller past landslides probably less than 100 years old, were found on the steep escarpment just south of the proposed Coupe. Because of the steepness of this escarpment the slipped materials from these scarps would have moved well down the slope, in some cases as debris flows. These three features were found during only one traverse down and one traverse up the escarpment. Visibility was generally limited to less than 30m on either side of us, so in these two traverses we would have seen effectively less than 120m of this 2000m long escarpment. It is likely therefore that there are many more scars of past slides of this nature, on this slope. Further to the south, below the line of the 500m contour, the slope of the old Triassic land surface appears to steepen, and some larger slides may have developed here in the past.

We also examined the steep slopes above the proposed Coupe, close to South Sister. I am not convinced that large dolorite mass just below the Sister was moved there by landsliding. We did not find evidence of old landslides on these upper slopes, but it could be there. We found 2 suspect areas on the gentle slopes within the proposed Coupe area. I consider that the water level rising which would occur during the first few years after 50% thinning would increase the risk of renewed movements at the old slides. Further more detailed studies should be carried out to quantify the risk at these slides, particularly along the whole north-eastern face, and to locate other old slides - particularly on the southern escarpment.

I have not made any assessment of the consequences of renewed landsliding, but I have been to the sites of two major (overseas) landslide disasters, and seen the faces of the survivors; not pleasant but it sharpens the mind.

1. INTRODUCTION

I have been involved in this matter since October 2004, when I agreed to provide geological advice to a group of residents in the South Sister area. The residents were concerned about the possibility of loss of water supplies, and landsliding in the slopes below South Sister, if logging (50% thinning) was carried out at the proposed Coupe NI 114A. I agreed to assess the landsliding issue only. Between October 2004 and March 2005, I reviewed a number of expert reports relating to the proposed harvesting operations (see References 1-3, 6-8) and general information, including:

St Marys Geological Sheet (Appendix P)
'Landslide areas in St Marys area' - map prepared by Mineral Resources Tasmania (based on Sloane, 1976)
A contour plan which forms the base for Figure 1 and Appendix R
Colour air photos 1:42000 scale, Nos. 41 & 42, Northern Revision Run 15, 2000 (examined stereographically, while in Adelaide)
Forest Practices Code (note: I have reviewed an incomplete copy)
Historical data on coal mining near South Sister, including that in Appendices V and T

I initially prepared two short letter-reports commenting on the landslide risks presented by the proposed operations (References 4 & 5).

I visited the site of Coupe NI 114A and surround on 12 - 14 April 2005, accompanied by Mr. Ralph Rallings. Appendix R shows the routes taken during this inspection.

While preparing this evidence I have made all enquiries which I believe are desirable and appropriate and declare that no matters of significance which I regard as relevant have, to my knowledge, been withheld from the Tribunal.

2. QUESTIONS TO BE ANSWERED

I started this assignment by defining the following Key Question:

Would the proposed forestry operations on Coupe NI 114A cause the emission, discharge or escape of water which would cause unacceptable risks of landsliding below, above or within it, such that the Coupe should be modified or abandoned?

Comments on the question

I have assumed that there would be no cutting into the slopes within or below the Coupe as part of the proposed forestry operations.

It seems to be accepted by both Dr. Leaman (Ref. 1) and Dr. Lane (Ref. 8, Page 9) that up to 200mm of additional water will infiltrate annually beneath the Coupe, initially. This should result in substantial rises in water levels for the first year or so, diminishing to zero in 10 years (Ref. 8, Figure 5). Such initial rises would increase the probability of sliding in slopes within and downslope from the Coupe.

Based on logic, and long personal experience at construction and mining sites, I believe that there would be a significant increase in runoff from the coupe during period of prolonged and/or intense rainfall, at least in for a few years following logging. In times of extreme rainfall, this would increase the probability of erosion, landsliding, and the formation of debris flows.

There is evidence of past landsliding in the slopes below the Coupe. During the site inspection of 12-14 April 2005, we found definite old slides A and B on the northeastern slope above Dublin Town Road. Each show some leaning trees, and the rocky ridge between them also has some leaning trees. The southern part of this slope is likely to be affected by the northern extension of the Gould Fault and its connection with the mapped fault 400m to the north (see notes on Feature 14, in Section 5). I suspect that careful studies will find that most of this northeastern slope, from the Cardiff Mine corner to the North Sister corner, has suffered some past landsliding. In my opinion, this should be investigated thoroughly before any forestry operations are considered or allowed.

With respect to the south-facing escarpment below the 600m contour, it is my opinion that careful studies here also would find evidence of past, probably shallow, sliding. I base this view on the steepness of the slopes, the fact that the beds are almost horizontal, talus-covered, and that in only one traverse down the slope we found the scarps of 2 small slides, and in only one traverse up the slope 600m away we found another larger but similar scarp. The landslipped materials from these 3 events had gone down the slope - in one case we found the channel of the debris flow initiated by the slide. This also needs to be investigated thoroughly prior to allowing any forestry operations to proceed.

I do not know whether water level rise and runoff effects from the proposed logging would definitely reactivate any of the definite or probable past landslides. However, in my opinion this is likely and should be thoroughly investigated. I have not addressed the consequences of landslide activity, but in my opinion this matter should be considered in detail before proceeding with forestry operations.

I understand that selective logging was carried out on the Coupe mainly during the late 1940s and early 1950s, when the slopes were being drained due to pumping by Jubilee Mine (See Appendix W5, Page 13). The stabilising effect of coal mine pumping at Jubilee mine would be lost now, and the mine is likely to be full of water. As explained in the discussion of Feature 14, in 3.0 below, subsidence of the ground above totally extracted areas could increase the probability of sliding. See Appendices V and W4.

3. TOPOGRAPHY AND GEOLOGY AT THE COUPE AND SURROUNDING AREA

Figures 1, 2 and 3 summarise my understanding of the most relevant topographic and geological features of the area.
Figure 1 was made using the St Marys Geological Sheet, interpretations made from stereographic examination of the air photos, and from the ground inspections. The features numbered 1 to 14 were examined either on the ground or on the air photos, or both.
Figure 2 was compiled from the best available contour plan, the geological boundaries on Figure 1, and the Jubilee mine data on Appendix T.
Figure 3 was compiled from the best contours available, and observations made on the ground.

4. DESCRIPTION AND DISCUSSION OF THE FEATURES SHOWN ON FIGURE 1.

Feature 1 was the most prominent feature on the air photos. I interpreted it as a very steep, abrupt scarp. On the ground we found that it included the 5 - 6m high sandstone cliff, shown on Figure 2, Section E-C, and Photo 4. The cliff was followed for more than 100m on the ground. The slope above it is very steep and includes more cliffs. The ground below (to the south) is almost flat and has few large trees. The dip of the sandstone in the cliff was measured as horizontal.
Feature 2 is an exposure of sandstone and mudstone, dipping about 5 degrees south-east, at the site of an old coal mine. From the air photos, and contours, a landslipped mass was suspected here initially. I now have doubts about this, but further study is recommended.
Feature 3, about 500m west of Cheeseberry Hill, refers two areas showing denuded vegetation, on the air photos. I suspected they were recent slide scars but now believe they are scars of debris from the Cardiff mine.
Feature 4 refers to the scars of 2 major landslides, Slides A and B, to the East of South Sister. They were inferred from the air photos and contours, and confirmed on the ground. Photos 5 and 6 were taken within Slide B. Note 5 leaning trees in Photo 6, and several also in Photo 5. The feature G, shown in the middle of the slide scar on Figure 1, is a shallow trench-like feature which I interpreted to be the scar left by a small graben structure (see Appendix S, Figure S1). Weather and time did not allow a detailed look at Slide A - also we knew it had been recorded by others (Appendix Q). However we saw some leaning trees. The sketch cross sections on Figure 3 were drawn to get an initial impression of the possible dimensions of the landslipped masses. Because of the tree cover, the contours don't show enough detail (particularly below the road) to allow plotting any definite boundaries or depths. However I believe that both of these slides probably extended into the Triassic bedrock. I note that MRT (Appendix Q) consider a kilometer long area below the road to be a 'Potential landslide area.' We didn't have time to look. Figure 1 shows an 800m long exposure of Triassic rocks, and bedding dip measurements which show that the beds are folded, in some places. It is possible that gently dipping bedding surface faults (Ref. 9, Page 98) and steeply dipping faults like those mapped in the nearby mine (shown in red on Figure 1) provided weak basal and lateral surfaces to assist slide development in the bedrock.
Feature 5 includes the valley between South Sister and the large mass of dolerite blocks about 100m to the south (see also Figure 2, Section E-C). On the air photos and on the ground I saw that this lower dolerite mass comprises columns and masses of columns most of which have fallen over. The northerly dip of one of these large masses has previously been interpreted by Mr. Rallings (Ref. 6, and 3.0 above) as an indication that the Feature 5 valley had possibly been formed when the lower dolerite mass pulled away to the south, during an ancient landslide. Mr. Rallings no longer proposes this. Any slide extending down to the base of the Triassic sedimentary rocks (see Figure 2, Section D-C) would have included the rock mass subsequently mined for coal. If this mass had moved in such a slide it would have been so disrupted that the mining would not have been possible. Dr. Leaman (Ref.1) also interpreted the valley and these collapsed blocks as evidence of an old landslide. However, during the site visit we saw one large dolerite mass (Feature 6 and Photo 1) which was vertical. In the light of this vertical block, the near-horizontal or slightly northerly dip of the Triassic rocks, and the lack of any obvious topographic indication of a bulging toe area, I doubt the existence of this landslipped mass, also. I suggest that the lower dolerite mass on Figures 1 and 2, Section E-C, may be simply another disintegrating dolerite remnant (like South Sister).
Features 7 and 8 are swampy depressions with gentle scarp-like features and could be interpreted as landslide scars.
Feature 9 is on the steep escarpment about a kilometer west of Cheeseberry Hill. It refers to two small landslip scarps, about 30m apart, shown in Photos 2 and 3. Each was judged to be less than 100years old - Scarp 2 showing exposed dolerite soil. These slides have clearly discharged soil and rock downslope, into gullies. The gully below Scarp 2, just below the scarp level is a deep, well-defined feature but is not evident on either the air photos or the contours on Figure 1.
Feature 10 refers first, to the Jubilee Mine portal area, to the west. I noted that there was no water flowing out of the tunnels. One tunnel was blocked off only by spoil. There is a deep gully 50 -100m east of the portals, but again no indication of this on the contour plan. Further east, below the mine access road there were remnants of a dump of mine spoil which had slumped downslope. About 250m east of the portal area we found another big gully and an erosion channel about 3m deep cutting through the road. I judged that this channel was caused by a debris flow from one of the slides at Feature 9.
Feature 11 is an inferred landslip scarp about 15m across and 10m deep, about 100m upslope from the Feature 1 scarp. I recorded the overall slope below the Feature 11 scarp as 38 degrees. Further upslope the grade flattens, and at about RL600m I recorded 'slumps and springs'.
Feature 12 is an exposure of fresh, very strong basalt, in Gardiners Creek, under a bridge on Germantown Road. The basalt contains steeply dipping joints spaced from 5 to 150mm and also some flat-lying joints.
Feature 13 is the remnants of the Cardiff Mine. Open holes up to 15m wide formed by roof collapse into shallow workings. Some were empty and others contained water.
Feature 14 points on the east side, to the Gould Fault which is inferred from the separation between the Jubilee and Cardiff mines. The workings of each of these mines are shown on Appendix V. The eastern edge of the fault zone was mapped in the Cardiff mine. In the Jubilee mine the western edge is not shown as mapped, but we can assume that the miners stopped when the rock and coal began to become more fractured, close to the edge. From the gap between the two workings I suggest that the fault zone was (is) at least 50m wide, in this section. Much of the material in the zone would be sheared and/or crushed rock, with 'soil properties' (in the engineering sense). To the north, this weak zone will probably pass beneath the steep northeast-facing slopes above and below Dublin Town Road. It may be connected in some way with the fault bounding the Triassic rocks, 400m to the north. This is another good reason for not raising the water table beneath that north-east facing slope

It should be noted on Appendix V that there are 3 main 'total extraction' areas (shown in dark grey) labelled X, Y and Z. In these areas the pillars between the tunnels were removed. As pillars are removed, the overlying rock collapses to fill the space, and the settling down of this rock is reflected in subsidence at the ground surface above (see Appendix W, Item W4). There will have been some subsidence over each of Areas X, Y and Z. As explained in Figures 12 and 13 of Appendix W4, the amount of subsidence reaches a maximum amount, always less than the thickness of the coal seam, when the area of total extraction is a little wider than the depth below the ground surface. This criterion for maximum subsidence is not quite met at total extraction area X, which is about 150m square, and about 160m below the swampy depression at Feature 8. However, the subsidence at Feature 8 area could cause movements at the talus/bedrock interface and thus contribute to slope instability here.

The most significant part the operating Jubilee mine played in the stability of the overlying slopes, would have been the drainage of the ground it achieved by pumping. The beneficial effect of this is now lost (see Appendix W5).

DAVID STAPLEDON
8 May 2005

REFERENCES

1. Leaman, D.E. (2003) Appraisal of initial forest plan, South Sister - Nicholas Range. Hydrological and Landscape Observations. Report dated 22 November 2003

2. Comments by P.D. McIntosh on report of D.E. Leaman's November 2003 report

3. Comments on P.D. McIntosh criticisms, by D.E. Leaman

4. Stapledon, David (2004) Initial Forest Plan, South Sister Nicholas Range, Comments on reports by D.E.Leaman and P.D. McIntosh. Dated 6 October, 2004

5. Stapledon, David (2005) Letter to Frances Daily, dated 30 Jan. 2005

6. Letter dated 5 February 2005 from Chief Forest Practices Officer to Dr Frances Daily, with comments by Peter McIntosh, on various reports

7. Letter dated 7 March 2005 from Ralph Rallings to Hon B Green, Minister for Infrastructure, Environment and Resources

8. Lane, P. (2005) Scientific Review of Water supply impacts of Proposed Forestry Operations in State Forest Coupes NI 114A at South Sister, North of St Marys

9. Fell, R., MacGregor, P and Stapledon, D. (1992). Geotechnical Engineering of Embankment Dams. Balkema, 675pp.

APPENDICES

P - St Mary's Geological Sheet

Q - Landslide areas in St Marys area

R - Where we went

S - Common indicators of past slope stability

T - Jubilee Mine, Sketch Cross Section

U - David Stapledon, CV, list of publications, and summary of experience with landslides

V - Plan showing layouts of workings, Jubilee and Cardiff Mines

W - Supporting Evidence

W1 - Reservoir Landslides, Guidelines for investigation and management (ICOLD, 2002) Summary.
W2 - Cromwell Gorge Landslides - A General Overview. Page 101 confirms DHS involvement
W3 - Extract from textbook: Robin Fell, Patrick MacGregor, David Stapledon and Graeme Bell (2005) in press
W4 - Coal mining under stored waters (1977) by Hon. Justice Reynolds. Page 29 and Figures 12 and 13.
W5 - Coal mining beneath reservoirs, 1979-1989. Extract from report of NSW Dams Safety Committee

APPENDIX U

SUMMARY OF QUALIFICATIONS AND EXPERIENCE

Education Qualifications:

1961 - Master of Science, University of Adelaide
1951 - Bachelor of Science, University of Adelaide

Board/Panel Memberships:

1978 - 1989 New South Wales Dams Safety Committee
1982 - 1990 Dam Surveillance Review Panel, Melbourne and Metropolitan Board of Works
1985 - 1987 Consultative Committee, CSIRO Division of Geomechanics
1987 - 1989 Advisory Committee, CSIRO Division of Soils
1987 - 1990 Electricity Trust of South Australia

Awards:

1996 - The John Jaeger Memorial Medal. Awarded every 4 years to recognise and promote contribution of the highest order in Australian Geomechanics

Professional Experience:

1994 to date	Geotechnical Consultant
1993	Engineering Geology Consultant, Golder Associates, and part-time Professor of Applied Geology, University of South Australia
1987 - 1992	Geotechnical Consultant, and part-time Professor of Applied Geology, University of South Australia
1977 - 1986	South Australian Institute of Technology, Professor of Applied Geology (1978), Head of Applied Geology (1977) Teaching (at undergraduate and graduate levels) the applications of geology in civil and mining engineering; School management; geotechnical consulting
1970 - 1977	Coffey and Partners, Consulting Engineers in the Geotechnical Sciences. Director (1974), Responsible for direction of geotechnical investigations for major civil engineering and mining projects. Associate Director (1971), Founder of Adelaide Office (1970)
1964 - 1970	Department of Mines, South Australia. Director of Division including Engineering Geology and Hydrogeology Sections. Responsible for engineering geological and hydrogeological studies for major and minor civil engineering projects, mostly associated with water supply. Supervising Geologist, Engineering Division (1965) Senior Geologist, Engineering Geology Section (1964)
1951 - 1963	Snowy Mountains Hydro- Electricity Authority. Supervising Scientific Officer (1962) Regional Engineering Geologist, Lower Tumut Region, and member of the Authority's Mekong River Project team, working in Cambodia, Thailand and Laos Senior Scientific Officer (1957) Regional Engineering Geologist, in charge of geological work during construction, Upper Tumut works. Geologist Grade 1 (1951) Routine engineering geological investigations during the planning of hydroelectric works.
1951	APAC Industries Ltd, Adelaide Clerical Officer, clerical duties in Production Control Department

SUMMARY

Publications: 16 papers and 1 textbook, in the geotechnical field

Experience:

A geologist with 53 years experience, 20 of these while employed within engineering organisations.
The work with Snowy Mountains Hydro-Electric Authority was for the planning and construction of major civil works: roads, dams, tunnels and hydro-electric power stations, both surface, and underground in rock.
At the South Australian Department of Mines the scope was widened to include a wider range of civil engineering projects, and groundwater supply and subsurface drainage.
With Coffey and Partners, geotechnical services during feasibility, design and construction were provided for major projects including highways, railways, industrial and mining complexes, and water supply and hydro-electric schemes.
At the South Australian Institute of Technology (University of South Australia), undergraduate and postgraduate teaching and school management, together with consulting in the geotechnical area.
Between 1987 and 1993 involved in consulting (mainly review) and teaching (part-time)
From 1994, consulting.

Professional Society Memberships:

The Institution of Engineers, Australia (Fellow)
Australian Geomechanics Society
New Zealand Geomechanics Society
International Society for Rock Mechanics
International Association of Engineering Geology, (Vice President for Australasia 1979 - 1983)
Association of Engineering Geologists
Australasian Institutes of Mining and Metallurgy (Fellow)
Geological Society of Australia (President 1979, SA Division)
Australian National Committed on Large Dams (Associate Member)

LIST OF PUBLICATIONS - David Stapledon

Stapledon, D.H, 1967: Geological Investigations at the Site for Kangaroo Creek Dam, South Australia, Trans IE Aust, Vol CE9, No 1, pp 31-43

Stapledon, D.H, 1971: Changes and Structural Defects Developed in some South Australian Clays, and their Engineering Consequences. Proc. Symp. On Soils and Earth Structures in Arid Climates, Adelaide, 1970, IE Aust. Also published in Golden Jubilee of the International Society for Soil Mechanics and Foundation Engineering, Commemorative Volume, IE Aust, 1985, pp145-154

Stapledon, D.H, 1976: Geological Hazards and Water Storage. A paper presented to the International Geological Congress, Sydney, 1976. Bull IAEG, No. 14

Stapledon, D.H and Casinader, R.J, 1977: Dispersive Soils at Sugarloaf Dam Site, near Melbourne, Australia. Dispersive Clays, Related Piping, and erosion in Geotechnical Projects, ASTM. STP 623, JL Sherard and RS Decker, Eds, American Society for Testing and Materials

Stapledon, D.H, Woodburn, JA and Fitzhardinge, CFR, 1977: Planning construction and operation of Kanmantoo Mine Tailings Dam. Australian National Committee on Large Dame, Bulletin No. 49

Casinader, R.J. and Stapledon, D.H., 1979: The effect of geology on the treatment of the dam foundation interface of Sugarloaf Dam. International Commission on Large Dames, 13th Congress, New Delhi.

Stapledon, D.H, 1979: Investigation and Characterisation. Extension Course on Tunnelling Design and Practise, Aus Geomechanics Society, sponsored by the Institution of Engineers, Australia and the Australasian Institute of Mining and Metallurgy, Melbourne.

Stapledon, D.H, 1982: Subsurface Engineering - In Search of a Rational Approach. Australian Geomechanics News, June 1982

Stapledon, D.H, and Rissler, P., 1983: Site Exploration and Evaluation, General Report on Theme A. Proc 5th Int. Congress on Rock Mechanics, Melbourne

Stapledon, D.H, 1983: The Geotechnical Specialist and Contractual Disputes. Invited Pater, in collected Case studies in Engineering Geology, Hydrology and Environmental Geology. Geological Society of Australia, Sydney.

Stapledon, D.H, 1983: Towards Successful Waterworks. Keynote Pater. Proc of the Symposium on Engineering for Dams and Canals, Alexandra, Inst. Prof. Eng NZ

Stapledon, D.H, 1986: Let's keep the 'geo' in Geomechanics. Keynote paper. Proc. Speciality Symposium of Insitu Testing, Adelaide, Aus. Geomechanics Society

Stapledon, D.H, 1988: Engineering Geophysics: a geologist's view. Aust. Geomechanics, 15, pp 57-62

Stapledon, D.H, 1988: Engineering description of weathered rock - a standard system? Australian National Committee on Large Dams, Bulletin 81, pp 35-48

Stapledon, D.H, 1995: Geological Modelling in landslide investigation. Invited paper on Theme 1, 6th International Symposium on Landslides, Christchurch

Fell, R., MacGregor, J.P. and Stapledon, D.H. 1992: Geotechnical engineering of embankment of dams. Balkema pp669

Stapledon, D.H, 1996: Keeping the 'geo'; Why and How. Fourth Jaeger Memorial Lecture. Proc. 7th ANZ Conference on Geomechanics, Adelaide. The Institution of Engineers, Australia, pp3 to 18.

SUMMARY OF EXPERIENCES WITH LANDSLIDES

My landslide experiences began with unforgettable terror; a narrow escape from death under one of three debris flows initiated by landslides just below recently cleared slopes. The slides occurred during a thunderstorm in which 110mm of rain fell in 70 minutes. This was in the Snowy Mountains, NSW, in 1955. Since that time I have contributed to the investigation of, and in many cases to decision on the treatment of more than 50 landslides, in Australia, New Zealand, Papua New Guinea and Indonesia. The slides have ranged from small (affecting roads, housing areas and pipelines) to large (affecting open pit mines, dams and reservoirs).

The following key (and most stressful) landslide projects are referred to in Stapledon (1995)

1985 - 1989 Member of the 3 man Review Panel during the construction of the 166m high Thomson Dam in Victoria
1989 - 1992 Geological Reviewer of the work of up to 50 engineering geologists and geotechnical engineers investigating and planning the treatment of the Clyde Reservoir landslides
1991. Referee for the High Court of NSW in an alleged professional negligence case (stability of a coastal cliff)

During 1997-1998 I took part in investigations at the site of the Thredbo landslide, and reported on evidence indicating that water entry beneath the retaining wall was the most likely factor contributing to the slide. When the wall was demolished it became clear to me that it could not have been the main factor. I admitted this and endorsed the evidence of Mr Tim Sullivan, the geotechnical expert assisting the Coroner.

My most recent landslide-related work was in November 2004, back where it all started, in the Snowy Mountains.