Van Der Valk v Gold Coast City Council
[2008] QPEC 29
•30/05/2008
PLANNING & ENVIRONMENT COURT
OF QUEENSLAND
CITATION: Van Der Valk and Anor v Gold Coast City Council and Anor
[2008] QPEC 29PARTIES: B M VAN DER VALK
and
D M VAN DER VALK(Appellants)
vGOLD COAST CITY COUNCIL (Respondent)
andCHIEF EXECUTIVE DEPARTMENT OF NATURAL
RESOURCES & WATER(Co-Respondent) FILE NO/S: 239/2007 DIVISION: Planning and Environment PROCEEDING: Appeal ORIGINATING COURT: Brisbane DELIVERED ON: 30 May 2008 DELIVERED AT: Brisbane HEARING DATE: 10 and 15 April 2008 JUDGE: His Honour Judge Searles ORDER: 1. Appeal allowed
2.
Matter adjourned to allow parties to resolve appropriate conditions of approval
CATCHWORDS: PLANNING – PLANNING LAW – Appeal against refusal of
application for material change of use – Whether proposal
offended DEO s of Our Living City Gold Coast Planning
Scheme 2003 – Whether proposal conflicted with Steep
Slopes or Unstable Soils Constraint Code.COUNSEL: M. A. Williamson - Appellants
S. M. Ure - RespondentSOLICITORS: DLA Phillip Fox - Appellants
King & Co - Respondent
The appellants appeal against the respondent’s refusal of their application for a material change of use for a second dwelling house at their property at 262 Petsch Creek Road Tallebudgera Valley being Lot 2 on RP 163195 containing an area of 44.553 hectares.
Presently the appellants have a partly built house constructed on the house pad cut in to the site and wish to complete its construction and live in it. The Council has concerns as to the stability of the land which, it says, could put life and property at risk in the event of soil failure. The partial construction was undertaken without approval but that’s not a matter which can, in any way, prejudice the consideration of the issues here raised.[1]
[1] Trewheellar v Council of the City of Gold Coast (1981) QPLR 17.
History of Application
The appellant’s application was made to the respondent under cover of a letter dated 3 August 2006.[2] The development application was a code assessable application and was accompanied by a number of expert reports dealing with town planning matters, geotechnical engineering issues and bushfire risk management.
[2] Exhibit 1, development application documents page 1.On 17 August 2006 the Council issued an Acknowledgment Notice under s 3.2.3 of the Integrated Planning Act 1997 (IPA) for the development application.[3] That Acknowledgment Notice advised that the application was to be referred to two concurrence agencies The Department of Natural Resources, Mines & Energy and the Office of Urban Management. It also identified the applicable codes including the Steep Slopes or Unstable Soils Constraint Code.
[3] Exhibit 1, development application documents pages 166-167.By Decision Notice dated 22 December 2006[4] the Council refused the application on ten grounds namely:-[5]
[4] Exhibit 1, development application documents pages 173-184. [5] Exhibit 1, development application documents pages 173-174.
(1)
The proposal is in conflict with the intent and purpose of the Sediment and Erosion Control Constraint Code and does not seek or demonstrate the ability to minimise environmental harm caused by the effects of erosion and sedimentation, associated with the development of the land.
(2)
The proposed second detached dwelling is located within a region having a slope instability hazard rating of ‘High’, which indicates that a landslide event could occur as often as one event every ten years on the site (SMEC, 1999).
(3)
The submitted geotechnical report did not contain a quantitative landslip hazard assessment for the site, nor did it contain any certification stating that the site is stable. Therefore, the proposal is in conflict with the objectives of the Steep Slopes or Unstable Soils Constraint Code to minimise the potential for erosion or land slippage and minimise erosion events on slopes exceeding an average gradient of 15 percent.
(4)
The proposal is in conflict with the intent and purpose of the Steep Slopes or Unstable Soils Constraint Code and compromises the achievement of the code’s objectives to regulate development which occurs on land, or part of any land, containing steep slopes or unstable soils.
(5)
The proposed access driveway is within a region having ‘High to Very High’ slope instability, as well as passing through areas noted as having historic landslips. This has not been addressed within the geotechnical report and the proposal is in conflict with the intent and purpose of the Steep Slopes or Unstable Soils Constraint Code which seeks to encourage safe and efficient vehicular access onto steeply sloping land.
(6)
As the majority of the site is currently classified as having an instability hazard rating of ‘High to Very High’, and the presence of a series of historic landslips across the site indicates that there may be no suitable area to construct a second detached dwelling and associated driveway.
(7)
The proposed development is in conflict with the Desired Environmental Outcome DEO ECOL 1 and Planning Objectives ECOL 1.6 of the Our Living City Gold Coast Planning Scheme, 2003.
(8)
The proposed development is in conflict with Desired Environmental Outcome DEO ECOL 2 and Planning Objectives ECOL 2.7 of the Our Living City Gold Coast Planning Scheme, 2003.
(9)
The proposed development is in conflict with Desired Environmental Outcome DEO SOC 7 and Planning Objectives SOC 7.1, 7.2 and 7.3 of the Our Living City Gold Coast Planning Scheme, 2003. Allowing this application to proceed, additional lives will be put at risk, as there will potentially be a greater number of people residing on the site.
(10)
The proposed development is not suitable and is in conflict with the intent and purpose of the Rural Domain. Specifically, the objective of preserving and landscape character and important topographical features of these parts of the City and maintaining nature conservation values within the domain by promoting the conservation of wildlife and wildlife habitats will be compromised.
Statutory Assessment Regime
The appeal is an applicant appeal pursuant to s 4.1.27 of IPA and as such the appellant bears the onus of proof.
Section 3.5.4 of IPA provides the assessment regime for an application requiring code assessment. It provides relevantly:-
“3.5.4 Code assessment (1) This section applies to any part of the application requiring
code assessment.(2) The assessment manager must assess the part of the
application only against-
(a) applicable codes (other than concurrence agency codes the assessment manager does not apply); and (b) subject to paragraph (a) – the common material; and (c) … (d) … (2A) … (3) … (4) …”
Section 3.5.13 regulates the decision making process with respect to code assessable applications. It provides:-
“3.5.13 Decision if application requires code assessment
(1) This section applies to any part of the application requiring
code assessment.(2)
The assessment manager must approve the application if the assessment manager is satisfied the application complies with all applicable codes whether or not conditions are required for the development to comply with the codes.
(3)
Subject to subsection (2), the assessment manager’s decision may conflict with an applicable code only if there are sufficient grounds to justify the decision despite the conflict, having regard to—
(a) the purpose of the code; and (b) … (4)
However, if the decision is made under subsection (3)(a) and the assessment is against a code in a planning scheme – the assessment manager’s decision must not compromise the achievement of the desired environmental outcomes for the planning scheme area.”
The approach to be undertaken in deciding an application subject to code assessment was helpfully set out by Wilson SC DCJ in Central Equity Limited v Gold Coast City Council[6] as follows:-
“[10] Under the planning scheme the application was code assessable and the fundamental question is whether or not compliance with the applicable codes has been achieved. Section 7.2 of the LAP shows the High-Rise Residential and Tourist Accommodation Specific Development Code, the Surfers Paradise Local Area Plan Place Code and various others touching car parking, access and transport integration fall to be considered.
[11] Under s 3.5.4 of the Integrated Planning Act 1997 (IPA) assessment is undertaken against the applicable Codes. The process is explained in s 3.5.13 which requires the assessment manager to, firstly, assess the proposal against the Acceptable Solutions. If it complies, approval must be granted. If not, the proposal is assessed (as an ‘alternative’ solution) against the Performance Criteria of the Codes. If, according to this exercise, the proposal complies it is taken to satisfy the Codes and must, again, be approved. If it does not comply, the assessment manager must determine if conditions can reasonably be imposed to achieve that end. If so, approval may follow through this third avenue: s 3.5.13(2).
[12] If, at the end of these exercises, the proposal is still in conflict with the applicable Codes the assessment manager must consider whether there are sufficient grounds to justify the conflict, having regard to the purpose of those Codes. If no sufficient grounds arise, the proposal must be refused. If grounds do present, the assessment manager must consider whether the decision would compromise the achievement of the DEOs for the planning scheme area and, if compromise is found to arise, refuse the application. In the absence of compromise, the proposal may yet be approved.
[13] The process of using the Codes in the Gold Coast Scheme was helpfully explained by Rackemann DCJ in SDW Projects Pty Ltd v Gold Coast City Council [2006] QPEC 074. They follow a familiar ‘performance based’ structure similar to those found in many IPA planning schemes. They commence with a statement of purpose and then contain development requirements set out in tables of Performance Criteria (PC) and Acceptable Solutions (AS). As Rackemann DCJ said, the PC are generally outcome focussed and the AS indicate a desirable way to ensure compliance – but they are not the only available solution, and PC ‘…generally ought not be interpreted as requiring adoption of the Acceptable Solution, or even as requiring an alternative solution to be akin to the Acceptable Solution’.”
[6] [2007] QPELR 356 at 357.
The Desired Environmental Outcomes
Chapter 1 of Division 1 of Part 2 provides:-
“The Desired Environmental Outcomes (DEOs) are the core of the Planning Scheme. They provide the fundamental context (derived from the foundation research discussed in Part 1, Division 2) for the Planning Strategies that follow in Part 3, and subsequently, for the development assessment codes and other measures contained in the remaining parts of the Planning Scheme. They therefore provide a primary focus or direction for the entire Planning Scheme.
They are expressed in terms of broad policy outcomes which seek to achieve ecological sustainability for the City as a whole. As such, they are grouped under the three main aspects of ecological sustainability, being ecological, economic and social consideration. By their nature, the DEOs define the essential balance proposed for the City of Gold Coast between these three aspects. They present the most fundamental outcomes for each aspect that are necessary for the achievement of ecological sustainability in the local context. This balance is then further refined in the more detailed considerations discussed in Part 3 of this Planning Scheme, which synthesises the three aspects of ecological sustainability into integrated planning strategies.
…”
The relevant DEO is DEO SOC7 which is:-
“7.0 DEO SOC.7 The location and design of development to minimise the potential risk to life and property from known natural hazards.
7.1 Explanation Gold Coast City’s large population is vulnerable to a range of natural hazards. While some of these hazards are unavoidable, the risk to property and life can generally be reduced or mitigated by appropriate design and siting. Initially, this requires sound knowledge of the potential impacts from natural hazards in the various parts of the City and appropriate decision making regarding land use. Where development is considered suitable, design measures and environmental management techniques can then be utilised to further mitigate any risks.
Steep slopes, flood prone areas, acid sulphate soils and bushfire hazard areas are examples of areas subject to natural hazards that require careful assessment prior to any development activity. For development to proceed in such areas, the measures needed to effectively mitigate the identified hazard should be carefully appraised against the capacity of the local environment to accommodate those measures in a sustainable manner. Gold Coast City’s existing development pattern must also be taken into account when assessing the potential impact of natural hazards and in implementing any new mitigation measures, along with the capacity and operating efficiency of emerging services organisations.
7.2 Planning Objectives to Support DEO SOC.7 Soc.7.1 to ensure that development is located away from areas where the risk to life and property from the impact of natural hazards is unacceptable, in terms of either the likely cost of damage or the measures needed to effectively mitigate the risk.
Soc.7.2 to ensure that development is designed to mitigate the risk to life and property from known natural hazards.
Soc.7.3 to facilitate cost effective counter disaster and emergency
procedures
7.3 Planning Measures to Support DEO Soc.7 … It will be largely achieved through the following provisions of this
Planning Scheme:
•
Constraints Codes for Bushfire Management Areas, Flood Affected Areas, Ocean Front Land and Steeps Slopes or Unstable Soils;
• …” (my emphasis)
The only code ultimately relevant to the issues agitated is the Steep Slopes or Unstable Soils Constraint Code. The parties’ town planners Mr Grummitt for the appellant and Mr Perkins for the respondent, met in conclave on 27 March and discussed the ten grounds of refusal and concluded:-[7]
“The key issue of geotechnical suitability relates to areas and matters outside the particular expertise of the signatories. The Planning Scheme identifies that geotechnical suitability is an important issue to consider in assessing development applications and identifies a number of ‘tests’ to be satisfied by development proposals. Two, if geotechnical suitability issues can be resolved in this appeal, appropriate conditions can be applied to satisfy other issues related to erosion and sediment control and colours and materials of construction.”
It was in fact the case that the geotechnical issues were the issues of dispute.
[7] Exhibit 7 p 4.
The Steep Slopes or Unstable Soils Constraint Code
Chapter 16 of Division 3 of Part 7 contains the Steep Slopes or Unstable Soils Constraints Code. It provides relevantly:-
“1.0 PURPOSE The primary purpose of this code is to regulate development which occurs on land, or part of any land, containing steep slopes or unstable soils. This code also seeks to: …
2.0 APPLICATION … 2.2
In particular, this code applies to development on land that is steep or geologically unstable, as identified on Overlay Map OM16 – Areas of Unstable Soils and Areas of Potential Land Slip Hazard.
2.3
Performance Criteria PC1-PC9 apply to all code and impact assessable development subject to this code. For development identified as self assessable, only the acceptable solutions to Performance Criteria PC1-PC2 apply.
2.4
Any variation to the acceptable solutions contained in this code must be certified. The long term stability of any design, beyond the limits specified in this code, is to be certified by a registered professional engineer, appropriately experienced in slope stability investigations.”
Construction of Planning Documents
The rules of construction of planning documents were summarised in Westfield Management Ltd v Pine Rivers Shire Council and Ors[8] and may be broadly summarised in this way:-
[8] [2004] QPELR 341; see also Kotku Education and Welfare Society Inc. v Brisbane City Council [2005]
(a)
They should be construed broadly rather than pedantically or narrowly with a sensible, practical approach;[9]
(b) They should be construed as a whole;[10] (c)
They should be construed in a way that best achieves their apparent purpose and objects; and[11]
(d)
Although they have the force of law, they are not drawn with the precision of an Act of Parliament.
[9] ZW Pty Ltd v Peter R Hughes & Partners Pty Ltd [1992] 1 Qd R 352 at 360; Yu Feng Pty Ltd v Maroochy
[10] Luke v Maroochy Shire Council & Anor [2003] QPELR 447.
[11] Section 14 Acts Interpretations Act.
Issues to Be Determined
The first issue for determination is whether the application complies with the Steep Slopes or Unstable Soils Constraint Code. The second issue is whether approval of the application would compromise the achievement of DEO Soc.7. Mr Ure for the Council said in his opening the reports of the geotechnical experts Messrs Morrison & Samuels would leave me in no doubt that the issues in the appeal are the stability of the house site and its environs and the stability of the access road.[12] He was correct.
APPELLANT’S CASE
Building Location and General Site Features
Before discussing the Appellant’s case it is appropriate for me to mention a matter raised by Mr Williamson for the appellants in his final submissions.[13] He said the Council relied upon a conflict between the Appellant’s proposal and performance criteria PC6 and 7 in the Steep Slopes or Unstable Soils Code in its final submissions when it had not raised that issue in its reason for refusal or its primary submissions of 21 April 2008.[14] He said the Council had, by a side wind, attempted to a raise a new issue and should not be permitted to do so in reply.15 I do not agree. Whilst Mr Williamson made the point in his opening16 that the Council’s reasons for refusal17 did not identify conflict with any particular performance criteria of the code, nevertheless clause 2.3 of the relevant code set out above makes it clear that all Performance Criteria PC1-PC9 apply to all code assessable developments which this is. So, whereas it may have been a matter for further particularity earlier on, it is not a new issue.
[13] Written submissions 29 April 2008 para 8.[14] Appellant’s written submissions 29 April 2008 para 8. 15 Appellant’s written submissions 29 April 2008 para 9. 16 Transcript p 8 line 48.
The application18 gives this relevant description of the site. The proposed dwelling is to be located on an already prepared, level area. Although this site slopes away steeply to the north east, generally the surrounding area is gently sloping, grassy hills with some regrowth forest present in nearby gully areas and more dense forest several hundred metres to the west. The north easterly slope is predominantly grass. The area is accessed by gravel driveway, quite steep in parts, however the initial, steepest, part of this access is a gazetted Council road. The site is easily accessible by 4WD rural vehicles with ample room for turning provision. Adequate water is well covered by the presence of the $10,000 gallon concrete tank and the proximity of the small dam to the site (Refer photos and site plan appendix 1). Annexure A is a plan of the building site taken from Exhibit 3.
Mr Van Der Valk
Mr Van Der Valk gave evidence and provided two signed statements.19 Exhibit 3 details drainage trenches around the house site carried out on the advice of geotechnical experts including the appellant’s expert witness Mr Morrison. A plan attached shows three drains around the house pad. To the west is a 450 mm x 900 mm drain with agricultural pipe covered with 70/30 crushed concrete. A similar sized drain is to be found on the north side of the pad projecting toward the north east. On the north eastern side of the pad is a north west/south east facing drain 500w x 500d (width and depth) with a 90 millimetre agricultural pipe covered with 70/30 crushed concrete. Under cross examination Mr Van Der Valk confirmed that the two 450 x 900 drains were surface drains and drained, not into the effluent area as the plan may suggest, but down towards the area notated “land application area” and then under the roadway. He said the 450 mm x 900 mm drain to the north of the pad and the 500 mm x 500 mm drain to the east both presently discharge out to the escarpment at the face to the east of the house pad but the proposed landscaping works will result in them discharging into a settlement tank. In other words the existing flow, which he acknowledged was inappropriate, was a temporary measure.20
In the second and longer of his statements (Exhibit 8) Mr Van Der Valk made following points:-
(a)
The boulders shown in the report of Mr Samuels, the respondent’s engineering geologist[21] are not intended to act as a retaining structure;
(b)
That the ponding of water at the toe of the house pad cut[22] was the result of a leak in the water tank located on the level above the house pad which leak was to be repaired as soon as possible;
(c)
In relation to the swale drain referred to by Mr Samuels23 and Mr Samuels’ concern that surface water collecting in the swale may in a significant storm “overtop” and flood the house pad, Mr Van Der Valk said in the three and a half years he has lived on the property he has never seen the water “overtop” even during the heavy storms in January and February 2008 when the swale drain was filled with water to a height of four feet. He said that water drained away in one to two hours;
(d)
In relation to Mr Samuels’ statement24 that, to his knowledge, there were no sub-surface seepage drains on site nor any overall surface and sub- surface drainage solution provided, Mr Van Der Valk attached a plan identifying the location of a number of silt and sedimentation ponds and showing the drainage channels discharging into those ponds;
(e)
In relation to the drainage channel adjacent to the access driveway,25 he said it was enlarged by him in April 2007 with the result that it drains through a culvert which ultimately leads to a silt and sedimentation pond identified on the map attached to his statement. The culvert underneath the access driveway is approximately 1400 millimetre in diameter;
(f)
In relation to the screw piles upon which the house sits and which Mr Samuels reported had skewed during construction,[26] he confirmed;
[21] Exhibit 6 plate 10
[22] Exhibit 6 page 9 23 Exhibit 6 page 8 24 Exhibit 6 page 8 25 Exhibit 6 page 5 plate 3
[26] Exhibit 6 page 6(i) The screw piles were anchored five metres deep into the ground and cantilevered above the ground; and
(ii) Only one pile skewed during the installation process which pile he identified on the plan attached to his statement. He said the engineer employed by him to inspect and report on the pile installation process required the pile which had skewed to be tied to other piles with extensive concrete footings;
(g)
Finally, he intends to landscape around the house pad when the house is completed and undertake top dressing around the house and incorporate additional surface drainage measures if necessary.
Mr N J Morrison
The appellants retained Mr Neville Morrison a consulting engineer specialising in the field of geotechnical engineering. Mr Morrison has had over 40 years experience in civil engineering projects both in Papua New Guinea and Australia and since 1973 has been involved entirely in geotechnical aspects of infrastructure investigations and design mainly in South East Queensland. This has involved large buildings, industrial complexes, bridges, reclamations in soft ground and stability problems, both on reclaimed and natural slopes.27
Mr Morrison inspected the site on two occasions on 10 April 2007 and 2 April 2008 and Exhibit 2 contains his findings in relation to both those inspections.
Morrison Inspection 29 March 2007 – Report 10 April 2007
The report in relation to this inspection is Annexure B to Exhibit 2 being his statement tendered to the Court. He said the purpose of that inspection was to make an assessment of the stability of the site which was of concern to the respondent Council. He was provided with the application and the respondent’s grounds for refusal together with geotechnical information on the house site and house design data. He describes the partially built home as a new residence on a moderately sloping land above the existing residence which site was levelled some years prior to his inspection. The geological reports28 he was given included bore hole and test pit data in the area of the new house site. The most recent results were carried out by Maiden Geotechnics specifically relating to the subject house. They found 2.5 and 2.4 metres of cobble and boulder colluvium over weathered rock in two of the bore holes. An earlier 1995 result had found a similar profile of clay and cobble colluvium 2.9 metres deep over extremely to very weak argillite. A later 1997 test pit and borehole penetrated the colluvium at 2.7 metres and 3.9 metres respectively.29 Colluvium is slope wash which has been washed down by gravity.30 The colluvium above referred to is, according to Mr Morrison, rock fall and clay debris which has come down from the mountain range above the site although the period of this erosion and rock fall activity is not known.31
He said the house pad is located about 300 metres east of a narrow mountain range with almost vertical cliffs at its east face and the debris accumulation at the base of the cliff was termed colluvium in the geotechnical reports he read. In his opinion it was not necessarily landslip debris although there was some evidence of recent movement at the tail of the colluvium in the neighbouring property to the south of the land.[32] He said that, over time, rainfall runoff from the mountain range had eroded a channel parallel to the cliffs with an outlet to the north and south. This is the swale drain earlier referred to in the evidence of Mr Van Der Valk. This swale channel is some 5 to 10 metres below a ridge in the colluvium to the east of the cliff face which Mr Morrison described as a ridge of boulders cobbles and clay with an effective drain around it. The house pad is located east of this ridge.
[32] Exhibit 2 page 9 para 8.
Referring to the house pad, Mr Morrison said the moderate permeability of its colluvium has given rise to a high moisture content and low strength in the lower layers. Of four of the abovementioned test results he refers to, one describes gravelly clay as moist to wet with no free water found and the material being described as firm. The second noted slight seepage below 1.5 metres and clay strength grading to soft below 2 metres. The third also noted seepage and the fourth noted slight seepage at 1 to 3.9 metres.
Landslip
Mr Morrison assessed the landslip potential of the site using the respondent’s own data (SMEC-GCCC 2002)[33] and the analysis method of the Australian Geomechanics Society (AGS).[34] His analysis also considered the present site with no apparent landslip in the immediate vicinity, the existing residence on this site, and the performance of nearby sites.[35] In the result he assessed the landslip risk by reference to the above data as:-
AGS low to moderate
SMEC – GCCC low to moderate.
He said that, given the nature of the colluvium containing boulder and cobble sized rock affects permeability and it was not surprising to him that pits and boreholes found minor seepage. However he said that, around the residence site, there were no features which would indicate any more than a low landslip potential which could be managed with construction. Using the AGS or SMEC the landslip risk was low to moderate.36
[33] Snowy Mountains Engineering Corporation Pty Ltd. Landslip study for the City of Gold Coast; Final[34] Australian Geomechanics Society “Landslide Risk Management Concepts and Guidelines” Australian
[35] Exhibit 2 page 10, paragraph 13. 36 Exhibit 2 page 10, paragraph 15.
Mr Morrison concluded that the resident’s site/house pad was stable and slip free but suggested the following conditions on the use of the site for building to minimise the risk of a future slip:
(a) Take all footing support for the house through the colluvium into the basement Neranleigh Fernvale Basement; (b) Landscape the northern (fill) edge of the house platform to minimise damage by erosion; and (c) Keep the swale drainage channel clear. No future dams should be considered for this area as the drainage maintains the water table at a low level, as a positive effect on stability of the colluvium.
The above reference in (a) to Neranleigh Fernvale Basement is a reference to the regional geology described as Neranleigh Fernvale Metamorphics.37 He said founding conditions had been recognised by the owner manifested by the screw piles through the colluvium and the shifting of the house location away from the fill edge. That decision was made as a result of test piles showing that, on the house pad platform generally, a design load of 5-7 tonnes could be achieved at a depth of about six metres, less at the rear (cut) end of the platform and more at the northern edge.
Access Road
In relation to the access road Mr Morrison acknowledged there was a seepage zone above the road which had caused movement at the road edge. He said that was understandable and could be managed with maintenance and had already been addressed with the construction of a deep drain on the topside of the road and a pipe drainage under the road to an outlet in the main creek drainage from the slopes above. He said access could be affected by future slope movement commencing in the neighbour’s property but engineering solutions involving drainage improvements could be put in place at that time should they be required.
Summary
Mr Morrison summarised his report as follows:38
(a) The residents’ site is stable and slip free and suitable for building; (b)
Construction to date using screw piles to support the residential dwelling is considered to be the most appropriate foundation solution;
(c)
The owner is fully familiar with the site and is aware of the means to keep the site safe;
(d)
There is no need from the issues of stability or erosion for the respondent to refuse the application. The grounds for refusal given by the respondent relate to omissions in the application which now have been addressed in this report namely:
(i) The stability risk is low to moderate but can be managed. This is acceptable under the AGS guidelines (refer Annexure B);
(ii) A stability assessment has now been provided;
(iii) ‘P’ sites relate to poor ground conditions by the definition given in AS2870 (Australian Standard “Residential Slabs and Footings – Construction”) and require engineering design which has been provided;
(iv) Access to the residents’ site will require periodic maintenance but is satisfactory.
Morrison Report 8 May 2007
Subsequent to the provision of Mr Morrison’s 10 April 2007 report to the Council, the latter, through its solicitors’ letter dated 27 April 2007,39 sought further information from him including, importantly, a certification, the terms of which the Council’s solicitors set out.40
Accordingly, a further report dated 8 May 2007 was prepared by Mr Morrison41 designed to provide further quantification of matters relating to the stability of the house site and the land stability in general. This report clarified the basis of the earlier assessment of land slip risk by reference to Appendix G, a document headed – ‘Land Slide Risk Assessment – Example of Qualitative Terminology for Use in Assessing Risk to Property’. That document was an exhibit to his 10 April 2000 report as well as this 8 May 2007 report. It set out on page 2 a matrix of stability assessment of the General Area of the site, the House Site and the Above House Site.[42] In terms of a Landslide Frequency Hazard rating it rated the General Area of the site as high, the House Site very low and Above House Site as moderate. In that report Mr Morrison said that, to maintain that hazard rating of very low to moderate in the house site and Above House Site, it was essential that the building platform was not unduly affected by further construction works or drainage. He set out four further requirements to achieve that:
[42] Exhibit 2A page 2 second dot point.
(a)
Any further building on the present building platform, as detached construction or an extension, should be supported on steel screw piles taken below the boulder colluvium into the shale type rock;
(b)
The final shape of the platform should be such that water does not pond. All roof water should be collected and piped to an outlet south of the building. Discharge over the eastern filled edge is not acceptable;
(c)
The small earth dam on the north side of the building platform should be abandoned and filled;
(d)
The disposal of domestic waste water is only permitted away from the residence to the south as shown in the Queensland waste water management plan, or on any site further to the south on similar ground.
Access Driveway
Mr Morrison classified the hazard rating of the access driveway as high risk requiring investigation and the implementation of a repair or landslip treatment to reduce the risk to an acceptable level. He confirmed that this had largely been done by the owner. He said that future landslip above the road was possible according to his qualitative AGS assessment but the likely road damage would be minor requiring the cleaning out of side drains, the removal of slip debris from the road and the improvement of road drainage as required. He said with the type of maintenance which had been implemented to date the hazard rating should remain.
Effluent Disposal
He said that when compared with rainfall the domestic waste water disposal affect on the overall stability risk was minimal but still should be controlled to ensure there was no locally water induced risk. The hazard rating he gave the effluent disposal was very low to low risk.
Finally, in his 8 May 2007 report, Mr Morrison provided the certification in the terms requested by the Council.[43] There was no evidence that the Council had ever rejected or cast doubt on that certification and, indeed, the Council’s own witness Mr Samuels conceded there was nothing wrong with it and that the Council were entitled to rely upon it.[44] Mr Ure in his final submissions[45] argued that the Council did not accept the certification but there was no probative evidentiary attack made on the certificate.
Morrison Inspection 2 April 2008[46]
Mr Morrison carried out a further inspection of the site on 2 April 2008 to assess the impact of the severe storm rainfall recorded in January to February 2008 period which caused significant flood damage to Petsch Creek Road. He said there was no damage to the house site, to the construction on the site or to the access road from those events.[47]
In his view, the site has been tested by those severe rainfall events and the satisfactory performance of both the residential site and the access road was consistent with what he would have expected.
[47] Exhibit 2 p 2 para 3.He carried out a further stability analysis of the house site using the Slope Stability Programme GSLOPE VERSION 4.07. He said that analysis confirmed his 10 April 2007 assessment even when consideration of a design earthquake, a water table at the housepad level and a weak interface layer between the colluvial soils and the underlying rock was had.[48] By that I take him to mean that he assumed those conditions which were more extreme than what he had found, and his original analysis still stood up.
[48] Exhibit 2 p 2 para 4.His summary of his 2 April 2008 report was that the residential construction was not at risk of failure due to landslide and that qualitative assessments referred to above put the risk at the house site as small (low to moderate) in line with commonly accepted procedures. Having said that however, he said it would be prudent to mitigate against any risk which he said had already been done by:
(a) A series of open drains dug around the house site; (b)
The building platform drainage being improved by gravel surrounded pipe drainage which could be further improved with landscaping to direct surface run-off water away from the house perimeter.
So far as the access road was concerned, he said that he would expect it to remain serviceable with minimum maintenance. He accepted though that, given there was a spring above the road, small ground movements would occur from time to time.
It is said by the Council that Mr Morrison erroneously focused on the house pad site only and did not give due consideration to the instability of lands immediately upslope of the house pad or other surrounding land.[49] I do not agree with that. When one reads his two reports of 10 April 2007 and 8 May 2007 together with his court statement dealing with his further inspection of 2 April 2008 it is apparent that his consideration of the issues were not limited to those affecting the house pad and I so find.
[49] Council’s written submissions 21 April 2008 paras 21, 22; submissions 23 April 2008 paras 1 and 4.
Mr Morrison’s Oral Evidence
In evidence Mr Morrison explained to the Court that the qualitative hazard risk assessment by which he assessed the landslip potential and reported in his 10 April 2007 report[50] resulted in his identification of a key indicator of hazard. From there he said one had to assess those overall parameters to a specific site requiring specified detail investigation which he said had been done in relation to the subject site by several people.[51] The people he referred to are those whose geo-technical reports here relied upon his 10 April 2007 report.52
[50] Exhibit 2 p 10 para 13.[51] Transcript p 35 lines 50-60; p 36 lines 1-5.He was then asked if the highest level of risk of landslip had been thrown up by the qualitative hazard risk assessment, would that be the end of the matter? He said not, and that there were two parameters which were most important in any analysis namely soil strength (both short and long term) and the water table. He said that if those things were taken into account one could come up with a reasonable risk assessment even though the qualitative measure might say it is pretty high.53 He later added a third matter of importance namely the geometry of the site and said that there was sufficient data available to make a reasonable assessment of the soil strength.54
He was asked by his counsel Mr Williamson about the reference in Mr Samuel’s report to the hummocky and irregular ground. He said that in a landslide area you will find certain shapes and the hummocky nature was indicative of movement of material down slope. He said it might be rounded bulbous at the toe and concave at the scarp at the top and then may be a break in the slope leading to unevenness in the ground. He said, by contrast, the subject site was uneven because it contained boulders. He said the surface shape was a function of erosion around those boulders and was not hummocky to the extent that you would worry about it or consider landslides had occurred.55
Cross-examination of Mr Morrison
Despite a thorough and intensive cross-examination by Mr Ure ranging over all Mr Morrison’s reports and evidence he was steadfast in his views as expressed in those reports and evidence.
He was questioned in relation to his Landslide Frequency Analysis.56 It may appear at first reading that he accepted that, in relation to the land slope in the above house site region, his average gradient of 5 to 15 degrees should have been 15 to 30 degrees.[57] On a careful reading of the transcript it can be seen that when Mr Ure was questioning him about the change of gradient to 15 to 30 degrees, which resulted in the ·5 Slope Angle Factor in his Landslide Frequency Analysis[58] changing to ·8,[59] he was asked if he agreed that the Factor of ·8 was more appropriate. His answer was “no, I will accept that some areas might be steeper than 15 degrees and it is a factor but all we are doing here is ticking boxes but you can go on”. When one looks at Exhibit 11 which is a Landslide Frequency Analysis matrix, a correct reading of it dictates that if one selects a slope angle of between 5 and 15 degrees the relevant Factor is ·5, with that changing to ·8 if the slope angle is between 15 and 30 degrees. In other words it would not be possible for a person familiar with the matrix, which Mr Morrison was, to accept a 15 to 30 degree slope angle but not a ·8 Factor. His hesitation in accepting that ·8 Factor evidences that he did not make any concession.
[57] Transcript p 52 line 40.[58] Exhibit 2A, page 2.[59] See Exhibit 11, para 2.He did make a concession in relation to item 4 of his Landslide Frequency Analysis relating to soil strength. He agreed it should carry a Factor of 4.[60] He was also questioned in relation to soil stability. In his analysis he used a Factor of ·8.[61] Mr Ure put to him that it should have been a Factor of 2.[62] The transcript of his response is equivocal and I am not prepared to accept that he made a concession in relation to soil stability.
[60] Transcript p 55 line 18; Exhibit 2A p 2; Exhibit 11; para 5.[61] Exhibit 2A, p 2.[62] Transcript p 55 line 45.The result of the one concession outlined above is that it changes Mr Morrison’s Landslide Frequency Analysis. However it does not change it to the figure of 14.256 which was the result of Mr Ure’s calculations[63] which was arrived at based on the wrong assumptions that Mr Morrison had conceded in cross-examination that his factor of ·5 for the slope should have been ·8, and that his ·8 factor for instability should have been 2. The correct figure is 2.1384 which is calculated on the correct assumption that the only figure changed in Mr Morrison’s Landslide Frequency Analysis[64] is the figure for strength which should be 4 and not 2. This calculation is relevant to the calculation of the quantitative hazard rating.[65] Any figure in excess of 6 correlates to a very high Landslip Likelihood Rating.
[63] Transcript p 26, line 15.[64] Exhibit 2A p 2, right hand column “Above House Site”.[65] Exhibit 6 p 23 paragraph 6, table 2.The correct calculation of 2.1384 does take Mr Morrison’s landslip Likelihood Rating to high66 but despite this concession it did not result in Mr Morrison backing off any of his opinions as to the suitability of this site for the house construction. In short, Mr Morrison adhered throughout his evidence to his firm belief in the opinions he expressed in his reports and in evidence. And as he had said, the ascertainment of a risk factor was not the end of the matter, even if that factor was pretty high.67
RESPONDENT’S CASE
Mr Gary Samuels
Mr Samuels is an engineering geologist who has worked in his profession since 1987 with experience in geotechnical investigation including slope stability assessment, detailed structural core logging and sediment and erosion control investigation. By mentioning those areas I do not mean to in any way limit the detailed experience set forth in the curriculum vitae he presented, but rather seek to identify those areas relevant to this case. He has provided four reports dated 21 June 2007, 16 August 2007 and 20 March 2008 and 3 April 200868 and had access to the same geotechnical reports made available to Mr Morrison. It would not be an overstatement to say there was a fundamental disagreement between Mr Samuels and Mr Morrison as to the stability of this site and each of the discrete areas in the site namely the house pad, the up slope area between the house pad and the cliff, the access road and the general area.
Samuels’ Report 21 June 2007
This report was limited to Mr Samuels’ reviewing past geotechnical engineering reports including those reviewed by Mr Morrison and Mr Morrison’s two reports of 10 April 2007 and 8 May 2007. He also carried out a desktop quantitative Landslide Frequency Analysis to determine an instability hazard rating for the house pad site and the proposed access driveway. He determined that the hazard rating for the house pad site was Moderate and for the general area and the access driveway area, both Very High.69
Samuels’ Report 16 August 2007
This report followed the carrying out of field investigations to further access slope stability issues. It covered a review of historical ariel photographs, a site walkover and mapping of the area, field work involving test-pitting and soil profile logging and discussions and a drive-over with the male appellant. Mr Samuels’ earlier hazard ratings for the house pad site (moderate), access (very high) and general area (very high) remained the same in this report. He found the soil under the house platform included at least 2.2 to 2.8 of colluvium cobbley-bouldery clay overlying possible residual clays and with perhaps deeper colluvium towards the middle of the platform. Four test-pit boreholes were dug. TP1 and TP2 were in the general area of the house pad site and were dug to 2.9 metres. TP3 and TP4 each near the driveway went to 3 metres in depth.70 In TP2 clay soils at 2.8 metres were said to be very moist although no free water was noted. He said further seepage could occur within various layers during and after heavy rains.
He said discussions with Mr Van Der Valk revealed there were a series of screw- piles installed mainly to depths of 5 metres to 6 metres with isolated ones as deep as 8 metres. These formed the foundation for the partly-built residence. According to Mr Samuels some of the screw-piles he understood to have skewed off at angles due to the presence of boulder sized floaters in the soil profile.71 The evidence of Mr Van Der Valk set out in paragraph [No.?] above clarified that issue by explaining that only one pile skewed and the appellants’ engineer required that pile to be tied to other piles with extensive concrete footings which was done.
As to the access driveway he agreed that on-going driveway maintenance could be considered to be a management options, other access options were present for use in emergencies should the main driveway be subject to a slip.72
Samuels’ Report 20 March 200873
In this report Mr Samuels set out a summary, as he saw it, indicating the differences of opinion between himself and Mr Morrison. He said:-
(a)
Fundamentally he and Mr Morrison disagree on the risk of potential stability of the site and how a failure might occur;
(b)
Given the site has slopes in the order of 15 to 30 degrees from the horizontal, a history of previous instability as does the surrounding area, subsurface conditions comprising permeable colluvial soil in excess of 3 metres thick, and evidence of seepage at depth. He believed that the site had a Moderate to Very High risk of instability. That was consistent with his earlier reports grading the instability risk from Moderate at the house pad to Very High at the access road and the site generally;
(c)
He thought there was a potential for movement within the colluvial strata as the strata allows for water to permeate through its soil structure, potentially washing away fines within the soil matrix increasing its bulk unit weight and reducing the shear strength of the matrix and causing transitional failure;
(d)
Approval of the building site he considered should include approval of the block in its entirety and not just the access and the house pad;
(e)
Although he said it was alleged that the house was supported on screw- piles socketted into rock, he said he saw no evidence of this. He referred again to the fact of the screw-piles being “skewed”. From that he said he was yet to be convinced of the adequacy of the dwelling’s footings;
(f)
Even on the assumption the dwelling house had adequate foundations he said that did not improve the stability of the land upslope from the house. He said that the whole block of land would remain a very high risk of instability in parts, and if there was movement of soil beneath the house this could reduce the support of the house floor with uncertain consequences;
(g)
As to the existing surface drainage measures, he said he did not consider those measures to be sufficient or enough with regards to controlling seepage as they would have no effect on the subsurface seepage that may occur through the colluvium.
Samuels’ Report 3 April 2008[74]
This report in effect drew together all Mr Samuels’ reports so I shall refer only to those opinions which have not been expressed so far. They are these:-
(a)
There was evidence of some irregularity in the ground (hummocky) upslope of the dwelling;[75]
(b)
There was some slopping noted at the crest of the embankment down slope of the dwelling;
(c)
For the overall site slopes of up to 30 degrees were evident, the land varied from planar to convex, was very uneven and hummocky and showed evidence of soil creep, slumping, slip and seepage. In excess of 3 metres of colluvial soil was evidence with seepage at depth which gave the site very high risk of likely instability;
(d)
He was concerned that the screw-piles which he said were supposedly socketted into rock may not be, but may push sideways into the colluvium strata causing the dwelling to move. That could also result from a pile refusing on a boulder when the boulder moved.76
(e)
He said no subsurface seepage drains existed onsite nor was there any overall surface and subsurface drainage solution provided;
(f)
It was not known where the discharge of any collected surface water from the swale would emerge so that he could not comment on what effect this would have in aiding any surface water control on the overall block; he said that a shed and several tanks onsite were also likely to be founded within the colluvial strata and thus susceptible to damage if ground movement occurred.[77]
[75] Exhibit 6 p 3. 76 Exhibit 6 p 7.
[77] Exhibit 6 p 8.
In his oral evidence Mr Ure usefully asked Mr Samuels to identify the areas of difference between him and Mr Morrison which he did. At the risk of some repetition, they are:
(a) Hummocky Ground[78] [78] Transcript p 76 lines 1-43.Mr Samuels said that the hummocky ground was quite consistent with the flows or landslip aspects particularly in colluvial soils and that the particular site was quite irregular and uneven which to him indicated that there had been some previous movement. His opinion extended to the house pad site which he suspected would have similar ground conditions to the rest of the site. When asked to comment on Mr Morrison’s evidence that the hummocky ground was a consequence of boulders in the colluvium, he said he did not agree. He said that if that was the case on the high areas of the site, it was likely that the boulders would be visible at surface almost like a ridge line interconnecting possibly washing away fines and having no sort of grass coverage on top of it. He said he suspected the hummocky ground was an ununiformed difference in size of boulders and was set within a clay matrix which he said was quite typical of colluvial soils.
(b) Bows and Leans in Trees[79] [79] Transcript p 76 lines 45-55; p 77 line 1.In his report Mr Samuels set out photographs of trees which were leaning at an angle.[80] Mr Morrison said that he didn’t think those trees had any significance at all and could have resulted from a horse leaning on them or the tree seeking light.[81] Mr Samuels said that he thought the leaning trees indicated some sort of surface creep. He said that was quite common in colluvial soils, referring to the type here encountered by him.
[80] Exhibit 6 pages 5 and 6 plates 4 and 5.[81] Transcript p 46 line 55; p 47 line 1; p 53 line 44.
(c) Landslips[82] [82] Transcript 77 lines 2-22.There are two photographs in Mr Samuels’ report showing slips, one near the access road[83] and the other being a large concave section above the start of the access driveway.[84] In Mr Samuels’ opinion they indicate some previous movement on the site at both those locations. The slip movement he said is where there is a bit of slumping, a drop in the ground.
[83] Exhibit 6 p 4 plate 2.[84] Exhibit 6 p 21 plate 6.He also relied upon an extract from the Snowy Mountains Energy Commission’s map.[85] That map shows slips depicted in the vicinity of the subject house pad which Mr Samuels said he thought would be typical of the area itself. The map showed historical slips both on the site and in the surrounding area and he said it was not uncommon to get some minor slips which are difficult to pick up throughout the rest of the site.
[85] Exhibit 6 p 28.
(d) Slump[86] [86] Transcript p 78 lines 1-10.A photograph of a slump is in his report.[87] Mr Samuels explained a slump as being undermining where gravity has just dragged the soil down the slope. He said regression of that type of movement may go further back into the allotment itself on a larger scale under certain conditions.
[87] Exhibit 6 p 6 plate 6.
(e) Water in Colluvium[88] [88] Transcript p 78 lines 10-30.Mr Samuels was of the view that the colluvium soil is itself porous and permeable material which allows for ground seepage of water to move through it and that under continual adverse conditions there is potential for fines to be washed away or shear strength of materials to be reduced.
(f) Surface Drains[89] [89] Transcript p 78 lines 30-60; p 79 lines 1-10.In relation to the drainage evidenced in the statements of Mr Van Der Valk,[90] Mr Samuels said the surface drains there depicted were superficial and fundamentally did not address the issue of any potential deep seated movement in colluvial soils or the control of any deep seated seepage which may occur. He said the bore holes themselves had picked up moisture and wet conditions at depth and that the surface drains would only pick up surface water. As to that surface water, he said a degree of it would migrate vertically and possibly horizontally through the pores permeable colluvial strata unless there was some sort of impermeable membrane to stop that occurring.
In relation to Mr Van Der Valk’s evidence of witnessing four feet of water in the swale drain which remained there for one or two hours, Mr Samuels said that, given the timeframes, in his opinion there was certainly enough time for the water to penetrate into the colluvial material. He had no doubt about that.
(g) Ponding of Water – House Pad[91] As to the data on the previous borehole logs and test pits Mr Samuels said the reference to the soil being at least moist and on occasions wet is significant. He said those core sample materials were porous and permeable in character in allowing water to either pond or to run through it which had the potential to continue to wash away the fines and potentially reduce the shear strength of the soil. He saw that as quite critical.
[90] Exhibits 3 and 8.[91] Transcript p 79 lines 10-40.
Mr Samuels’ evidence dealt with further issues where he did not agree with Mr Morrison. He cast doubt on the reliability of the screw piles in the house foundation.[92] He questioned the factors of safety in Mr Morrison’s slope stability computer programme for both short term and long term risk.[93]
[92] Transcript p 81 lines 15-40.[93] Exhibit 2 p 20 and 21, Transcript p 81 line 55; p 82 lines 10 and 40.Mr Samuels regarded the access road as presenting a high risk of instability given the permanent spring watering the colluvium and an historical slip at that location. He saw a risk of damage to the road or the washing away of the road depending on the size of the slip which may occur.94 As to the swale drainage, he said there was a significant catchment area for surface and sub-surface water flow between the swale and the house pad. He thought there was potential for a lot of water to run down that slope or through the slope pointing out again the risk of the material losing strength and potentially failing.95 Finally he looked at the conditions which were being proposed by Mr Morrison96 and said he did not believe that they would address the fundamental stability of the site,97 by which I take him to have meant the fundamental issue of site stability, namely its instability.
I have not in the above sought to analyse every point of difference between Mr Samuels and Mr Morrison. It will be apparent to the reader by now that there are very few if any relevant areas of agreement. What I have sought to do is to focus on those areas of disagreement which are or could be determinative of this matter.
Cross-examination of Mr Samuels
As I did in relation to the cross-examination of Mr Morrison, I intend to identify only those issues where a concession was made or I consider the evidence otherwise of significance.
Parameters of Mr Samuels’ Report
One issue which emerged early in his cross-examination was the fact that Mr Samuels is not eligible for registration as an engineer and accordingly cannot give a certificate of the nature given by Mr Morrison.98 That does not of course detract in any way from the evidence he has given as to the risk profile on the subject site. But he agreed that the landslip instability risk analysis involved two steps – firstly assessing the risk of instability, and secondly managing those risks.99 He conceded that he had not addressed the second step100 and, conceded that there was nothing wrong with Mr Morrison’s certification and that the Council were entitled to rely upon it.[101] He agreed this matter boiled down to a difference of professional opinion between Mr Morrison and him as to the risk of site instability and the measures each would adopt to mitigate those risks.
Mr Samuels agreed that, at the end of the day, Mr Morrison, as a registered engineer, was prepared to put his neck on the chopping block and to certify in accordance with the five paragraphs which appear in Exhibit 2A”. In agreeing, he said that all his company reports were certified by a registered engineer.[102] But, a certification by registered engineer does not thereby entitle Mr Samuels to give the evidence solely within the province of a registered engineer. Of the four reports he provided, those of 21 June 2007 and 16 August 2007 were signed by Mr David Bowler a registered engineer and one Claudia Gibney described as a senior geotechnical engineer.[103] Mr Samuels was not sure whether Ms Gibney was a registered engineer,[104] but one would expect if she was she would put her registration number near her signature as Mr Bowler has done. Mr Samuels’ report of 20 March 2008 was signed by Mr Bowler on his behalf[105] and his report of 3 April 2008 was jointly signed by Mr Bowler and him.[106] Despite that I am satisfied that the opinions expressed in the various reports are those held by Mr Samuels to the extent they relate to the first risk assessment step of risk indentifaction.107
[101] Transcript p 86 lines 22-30. [102] Transcript p 86 lines 25-40. [103] Exhibit 6 p 14 and 25.
[104] Transcript p 89 line 25.[105] Exhibit 6 p 39.[106] Exhibit 6 p 9.
Accepting that Mr Samuels has not addressed the second stage of the risk analysis namely how any risk is to managed, I confess to some uncertainty in my mind as to whether that step was not carried out because Mr Samuels, not being a registered engineer, is not qualified to opine on such a matter, or whether, alternatively, he is able to opine but simply did not do so. The former would make more sense. It is unlikely Mr Samuels would overlook addressing such an important aspect. In the result there is no need to resolve that question because the fact remains he has not addressed the management of the risks he has identified.
Screw Piles
Mr Williamson then turned to the certification by Rymark Engineers Pty Ltd of the screw piles in the present house structure.108 Mr Samuels had queried that certification which certified that the piles were installed to their satisfaction, because details of what works were actually undertaken were not provided. When questioned on what else he would need to be satisfied he said confirmation that the piles were indeed socketted into weathered rock. When asked how he would test that he said he didn’t know and would have to talk to the piling guys.109 I took that answer to mean that he did not have the expertise to express an opinion on the issue.
Access Road
The next matter is the assessment made by Mr Samuels in his report of 3 April 2008.110 He assessed the access track with a very high risk of instability, house pad with a moderate risk of instability and the overall site with a very high risk of likely instability. It was when being questioned on this issue that he agreed this assessment was the first step in the risk analysis process, that is the starting point from which one went on to consider the risk. He agreed that, with all that information, it was at the discretion of the consultant as to whether it could be taken further or not. He agreed a detailed investigation was required which ultimately might end up with one of two scenarios, an appropriate engineering solution which is either practical or impractical.111 In context, the consultant he referred to would be a consultant registered engineer.
Management of Identified Risks
Mr Samuels was then taken to Exhibit 6 containing a table entitled Risk Level Implications setting out the implications of each risk level he had assessed for discrete areas of the site.112 For the Very High Risk, the implications were “extensive detailed investigation and research, planning and the implementation of treatment options essential to reduce risk to acceptable levels; may be too expensive and not practical.” Mr Samuels agreed that once one moved to the second stage of risk assessment namely trying to manage the risk, that turned a lot on the professional judgment and expertise of the engineer and that minds may differ.113
Later there was this exchange between Mr Williamson and Mr Samuels:114
“Question:
Now, have you during your analysis considered – I will withdraw that and start again. I think we’re agreed that in broad terms we can say that this process has two steps. Firstly, you will get the risk of instability; correct?
Answer: Yes. Question: and the second is, you will put your – the way in
which you can address those risks?Answer: Mm, hmm. Question: Would I be right in saying that you have only done
the first of the two steps?Answer: Yes you would. Question: So you’ve not gone on to consider what would be
necessary to mitigate the risk?Answer: No. Question:
So in terms of the conditions proposed by Mr Morrison you have not undertaken the necessary analysis to determine whether those recommended mitigation measures are in fact sufficient?
Answer:
Well I think it’s a given that there is to the sub- surface drainage – which is one issue we are talking about at the moment has not been addressed by those conditions. So I think that would be a given to improve this ground.
Question: But what – my question was what analysis had you
done?Answer: No. I haven’t undertaken any analysis. Question:
Right. Now in terms of sub-surface drainage what would you be looking for? What possible options do you say there?
Answer:
Look, I think it would require some study. I wouldn’t be able to answer that off the top of my head.
Question:
Right. So in terms of what’s required then you don’t really know whether something is or is not required, that you want to undertake more work.
Answer:
I know there is a very high risk and in order to reduce those risks I haven’t seen anything to date that indicates that those risks will be reduced by what’s being presented in front of us.
Question:
Right. But what we do know is that Mr Morrison was prepared to accept that there is an appropriate level of risk and has provided a certification in that regard; correct?
Answer: Sure.”
In relation to the access road Mr Samuels was asked if it was fair to say that, notwithstanding its risk, it could remain serviceable with appropriate maintenance. He replied no because if there was deseative movement “the road goes”. He was then shown a contrary extract of his report[115] and asked whether he was retreating from the position expressed in that document to which he replied “I guess I am yes”.[116] He agreed that if a landslide occurred upside from the access road and found its way on to the road, then, in that event, the maintenance would be the cleaning up of the debris. As I have already referred to in relation to Mr Samuels’ report of 16 August 2007,[117] he agreed there were other access tracks in use which could be used by emergency vehicles if circumstances required and to maintain access to the second dwelling on the property. He also agreed that in the intervening period the access driveway could be maintained to bring it back, which I took to mean bring it back to an acceptable standard for use.[118]
[115] Exhibit 6 p 24, second last paragraph.
[116] Transcript p 99 lines 5-25.
[117] Exhibit 6 p 24, second last paragraph.[118] Transcript p 99 lines 25-55.In relation to Mr Morrison’s slope stability computer programme[119] Mr Samuels agreed that Mr Morrison had adopted two conservative assumptions namely a water table at the house pad level and a weak interface layer between the colluvial soil and the underlining rock.[120] Neither of these assumptions did Mr Morrison accept as existing. He further agreed that the factor of safety he was himself looking for in relation to both the short term risk (2.5) and long term (above 1.5) would both be achieved if Mr Morrison removed those conservative assumptions. When it was put to him that sub-surface drainage was not required under the house pad he said he did not know because he had not done any analysis himself.[121] He conceded that a retaining structure could be designed as a part of the landscaping works for the house once it was completed. In terms of the substantially completed dwelling itself, he agreed it was fair to say that when the engineers designed footings, foundation systems and structures generally factors of safety are built in so that it would be reasonable to assume that a factor of safety had been built in to the design of the appellant’s home.[122]
[119] Exhibit 2 Annexure D pages 20 and 21.[120] Transcript p 100 lines 15-60; p 101 lines 1-25.[121] Transcript p 101 lines 40-45.[122] Transcript p 102 lines 15-35.On the issue of Mr Samuels’ concern about the footings system in the house he said he understood that piles had been put into all locations in the relevant plans and that he had no reason to doubt that. When it was put to him that he had no reason to doubt how the house had been constructed in terms of its frame he said “no, no doubt at all” and agreed that the simple point was that he had not been convinced.[123]
[123] Transcript p 102 line 35-55.Earlier in his evidence[124] Mr Samuels was asked whether he agreed with Mr Morrison in his qualitative landslip analysis that a landslip was possible one in 1,000 years and the likely damage if the event occurred would be minor. He replied:-
[124] Transcript p 81 line 45.“No, I don’t think so. I think if there was a significant enough step up slope that hit this house or there is potential for at least major, I would thought but, yes but I don’t entirely agree with that, no.”
Whilst the focus of the answer was predominantly on the extent of any damage which would occur, nevertheless it is clear that he was disagreeing also with the incidence of risk of one in 1,000 years. Yet later this exchange took place:-[125]
[125] Transcript p 104 lines 45-60; p 105 lines 1-10.
“Question:
But that’s the reality of building on site, isn’t it Mr Samuels? Let’s not be scaremongering about it. Constructing and designing buildings on a slope or land that is at risk of instability has to take into account that it could fail tomorrow, a hundred years time or a thousand years time, isn’t that so?
Answer: I guess so, yes. Question: They are just constraints and parameters in which
people of your area of expertise operate?Answer: Mmm, yes. Question:
So in terms of this particular site, you say, well, look it could fail tomorrow. Equally, it could fail in a thousand years time?
Answer: True. Question: So what we’ve got to work with is the available date,
that is, the borehole logs, correct?Answer: Yes. Question: The test pits? Answer: Yes. Question: And the judgment of two – two experts? – Mm –
hmm?Question: And that’s not uncommon. That’s- Answer: No – no. Question: That’s, entirely, within the bounds of what happens
everyday?Answer: Sure.”
Conclusion
I have listened to the evidence from both Mr Morrison and Mr Samuels with great interest. Of course, I am not qualified to resolve the conflicts between them but, accepting that professional minds will commonly differ on issues, I have come to the view that I prefer the evidence of Mr Morrison to that of Mr Samuels where the evidence conflicts. I say that for these reasons:-
(a)
Mr Morrison is an registered engineer qualified to certify, and has certified, not only as to the risk profile of the site but also as to what engineering solutions are available to manage the risks identified. He has certified that the site is an acceptable risk for the construction proposed and has not deviated from that view despite intensive cross-examination;
(b)
Experience in the field makes him eminently suitable to provide the very important certification necessary;
(c)
Certification in circumstances where there is a risk of instability is not something one would undertake lightly having regard to one’s professional reputation and the potentially calamitous results of the certification proving to be faulty. Whilst it can never be an absolute guarantee, his certificate is an important assurance given against his lengthy background and experience in this field;
(d)
Mr Morrison’s risk assessment is, in my view a measured one without any attempt to deny the existence of some risk of land slip or to trivialise it;
(e)
Mr Samuels, quite correctly, has not sought to attack Mr Morrison’s certificate but, rather, conceded the Council could rely upon it;
(f)
I think it is very difficult for Mr Samuels to compete with Mr Morrison, in an evidentiary sense, given that he has not addressed the essential second step of the risk analysis, being the identification and consideration of the means by which any identified risk may be managed so as to make the proposed project practicable. That is not to be seen as a criticism of Mr Samuels who has, at all times, readily accepted the limitations on his risk analysis.
(g)
I have taken some time to identify in the evidence of Mr Samuels those areas where he has forthrightly admitted he is not in a position to express an opinion, whereas Mr Morrison was. Another most telling piece of evidence, to my mind, was the final exchange in his cross-examination which I have set out in paragraph [67] above. He agreed that the landslip risk on the site could crystallise tomorrow, in a hundred years time, or a thousand years time. There is something faintly surreal about that and one may well ask “or not at all?” As against that evidence, Mr Morrison assessed the risk profile and is satisfied that, despite the existence of landslip, those risks can be managed with engineering expertise. Given that Mr Samuels’ did not address risk management, Mr Morrison’s evidence of risk management stands uncontradicted. To the extent Mr Samuels ventured to express opinions in that area I do not accept them and rely on the evidence of Mr Morrison.
Does the Proposal Conflict With Steep Slopes or Unstable Soils Constraint Code?
The expressed primary purpose is to regulate development on land with steep slopes or unstable soils. The secondary purposes are:-
•
To minimise the potential for erosion or land slippage, and avoid the risk of land slippage arising from underground streams;
• Effectively manage stormwater run-off; •
Minimise erosion events on slopes exceeding an average gradient of 15 percent;
•
Reduce the visual impacts of buildings and associated works through suitable external building treatment and landscaping; and
• Encourage safe and efficient vehicular access onto steeply sloping land.
The Development Requirements of the Code set out Performance Criteria and Acceptable Solutions to address those Criteria. Each such Solution indicates a desirable way to ensure compliance but they are not the only available solution. The Performance Criteria are not to be interpreted as requiring adoption of the Acceptable Solution, or even as requiring an alternative solution to be akin to that Acceptable Solution.[126] Mr Ure for the Council says that I should be satisfied that the proposal is in conflict with the Code.[127] In support of that, he relies upon the following:-
[126] Central Equity Limited v Gold Coast City Council [2007] QPELR 356 at 357 paragraph 13.[127] Council’s written submissions, 21 April 2008, paragraph 29.
(a)
That the site’s access road / driveway exceeds an average of 15 percent referred to in the above set out secondary purposes of the Code and that I should take a careful, cautious approach where the safety of life is concerned. On that issue I prefer the evidence of Mr Morrison who puts the average gradient of the entire site at between 5 and 15 degrees;[128]
(b)
That I should accept the evidence of Mr Samuels that the site is unsuitable because of the unacceptable risk of the moderate to very high instability risk factor arrived at by Mr Samuels.[129] The difficulty with that submission is that Mr Samuels has only addressed one half of the risk analysis issue. I accept the evidence of Mr Morrison as to the level of risk and its manageability;
(c)
That the material in the vicinity of the house pad is moist to wet. I accept Mr Morrison’s evidence that there is no water table and that any moisture in the colluvium at the house site is not such as to put the site at risk;
(d)
That Mr Morrison seriously underestimated the stability risk of the site and limited his focus to the actual house pad ignoring the risk of slippage in the colluvium both up slope and down slope of the house pad.[130] As I have already said, I do not accept that Mr Morrison’s evidence is limited to the house pad and I am satisfied that he not underestimated those risks;
(e)
That there was surface creep evidenced by the bowed trees which is an indicia of instability. I accept Mr Morrison’s evidence that, whilst there may have been some slips down slope from the house site the bowed trees do not necessarily evidence movement in the land and do not impact on the landslip risk as assessed by them.[131]
(f)
That the uneven ground in the vicinity of the house pad evidences movement rather than the presence of boulders and that Mr Morrison was wrong in relation to the make-up of the soil under the house site.132 Again I prefer the evidence of Mr Morrison on this issue. Even though he conceded that there was evidence that the colluvium was in excess of 3 metres I do not accept that this affects Mr Morrison’s ultimate opinion on stability of the house site;
(g)
That the Court could not be satisfied that the screw pile foundations were anchored into bedrock but rather could be sitting on boulders and could shift. I prefer the evidence of Mr Morrison who in turn relied upon the engineers responsible for the partly constructed house rather than the speculative nature of Mr Samuels’ evidence that the foundations may be deficient. It is clear from the evidence of Mr Van Der Valk133 that the skewing of one of the piles was addressed by his construction engineer. I also find it of some significance that the foundations sustained very heavy rainfall in January and February 2008 yet did not move which they may well have done on Mr Samuels’ opinion that water in the colluvium would wash away the fines.
(h)
That the drainage is inadequate. I am satisfied from the evidence of Mr Van Der Valk and Mr Morrison that the drainage is sufficient both subsurface and above surface.
[128] Exhibit 2A p 2.[129] Council’s written submissions, 21 April 2008, paragraph 18.[130] Council’s written submissions, 21 April 2008, paragraphs 19-21.[131] Transcript p 46 lines 45-60.
In all the circumstances I am satisfied that there is no conflict between the proposal and the above Code. But even if there was I am satisfied that the evidence from Mr Morrison and Mr Van Der Valk is sufficient to justify approval of this application notwithstanding any such conflict.
Would the approval of the Application Compromise the Achievement of Desired
Environmental Outcome DEO SOC.7?
DEO is set out in paragraph [11] above. Its declared objective is to ensure that development is located away from areas where the risk to life and property from the impact of natural hazards is unacceptable and to ensure that development is designed to mitigate any such risks to life and property. I am satisfied that there is nothing in the proposal which, if approved, would be other than harmonious with those objectives and DEO SOC7 generally.
The application should be allowed subject to the parties formulating appropriate conditions of approval which should include those conditions recommended by Mr Morrison[134] and by the town planners Mr Grummitt and Mr Perkins.[135]
[134] Exhibit 10. [135] Exhibit 7.
QPELR 267 at 271 – 272 para 18.
Shire Council (1996) 92 LGEA 41 at 73, 75, 78; Harburg Investments Pty Ltd v Brisbane City Council
[2000] QPELR 313 at 318.
Report (8 August 1999) incorporated into Gold Coast City Council (Stability Assessment) report
requirements (April 2002).
Geomechanics Vol 35 No. 1 March 2000.
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