Yared v Glenhurst Gardens

IN THE SUPREME COURT OF NEW SOUTH WALES EQUITY DIVISION

4605/99 PHYLLIS YARED V GLENHURST GARDENS PTY LTD JUDGMENT (revised 28 February 2002 to correct typographical errors) 1 HIS HONOUR: This case has arisen in consequence of the partial collapse of a high retaining wall at the rear of the plaintiff's property at 56 New Beach Road, Darling Point. The property comprises a substantial principal residence and (until the happening of the events I shall describe) a self-contained cottage in the backyard, between the main house and the retaining wall. The back (eastern) wall of the cottage was located about half to one and a half metres to the west of the retaining wall. 2 The plaintiff took up residence in the main house in 1967, and has lived there since that time, at first with her husband and then alone, after his death in November 1985. Until August 1998 she derived income from renting the ground floor of the principal residence, and also renting the cottage. 3 The defendant is the owner of the property to the rear of the plaintiff's property, 11 Yarranabbe Road, Darling Point, and has owned the property since 1958. There is a large residential home unit building on the defendant's property, though the building is well away from the boundary with the plaintiff's land. 4 The plaintiff's property faces east on to New Beach Road. The eastern boundary at the rear of the plaintiff's property, where the retaining wall is located, is a common boundary with the defendant's property. The common boundary runs approximately in a north/south direction. The surface level of the defendant's property adjoining the common boundary slopes from north to south, some 4 to 7 metres above the surface level of plaintiff's property. 5 It appears (in view of the evidence of Dr John Cooke, an architect who inspected the property in August 2000) that the retaining wall was constructed in 1927, at about the same time as the construction of the principal dwelling on the plaintiff's land. The retaining wall gave lateral support to a high embankment, at about the common boundary line. It was constructed according to the methods and standards in use in 1927. The wall was approximately 600 mm thick its base and 230 mm thick at the top, apparently without any buttressing except at the southern end. A lime-based mortar was used. Evidence given by one of the defendant's experts indicated that this kind of mortar increases in strength over time, but on the other hand the weathering of the exposed portion of the wall would have led to a loss of mortar. 6 The defendant says that the retaining wall was wholly on the plaintiff's land, but the plaintiff disagrees. A survey report by Charmers & Finney dated 30 May 1927 appears to show a "brick wall on rock foundation" on the rear boundary of the property. A report by Ed Palaitis & Associates dated 25 August 1998, while noting that the boundaries are difficult to determine and that a registered strata plan relating to the property to the north appears to dispute the northern boundary, states that the remains of the retaining wall at the northern end of the rear boundary of the property indicate that the boundary is the centre of the wall. It is probable, in my view, that the boundary ran through the wall. A contrary survey was tendered by the defendant but ruled to be inadmissible. 7 The plaintiff's backyard is on two levels. The lower level, the area closer to the house, has been paved. Until the collapse of the wall, the upper level was reached by climbing over a stone wall about 1.5 metres above the paved area, to a passageway between the cottage and the brick wall. The passageway varied in width from approximately 50 centimetres to about 1.5 metres. 8 Before its collapse, the retaining wall had nine or 10 weep holes at its base and at a level approximately three bricks above the ground. The weep holes were in a single line. Each weep hole was the height of a brick and approximately a mortar space in width. 9 The defendant's expert evidence is to the effect that the wall had a design life of no more than 70 years. In my opinion, the design life of the wall has no legal significance in this case, however useful the concept may be for engineers. A duty not to cause the failure of a wall with a design life of 50 years does not exist for years 1 to 50 and terminate at the end of the 50th year. A duty not to cause its failure will endure so long as the wall stands, even if the wall is still standing after 100 years. 10 During the period from about November 1960 to March 1961 the defendant erected a concrete platform for a car parking area on part of its land, which extended not far from the common boundary with the plaintiff's property, but at the top of the embankment and therefore at a much higher level than the plaintiff's property. Plans for the car park were approved by Woollahra Council on 29 November 1960. In connection with the erection of the car park, the defendant deposited some fill material on its land above and behind the retaining wall, so as to support the southern end of the car park. The expert witnesses of the parties generally agree that the erection of the car park did not increase the flow of stormwater onto the land between the car park in the retaining wall, and if anything, the car park reduced the flow of water by directing water from the car park slab and roof to the defendant's property away from the retaining wall. 11 In November 1960, and progressively thereafter, the defendant permitted trees, shrubs and other vegetation to grow in the area above the retaining wall and where the fill material had been deposited, which may have contributed to retaining soil (including the fill material). During the period from approximately 1980 until August 1998 the defendant removed some trees and other vegetation. There is controversy between the parties as to what was done, and whether the risk of subsidence of the fill material and retaining wall was thereby increased. The collapse of the retaining wall 12 From time to time in Sydney there are periods of very heavy rainfall. For example, in August 1986 approximately 290 mm of rain fell in the eastern suburbs of Sydney over a period of 24 hours. There was a similar storm event on 6 and 7 August 1998. At Observatory Hill approximately 227.8 mm of rain fell between 9 am and 5 pm on 7 August. There is evidence of a substantial number of landslides and the collapse of retaining walls in the Sydney area on that day. On that day the retaining wall partly collapsed, depositing a large quantity of bricks, soil, vegetation and debris on the plaintiff's land. The collapse damaged the cottage at the rear of the main house. 13 Photographs taken after the collapse (for example, those annexed to the affidavit of Steven Lewis, the plaintiff's solicitor, sworn on 8 November 1999) indicate that large portions of the retaining wall and the soil behind it fell onto the plaintiff's property. What was left standing was a small portion of the retaining wall at the northern end, attached to the wall which ran along the northern boundary, and also a part of the retaining wall a few metres high and a few metres long at roughly the middle or a little to the south of the middle of the eastern boundary ("the centre segment"). It appears that the centre segment wholly moved forward a small distance, laterally, off the stone shelf on which it had stood and onto the plaintiff's land, and the top part of the wall along the centre segment broke off and fell, but the rest remained standing. Mr D W Knox, a consulting engineer who inspected the property for loss assessors on 10 August 1998, estimated that the retaining wall shifted laterally towards the house by about 500 mm at the northern end about 2000 to 2500 mm at the southern end. Part of the wall and the soil behind it collapsed on to the roof of the cottage, demolishing part of the roof and damaging the walls at the eastern end of the cottage. The collapse of the wall and the subsidence left an exposed face of rock and soil along the defendant's land, highest at the northern end and falling away to the south. 14 A pine tree and a smaller tree fell over the centre segment of the wall and onto the roof of the cottage, though some of their roots remained in the soil on the defendant's land a little behind the centre segment. On the basis of visual observation by means of the photographs, it seems to me unlikely that either of the trees contributed to the collapse of the wall. Neither of the trees is large - the diameter of the trunk of the pine tree, at its thickest point, appears to the about the length of a single brick, and the other tree is much smaller. 15 Photographs in evidence, taken on 10 August 1998, show that the cottage had moved, causing its support columns to crack and tilt. Following the collapse of the wall, the plaintiff's property was inspected by the State Emergency Service, who advised the plaintiff that the house, including the downstairs flat, and the cottage, could not be occupied due to the potential danger of further subsidence. The cottage was demolished down to the first floor level in late August 1998, after discussions between the plaintiff and her insurer, AAMI. This was after the property had been inspected for the loss assessors by Mr Knox, who wrote a report for them dated 21 August 1998. 16 Mr Fernando Barros of F & L Building Consultants Pty Ltd, a structural engineer, wrote a report dated 20 March 2001 after several site inspections over the previous weeks, noting that the ground floor walls, which remained standing after demolition of the upper floor, were cracked and some of them were out of plane, and that the timber flooring and framing of the upper floor had been exposed to the elements and had become distorted due to the wall movements. He advised that it would not be feasible to repair the existing ground floor walls and upper flooring, and that the complete rebuilding of the dwelling would be a more feasible and cost-effective alternative. This conclusion conflicted with the opinion expressed by Mr Rick Pilz, a principal structural engineer at Gutteridge Haskins & Davey Pty Ltd, who issued a structural report to the defendant's solicitors on 22 June 2001. Mr Pilz said that the ground slab and full brick walls of the cottage were in reasonable condition and could be incorporated into the rebuilding of the extension, but the upper storey of the cottage had deteriorated through being left open to the weather in the period since collapse of the wall and would require replacement. 17 In approximately mid-September 1998 the house and downstairs flat were reoccupied. The tenant of the cottage took up occupation of the downstairs flat. At the time of the collapse of the wall, the downstairs flat was unoccupied but a lease had been signed. The proposed lessees were unable to take up occupation. 18 On 29 October 1998 Woollahra Municipal Council issued a Notice of Proposed Order pursuant to Order 4 of the Table to s 121 of the Environmental Planning and Assessment Act 1979 (NSW), directed to the plaintiff. The terms of the proposed order were "to repair or replace the collapsed retaining wall on the boundary adjoining 11 Yarranabbe Road Darling Point". The reason for the proposed order was stated to be that "the retaining wall has collapsed and is a danger to the public". The time for compliance with the proposed order was to be 90 days from the date of the order. The plaintiff was invited to make representations before the order was made. 19 The plaintiff's solicitors wrote to the Council on 9 February 1999, replying to the Council's notice of proposed order. They asserted that the defendant was liable to stabilise the soil on its property and make good the retaining wall. They said that since the defendant had denied liability, their client was faced with commencing a proceeding in this Court for an injunction to require the defendant to take reasonable steps to prevent damage to her property. They asked the Council to inform them whether it proposed to take any further action against the plaintiff in respect of the notice. The plaintiff's solicitors have received no reply from the Council, and the Council has not made an order under s 121 of the Act. 20 Although there has been some cleaning up on the site, the retaining wall has not been repaired. There is some rather unedifying correspondence in evidence between the solicitors for the parties, demonstrating failure on both sides to extend that degree of trust, co-operation and common sense that would have led to agreement as to the appropriate remedial work. Essentially, both parties proceeded on the basis that brick rubble and dirt needed to be removed before the engineers could recommend an appropriate new retaining wall or other structure, and that the plaintiff would pay for removal of the brick rubble while the defendant would pay for removal of the dirt that had fallen from its to the plaintiff's land. But they could not agree to use a single contractor nor as to the proper sequence of the removal of bricks and dirt. 21 After several months the parties did agree to a joint site meeting of lawyers and engineers, which took place on 29 June 1999. Then the engineers met with contractors on the site on 6 July 1999. The engineers in attendance were Dr Felix Barda of Alba Associates, a structural engineer engaged by the plaintiff; Mr Brett Hawkins of PPK Environment and Infrastructure, a geotechnical engineer engaged by the plaintiff; and Mr R P Jeffery of Jeffery & Katauskas Pty Ltd, a geotechnical and environmental engineer engaged by the defendant. The primary purpose of the 6 July meeting was to establish whether contractors, who attended separately to inspect the site, believed it was feasible to construct anchored shotcrete protection to hold back the defendant's land. 22 After the site inspection, Jeffrey & Katauskas Pty Ltd produced a report dated 15 July 1999, which was effectively a joint report by the three engineers. The report set out a proposal for remedial work in which the land between the defendant's car park and the plaintiff's property would be regraded and then retained with reinforced shotcrete, attached to the subsurface rock shelf on the defendant's land by permanent stainless-steel rock bolts. Indicative costs given by contractors ranged from $80,000 (which the engineers thought to be on the low side) to $150,000. The work would take about six to eight weeks to complete, with the use of a crane, compressor, and storage bins for rubble - and consequently access to both properties would be essential and (I infer) there would be considerable noise and disruption. The engineers recommended a preliminary geotechnical investigation involving one or two days' drilling work to establish the location and nature of the subsurface rock shelf, at a cost of approximately $10,000 to $12,000. 23 The defendant responded to the report, in a constructive manner, by offering to pay half of the cost of the preliminary investigation. However, the plaintiff's response was anything but constructive. Her solicitor wrote to the defendant's solicitor on 16 August 1999 saying that unless within 14 days the defendant accepted liability for restoration of the wall and ancillary work, a proceeding would be commenced in this Court. The defendant's solicitor replied by asking the plaintiff's solicitor to indicate the legal principles and factual matters on which the plaintiff based her claim that the defendant was liable to restore wall. There was further correspondence, but this question was not satisfactorily answered before commencement of the present proceeding. 24 The plaintiff's property, and the defendant's land between the car park and the collapsed retaining wall, remains essentially as they were in August 1999. The bank of the defendant's land is supported by the collapsed material lying on the plaintiff's property. This collapsed material cannot be expected to remain in that state indefinitely. When it is removed, the defendant's land will have to be artificially supported in some way, to prevent soil and rubble from falling either gradually or by landslip onto the plaintiff's property. The plaintiff's claims 25 The plaintiff commenced this proceeding by summons filed on 9 November 1999, but subsequently orders were made for pleadings. By her further amended statement of claim filed on 1 August 2001, the plaintiff seeks relief of two kinds. First, she seeks an order that the defendant forthwith take reasonable steps to abate the nuisance subsisting on its land constituted by the exposed, unretained, face of the bank adjoining the plaintiff's property. The order would require restoration work to be done in the manner contemplated by the report by Jeffery & Katauskas Pty Ltd dated 15 July 1999. The plaintiff would consent to the defendant having access over her land in order to carry out the restoration work, provided that the defendant reinstated the land at its cost in the event that any damage occurred during the restoration. 26 Secondly, the plaintiff seeks damages and interest to compensate her for the loss and damage she has suffered due to alleged wrongdoing by the defendant. She seeks compensation for: · the cost of construction of a new retaining wall, if her claim for a mandatory order is unsuccessful; · the cost of the demolition and full reconstruction of the cottage, which she seeks to quantify at approximately $350,000; · economic loss arising from damage to the cottage, based on loss of rent which she seeks to quantify at approximately $100,000; · the destruction of "garden amenities"; · loss of enjoyment of the garden; and · inconvenience, embarrassment and anxiety - that is, general damages for suffering. · She claims interest on the damages awarded. 27 On 30 July 2001 I made orders, by consent, under Part 31 of the Supreme Court Rules, for the determination as a separate issue of the amount of damages (if any) to which either party may be entitled, and for the determination of that question to be made after determination of all other issues. The present judgment relates, therefore, to issues other than quantum of damages and in particular, to questions of liability. 28 The plaintiff relies on causes of action in nuisance and negligence. The plaintiff alleges, in paragraph 8 of the statement of claim, that the defendant had a duty not to create or maintain a nuisance by unreasonably exposing the plaintiff as occupier to the risk of substantial interference with her land, or loss of the use and enjoyment of it. She says that the fill material deposited by the defendant above and behind the retaining wall, which the defendant allowed to remain in place, constituted a legal nuisance. The plaintiff also alleges, in paragraph 9B of the statement of claim, that the defendant owed her a duty not to remove the trees and other significant vegetation on its land above the retaining wall, without replacing what was removed with something that would hold the fill material in place. She says that this duty was breached during the period from 1980 to August 1998 when trees and vegetation were from time to time removed. 29 An essential ingredient of the plaintiff's case, both in nuisance and in negligence, is to establish causation. The plaintiff says that the "dominant direct cause" of the failure of the wall was an increase in hydrostatic pressure against it. The plaintiff's experts say that immediately prior to the failure of the wall, water collected behind it and, as a result of the heavy rain immediately prior to the collapse, sufficient hydrostatic pressure built up to move the wall from its base. The defendant does not dispute this contention. 30 The plaintiff says that a "second material cause" of the failure of the wall, sufficient to provide a causal nexus between the defendant's wrongdoing and her loss, was that unretained fill material on the defendant's land above the wall moved down to the wall, and absorbed and held water, thereby increasing the lateral pressure on the wall. She says that the fill material was vulnerable to movement because the defendant had, over preceding years, removed several large trees from the vicinity, the roots of which had retained the fill material. The defence 31 The defendant denies liability. First, it denies that it had the duties alleged in paragraphs 8 and 9B. Secondly, it contends that its conduct, including the deposit of fill material in 1960, was a reasonable user of the land (thus meeting the plaintiff's claim in nuisance), and that changes in the state of the vegetation on the defendant's land above the retaining wall occurred without negligence on its part. 32 Thirdly, it says that the failure of the retaining wall was not caused by any act or omission on its part, but the material cause was the plaintiff's own conduct and omissions, in failing to take reasonable care to maintain the wall. 33 The defendant's experts contend that the fill material in the vicinity of the retaining wall played no material part in the failure of the wall, and by reason of its composition, could not hold any significant quantity of water. Further, the defendant's experts contend that the asserted changes in the plant cover would have had no significant effect on the lateral pressure applied to the wall. They say that failure of the wall was probably due to a combination of factors, including the unusual rainwater loading during the storm just prior to the failure, design defects in the wall, the blocking of weep holes, and the deterioration of the mortar over a period of 70 years. 34 Fourthly, the defendant raises a defence of volenti non fit injuria, contending that the plaintiff voluntarily, and with full knowledge of the circumstances and of the risk and consequences of failure of the wall, accepted that risk and those consequences. Fifthly, the defendant says that the plaintiff has failed to mitigate the damage that arose from any act or omission on its part that the Court may find to be wrongful. Sixthly, the defendant raises a defence of contributory negligence, alleging that the plaintiff failed to take reasonable care to maintain the structural integrity of the wall. The defendant's cross-claim 35 By its cross-claim the defendant alleges, first, that the plaintiff owed it a duty of care to maintain and not reduce the structural integrity of the wall, and not to cause its collapse, and says that she breached that duty. Secondly, it alleges that the wall constituted a hazard on the plaintiff's property, which she failed to abate. Thirdly, it alleges that the defendant has acquired by prescription an easement for support of its property from the plaintiff's property, by its continuous assertion of a right of support for a period in excess of 20 years prior to the failure of the wall, and that the plaintiff breached her obligations under the easement. As cross-claimant, the defendant seeks damages, an order that the plaintiff abate the nuisance caused by failure of the retaining wall, and a declaration that it has acquired an easement for support, with a consequential order that the Register be amended to record the easement. Factual and legal issues 36 The parties are in dispute with respect to some crucial factual matters, namely: · the nature, quantity and location of the fill material deposited by the defendant near the car park in 1960/61; · the extent to which the defendant removed trees and vegetation from its land above the retaining wall during the 1980s and 1990s; and · the cause or causes of collapse of the retaining wall. 37 I shall consider the evidence on these questions and make findings, and then I shall apply these findings to the plaintiff's and defendant's causes of action. In doing so, I shall consider some aspects of the law with respect to nuisance, duties of care and easements by prescription. I shall consider the conflicting submissions of the parties on some aspects of the law, including the circumstances in which the Court will grant a mandatory injunction to require a defendant to construct a retaining wall to prevent future slippage of the defendant's land onto the plaintiff's land, having regard to Leakey v National Trust [1980] 1 QB 485. For reasons I shall explain, it is unnecessary to resolve disagreements between the parties as to the precise test of causation in the law of torts, the meaning and effect of s 177 of the Conveyancing Act 1919 (NSW), and the availability of an easement for support by prescription with respect to Torrens title land. Deposit of fill material near the car park 38 The carport structure for the defendant's property was designed by H. R. Smith & Lascelles in approximately December 1960. The evidence, including drawings prepared by Smith & Lascelles and the oral evidence of Mr Lascelles, indicates that the floor slab of the car park is supported by columns founded on sandstone bedrock (or on natural ground at a distance having no effect on the retaining wall). That being so, the structure did not impart any load on the retaining wall below it. 39 The plans prepared by Smith & Lascelles provide for "back fill, rock faced" to be placed on the defendant's land between the car park and the retaining wall. At the northern end, the fill is shown as sloping upwards to the car park slab at a point approximately half way between the retaining wall and the car park, the ground being almost level in the area from the retaining wall to the midpoint. However, at the southern end the fill slopes up, apparently more steeply, from the retaining wall to the car park, and there is no level area. The plan shows a stone buttress supporting the wall at the southern end. 40 Mr Lascelles gave evidence that late in 1960, he inspected the site and examined the retaining wall, both from the defendant's land and from the plaintiff's land. He said the wall presented as solid and secure, and he concluded that it was sound. He wrote to the Council on 6 December 1960, reporting on his inspection of the retaining wall. He said: "The filling to be placed under the car park area will only have an effect on the retaining wall at the end where the two structures converge and at this end the filling amounts to very little more than is at present on the site. Moreover at this point the wall has a stone buttress which will considerably assist it to take any additional load. In our opinion the amount of extra load being placed on the wall is negligible." 41 In his report dated 21 August 1998, Mr Knox said that the collapse of the wall had exposed sandy material below the original topsoil. He said: "Filling material is evident above the natural ground material although this may only be of minimum depth, as the natural ground possibly rises further up the slope". He also expressed some concern about the stability of the carport slabs on the top of the slope, which appeared to him to have undergone some remedial work. He advised that the adjoining owners be informed of the need to stabilise the car parking area, independently of the recent collapse, because of a "long-term movement problem, of the poorly compacted filling that these slabs were cast on in the mid-1960s when originally constructed". Other evidence indicates, however, that the carport slab was built on columns placed on the sandstone shelf at its western end, and the plaintiff has not contended either that the car park was poorly constructed or that it had become unstable by the time of collapse of the retaining wall. 42 Mr W O Sherrard of AH Baigent & Associates Pty Ltd, a consulting engineer, prepared a report dated 28 August 1998 for the insurer, AAMI. He observed that the soil profile at the face of the defendant's land consisted of weathered sandstone rock overlain by brown loam and then brown topsoil, on top of which was fill material of varying depth, but he said that the soil profile should be confirmed by geotechnical report. 43 According to Mr Pilz, the fill material was a sandy fill that would allow water falling on it readily to pass through. Mr Lascelles gave evidence that he directed that the fill be "good clean fill". The plaintiff alleges that material other than fill material was placed by the defendant above the retaining wall. She gave evidence that in April 1999 she inspected the debris on her property following the collapse of the wall some months earlier. She noticed that the debris included rusted metal which resembled guttering, broken slate tiles, building debris and broken bricks, as well as soil, dirt, rocks and rock fragments. 44 I found Mr Lascelles to be a helpful witness whose evidence I accept. He was closely involved in planning for the construction of the car park and advised on the deposit of the fill material. The other witnesses observed the site substantially later than the time when the fill material was deposited, and their evidence (though it is expert evidence) is necessarily the reconstruction of what was done when the car park was constructed, involving an element of speculation. Assessing the evidence as a whole, I have concluded that a quantity of fill material was deposited by the defendant on its land between the car park and the retaining wall in 1960/1961, at a time when the car park was constructed. On the basis (discussed below) that Mr Lascelles's plan was followed by the builder, the greatest quantity of fill was towards the southern end of the boundary. However, even there, the quantity of fill was not large enough to place any substantial additional lateral pressure on the retaining wall. The fill material was sandy and porous and did not retain water for a greater time than the topsoil in the area. 45 With some hesitation, I have concluded that I should reject the plaintiff's evidence to the effect that building rubble and building debris (as distinct from sandy fill material) had been deposited above the retaining wall. Her evidence that she observed material of this kind after the collapse of the wall is not supported by the other evidence. Neither Mr Knox nor Mr Sherrard, who inspected the site shortly after the wall collapsed, records the presence of any such material. 46 I am not able to conclude, on the evidence before me, that the defendant failed to comply with Mr Lascelles' stipulation that the fill be "rock faced". The evidence on this point is unsatisfactory. Mr Lascelles did not supervise the placement of the fill, but he said (and I accept) that the builder was reputable. Mr Lascelles also gave evidence, not challenged, that the "rock faced batters" were not necessary to retain the compacted fill in place. 47 Witnesses who inspected the site after the collapse (including Mr Knox and Mr Sherrard, whose inspections were soon after the collapse) did not identify any material that was clearly rock facing, but in the period from 1961 to 1998 the whole area between the car park and the retaining wall was overgrown with vegetation, and any initial rock facing may well not have been obvious in either the collapsed or the stable areas of the land. 48 The defendant submits that as the works required council approval, there is every reason to infer that they were either inspected or certified. I am prepared to make that inference, and the inference (coupled with the evidence of Mr Lascelles) leads me to conclude on balance that his requirements for the fill to be rock faced were complied with by the builder. If I had been unable to reach this conclusion, the onus would still have been on the plaintiff will have been to prove, as she puts it, "culpable conduct" on the part of the defendant, and in the state of the evidence she has failed to prove any culpable conduct by failure to comply with Mr Lascelles drawing. 49 I agree with the plaintiff that there is no evidence that the defendant took any step, after the car park had been erected, to ensure that what had been done did not impose any additional load on the retaining wall. I infer, however, that having engaged a competent engineer and builder to do the job, which required Council approval, they relied on the engineer and builder to produce work that was reasonably safe and to satisfy Council's requirements. Removal of vegetation 50 The plaintiff gave evidence that, when she first moved into her property, there were trees and vegetation on the defendant's land adjacent to the retaining wall boundary. She said the trees and vegetation were so dense she could not see the car park from the rear of her house. While she could not recall the number of trees, she recalled that there were poplars, pines, a ficus and a palm and other vegetation. 51 According to the plaintiff, over the years of her occupation of her house, a number of trees and some vegetation were removed from the defendant's land above the retaining wall, including a poplar and a pine. She was unable to specify when this occurred, but it was several years before 1998. The consequence was that for some years prior to August 1998, the car park was visible from the rear of her house, according to her evidence. 52 The plaintiff's daughter Amy lived at the plaintiff's property until late 1991. In approximately 1983 she moved from the house to the cottage. Her evidence was that when she was a child, the land immediately above the wall was densely covered in vegetation, undergrowth and trees. She said that she could not see the car park from the rear of her mother's property. However, she said she remembered that over time, trees were removed and vegetation thinned out so that the car park became visible from her mother's property. 53 Before the collapse of the wall in August 1998, the top of the wall was covered with honeysuckle, lantana, ivy and other weeds and vines. The plaintiff gave evidence that this vegetation would constantly grow over the wall and down into her property. Approximately twice each year, she said, she would try to clear as much of the growth as she could from the wall. She was sometimes assisted by her daughter Amy, and after Amy's marriage, her husband. Amy's evidence corroborated the plaintiff's evidence on these points. 54 The plaintiff gave evidence that from the late 1970s onwards, she rang the office manager of the defendant at least once per year requesting him to clear the weeds which were growing on to her property. She said on one occasion in about 1979 or 1980 the vegetation, over a very short time, had grown across the roof of the cottage and into the chimney pot. 55 She said that, at the time of collapse of the wall, there remained only some vegetation, the ficus (located near the car park), two other trees, and a pine and a smaller tree both of which fell onto the cottage. As I have said, photographic evidence shows a pine tree and another smaller tree lying horizontally across the remains of the retaining wall and onto the roof of the cottage. 56 The evidence of the plaintiff and her daughter was contradicted to a degree, by the evidence of Mr John Wood, a director of the defendant. He has lived in a residential home unit in the defendant's building since 1977, facing over the car park. He said in his affidavit that as far as he could recall, during the period of his residence the vegetation between the car park and the retaining wall consisted of vines, grasses and weeds in the nature of ground cover and a few trees, and that he was not aware of the removal of any trees. His oral evidence was not entirely consistent with his affidavit, because he said that he became aware of the nature of the ground cover to the west of the carport only around 1996/97. This suggests that he did not pay much attention to the vegetation near the car park, and consequently that his evidence of unawareness of the removal of trees should not be given great weight. 57 He inspected the defendant's files and said there was no record of any complaint by the plaintiff concerning the presence of plants on or near the retaining wall, and he was unaware of any such complaint. There are some minutes of meetings of the defendant's directors at which the pruning and removal of trees were discussed, but they do not indicate whether the trees were in the vicinity of the car park. 58 On 12 July 1991 Woollahra Council issued a Tree Preservation Order authorising the lopping or removal of two pines and the trimming of a poplar located at the rear of the carport. The conditions of the consent noted that two umbrella trees and two pines appeared to be poisoned, and that a poplar behind the carport was dead. The Council required removal of dead wood from jacaranda trees and wattle. On 25 October 1991 the Council issued another order authorising the removal of a poplar located at the rear of the carport. Mr Wood said he had no recollection whether the works authorised by the Council were in fact performed, and that he was not aware of the removal of any trees or vegetation from the area between the car park and the retaining wall. 59 The evidence of the plaintiff and her daughter is rather unspecific and unclear, and yet it seems to me probable, on balance, that some trees were removed from the defendant's land between the car park and the retaining wall during the period from 1980 to 1998, as they say. The important questions are: when did this occur, and how many trees were removed? It does not appear that any trees were removed in the second half of the 1990s, for if they were, the plaintiff and Mr Wood should have been able to give more specific evidence of those events. 60 On the scant evidence available, it seems to me appropriate to infer that the poplar tree and some dead trees were removed in 1991 in accordance with Council's orders, and that these are the events recollected by the plaintiff and her daughter. The evidence does not permit me to find that trees were removed at any other time, although in response to the plaintiff's complaints, it is likely that the defendant thinned the vegetation occasionally. Nor does the evidence permit me to find that the roots of trees were wholly removed. That is of some significance, because of the binding effect of trees, according to the expert evidence, is produced by the size and complexity of the root formation. 61 I should note that there is no evidence that the plaintiff complained to the defendant about the removal of the trees, or expressed concern about the affect their removal may have on the stability of the embankment. The plaintiff's maintenance of the retaining wall 62 The plaintiff gave evidence that approximately twice per year, usually when she was clearing the vegetation that had grown over the wall, she cleared the weep holes by inserting her garden fork into each hole and removing any dirt or other material. She said that on occasions the holes would be partly filled with a black, soft, fungus-like material which was easy to remove with her fork. On occasions there would be tiny ferns growing out of the holes, which she also removed. She says she never saw any evidence of the mortar in the wall crumbling, nor any cracks in the wall. The evidence of the plaintiff's daughter Amy corroborated the plaintiff's evidence on these points. 63 Mr Knox, who inspected the site on 10 August 1998 after the wall had collapsed, said that weep holes, if they existed in the collapsed section of the wall, may possibly have been blocked and insufficient to cope with the amount of saturation contained in the ground. Mr Sherrard, whose report dated 28 August 1998 followed an inspection, observed only one weep hole in the remaining part of the wall and said it appeared to be partially blocked by a bituminous substance. 64 The plaintiff's evidence that she occasionally cleaned the weep holes of a black substance is consistent with Mr Sherrard's evidence that he observed a weep hole partially blocked by a bituminous substance. I accept the plaintiff's evidence on this subject. Dr Barda accepted that if the weep holes were blocked, rainfall would have "tanked" behind the wall, and it was likely that the weep holes were blocked. His evidence does not mean, however, that the plaintiff failed to do what she could reasonably do to keep the weep holes clear. The wall was quite thick at the level of the weep holes, and it would be unreasonable to expect that the full length of the weep holes would be regularly cleared, and unlikely according to Dr Barda that if they were, the wall would have survived. 65 Dr Barda accepted that lime mortar powder would have been visible on the wall when it was dry, and Mr Knox gave evidence that if the wall was being progressively moved by natural forces, then it would have bowed and this would have been visible. However, there is no evidence that the plaintiff or her daughter saw anything to cause apprehension. I do not accept that there was anything observable to suggest that the wall was in decay. Causes of collapse of the retaining wall 66 In his report dated 15 June 1999, based on an inspection shortly before that time, Dr Barda expressed the view that a large section of the defendant's property had undergone a substantial slip that had been responsible for the collapse of the retaining wall: "The collapse of the wall has resulted from a build up of soil pressure that has probably been aggravated by the presence of water in the subsoil." 67 He said it was impossible to ascertain the cause of the landslip, but that there was a possibility that the landslip had resulted from additional fill being placed on the defendant's property following the construction of the parking area. He recommended a search of Council's records to ascertain the state of the property prior to the construction of the parking area. 68 Dr Barda inspected the property again and wrote a report dated 30 March 2000, after reading the report by Mr Hawkins dated 23 March 2000. He adhered to his view that the collapse of the wall was caused by the movement of fill material placed on the defendant's land at the time of construction of the parking area. He said the effect of the fill was less significant at the northern end of the wall because the horizontal distance between the fill and the wall was greater, but at the southern end the fill was quite close to the wall and its effect was much more significant. Groundwater had a contributing effect to the collapse of the wall, and water penetration of the fill material saturated it and increased pressure, but the effects of groundwater and soil saturation alone would not be enough to cause the collapse. He noted that vegetation in the area of the fill material had the effect of binding the fill with roots, and absorbing groundwater, and so the removal of significant trees prior to August 1998 would have contributed to the collapse of the wall. 69 I have found Dr Barda's evidence as to the cause of the collapse of the wall to be unconvincing. He did not inspect the site until about 10 months after the collapse of the wall, and seems to have approached the problem with a preconceived idea of the cause. I say this because, in his first report, he asserted categorically that the collapse was caused by a landslip and that the presence of water was only an aggravating factor, without advancing any reasons for that view. Moreover, he said that there was a possibility that the landslip resulted from additional fill being placed by the defendant on its property following construction of the parking area, without having searched Council's records. 70 His second report was an attempt to justify the conclusions in his first report. Both reports, and his oral evidence, gave me the impression that his opinion was intended to assist the plaintiff and to support a theory of causation that she or her advisers had put to him. He did not satisfactorily explain why, if the movement of fill material caused the wall to collapse, it collapsed near the northern end as well as at the southern end. His explanation of the cause seems to me inconsistent with the fact that the centre segment of the wall moved laterally rather than toppling over. Further, his conclusions in his two reports are inconsistent with the joint view to which he subscribed, in a report dated 13 June 2000 (noted below). 71 Mr Hawkins and his colleague, Mr Yip, wrote a report dated 23 March 2000. The report was based on several site visits during the period from 11 June 1999 to 17 January 2000. They expressed the opinion that the failure of the brick retaining wall should be attributed to: (a) the presence of additional surcharge loadings on the wall due to the close proximity of the fill and carport structures on the defendant's land; (b) the heavy rainfall on and before the day of collapse, causing the fill material to increase in moisture content (possibly becoming saturated), which further increased the potential for surcharge loading on the wall; (c) the apparently poor or non-existent drainage system at the fill batter and behind the retaining wall; and (d) removal of a number of significant trees from the fill batter in recent years. 72 They calculated that any fill placed within two metres behind the face of the wall was likely to have acted as a surcharge load on the wall, resulting in additional lateral pressure. They also calculated that if fill were placed directly behind the wall it would increase the lateral pressure on the wall by more than 100%. For the fill to be more than two metres from the wall at the southern end, the batter would have had to be placed at an angle of approximately 58 degrees. Instability of the batter surface, and slumping of the batter, would be very likely, particularly when water was introduced into the slope. 73 Mr Hawkins gave oral evidence, and was cross-examined on some correspondence between him and the plaintiff's solicitor. It appeared to me, observing him in the witness box and reading that correspondence, that Mr Hawkins did not properly understand his role as an expert witness, even though he read the Expert Witness Code of Conduct. He saw himself as briefed to develop the plaintiff's case that the collapse of the wall was the defendant's fault. He put forward several ideas as to the possible cause of the collapse, and then selected and advocated the one that seemed most plausible. He did not observe substantial fill material during his inspections, the earliest of which was in any event more than 10 months after the wall had collapsed. He did not take into account Mr Knox's observation that filling material evident above the natural ground material may only have been of minimum depth. 74 Mr Hawkins was reluctant to spell out the contribution that the fill material may have had to the collapse of the wall. I was left with the impression that both Mr Hawkins and Dr Barda regarded the fill material as contributing to the failure in a "scientific" sense - that is, as a mass theoretically capable of adding a lateral loading. Supporting this conclusion is Dr Barda's acknowledgement in cross-examination that 10 kilos of lawn clippings would be considered a surcharge. 75 Overall, I accept Mr Hawkins' calculations as to the lateral pressure created by the deposit of fill material in the vicinity of the wall, but I do not accept some of his factual assumptions. Specifically, I do not accept that a quantity of fill material sufficient to create any significant lateral pressure was placed within two metres of the wall, for the reasons I have already given (relying in particular on the evidence of Mr Lascelles). Moreover, his assertions about poor drainage of the fill batter and the removal of trees in recent years are contrary to my findings on these matters. 76 Mr Knox's conclusion, in his report dated 21 August 1998, was that the wall failed as a result of the hydrostatic pressure build up behind it, due to the wet period around the time of the collapse, resulting in lateral forces greater than expected of the wall during its design life. Mr Knox said the weep holes, if they were provided in the portion of the wall that had collapsed, may possibly have been blocked and insufficient to withstand the amount of saturation contained in the ground. I find his observations to be plausible. 77 Mr Sherrard, reporting to the insurer on 28 August 1998, expressed the opinion that the fill material on the defendant's property had moved but there had been no general landslip. In his view, the wall collapsed due to a build up of hydraulic pressure behind the wall during the extended period of wet weather being experienced in Sydney during the previous months. The hydraulic pressure moved the wall forward and it fell off the rock shelf on which it had been constructed. He said it was likely that the fill on the slope behind the wall "contributed to the overturning forces on the wall" and was thus a contributing factor to the collapse. I find Mr Sherrard's observations as to the cause of the collapse to be plausible, except that in view of the evidence of Mr Lascelles, to treat the fill material as a "contributing factor" to the collapse is to overstate its effect. Mr Sherrard did not consider the stabilising effect of the stone buttressing at the southern end. 78 Expert evidence was given on behalf of the defendant by Mr Rick Pilz, a principal structural engineer at Gutteridge Haskins & Davey Pty Ltd. His first report, giving answers to specific questions asked by the defendant's solicitors, was dated 25 May 2000. His second report, though undated, was approved for issue on 21 June 2001. He first inspected the site on 1 February 2000, and he relied on information contained in other reports. 79 He identified four contributing factors to the collapse of the wall. The first and most significant was the structural inadequacy of the wall. He said that the wall had both insufficient overturning stability and insufficient sliding resistance. The second factor, which he also regarded as very significant, was the storm event on 7 August 1998. He said that the hydrostatic force imposed on the wall during the lengthy period of heavy rainfall was the trigger for the wall's failure at that time. Thirdly, he drew attention to the inadequacy of drainage through the wall, either because of insufficient weep holes, or their blockage. 80 Fourthly, he said that fill material placed within the "zone of influence" of the wall when the car park was constructed could have contributed to the failure. In his first report he said that the lateral soil pressure to the retaining wall was increased by the fill material, and therefore would have been a "contributing factor", but the increase would have been relatively small and localised towards the southern end and therefore the placing of fill material on the land could not be referred to as the cause of the wall's collapse. In his second report he said that, having regard to the inadequacies of design and of drainage through the wall, the wall would be likely to have collapsed even without the fill material. His opinion, based on the drawing prepared by Smith & Lascelles, was that the fill material that the northern end was remote enough from the retaining wall that it was unlikely to have any effect, but at the southern end it may have been placed close to the wall and may have increased the lateral loading. He noted, however, that it appeared that the fill material was placed in proximity to an intersecting stone buttress which would have improved stability at that point. 81 In his first report, Mr Pilz said that in his opinion, removal of a number of significant trees was not likely to have been a contributing factor to the failure of the wall, although removal of trees could lead to local slumping of the batter slope, transporting the fill material closer to the retaining wall and thus increasing lateral pressures. 82 Mr Pilz did not inspect the site until well after the collapse, but it is clear from his reports that he reviewed in a comprehensive fashion the observations and work of other experts. His views are consistent with the views of Mr Lascelles. I accept his evidence. 83 As a result of directions made by the Court on 26 May 2000, Dr Barda, Mr Pilz and Mr Hawkins met on the site on 13 June 2000, and each of them signed a brief joint report consequent upon the meeting. The joint report is not particularly informative, because it represents a "lowest common denominator" of the experts' views, especially on the significance of the fill material. The experts said that while the construction of the wall was theoretically inadequate, the fact that the wall stood up for a period of 80 years indicated that it was behaving in a marginally adequate manner. They agreed that the addition of the fill material associated with construction of the car park locally increased the lateral forces applied to the wall and would have "aggravated the marginal condition" of the state of the wall. They observed that "the predominant cause of failure of the wall was the increase in ground water flow, which resulting from the unusually intense storm period preceding the collapse". The joint report did not say whether the increase in lateral forces caused by the fill material was negligible (as Mr Lascelles said) or was a contributing factor (as Mr Sherrard said). Nor did it consider the effect of the stone buttressing at the southern end. 84 All the experts agree that the increase in the hydrostatic pressure to the wall after heavy rainfall was a very significant causal element. Hydrostatic pressure applied at the base of the wall provides a plausible explanation for the lateral movement of the wall off the rock shelf. The experts also agree that there were other causal factors at work. I find that both of those propositions are true. Once there was a build up of hydrostatic pressure, water could not drain away because of inadequacies in the design of the wall and the inefficient operation of the weep holes. There is no specific explanation for the fact that for more than 70 years after the construction of the wall, and 37 years after the work on the car park, the wall remained standing, notwithstanding many storms comparable to the one that occurred on 7 August 1998. However, that does not destroy the plausibility of the view that the hydrostatic pressure created by storm water on 7 August 1998 was the predominant cause of the collapse - the collapse of a wall which, by then, was over 70 years old. There is some evidence that the wall may possibly have collapsed within the ensuing 24 hours in any case, irrespective of the presence of fill or other postulated causes. 85 Counsel for the plaintiff made numerous submissions on the significance of the fill material. First, counsel invited me to infer that the fill material substantially surcharged the wall at its southern end. He referred to the evidence of Dr Barda, which I accept, that the natural angle of repose of sand is about 26-30 degrees, while noting that according to Mr Hawkins' report of 23 March 2000, the necessary batter of the fill material if placed so as not to surcharge the wall would be 58 degrees. He invited me to infer that, if the fill material was placed at that sharp angle initially, it would inevitably have slipped towards its natural angle of repose and thus moved to the wall. But I am not prepared to make that inference, given my findings as to compliance with Mr Lascelles' plans and directions and the probability, therefore, that the fill was "good clean fill" tightly compacted and supported by rock facing. 86 Counsel said that if the fill material had been compacted or rammed when it was deposited, this would have spread it. But as counsel for the defendant submitted, this amounted to giving evidence (indeed, not particularly plausible evidence) from the bar table. In any event, it is far from self-evident that ramming would cause the fill to spread rather than to compact into a smaller space. 87 In the course of cross-examination and in submissions, counsel for the plaintiff developed two theories about the significance of the fill material to the collapse of the wall. Perhaps under the influence of the engineering experts, we adopted quasi-scientific labels for the theories, calling them the dynamic theory and the static theory. 88 According to the dynamic theory, moments prior to the failure of the wall, a significant quantity of the fill material, then saturated with rainwater, slumped toward the wall and thereby suddenly and substantially increased the lateral loading on the wall. There is no direct evidence that such an event occurred. Dr Barda described the proposition as theoretical. Mr Knox and Mr Pilz pointed out that since the natural ground level sloped to the wall, if the fill had moved it would simply have fallen over the top of the wall. The theory is not compatible with the observed fact that the wall (or at least the centre segment) moved laterally at its base, rather than toppling over through the application of pressure at its top. Mr Pilz agreed in cross-examination that saturation of uncompacted fill can be a factor leading to its slumping and that the removal of vegetation (by which he meant removal of the root system as well as the plant) is the removal of a stabilising factor. But this evidence falls far short of supporting the dynamic theory. My finding that the fill was deposited in accordance with Mr Lascelles' requirements adds to the unlikelihood of a slump occurring in the manner postulated by counsel. My conclusion is that the dynamic theory is implausible and I reject it. 89 According to the static theory, the fact that the fill material was not sufficiently retained and had no adequate diversionary drainage system meant that the saturation of the fill by rainwater would, of itself, increase materially the loading on the wall; and this would have been sufficient, even without slumping, to trigger the failure of the wall. Counsel points to the evidence of Mr Pilz that the wall had a margin of safety of less than 1, and therefore invites the Court to infer, although Mr Pilz was reluctant to concede the point, that the additional load required to cause the wall to collapse was relatively small. I am prepared to accept that, because of design inadequacies in the wall, the margin of safety was low. It does not follow, however, that the presence of fill material was a significant causal factor. In my opinion the fill material deposited on the defendant's land in 1960/1961 was not a significant causal factor, in light of the opinions of Mr Lascelles and Mr Pilz, even though it increased lateral forces to a minor or negligible extent towards the southern end of the wall. 90 Further, in my opinion the removal of the poplar and dead trees in 1991 was not a causal factor, having regard to the presence of other vegetation to bind the soil and fill material, the limited number of trees involved, and the expert opinion of Mr Pilz. Leakey's case 91 In support of her claim for an injunction and damages, the plaintiff invokes Leakey v National Trust. In that case the National Trust owned land called "Burrow Mump", a conical hill rising steeply from the Somerset plain. The home of Mr and Mrs Leakey was at the base of the hill. The hill was unstable and prone to slip, although nothing had been done by the National Trust to affect that propensity. From time to time minor landslides deposited material on the Leakeys' property, and they complained to the National Trust, which did not act. Since at least 1968, the National Trust appreciated that the bank of the hill adjacent to the Leakeys' property belonged to the Trust and was a threat to the houses below it. 92 After a hot, dry summer in 1976 followed by an unusually wet autumn, a large crack opened up in the bank and Mrs Leakey drew the National Trust's attention to it, but they declined to do anything about it. A few weeks later, there was a large fall of the bank causing extensive damage to the Leakeys' property. The estimated cost of clearance and protective works was substantial. 93 Mr and Mrs Leakey took proceedings for injunctions to prevent the National Trust from permitting its earth to move onto their property and to require the Trust to remove the material that had already fallen. They also sought damages for nuisance. They sought and obtained an interlocutory injunction, on their undertaking as to damages, which had the effect of requiring the National Trust to take steps to prevent earth from moving from Burrow Mump onto the Leakeys' property. That work having been done by the Trust before the final hearing, it appears that Mr and Mrs Leakey sought only damages by way of final relief, and they were successful. 94 Prior to Leakey's case, it had been thought that in English law, neither the owner nor the occupier of land from which, solely as a result of natural causes, natural mineral material encroached on to, or threatened to encroach on to, adjoining land, causing damage, was under any liability to the adjoining landowner. A dictum of Lord Cairns LC in Rylands v Fletcher (1868) LR 3 HL 330, 338, was thought to have this effect. But the proposition had been eloquently criticised by Professor A L Goodhart ("Liability for Things Naturally on the Land", (1930) 4 CLJ 13), and there were some cases (cited by Megaw LJ in Leakey's case) that had reached results inconsistent with the proposition. 95 In Sedleigh-Denfield v O'Callaghan [1940] AC 880 a local authority trespassed on the defendant's land and placed a culvert in a ditch on the land. The culvert was improperly constructed and created a danger of flooding onto the plaintiff's land. Subsequently the defendant came to know what had been done, and should have realised the risk of flooding to the plaintiff's land, but he did nothing. The plaintiff's land was damaged by a flood, and the House of Lords (speaking after the development of the law of negligence in Donoghue v Stevenson [1932] AC 562) held that the defendant was liable to pay damages. While the defendant had not done anything amounting to an unnatural user of his land and had not brought anything unnatural onto his land, he knew of the risk of flooding and had a duty to use reasonable care to prevent it. 96 Sedleigh-Denfield was not a case in which the damage to the plaintiff's land had been brought about by natural causes, but (as Megaw LJ pointed out in Leakey's at 517) the whole tenor of the speeches in the House of Lords suggested that in their Lordships' opinion, the same duty of care would have arisen if the condition had been brought about by natural causes. The High Court of Australia and the Privy Council applied the Sedleigh-Denfield principle to a case where the risk of damage arose out of natural causes, in Goldman v Hargrave [1967] AC 645 (Privy Council); (1963) 110 CLR 40 (High Court). There a tall tree on the defendant's land was struck by lightning and caught fire. The defendant cleared a space around the tree and sprayed the surrounding area with water to prevent the fire from spreading, and on the next day, the tree was cut down and the defendant left it to burn itself out. He did nothing else to prevent the fire from spreading on his land and to adjoining land. Two days later, the weather changed and a hot wind revived the fire and spread it onto the plaintiff's property. The Supreme Court of Western Australia held that the defendant was not liable to compensate the plaintiff, because he owed no duty to the plaintiff to extinguish the fire, which had been ignited and had spread through natural causes. The High Court allowed the plaintiff's appeal, holding that after he arranged for the tree to be cut down, the defendant had a duty to use reasonable care to prevent it causing damage to his neighbours. The Privy Council agreed. 97 Their Lordships expressly rejected the suggested distinction between risks originating from natural and "non-natural" causes. They said (at 661): "It was suggested as a logical basis for the distinction that in the case of a hazard originating in an act of man, an occupier who fails to deal with it can be said to be using his land in a manner detrimental to his neighbour and so to be within the classic field of responsibility in nuisance, whereas this cannot be said when the hazard originates without human action so long at least as the occupier merely abstains. The fallacy of this argument is that, as already explained, the basis of the occupier's liability lies not in the use of his land: in the absence of "adoption" there is no such use; but in the neglect of action in the face of something which may damage his neighbour. To this, the suggested distinction is irrelevant." 98 In Leakey's case the English Court of Appeal chose to follow Goldman v Hargrave even though the decision of the Privy Council was not strictly binding on it. The Court held that the National Trust owed a duty of care to Mr and Mrs Leakey in relation to the hazard constituted by the propensity of the earth on Burrow Mump to slip onto their land. Since the Trust was well aware of the propensity of the earth to slip, it had a duty to take such steps as were reasonable in all the circumstances to prevent or minimise the risk of injury or damage to Mr and Mrs Leakey and their property. As to the scope of the duty, Megaw LJ said (at 524): "The duty is a duty to do that which is reasonable in all the circumstances, and no more than what, if anything, is reasonable, to prevent or minimise the known risk of damage or injury to one's neighbour or to his property. The considerations with which the law is familiar are all to be taken into account in deciding whether there has been a breach of duty, and, if so, what that breach is, and whether it is causative of the damage in respect of which the claim is made. Thus, there will fall to be considered the extent of the risk; what, so far as reasonably can be foreseen, are the chances that anything untoward will happen or that any damage will be caused? What is to be foreseen as to the possible extent of the damage if the risk becomes a reality? Is it practicable to prevent, or to minimise, the happening of any damage? If it is practicable, how simple or how difficult are the measures which could be taken, how much and how lengthy work do they involve, and what is the probable cost of such works? Was there sufficient time for preventive action to have been taken, by persons acting reasonably in relation to the known risk, between the time when it became known to, or should have been realised by, the defendant, and the time when the damage occurred? Factors such as these, so far as they apply in a particular case, fall to be weighed in deciding whether the defendant's duty of care requires, or required, him to do anything, and, if so, what." 99 Counsel for the plaintiff in the present case submitted that Leakey's case reflects Australian law. He was not able to cite any Australian case in which Leakey's case had been applied, but he referred to Morgan v Lake Macquarie City Council (New South Wales Court of Appeal, unreported, 2 September 1993) in which Clarke JA assumed that a cause of action based upon Goldman v Hargrave and Leakey's case was soundly based in law, and Gunnedah Shire Council v Hansen (Supreme Court of New South Wales, Powell J, unreported, 12 August 1993) in which his Honour referred to Leakey's case but did not deal with the general principle upheld by the English Court of Appeal. Despite the absence of direct authority, I have no doubt that the principle in Leakey's case would be applied in this country, since Leakey's case in turn is an application to English law of the principles of Australian law enunciated by the High Court and Privy Council in Goldman v Hargrave. 100 The plaintiff also refers to some earlier cases bearing factual analogies with the circumstances of the present case: Broder v Saillard (1876) LR 2 Ch 692; Wilkins v Leighton [1932] 2 Ch 106. These cases were decided before the Sedleigh-Denton, Goldman and Leakey cases, and it would not be safe to regard them as reflecting the modern law. 101 The plaintiff seeks to apply Leakey's case to the present facts in two ways. First, she relies on Leakey's case to support her claim for a mandatory injunction, and secondly, she relies on the case to support her claim for damages for nuisance. The mandatory injunction to restrain future slippage 102 I agree with the plaintiff that the evidence establishes that, as at the time of the hearing: (a) if soil on the defendant's land is not retained, it will subside onto the plaintiff's property; (b) there is no effective retention of the defendant's land at the boundary with the plaintiff's property; (c) the cost of retaining the defendant's land to prevent further subsidence onto the plaintiff's property is materially less than the value of the plaintiff's land (there being some evidence that the plaintiff's property is worth over $1 million); (d) therefore it is reasonable that steps be taken so that the soil on the defendant's land is properly retained; and (e) by some means and by some person, an effective mode of retention must be provided. 103 The defendant submitted that the plaintiff had not discharged her burden of adducing clear evidence of the extent of the risk of future damage. I agree that the evidence is not overwhelmingly clear, but there is enough in the plaintiff's case to demonstrate, as I have found, that if the material now lying on the plaintiff's property is removed there will be a real risk that substantial quantities of earth and other material will fall from the defendant's to the plaintiff's land, either gradually or by landslip, and so it is necessary for the defendant's land to be artificially supported in order to avoid that risk. 104 However, it does not necessarily follow from the plaintiff's propositions that the defendant should bear the responsibility for solving the problem. Nor does it follow that the problem should be solved by curial intervention, as opposed to co-operation of the landowners, or perhaps some form of self-help, or administrative intervention by Woollahra Council pursuant to its powers under s 121B of the Environmental Planning and Assessment Act 1979 (NSW). The plaintiff makes her case for curial intervention by relying on Leakey's case. 105 I agree with the plaintiff that the principle in Leakey's case is not confined to damages for past wrongdoing. The case supports the proposition that a landowner in occupation of his land has a duty, when he is aware or ought to be aware of a hazardous condition on the land which puts the neighbouring land at risk, to take such steps as are reasonable in all the circumstances to prevent or minimise the risk of injury or damage to the neighbour's property. In an appropriate case, the duty may be enforced by a mandatory quia timet injunction, available on general equitable principles. 106 The defendant purported to distinguish Leakey's case partly on the ground that Leakey does not concern future loss in the law of nuisance. The defendant pointed out that a mandatory quia timet injunction was refused by the trial judge ([1978] QB 849) and there was no appeal from that refusal. However, it was relevant to the trial judge's decision that by the time of the final hearing, an interlocutory injunction of a mandatory character had been granted and complied with by the National Trust: see [1980] 1 QB 485, 511. There is no reason to believe that their Lordships intended to recognise a duty to prevent or minimise the risk of injury in the stated circumstances, but to prevent specific enforcement of the duty. Given that interlocutory specific relief was ordered and there was no criticism of that order in the Court of Appeal, Leakey's case supports the view that injunctive relief is available to vindicate the duty, provided of course that equitable discretionary considerations favour the granting of such relief in the instant case. 107 In my opinion, however, the principle in Leakey's case does not lead to the conclusion that in the present case, the defendant has a duty to take all necessary steps at its own expense to retain its land, after the collapse of the retaining wall. There is an analogy with Leakey's case, in that in the present case the defendant's land now overhangs the plaintiff's land and there is a real risk of slippage and consequently further damage to the plaintiff. But the present state of affairs has arisen because of the collapse of the retaining wall, which retained the defendant's land adequately for the whole of the time that the defendant and the plaintiff had been owners and occupiers of their respective properties, until August 1998. The retaining wall was not, as I have said, wholly on the defendant's land. It benefited the defendant by retaining the defendant's soil, and it benefited the plaintiff by maximising the plaintiff's use of her land and protecting the plaintiff from landslip. The problem has arisen because the wall is no longer there to confer these mutual benefits. 108 These considerations suggest that while the defendant has a relevant duty under the Leakey principle, it is not a duty to replace the retaining wall or otherwise retain its land wholly at its own expense. As Megaw LJ said (at 524) in the passage quoted above, it is a duty to do that which is reasonable in the circumstances, and no more or less than that. Citing a passage from the Privy Council's advice in Goldman v Hargrave, his Lordship contemplated (525) that where the hazard arises on a small parcel of land, threatening a neighbour with substantial interests, the owner of the small property should not have to do so much as one with larger interests of his own at stake and greater resources to protect them: if the small owner does what he can and promptly calls on his neighbour to provide additional resources, he may be held to have done his duty. In my opinion those observations, while not directly applicable to the present case, suggest that in an appropriate case the landowner's duty may be to contribute to the cost of remedial work, rather than to pay the whole of the cost. In my opinion this is such case. Here the defendant's duty with respect to the risk of further landslip might be discharged by contributing an appropriate portion to the cost of remedial work, and by allowing access to contractors so that the work can be carried out. 109 Therefore, in my view the plaintiff is not entitled to the mandatory quia timet injunction that she seeks, because the defendant has no duty to carry out the whole of the remedial work alone. Even if the law as stated in Leakey's case required me to recognise such a duty, I would decline for discretionary reasons to make the mandatory order that the plaintiff seeks. The leading authority on final mandatory injunctions is Redland Bricks Ltd v Morris [1970] AC 652 (cf Lawlor v Johnston [1905] VLR 714). The Redland Bricks case indicates that the granting of a mandatory injunction is always a discretionary matter (at 655 for Lord Upjohn). 110 Dr IC F Spry, Equitable Remedies (5th ed, pp 539 and 540) describes the general discretionary considerations in this way: "… on applications for mandatory injunctions it sometimes appears that the making of an order against the defendant will cause him very great expense or inconvenience and that matters of this nature may be of considerable weight in inducing the court to confine the plaintiff to damages, in accordance with the general equitable principles in reference to which the balance of justice is determined." "… it must appear that in all the circumstances, and particularly in view of equitable considerations such as laches and hardship and inconvenience as between the parties, that the most just course is that the particular injunction that is sought should be granted." 111 The defendant contends that the court would not make a mandatory order because the parties are obliged to comply with notices issued by Woollahra Council. I am not persuaded that the existence of orders by the Council should itself prevent the court from issuing an injunction in an appropriate case. Nor am I persuaded by the defendant's submissions that the anticipated harm to the plaintiff may not eventuate as forecast and if it does, it may be far less grave than forecast. The plaintiff's use of her property, including the reinstatement of the cottage to produce an economic return, is likely to be seriously impeded unless remedial work is carried out. 112 However, there is another powerful consideration pointing against my making a mandatory order to compel the defendant to carry out remedial work wholly at its expense. To make a mandatory order in the present case would be to commit the defendant to very substantial expenditure which would disproportionately enrich the plaintiff. The old and substandard wall would, of necessity, be replaced by modern and effective retention works. Although there is no direct evidence on the point, it is plausible to infer that the value of the plaintiff's property would be enhanced by that work, at no cost to her. That consideration, in its context in the present case, would probably have led me to decline specific relief. 113 I have not been asked to make any order reflecting the defendant's duty to contribute an appropriate part of the cost of remedial work. Nor have I been asked to determine what an appropriate contribution would be. It seems to me desirable that I should express an opinion on the latter question, although it is not directly before me at this stage, because my doing so may assist the parties to reach a sensible resolution of their dispute, at long last. In my view it is unlikely that anything would be gained by making provision for further submissions on the subject, and it is highly unlikely that there is any relevant evidence, not presently before me, that would assist me on this matter. Therefore, bearing in mind that the defendant offered to pay half the cost of the preliminary remedial work and weighing up all the circumstances, I express the opinion that the defendant would have no duty to contribute more than one half of the reasonable total cost of remedial works. Damages for nuisance and negligence 114 The plaintiff accepted at the hearing that if the retaining wall failed solely because of the hydrostatic pressure produced by the rain, she cannot recover damages from the defendant for losses consequent upon the failure of the wall. In my opinion that is correct. Leakey's case is distinguishable because there is nothing in the evidence in the present case to suggest that the defendant knew or ought to have known that the plaintiff and her property were at risk of injury or damage through the collapse of the wall caused by heavy rain, and therefore it cannot be said that the defendant had any duty to take steps to prevent or minimise that risk. 115 The plaintiff submits that to recover damages for losses sustained in consequence of failure of the retaining wall, she must show that a material contributing cause of the failure of the wall was some unreasonable act or failure to act ("culpable conduct") on the part of the defendant. The plaintiff submits that it was not necessary to prove that the culpable conduct was the only cause or even the dominant cause of the loss, provided she proves that it was a material contributing cause of the loss. For those propositions counsel for the plaintiff relies on Goldman v Hargrave in the High Court, especially the judgment of Windeyer J, and Morgan v Lake Macquarie City Council, in which Clarke JA applied Windeyer J's judgment. The defendant submits that the plaintiff's formulation is incorrect in law. The law requires, in the defendant's submission, that the court must approach causation "by applying common sense to the facts of the case" (March v Stramare (1991) 171 CLR 706, at 509, 515 per Mason CJ, 523 per Deane J), and that the less demanding "but for" test is not the exclusive test of causation (Chapel v Hart (1998) 195 CLR 232, at 244 per McHugh J (dissenting on the facts)). 116 I agree with the defendant's careful submissions on causation, though I am not sure that the plaintiff's formulation is inconsistent with them. It is open to a court applying the March v Stramare test to hold that causation is established where the defendant's conduct materially contributed to the plaintiff's loss, even though there were other factors at work, provided that common sense supports this conclusion. However, on the view I take of the facts, it is unnecessary for me to decide whether there is any difference between the plaintiff's and defendant's formulations of the test of causation, and if there is, which is to be preferred. 117 The plaintiff's case against the defendant is as follows: (a) to place fill material on steeply sloping ground above her land and in relative proximity to the retaining wall was an inherently potentially dangerous (and therefore hazardous) activity; (b) therefore, to justify placing fill material on steeply sloping ground above her land and in relatively close proximity to the retaining wall required the defendant to take all reasonable care to ensure that such activity was undertaken safely; (c) all reasonable care in this context required both care at the time the fill was placed and care thereafter to ensure that the fill, if safely and securely placed initially, remained safely and securely placed thereafter; (d) the defendant did not take all reasonable care to ensure that the fill material was placed safely and securely in 1961; (e) the defendant did not take all reasonable care to ensure that the fill material remained safely and securely placed after 1961; and (f) the fill material was a contributing cause to the failure of the retaining wall. 118 In light of the findings of fact that I have made, the plaintiff's case falls down in three respects. First, the fill material added to the lateral forces on the wall only to a minor or negligible extent; secondly, by employing competent contractors to carry out the construction of the car park and associated works, and relying on their designs and advice, the defendant discharged its duty of care in 1961; and thirdly, the removal of trees from the defendant's land did not contribute to the collapse of the wall or constitute a failure to ensure that the fill material remained safe and secure. Findings as to defences 119 Since, in my view, the plaintiff has not made out her case in private nuisance or negligence, it is not strictly necessary for me to deal with the defences. However, my findings of fact imply conclusions which I shall set out for the sake of clarity. 120 It follows from my findings of fact that, in my view, the deposit by the defendant of fill material at the time of construction of the car park, and its subsequent use of the land between the car park and retaining wall, constituted a reasonable user of the land for the purposes of the law of nuisance. 121 In my view, nothing in the evidence supports the contention that the plaintiff voluntarily assumed the risk of the wall failing. There is no evidence that she had any appreciation of the inadequate design of the wall, and therefore no evidence that she had the requisite knowledge of the risk. Knowledge, probably actual knowledge, is a precondition to any agreement to accept the risk: Insurance Commissioner v Joyce (1948) 77 CLR 39, 57. 122 The defendant has not discharged its onus of proof of contributory negligence. I have found that there is no evidence that she observed any bowing or other deficiency in the wall (or, indeed, that there was any observable deficiency apart from some lime dusting when the wall was dry), and that she did what she reasonably could be expected to do in cleaning the weep holes. 123 As to the contention that the plaintiff failed to mitigate her loss by taking more active steps to safeguard the remnants of the cottage from further damage by the elements, the evidence of Mr Barros, and also the evidence of Mr Knox in cross-examination, is to the effect that the cottage was so damaged as to be beyond even partial salvage and reinstatement, and needed to be demolished. Mr Pilz expressed a contrary view. Regardless of whether part of the cottage could have been salvaged, the fact is that at the relevant time the plaintiff received apparently competent advice that the correct option was demolition, and it was not unreasonable for her to accept that advice and act on it. That being so, she had no duty to protect the remnants of the cottage from the elements. The cross-claim 124 As I have explained, the cross-claim is grounded in negligence, nuisance and the law of easements. 125 As to negligence, the defendant refers to s 177 (1), (2) and (9) of the Conveyancing Act 1919 (NSW). I should also note s 177 (11), invoked by the plaintiff. Those provisions are in the following terms: (1) For the purposes of the common law of negligence, a duty of care exists in relation to the right of support for land. (2) Accordingly, a person has a duty of care not to do anything on or in relation to land (the supporting land ) that removes the support provided by the supporting land to any other land (the supported land ). (9) Any action in negligence that is commenced after the commencement of this section in relation to the removal of the support provided by supporting land to supported land may be wholly or partly based on something that was done before the commencement of this section. However, this subsection does not operate to extend any period of limitation under the Limitation Act 1969. (11) This section does not apply in relation to any proceedings that were commenced before the commencement of this section." 126 The section was intended to remove doubt as to the existence of a duty of care in relation to the maintenance of lateral support of a neighbour's land. The effect of the section is to remove from consideration of the negligence claim, the highly artificial rules in nuisance which had developed out of the decision of the House of Lords in Dalton v Henry Angus & Co (1881) 6 App Cas 740: as to the old rules, see Kebewar Pty Ltd v Harkin (1987) 9 NSWLR 738, 741. In nuisance, a defendant's omission to maintain lateral support was not sufficient to establish liability. However, on ordinary principles of negligence, a defendant has an obligation to take reasonable care to prevent or reduce foreseeable injury caused by failure to maintain lateral support. 127 As counsel for the plaintiff has pointed out, the present proceeding commenced before the commencement of s 177. Strictly, therefore, the section does not apply. But the defendant says that the section reflects the preponderant view of lawyers before its enactment, and was only intended to remove doubt as to the correctness of that view. To resolve this issue, it would be necessary for me to decide whether the pervasive influence of the law of negligence had, before the commencement of s 177, asphyxiated yet another brace of older and more artificial rules, just as it has in so many other areas. 128 However, in my opinion it is unnecessary to make a decision on that point in the present case, because the facts do not support the defendant's claim in any event. 129 Any duty of care would depend upon the establishment of foreseeable injury, and therefore that the plaintiff was aware or ought to have been aware of the risk that the wall would collapse. I have found that the evidence does not support any such findings. 130 The cross-claim also relies on nuisance, seeking to turn Leakey's case (along with the Sedleigh-Denfield case and Goldman v Hargrave) against the plaintiff. However, it cannot be said, in view of my findings of fact, that the plaintiff failed to discharge any duty she may have had to take the steps reasonable in the circumstances to prevent or minimise the risk that the wall would collapse. 131 The third ground advanced in the cross-claim is that the defendant had an easement for support and that the plaintiff breached her obligations under the easement. The easement for support is said to have arisen by prescription, under the rule of the "lost modern grant". This raises two issues: first, whether such an easement by prescription may arise where title to the land in question is, as in the present case, held under the Real Property Act; and secondly, if the answer to the first question is in the affirmative, whether such an easement has arisen on the facts of the present case. 132 I regard the first of these two issues as the more difficult and uncertain. The defendant says that there is no direct or binding authority as to whether easements by prescription arising under the doctrine of lost modern grant are affected by the Real Property Act, noting that s 45C does not exclude such easements. The defendant refers to Delohery v Permanent Trustee Co of New South Wales (1904) 1 CLR 283, where Griffith CJ indicated in obiter dicta that the doctrine applied to Torrens land in New South Wales. In Dobbie v Davidson (1991) 23 NSWLR 625, the Court of Appeal of New South Wales held that there was no reason why a prescriptive easement acquired over land prior to its being brought under the Real Property Act should be extinguished by the issue of a certificate of title - but that is, of course, another case. 133 The plaintiff claims, categorically, that an easement affecting land, title to which is held under the Real Property Act, cannot be acquired by prescription, citing Australian Hi-If Publications Pty Ltd v Gel [1979] 2 NSWLR 618,622, and Kostos v Devitt [1979] ACLD 516. 134 In my opinion the cases relied upon by the plaintiff cannot support the categorical proposition which she asserts. I regard the question as an open one on the authorities. However, it is unnecessary for me to make a decision in this case because, in my view, if a right of support can arise by prescription in respect of Torrens title land, the requirements for such a right to arise are not satisfied here, for two reasons. First, since according to my findings the boundary between the plaintiff's and defendant's land ran through the retaining wall, so that the eastern face of the retaining wall was the property of the defendant, there was no actual support derived by the soil of the defendant's land from the plaintiff's land. The plaintiff believed, reasonably (see Anthony v Commonwealth (1973) 47 AJLR 83, 91), that the retaining wall was erected over the boundary so that part of it was the defendant's property. In such a case, the exercise of a right of support is not "open" (Richardson v Browning (1936) 31 Tas LR 78), and therefore no right of support could be acquired by the defendant against the plaintiff by prescription (Milne v James (1910) 13 CLR 168,178). 135 Moreover, it was not possible for the plaintiff to prevent the defendant from obtaining support from the retaining wall without unreasonable waste of labour and expense (Webb v Bird (1861) 10 CB (NS) 268, 238 [142 ER 455, 461]), for to do so would have involved demolishing the wall and so causing serious injury to the plaintiff's own property (Union Lighterage Co v London Graving Dock Co [1902] 2 Ch 557, 568). For this reason, too, the defendant cannot derive a right of support by prescription. Conclusion 136 The plaintiff has failed to make out any entitlement to relief (other than perhaps with respect to costs) on the grounds advanced in her further amended statement of claim. The defendant has failed to make out any of the claims for relief in its cross-claim (other than perhaps with respect to costs). I therefore intend in due course to dismiss the proceeding and the cross-claim, except with respect to costs, and arrange a time to hear submissions on costs. **********

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