O'Brien v Pittwater Council

(1) The catchment areas

1. Mrs O'Brien and Council each retained experts who prepared reports and plans indicating the catchment of Mrs O'Brien's land at various times. In each case they have assessed the catchment area of the rear boundary of Mrs O'Brien's property, and any water flowing onto the land from either side boundary has been ignored. Whether or not this approach is strictly correct, no party took issue with it and I propose to adopt it.

(a) The existing catchment

1. The experts agreed that the existing catchment area included 15 Norma Rd, as well as part of the two blocks immediately to the southwest of 15 Norma Rd (presumably 11 and 13 Norma Rd), and that the western boundary of the catchment area ran along the middle of Bynya Rd and Norma Rd. The north-eastern boundary of the existing catchment was likewise not the subject of significant disagreement.
2. The real areas of dispute concerned the northwest boundary of the existing catchment, near the corner of Bynya Rd and Cynthea Rd, and the easterly boundary including the extent to which lots 17 and 19 Norma Rd, and Norma Rd itself, formed part of the catchment.
3. During the course of a site visit at the trial, the expert retained by Mrs O'Brien, Dr Daniel Martens, accepted that there was a collection of rocks extending to the northeast of Mrs O'Brien's northern boundary which resulted in a significant part of numbers 17 and 19 Norma Rd falling within the catchment area. I also noted during that site visit that the westerly part of the rear of number 17 sloped toward the channel on number 15, and this ensured that water falling on that part of the land would reach the open drain and thus be within the catchment of Mrs O'Brien's land. I understood Dr Martens, by his subsequent drawings, to concede that the existing catchment included this area.
4. Mr Andrew Bewsher, the expert retained by Council, conceded that his assessment of the extent to which the catchment extended down Norma Rd was exaggerated.
5. In the result, there was ultimately little difference between the experts on the eastern extent of the existing catchment area. In my view, the dark blue line (Mr Bewsher's catchment) on the contour plan known as Figure 1 of Dr Martens' Second Statement of Evidence (Exhibit A, Tab 10) most accurately shows the existing catchment, save that the boundary shown on Norma Rd concluded before the driveway to number 19 Norma Rd, and extended no further down Norma Rd than the point where the dark blue line crossed the Norma Rd boundary of 17 Norma Rd.
6. The difference between the experts regarding the upper or north-western boundary of the existing catchment was more difficult to resolve. However, Mr Bewsher's larger area there added approximately the same amount to the catchment he determined as was added by Dr Martens in including additional parts of numbers 8 and 11 Norma Rd and the Norma Rd roadway, and thus, the total existing catchment areas determined by Mr Bewsher and Dr Martens did not differ significantly.
7. Accordingly, in my view, the square metre area of the existing catchment is that determined by Mr Bewsher, less a small amount of about 20m2 from the Norma Rd roadway. I thus accept the area of 1.47ha determined by Mr Bewsher (Exhibit 1, Mr Bewsher's report dated 29 February 2012 at [3.27]) to be the existing catchment. Dr Martens, at least initially, also assessed the existing catchment area to be 1.47ha (Exhibit C, Statement of Evidence of Dr Martens dated 19 November 2014 at [12.d]).
8. Mr Ralph Williams, another expert retained by Mrs O'Brien, estimated the existing catchment area to be 1.21ha (Exhibit C, Mr Williams' report dated 28 July 2011 at p2). The reasoning behind this conclusion is not clearly disclosed, and the annexures, Annexures C and D, he relied on do not appear to allow an accurate calculation. For that reason, I prefer the evidence of Mr Bewsher and Dr Martens on this issue. A lesser existing catchment area, it should be noted, would lessen the amount of water in a rainstorm that would currently impact Mrs O'Brien's land and thus would diminish any nuisance.
9. Accordingly, I conclude that the current catchment area is 1.47ha.

(b) The natural catchment

1. The differences between the parties as to the area of the natural catchment are more significant. Mr Williams assessed the "pre-development catchment area" to be "0.6 hectares" (Exhibit C, Mr Williams' report dated 28 July 2011 at p2). This opinion appears to be based on a hand drawn area by Mr Williams (see Exhibit C, Mr Williams' report dated 12 May 2008 at p4) which was based on a site inspection, although the method of calculation is not apparent.
2. Mr Bewsher calculated the natural conditions as producing a catchment area of 1.38ha (see Exhibit 1, Mr Bewsher's report dated 29 February 2012 at p13), which was based on analysis of a contour map and a site inspection.
3. Dr Martens used a flow path analysis derived from the contour map to calculate a catchment area of 0.43ha for natural conditions.

(i) The reliability of a contour map

1. As a tool to determine the catchment area, the contour maps used by the experts have limitations. These limitations were not disputed by the experts.
2. Firstly, the contours are drawn at 500mm intervals. Plainly, the direction water flows can be affected by differences in levels much smaller than half a metre. As a result, the direction water flows between the contours is not revealed by the contour maps.
3. Secondly, the contour maps have other inaccuracies. Rocky outcrops at the rear of 17 Norma Rd were not reflected on the contour maps, a matter Dr Martens conceded to be an inaccuracy. Nor is the open channel along the northeast side of 15 Norma Rd indicated by the contour plan. The contours appear to ignore houses and other man-made structures, which means they must only show approximate land levels where buildings and walls are located. Whether they reflect more modern landscaping is unclear. The slope of the land towards the channel on both its sides, both on 15 and 17 Norma Rd, is not reflected on the contour plan.
4. Thirdly, the contour maps result from drawing lines between points determined to be at the same level. There is necessarily a degree of interpolation between points, and the accuracy of the contour between those two points must be uncertain.
5. Fourthly, water flow can be impacted by vegetation and other objects on or connected to the ground, which are not indicated by the contour map. If water flow is affected, so also must be the catchment area.
6. Fifthly, the orthodox method of determining a catchment area from contours involves assuming water flows from a point on a contour line in a perpendicular direction to that line, and then flows perpendicular to the next contour. This assumption may work tolerably well, even perfectly, with a smooth surface with no obstacles and where the slope is constant between contours, and where the contours are accurate, but it is, at best, an unreliable approximation on a natural, rugged and uneven surface covered with rocks, ridges and vegetation. This is the nature of the land above Mrs O'Brien's property.
7. Sixthly, the catchment area itself may be affected by the level of the rainfall event. Fast running water may be unaffected by a small ridge. But a small ridge may, in lesser rainfall events, operate to redirect a smaller or slower flow of water.
8. Seventhly, contour maps created in recent years are less accurate in assessing a catchment area that existed decades ago. Excavation and the building of houses, driveways, gardens, walls, and roadways all impact on the catchment area, now and then. The contours appear to reflect, at least to some extent, a driveway on (presumably) number 10 Norma Rd opposite number 17, and also reflect Norma Rd itself. But as indicated above, it is unclear what if any other changes to the landscape are recorded by the contour plans. The result is that determining a catchment area in the 1950s or earlier from contour maps of the last decade must be inaccurate, even if some adjustment can be made for the location of roads.
9. At various stages of their evidence, each of the three experts conceded limitations or inaccuracies in the contour maps. In the joint report (Exhibit D, Joint Report of Hydrology Experts dated 5 July 2013, para 6), Mr Williams stated that the use of a contour survey to ascertain actual flow patterns was "not very accurate on steep and rocky terrain as these features can completely change flow paths."
10. For all these reasons, I conclude that the catchment area in the 1950s for Mrs O'Brien's land cannot accurately be determined from present day contour maps alone.

(ii) Other observations about the natural catchment area

1. Dr Martens' approach was to calculate the catchment area by the orthodox method where the water flow is assumed to be perpendicular to the contour. But this method was abandoned in several instances when determining the current catchment area, as his boundary of the existing catchment is on several occasions drawn parallel to, or close to parallel to, the contour (see green boundary in Figure 1, Tab 10, Exhibit A). This involves recognition of the limitations of the "perpendicular to the contour" rule when applying it to real terrain, especially rough terrain, or terrain with natural obstacles such as rocks and vegetation.
2. Secondly, Dr Martens accepted (Exhibit C, Dr Martens' Statement dated 19 November 2014, Figure 1) that the natural catchment included an area at the southern corner of 19 Norma Rd, which was subsequently, without explanation, not included by him in a more recent diagram (Exhibit A, Tab 10, Figures 1 and 2) for either the current or natural catchment. But at an onsite view and in oral evidence, Dr Martens accepted that an arrangement of rocks, extending about 6.5m along the lower border of 19 Norma Rd, currently directed water onto Mrs O'Brien's land, and, if it was natural, the natural flow of water would include some of the western part of 17 and 19 Norma Rd. This was Mr Bewsher's opinion of the natural catchment. There was a dispute about whether the arrangement of rocks was natural or artificial, but there was no suggestion that Council was responsible for it.
3. Thirdly, there was nothing in the observable levels of the rear yards of 15 and 17 Norma Rd which indicated that the rainfall at the rear of 15, and on the western side of the rear of 17 Norma Rd, would flow to a location other than beside, and immediately to the west of, the house at 19. This is the location where the Council drain currently directs water.
4. Fourthly, both Mr Bewsher and Dr Martens include the whole of the front boundary of 11 Norma Rd as within the current catchment (Exhibit A, Tab 10, Figure 1). Why half of that boundary is excluded by Dr Martens from the natural catchment (see Exhibit A, Tab 10, Figure 2 and Exhibit C, Dr Marten's Statement dated 19 November 2014, Figure 1) was not explained, other than that it was a product of the orthodox, perpendicular to the contour method of determining the direction of water flow.
5. For these reasons, including my concerns about the reliability of the contour maps in determining catchment areas, I am not satisfied that the natural catchment area determined by Dr Martens directly from the current contour maps is accurate.
6. Mr Bewsher also reviewed the contour maps. He also engaged in a process which he called "ground-truthing". This process involved a site assessment to check on conclusions indicated by the contours. While I think that some anomalies unrevealed by the contour plans may be detected from a careful site inspection, I do not think that visual observations of themselves would be a reliable guide to the extent of the natural catchment area, at least when rugged terrain is involved. Even after a view of the catchment area as part of the trial, differences remained in the natural catchment area drawn by Mr Williams and that drawn by Mr Bewsher, indicating that errors are not always corrected by a site inspection.
7. Although not strictly analogous, the problems may be illustrated by a professional golfer assessing the fall of a golf green. The golfer has the advantage of years of experience, a limited area of the green, and a smooth surface without obstacles. Yet minor gradients, and their impact on the path of a golf ball, are commonly undetected or misinterpreted. In my view, error is far more likely when visually assessing the impact of a significant area of uneven ground covered with vegetation and rocks on the flow of water.
8. Mr Bewsher called in aid site features - ridges, valleys, outcrops and the like - as support for his conclusion that a much larger natural catchment area existed. However, I was not persuaded that larger rock features observable from a distance fairly indicated the direction of water flow on the ground.
9. In the result, I was not persuaded that the natural catchment area below Norma Rd ("the lower catchment") substantially differed from the current lower catchment. At least, there did not seem to me to have been anything done by Council which increased the area of the existing lower catchment. In my view, doing the best I can, the natural lower catchment most closely resembles the area shown by Mr Bewsher, an area equivalent to the current lower catchment.
10. The relief sought by Mrs O'Brien, to block water flow from the area above Norma Rd ("the upper catchment") by means of the Council drain, indicates that her primary concern was with the upper catchment area.
11. The area of the upper catchment is more problematic. Dr Martens did not, above Norma Rd, extrapolate the lower catchment area determined by Mr Bewsher. Rather, Dr Martens has indicated, by points D and F on Figure 2 (Exhibit A, Tab 10), that some points within Mr Bewsher's catchment may drain to locations other than Mrs O'Brien's land. And Mr Bewsher's conclusions, particularly regarding the north-eastern area of the catchment, seem to have only his observations to support them. His north-eastern boundary differs markedly from his assessment of the existing catchment and I am not persuaded that such a difference is justified, notwithstanding the impact of the driveway on 10 Norma Rd opposite number 17.
12. Mr Williams concluded that the pre-development or natural catchment area was 0.6ha (Exhibit C, Mr Williams' report dated 28 July 2011 at p2). In Dr Martens opinion the area was 0.43ha (Exhibit C, Dr Martens' Statement dated 19 November 2014 at [12.a]), and in Mr Bewsher's, 1.38ha. I have concluded that the natural lower catchment is equivalent to the existing lower catchment for the reasons given. But Mr Bewsher's north-eastern area of the upper natural catchment is enlarged compared to the existing catchment and must be discounted. He gave evidence (transcript, 3 June 2015, 125.40) that he was "essentially assuming that the topography…under natural conditions, is the same - would have been the same as what's out there today." This is not reflected in the enlarged north-eastern area. Conversely, Dr Martens excludes a significant amount of the north-eastern area of the existing catchment in his determination of the natural catchment. In my view, neither change is justified on the evidence.
13. The current catchment area exceeds the natural catchment area, in my view, principally because of the impact of Bynya Rd and Norma Rd. Those roads operate to direct stormwater from lots fronting these two roads, and lots near the intersection of Bynya Rd and Norma Rd, along the northern side of Norma Rd to the inlet to the pit at the commencement of the pipe. This area appears to add about 0.4ha to the catchment area and is shown as the south-western area of the current catchment on the drawing of each of Mr Williams, Mr Bewsher and Dr Martens, and includes the north-eastern corner of the Bynya Rd and Norma Rd intersection. Bynya Rd has also changed the location of the catchment area at the upper northern end, but the difference in area produced by that change does not appear, on Dr Martens' or Dr Bewsher's drawings (Exhibit A, Tab 10), to produce a significant change in area to the existing catchment.
14. It is impossible to be precise about the area of the natural catchment. Principally because of the impact of Bynya Rd and Norma Rd adding an additional approximately 0.4ha to the catchment area, I conclude that there is, and propose to adopt, an area of 1ha as the natural catchment area. This is close to halfway (0.99ha) between the areas of the natural catchment assessed by Mr Williams on the one hand and Mr Bewsher on the other.
15. As I have assessed the current catchment to be 1.47ha and the natural catchment to be about 1ha, the current catchment area exceeds the natural catchment area by 0.47ha. This almost 50% increase in the catchment area is, as indicated, largely due to the extension of the existing catchment to the Bynya Rd, Norma Rd intersection.

(iii) Natural catchment, or catchment after the road was constructed but before the pipe was installed?

1. Mrs O'Brien submitted that the proper comparison with the existing catchment area ought not to be with the natural conditions but with the conditions immediately before the installation of the Council drain. She submitted that I should conclude that, at that time, there was no upper catchment because the rainfall above Norma Rd would be diverted to travel along the northern side of Norma Rd and would not flow to the southwest according to the natural fall of the land. This submission was based on the alleged circumstance that the road was installed before the Council drain (including the pit and the pipe), and that the camber of Norma Rd ensued that water would not travel across it.
2. The evidence of the timing of the construction of the road, the pit and the pipe is thin. Mr Williams gave evidence that the owner of 15 Norma Rd told him that the open drain was constructed in 1958. I have no means of assessing the reliability of that evidence. Although I do not doubt Mr Williams was told this, whether the owner of 15 Norma Rd had personal knowledge by his or her own observation, was told by an earlier owner, or was informed by some other means, was not the subject of evidence. The owner of 15 Norma Rd did not give evidence and no notice in compliance with s 67 of the Evidence Act 2005 was in evidence before me. Nor was any application made under s 67(4) of that Act.
3. Mr Williams also gave direct evidence, from his experience, not objected to, that the drainage system appeared to be constructed in the 1940s or 1950s, and that "the type of construction is indicative of that period and earlier periods". This period also covers the period that the road was constructed. Photographic evidence indicates that roads were in place in 1951, as were some houses, although whether those roads operated to divert water away from Mrs O'Brien's property is not clear. There was no indication that the pipe was installed after the road was constructed, and in the absence of direct evidence, I would conclude that it was installed as part of the road construction.
4. The easement for the open drain was obtained by Council sometime after December 1940. The drain (in its present form) may have been constructed after the road was constructed, although Mr Williams' opinion evidence indicates that it was at about that time. There is no evidence to indicate that water from the pipe would have flowed along a different path from the one which the open drain now takes.
5. In Gartner v Kidman (1962) 108 CLR 12 at 48, Windeyer J of the High Court stated: "What is a natural use is a question to be determined reasonably having regard to all the circumstances, including the purposes for which the land is being used and the manner in which the flow of water was increased".
6. In these circumstances, I accept Council's submission that these works were all part of the one project. The flows of water at any particular time in the course of that project should not be determinative of whether the current flow of water is a nuisance. Why, if Mrs O'Brien purchased the land in 2003 with a water flow created by Council works in the 1950s, should the current water flow be compared to a year in the 1950s (when the flow may have been somewhat retarded by partially completed works) rather than any earlier year, was not made clear.
7. In my view, a comparison of the current water flow caused by Council's works must be compared with the natural flow that existed before Council's works. Those works include the road, the pit, the pipe and the open drain. I have found that the Council drain and road works have increased the natural catchment area by about 50%.

(2) The limitations in the drainage system: the opening to the pit

1. The rainwater from this additional area of approximately 0.4ha captured by the camber on Norma and Bynya Roads, and also the rainfall from the residue of the upper catchment above the centre of Norma Rd, does not flow directly onto 15 Norma Rd, but via the Council drain constituted by the pit, pipe and channel. The opening to the pit limits the amount of water that can reach Mrs O'Brien's property via the channel in two ways, indicated earlier.
2. First, the opening is about 540mm by 150mm, or 810 cm2. As this is significantly less than the area of the pipe opening it limits the water that can enter the pipe. Excessive water that is unable to enter the pit opening flows around the pit and down Norma Rd away from the pipe, channel and Mrs O'Brien's property.
3. The water flowing down the pipe is increased slightly, beyond the area of the pit opening, by at least one stormwater pipe from a property upslope of Norma Rd that feeds directly into the pit. A 100mm diameter pipe would increase the opening to the pit by 78cm2 but this says little about its carrying capacity (which may be affected by its diameter along its entire length). The pipe, it might be inferred, carried water from one property only, the identity and area of which is not defined. Thus, the amount of water it would carry in any storm was not specified. There was no evidence as to the extent to which it would increase the capacity of the pit to receive water, and in what storms it would deliver such an increase. As it has not figured in any of the calculations of the experts, I propose to ignore it quantitatively, although noting its existence.
4. The second limitation resulting from the pit opening is that refuse or debris, especially leaf litter and other vegetable waste, is commonly carried by the water flowing towards the pit in a rainstorm. That refuse can block, wholly or partially, the opening to the pit. If the opening is blocked, negligible water would travel via the pipe into the channel, but rather would be diverted around the pit and continue down the northern side of Norma Rd in an easterly direction. As more debris is carried by more significant rainfalls, a blockage may be thought more likely to occur at those times. Dr Martens stated that there was a "high likelihood of the…pit being substantially blocked" during rainfall events (Exhibit C, Dr Martens' Second Statement dated 29 May 2015 at [13]). There was evidence of blockages occurring and of pressure upon Council by neighbours to the east of the pit (presumably complaining) who would experience a greater flow of water down the street when the pit opening was blocked.
5. Thus, not all of the water flowing from the catchment area ends up in the channel. Some may be diverted because of the limited opening to the pit or because of a further reduced opening resulting from leaf matter and other debris. These limitations are more significant in more extreme rainfall events because of the limiting effect of the pipe opening and because of the increased likelihood of the transporting of debris to block the opening in times of increased water flow.
6. Mr Bewsher calculated the maximum flow through the pit into the pipe and channel via the upper catchment to be about 122 l/s. He concluded that such a level of flow down Norma Rd towards the pit would not occur in a "once a year" event but would occur in more significant, less frequent events. In other words, the water flow from a rainfall event of a magnitude that is expected to occur once every two years, or a greater magnitude event, will be moderated because of the limited opening to the pit. Any partial blockage of the pit opening by vegetation would further moderate the flow, even in more frequent, lesser magnitude events. Mr Williams calculates a greater maximum flow but made no response to Mr Bewsher's criticism of his calculation (see Exhibit 1, Mr Bewsher's report dated 29 February 2012 at [3.29]). I found his calculation difficult to follow. Dr Martens' calculation appears to derive a maximum flow through the pit opening of 133 l/s (see Exhibit C, Statement of Evidence of Dr Martens dated 19 November 2014 at [14(a)(iv)] and [14(a)(v)]), not materially different from Mr Bewsher's figure. I have adopted Mr Bewsher's figure for convenience and because I found his reasoning to be more transparent.
7. Because of the limited opening to the pit, comparing the current flows with the natural flows has complications. The natural flow rate is dependent, in part, on the area of the natural catchment. I have found the natural catchment to be about 1ha, and I accept the natural lower catchment area of 0.36ha (approximately the same as the existing lower catchment) as determined by Mr Bewsher. Thus, the natural upper catchment is 0.64ha, some 0.38ha or 37% less than the area of 1.02ha calculated by Mr Bewsher. Assuming water flow is directly proportional to the catchment area, which seems both reasonable and adopted by the experts, it might be expected that the amount of water flowing from the upper catchment into the pit under natural conditions should be 37% less than the natural flow calculated by Mr Bewsher. On this assumption, a once in every two-year magnitude event would produce, from the upper catchment, a natural water flow of not 220 l/s as currently calculated by Mr Bewsher (Exhibit 1, Report of Mr Bewsher dated 29 February 2012, p 16, Table 2), but 138.6 l/s (220 - 37/100 x 220). This is still marginally higher than the maximum water flow allowed by the pit opening of 122 l/s. In other words, on Mr Bewsher's figures, the limited opening to the pit would preclude a greater water flow from the upper catchment than would occur under natural conditions, in a storm of a magnitude expected to occur once every two years or a greater magnitude event.
8. Dr Martens calculates lesser flows under existing conditions than Mr Bewsher, whereas Mr Williams used figures from ACOR Consultants Pty Ltd, which show a higher rate. Mr Bewsher's figure is about midway (for a 100-year event) between the figures derived by Dr Martens and Mr Williams, the two experts retained by Mrs O'Brien.
9. So far as the natural catchment is concerned, Dr Martens' figures for water flow in different magnitude rainfall events are between 10 and 20% of the figures calculated by Mr Bewsher. But Dr Martens' catchment area is 0.43 ha, about 30% of the catchment area determined by Mr Bewsher. Dr Martens accepted that the differences in the flow rates were "largely because of differences in the catchment area", although he indicated that the differences might also be due to a failure to recognise that a natural catchment yields lower flow rates than an urban catchment because of the greater presence of a permeable surface of soil and vegetation in the natural environment. However, the extent to which the increased flows resulted from increased development by others, and the extent to which the building works of others can be attributable to Council, was not the subject of evidence or submissions. I do not regard Council as responsible for the increased flow resulting from the actions of others (cf Gartner at 48) but only for the increased flow that results from the Council drain enlarging the upper catchment.
10. For these reasons, and because I found Mr Bewsher's reasoning to be more clearly disclosed, and because he distinguishes between the upper and lower catchments, I have adopted Mr Bewsher's figures modified according to my conclusions about the catchment area.
11. In my view, Mrs O'Brien's land suffers from an increased water flow (compared to natural conditions) from the upper catchment. It receives more water during storms of lesser magnitude than a once in two-year storm. But in higher magnitude events, expected to occur every two years or less often, Mrs O'Brien's land receives less water flow from the upper catchment than it would naturally receive, because of the limited opening to the pit. The increased flow in lesser magnitude events results from a larger existing upper catchment. Mr Bewsher calculates the existing upper catchment to be 1.1ha (see Exhibit 1, Mr Bewsher's report dated 29 February 2012, Figure 6, p 13). This is 72% larger than the size of the natural upper catchment calculated above (at [62]) to be 0.64ha. Across the whole of the catchment, the existing catchment (1.47ha) is almost a 50% increase on the natural catchment of 1 ha, and in lower magnitude events it would produce a proportional increase in water flow onto Mrs O'Brien's land.

(3) Nuisance and the existence of a natural watercourse

1. Council submitted that it was entitled to discharge water onto Mrs O'Brien's property because of the existence of a natural watercourse on the land. This issue raises questions concerning the law of nuisance in relation to flowing water, the relevance of a natural watercourse and the existence of riparian rights in Council.

(a) Nuisance and the flow of water

1. Windeyer J stated in Gartner at 37: "There is no right on the part of one landowner to drain the water from his land over that of his neighbour without the latter's consent. This rule prevents the gathering of water into a body and casting it onto the lower owner, or collecting it in artificial ditches for that purpose, or changing the course of drainage." Nevertheless, "the respondent was entitled to discharge upon [the appellant's land] any water that would naturally flow there from his land in the normal use by him of his land and…the appellant was obliged to receive that water."
2. In Melaleuca Estate Pty Ltd v Port Stephens Council (2006) 12 BPR 23,743 at [22]-[23], the Court of Appeal held that "[d]ischarge of water onto the appellant's land could be a nuisance if it was an unreasonable interference with the use and enjoyment of the land."
3. Council is not entitled to unreasonably enlarge the catchment area and thereby direct more water onto Mrs O'Brien's property. Council may be liable for the concentration or alteration of this natural flow (see Gartner at 48). But the Council drain does more than this: it also restricts the amount of water flowing to Mrs O'Brien's property in high magnitude events by reason of the limited pit opening.

(b) Is there a natural watercourse?

1. The common law meaning of a "watercourse" is considered by Barwick CJ in Knezovic v Shire of Swan-Guildford (1968) 118 CLR 468 at 475 - 476. The Chief Justice determined that: "it is settled that a watercourse consists of a stream with a bed, with banks, and water. That the flow of the water in the stream is intermittent or seasonal will not prevent what would otherwise be a watercourse from being accounted such: but though it is quite true that a watercourse may exist though its bed be dry for some periods, the watercourse, in my opinion, must exhibit features of continuity, permanence and unity, best seen, of course, in the existence of a defined bed and banks with flowing water. It must, in my opinion, essentially be a stream and be sharply distinguished from a mere drain, or a drainage depression in the contours of the land which serves to relieve upper land of excess water in times of major precipitation. It is not enough that the water, when it does flow, does so in what may be seen as a defined course or channel. In the case of a drainage depression, the water being drained off can be expected to flow in the lowest portion of the contours confined by the rising levels of the adjacent land: thus water can be seen when flowing to do so in what could be called a defined channel. If the seasonal rainfall is within an average tolerance in amount and timetable, the flow in the depression may well exhibit some regularity in the depth of water flowing in the contour depression and in the extent to which it spreads as it flows. If there is some such normality in the volume flowing, the impression of a defined channel with limiting margins will be enhanced. If, as I would expect to be the case, there is considerable variation in the rainfall and in the volume and velocity of the water flowing in the depression, the impression of a defined channel may be considerably less. But, in any event, the existence of such a defined channel will not make the drainage depression a watercourse nor the limiting margins of the water's flow in a rainy season or period 'banks' of a stream. Thus, though water when it flows in such a period flows in what can be called a defined channel, such a drainage depression will lack banks and a bed in the proper sense of that term, that is to say, identifiable margins of a continuous and permanent stream which contribute to its unity whether or not water is in fact continuously flowing over the bed. The word 'occasional' in the quotation from Angell on Watercourses will here, in my opinion, embrace seasonal events, even if they occur with some regularity from season to season."
2. As Windeyer J stated in Gartner at 27: "[T]he depressions which provide the natural course or outlet for [surface water flooding] may be called watercourses. But the law treats such valleys and depressions very differently from watercourses that have the qualities of rivers and streams."
3. In Gales Holdings Pty Limited v Tweed Shire Council [2013] NSWCA 382 at [132]-[133], the Court of Appeal stated that: "nuisance is a wrongful interference with another's enjoyment of land by the use of other land occupied or owned by the alleged wrongdoer...A balance must be maintained between an owner or occupier's right to do what it likes with its land and a neighbour's right not to be interfered with. The proper test to apply in most cases is what is reasonable, according to the ordinary usages of a particular society… The flow of water can give rise to nuisance. There is a difference between the flow of surface waters and the flow of natural watercourses. Riparian rights attach to the flow of natural watercourses such as rivers or streams, but not to the flow of surface waters. The word 'riparian' derives from the Latin ripa for riverbank. A riparian owner, being the proprietor of land on the banks of a natural stream of running water, is entitled to enjoy, and is obliged to accept, the flow of water past the land. The law of natural watercourses, not surface waters, applies even to waters of a river flowing in a wider channel than usual, when the river is swollen in time of flood, even though they flow on land outside the riverbed while still following the river's general course. Such flood channels are treated as part of the alveus, or riverbed. [Emphasis in original]
4. Thus, it appears that the downstream owner must accept water in or flooding from a natural watercourse, and from surface waters which flow naturally onto the land. But, other than a natural watercourse, "[t]he higher proprietor may be liable if surface waters are caused to flow onto the lower land in a more concentrated form than they naturally would" (see at Gales Holdings at [135]-[136]). And, as indicated in the Gartner passage at 48 quoted earlier, what is "natural use" involves questions of reasonableness.
5. Whether there is a natural watercourse on Mrs O'Brien's property depends upon whether there is a riverbed, riverbanks and a regular flow of water. Here there was a drainage depression so that during storms water would flow, roughly in the region of the channel on 15 Norma Rd and into the drainage system on Mrs O'Brien's property. But there was no evidence of beds or banks, and no regular water flow outside of a storm event.
6. Council relied on the title documents to submit that there was a natural watercourse on the land. The Deposited Plan contains a reference to a natural watercourse running in roughly the location of Mrs O'Brien's drainage system. The Deposited Plan also makes reference to a natural watercourse on the adjoining block to the south and on the block three blocks to the north. The terminology on the Deposited Plan is not determinative of whether a natural watercourse existed. That the notation on the Deposited Plan was evidence that "water flowed at that location" (at least during a storm), as Council submitted (defendant's submissions dated 24 July 2015, [128(v)]), does not establish the existence of a natural watercourse rather than a drainage depression.
7. In my view, the features of Mrs O'Brien's land do not satisfy the elements of a bed, banks and a regular flow of water so as to constitute a natural watercourse. Rather, there existed only a "drainage depression" where water flowed in times of rain. It follows that the features of Mrs O'Brien's land were not such as to allow Council to direct increased quantities of water onto her property.
8. Nor does the existence of an easement over 15 Norma Rd provide any justification for directing water onto Mrs O'Brien's property. Just as a lower proprietor cannot divert water onto the land of a third proprietor (Gartner at 49; Gales Holdings at [136]), neither can Council divert water onto Mrs O'Brien's property.

(c) Abolition of riparian rights

1. In case I found a natural watercourse, Mrs O'Brien argued, in the alternative, that any argument of Council based on riparian rights was not pleaded and thus ought not be permitted to be raised, that Council was not the owner of the land, and that in any event, riparian rights were abolished by s 393 of the Water Management Act 2000. As I have found that no natural watercourse existed, dealing with these questions is not strictly necessary. However, as parties have made some submissions on them I propose to add some brief comments. I would not regard a failure to mention riparian rights in the pleadings as a reason to refuse to consider that matter; the issue of the existence of a natural watercourse was clearly raised. As to whether, if there existed a natural watercourse, Council would be the owner of the banks of the watercourse, I am inclined to the view that the easement acquired by Council would put Council in the same position as a landowner.
2. Section 393 provides: "393 Abolition of common law riparian rights Any right that the owner of riparian land would, but for this section, have at common law with respect to the flow of any river, estuary or lake through or past the land, or to the taking or using of water from any such river, estuary or lake, is hereby abolished."
3. The title of the provision refers to the "Abolition of common law riparian rights". However, the text of the provision itself confines the abolition of rights to those which the owner of riparian land had "with respect to the flow" of the watercourse "through or past the land, or to the taking or using" of that water. Thus, the Water Management Act 2000 abolishes an entitlement to use the flow of water but does not in terms deal with an entitlement to direct water into the watercourse, or the obligation on a downstream owner "to accept the flow of water past the land" (Gales Holdings at [133]). Whether these particular rights and obligations, riparian in nature, remain unaffected by the terms of s 393 of the Water Management Act 2000 is uncertain. A wide view of the words "with respect to the flow" would embrace a right to add to that flow, but generally a common law right would not be found to have been statutorily denied, in the absence of clear words. I prefer not to express a concluded view on this matter in circumstances where no decision is required.

(4) Concentration of water, and the nature of the nuisance

1. Mrs O'Brien has, as part of the approval to build her house, installed a drainage system to cope with significant, 1 in 100-year rainfall events. As a result, damage from the flow of water itself is not of concern, as the drainage system that she installed is designed to, and apparently does, cope with that flow. Moreover, the drainage system she installed was required irrespective of the Council drain, because of the magnitude of the stormwater events with which it was designed to deal. Although the existence of abatement works does not relieve Council of liability for nuisance (see Melaleuca Estate at [31]-[33]), nevertheless the existence of the works affects whether the flow of stormwater substantially interferes with Mrs O'Brien's use and enjoyment of her land, and whether that flow impacts on its value.
2. The end of the open drain within the easement is about 20m upslope of the escarpment, which is 3m to the rear of Mrs O'Brien's property. Water flowing through the drain flows at the end of the drain over a rock face then across the rear of 15 and 19 Norma Rd until it reaches the escarpment. It is not visibly confined in its flow path by any natural or artificial features. To some extent the concentration of the water flow is thus dissipated. However, by one route or another, it appears that all or most of this water flows over the escarpment and onto the northwest corner of Mrs O'Brien's property.
3. The space of 20m between the end of the Council drain and the escarpment operated to slow the speed of the water flow, but did not appear to substantially lessen the concentration or volume of water flowing over the escarpment. Nevertheless, it was not clear that the concentration operated as a disadvantage to Mrs O'Brien. The concentration may have resulted in the water more readily being directed into Mrs O'Brien's drainage system.
4. The acceptance of responsibility by Council for any liability of its predecessor in constructing the Council drain removes the need to consider whether Council is in any way relieved by having "come into" the nuisance. But as Ward J noted in Quick v Alpine Nurseries Sales Pty Ltd [2010] NSWSC 1248 at [142], an occupier will be liable for continuing a nuisance if "with actual or constructive knowledge of its existence, he or she fails, within a reasonable period of time, to take reasonable measures to bring it to an end". Although Council submitted that I should not conclude that Council "knew or ought to have known that stormwater flows would exceed those flowing naturally through the watercourse" I do not see that conclusion as being available. Mr Bewsher's report obtained by Council establishes that in lower magnitude events commonly occurring annually or more frequently, the pit allows a greater volume of water to pass via the Council drain onto Mrs O'Brien's property than would occur in natural conditions. The circumstance of the road funnelling water into the pit indicates this, even to the casual observer. In my view, there can be little doubt that any nuisance occurring by means of the Council drain has been continued by Council, with knowledge.
5. Mrs O'Brien's primary complaints concern the consequences of the water flow rather than merely the flow itself. Firstly, the water brings silt and debris which litters her property and her drainage system on the side of her property and so it requires regular maintenance. Secondly, the water flow is noisy and thereby disturbs her amenity. She also raised some other more general complaints about the consequences of increased and concentrated water flow onto her property.

(a) Litter and other debris

1. I accept the evidence of Mrs O'Brien that debris is brought down the channel and deposited in her drainage system. Dr Martens' observations provide some support for this conclusion (see Exhibit C, Dr Martens' Second Statement dated 29 May 2015, p 8). It was not demonstrated what level of debris would be brought by a natural water flow. Nevertheless, it must be concluded that for regularly occurring and frequent (less than once every two-year) storms the magnitude of water flow is increased, and the water flow is more concentrated by the channel. This renders the water flow more capable of transporting debris. The possibility of debris blocking the pit entrance, and thus eliminating the transfer of debris through the pipe and into the channel towards her property, may lessen the transfer of debris to her property to some degree, but I am not satisfied it would reduce it substantially.
2. Council submitted that there was an absence of meaningful evidence about the debris and pollutants. But there was evidence of debris, and that it might likely be caused by the increased flow of water along Norma Rd. That is sufficient, in my view, to conclude, on the balance of probabilities, that there is an increased level of debris attributable to the increased flow of water flowing into and from the Council drain. By reason of the Council drain, the catchment area includes an additional approximately 150m of roadway along Bynya and Norma Roads, thereby increasing the amount of debris transported by the water flow. The circumstance that the roadway is a likely place for debris because of human traffic, and the increased concentration and speed of flow resulting from the camber of the roadway are both relevant in assessing the existence and genesis of increased litter and debris. In my view, the transport and deposit onto Mrs O'Brien's property of debris is an inconvenience that results from the Council drain that would not be present with the same regularity if the Council drain did not exist, even allowing for water flow from the natural upper catchment. The debris is a product of the increased amount of water from the upper catchment, some 72% more in frequent storms, and the concentrated flow of that water on the high side of Bynya Rd and Norma Rd into the Council drain.

(b) Silt

1. The magnitude of the silt and litter deposited by the Council drain in a 12-month period was not indicated by the evidence, save that the silt is removed from Mrs O'Brien's property twice a year. The added concentration of water in the channel may cause the transportation of silt picked up in the 20m or so between the end of the channel and the escarpment. On the other hand, the flow of the water on the sealed roadway of Bynya Rd and Norma Rd, and through the artificial channel may result in less silt being picked up and transported than in natural conditions. The presence of silt seems more likely to result from the impact of a concentrated flow of water from the end of the channel, rather than by being carried from the upper catchment. Is this sufficient?
2. Council submitted that: "[I]t is difficult to see, with the possible exception of some unidentified increase of pollutants that would be carried by the artificial channel, how a finding could be made that sand and sediment, could be attributed to the excess rather than natural flows."
3. A greater concentration of water flow is likely to increase the amount of silt transported. But the extreme events expected to occur less often than every two years would be expected to carry and deposit a larger amount of silt, and the effect of those events are moderated by the limited pipe opening. The evidence does not persuade me that the current conditions produce more silt on average than the natural conditions, especially when less frequent and more extreme events are moderated by the limited opening to the pit. I am not able to conclude that Mrs O'Brien suffers from an increased level of silt by reason of the Council drain.
4. In my view, the increased level of debris but not an increased level of silt, resulting from the increased flow of water, including along the roadway and into the pit, is a substantial interference with Mrs O'Brien's use and enjoyment of her land. It constitutes a nuisance to which Mrs O'Brien is entitled to a remedy, including in an appropriate case by an injunction (see Gartner at 49).

(c) Noise

1. Noise alone is sufficient ground for an injunction if a proper case of nuisance is made out: Vincent v Peacock [1973] 1 NSWLR 466, 470. But trifling inconvenience is insufficient; it must materially diminish the comfort and enjoyment of property (J M Paterson, Kerr on Injunctions, (6th ed, 1927, Sweet & Maxwell) at 185). See also Wherry v K B Hutcherson Pty Ltd (unreported, NSWSC, Hodgson J, 4 April 1986) at 16; Gray v New South Wales (unreported, NSWSC, Young J, 31 July 1997) at 1). There must be a "serious and not merely slightly additional interference with the comfort of the plaintiff and [her] family in the occupation of [her] house, according to the ordinary notions of reasonable persons in the locality" (Kerr, ibid). Although the learned author gives many examples of nuisance (see also Vincent at 470), none concern water noise. No cases were cited to me that indicated that the noise of flowing water would of itself suffice to require a remedy.
2. Mrs O'Brien complains about the noise of the water flow. There was some evidence of the noise indicated in a video in evidence: that noise was particularly apparent at the rear of Mrs O'Brien's property below the escarpment. However, the rear of the property is quite rugged and not easily accessed. Its topographical features indicate that it would rarely be accessed, especially during periods of rain, and there was no evidence of regular use of the rear of the property during storms.
3. Although there would undoubtedly be noise from flowing water through the drainage system, there was no analysis done of how that noise near the house compares with the noise of the rain on the roof and surrounds and the noise of the surf on the other side of Whale Beach Rd (cf. Seidler v Luna Park Reserve Trust (unreported, NSWSC, Hodgson J, 21 September 1995 at e.g. [58]). The noise of the surf was noticeable when standing below the escarpment at the rear of Mrs O'Brien's property during the site visit.
4. There was no evidence to indicate that the noise of water flow was present other than during an actual storm, nor evidence that the noise caused disturbance inside Mrs O'Brien's home when doors and windows were closed. Because of the increased flow in regular rainstorms (compared to natural conditions), it might be expected that outside of extreme events, the noise is more significant than it would be in natural conditions. But inside the house is where Mrs O'Brien and her family, if on the property, might be expected to be situated during a rainstorm. Closing windows and (presumably external) doors is a method Mrs O'Brien uses to abate the noise. The necessity of closing windows and external doors in a rainstorm, irrespective of the noise, might be expected (especially if wind is present) but that was not the subject of evidence.
5. Although water flow through the drainage system on Mrs O'Brien's property would persist beyond the period of a storm - up to two days said Mrs O'Brien - there was no evidence that that water was causally connected to water flowing through the Council drain. It may also have resulted from seeping groundwater from sodden soil. In any event, the level of noise of flowing water outside of the period of a storm was not the subject of evidence.
6. In these circumstances, I am not persuaded that the noise from the water flow during a storm was an unreasonable interference with Mrs O'Brien's use and enjoyment of her land so as to constitute an actionable nuisance.

(d) General matters

1. Mrs O'Brien also alleged that she was "deprived of using her land" and that: "The quantity, velocity and power of this water means that the part of Property over which that water flows can never be used or developed by Mrs O'Brien, whether for landscaping, building or other purposes. All that the land can be used for is to allow the water to flow and to endeavour to abate its effect."
2. The part of the land referred to is where Mrs O'Brien's drainage system is located. That drainage system was required to cope with a 1 in 100-year flood as part of her development approval. There was evidence that it may have been conservatively designed or over-engineered so as to more than cope with that event. But it was not suggested that this was as a result of any requirement of Council.
3. In my view, it is the drainage system rather than the water flow that operates to limit Mrs O'Brien's use of that part of the land. The size of the drainage system was not increased by the water flow generated by the Council drain. On the contrary, the limited opening to the pit lessens the impact of a 1 in 100-year magnitude event and thus, if that limited opening had been considered, it would have reduced the size of the necessary drainage system. The water that flows more regularly through that drainage system arises from lesser magnitude events.
4. Mrs O'Brien also relied upon evidence that, in respect of the previous building on the property, "some footings [had] been washed out and collapsed" and that sand beneath the previous residence and a garage showed "signs of water flow through" it.
5. It was not in dispute that the property historically had been significantly affected by water flow, and that the property now receives a significant flow of water. But the evidence did not establish that the washed out footings and water flow through the garage, of a previous building, which would not now recur because of the drainage system installed by Mrs O'Brien, were attributable to the Council drain magnifying a low level event, or attributable to a high level event which would be lessened by the Council drain's limited pit opening. I am not persuaded that these observations of an earlier time assist in determining the impact of the Council drain on Mrs O'Brien's property.
6. Further, the mere existence of water flow through the drainage system does not establish damage (see Bonaccorso v Strathfield Municipal Council [2003] NSWSC 408 at [49]). Mrs O'Brien is benefitted by having less water flow onto her property in high magnitude events, estimated to occur less than once every two years. Greater damage might ordinarily be expected to result from extreme events, yet in this case the Council drain moderates the impact of the event and also Mrs O'Brien has a drainage system designed to cope with extreme events. I am not satisfied that the mere water flow resulting from the Council drain deprives Mrs O'Brien of using her land or otherwise constitutes a nuisance.

(5) The statutory defences

1. Council relied on certain statutory defences.
2. Section 43A of the Civil Liability Act 2002 provides: "43A Proceedings against public or other authorities for the exercise of special statutory powers (1) This section applies to proceedings for civil liability to which this Part applies to the extent that the liability is based on a public or other authority's exercise of, or failure to exercise, a special statutory power conferred on the authority. (2) A special statutory power is a power: (a) that is conferred by or under a statute, and (b) that is of a kind that persons generally are not authorised to exercise without specific statutory authority. (3) For the purposes of any such proceedings, any act or omission involving an exercise of, or failure to exercise, a special statutory power does not give rise to civil liability unless the act or omission was in the circumstances so unreasonable that no authority having the special statutory power in question could properly consider the act or omission to be a reasonable exercise of, or failure to exercise, its power. (4) In the case of a special statutory power of a public or other authority to prohibit or regulate an activity, this section applies in addition to section 44."
3. This provision raises two issues: whether the power exercisable by Council under subs (2)(b) "is of a kind that persons generally are not authorised to exercise without specific statutory authority", and whether the act or omission of Council was "so unreasonable" under subs (3).
4. The resolution of these issues depends upon the specific act or omission of Council. Is it the act of installing the Council drain in the 1950's, or the failure to amend the system to protect Mrs O'Brien's property in recent times when complaint was made?
5. So far as Mrs O'Brien is concerned, no nuisance could occur until after she had purchased the property. So it is appropriate to focus on the more recent omission of Council to take any steps to remedy the problem.
6. For that omission to be a "special statutory power", the power of amending the Council drain so as to ameliorate the nuisance must be a power unable to be exercised "without specific statutory authority". That may depend upon the means taken to relieve the nuisance. Would the installing of a grate to capture debris before it is channelled onto Mrs O'Brien's property require specific statutory authority or is the power to do so a power "of a kind" that any person could exercise in managing drainage systems on their land or on easements benefitting them?
7. Section 634 of the Local Government Act 1993 prohibits an unlicensed person from doing any stormwater drainage work. Does the requirement for using licensed tradespersons, or to work under their supervision, mean that the power to do the work is "of a kind that persons generally are not authorised to exercise"? I do not think it is. Persons generally are authorised to do the work, although if a particular person is not licensed then they must do the work under appropriate supervision. Further, s 634 is not a provision giving Council specific statutory authority. Instead, it imposes conditions on the exercise of a power by anyone.
8. Council also relied on s 59A of the Local Government Act 1993, which permits Council to act in respect of the Council drain "to ensure that, in the opinion of the council, the works are used in an efficient manner for the purposes for which the works were installed."
9. Council is also granted ownership of the Council drain by s 59A. As the pit and pipe are on the roadway, the grant in s 59A is unnecessary in respect of them. As to the channel, the grant of the easement for drainage should ordinarily grant power to Council to do works in respect of the channel, even if, absent s 59A, it remained owned by the registered proprietor of 15 Norma Rd.
10. Unquestionably the Council drain was installed to drain water. But I remain unsatisfied that that is a fair description of the extent of the Council's opinion of the system's purposes under s 59A. The purposes of the Council drain might be to mitigate water flow easterly down Norma Rd, it might be to preserve the quality of Norma Rd for public or driver safety or there may be other purposes. There was no evidence from Council on this matter and in the absence of evidence, I would not infer that Council held the opinion that the Council drain was being used in an efficient manner for its purposes unless Council believed it was not causing to others damage by nuisance or negligence, see Bankstown City Council v Alamdo Holdings Pty Ltd (2005) 223 CLR 660 at [16]. Council would be negligent unless it conducted the operation "with all reasonable regard, and care for the interests of other persons": Melaleuca at [47]-[48].
11. I was not addressed on the question of whether s 59A overrides s 634, a matter which may affect whether there was "specific statutory authority" under s 43A(2)(b). Could Council use unlicensed tradespersons under s 59A notwithstanding s 634? Section 634(3), which exempts Council from the application of s 634(1) and (2) in certain circumstances, seems to indicate that Council is not absolved generally under s 59A. Further, s 634(3) makes no reference to stormwater drainage work, and thus indicates that in doing that kind of work, Council is subject to the prohibition in s 634(1) and (2) notwithstanding s 59A. It follows that Council has no more or less authority under s 634 to do the work than any other person: both are subject to the restraint of using licensed tradespersons.
12. Recent authority has broadened the circumstance where activities can be "based on" a special statutory power: see Curtis v Harden Shire Council (2014) 88 NSWLR 10 and Roads and Maritime Services v Grant [2015] NSWCA 138. This does not affect the need for this power to be a "special statutory power", including that the power is of a kind not authorised without specific statutory authority. For the reasons given, I do not accept that modification to the pit and pipe "could not be performed without the special statutory power" (Council's reply submissions dated 27 July 2015 at [21], see also Gales Holdings at [199]).
13. Accordingly, I am not satisfied that the stormwater drainage work of the type contemplated to relieve Mrs O'Brien from the nuisance requires the exercise of a special statutory power. It follows that I am not persuaded that s 43A(2)(b) of the Civil Liability Act 2002 is satisfied by ss 59A and 634 of the Local Government Act 1993, in the present case.
14. The second issue concerns whether Council, in omitting to take any steps to ameliorate the nuisance to Mrs O'Brien, has acted unreasonably within the terms of s 43A of the Civil Liability Act 2002.
15. Council submitted that there "is no expert opinion that a stormwater drainage authority should have regard to [less frequent than biennial] rainfall events in managing its drainage system" (Council's submissions dated 24 July 2015, [211]). I do not accept that Council need only consider 1 in 100-year events when considering whether it is committing a nuisance. In my view, Council should have regard to a potential nuisance when it is concentrating and enlarging a flow of water, whether in larger or lesser magnitude events, onto a property over which it has no drainage easement. No authority could properly consider it reasonable to direct water onto another landowner's property without legal authority, at least without considering the consequences to the landowner. There was no evidence that Council gave the matter any consideration. In my view, this omission satisfies the "so unreasonable" test within s 43A(3) (see Dubois v Noarlunga District Council [1959] SASR 127 at [122]).
16. Section 582A of the Local Government Act 1919 provides: "Exculpation from liability - flood liable land. 582A. (1) A council shall not incur any liability in respect of - … (b) anything done or omitted to be done in good faith by the council in so far as it relates to the likelihood of land being flooded or the nature or extent of any such flooding. (2) Without limiting the generality of subsection (1), that subsection applies to - … (e) the carrying out of flood mitigation works; and (f) any other thing done or omitted to be done in the exercise of a council's powers, authorities, duties or functions under this or any other Act. (3) Without limiting any other circumstances in which a council may have acted in good faith, a council shall, unless the contrary is proved, be deemed to have acted in good faith for the purposes of subsection (1) if the advice was furnished, or the thing was done or omitted to be done, substantially in accordance with the principles contained in the relevant manual published under subsection (4) at that time. … (6) This section applies to and in respect of any advice furnished or thing done or omitted to be done before the commencement of this section, as well as to and in respect of any advice furnished or thing done or omitted to be done after the commencement of this section."
17. This provision was repealed in 1993. It has no application to the conduct of Council in continuing the nuisance, and I have already found that Mrs O'Brien can have no claim in respect of the Council drain prior to her owning the property.
18. In any event, in the absence of any evidence from Council, I am not satisfied that Council held any regard and care, let alone all reasonable regard and care, for the interests of Mrs O'Brien, when it continued to divert additional water onto her property during storms. Nor in the absence of evidence from Council, could I conclude that Council has weighed up the benefit to Mrs O'Brien in limiting the water flow in higher magnitude events against the increased flow in lesser magnitude events, so as to have had reasonable regard for Mrs O'Brien's interest.
19. In Dubois at [122], Piper J held: "Indeed, it seems to me that the method of draining the water off the road onto the plaintiff's land without making provision for carrying it through the land was one which, on the face of it, was so unreasonable, so fraught with manifest danger to the plaintiff, that no council acting bona fide and rationally, having regard to its obligations to the plaintiff, would ever have undertaken it".
20. Accordingly, I am not satisfied that s 43A of the Civil Liability Act 2002 grants any immunity from civil liability in the circumstances of this case.
21. The only other statutory provision relied upon by the Council was s 733(1) of the Local Government Act 1993. It provides: "733 Exemption from liability - flood liable land, land subject to risk of bush fire and land in coastal zone (1) A council does not incur any liability in respect of: … (b) anything done or omitted to be done in good faith by the council in so far as it relates to the likelihood of land being flooded or the nature or extent of any such flooding. … (3) Without limiting subsections (1), (2) and (2A), those subsections apply to: … (g) any other thing done or omitted to be done in the exercise of a council's functions under this or any other Act. …" "Flooded" is defined in the dictionary at the end of the Local Government Act 1993. It provides: "flooded, in relation to land, means inundated by waters derived from the runoff of rainfall on land."
22. Section 733 does not identify a statutory power, but rather specifies a privilege or immunity of council. Powers are not the same as privileges or immunities (see Brennan CJ in Arena v Nader & State of New South Wales (1997) 71 ALJR 1604; [1997] 17 Leg Rep SL1).
23. Section 733 purports to grant Council immunity, apparently replacing s 582A of the 1919 Act. The extent of that immunity and whether it has application to the present case must be considered.
24. First, damage from water flow and damage from flooding are not synonymous. The principle of legality (see Coco v The Queen (1994) 179 CLR 427, 437) militates against extending the immunity from common law liability beyond the strict terms of s 733 (see Clissold v Perry (Minister for Public Instruction) (1904) 1 CLR 363, 373; Bonaccorso v Strathfield Municipal Council [2003] NSWSC 408 at [41]-[45]). Mrs O'Brien makes no claim against Council in respect of flooding, but in respect of water directed onto her property, depositing debris, causing noise and thereby disturbing her amenity.
25. Secondly, Council led no evidence to prove that any act was done in good faith. As held in Gales Holdings at [181]: "A defendant can only rely on the defence once it has identified the thing that it did or omitted to do in good faith. Further, good faith is more than honest ineptitude. There must be a real attempt to exercise a relevant power".
26. The remarks in Dubois cited earlier, are also apposite. The Court should, in accordance with Jones v Dunkel (1959) 101 CLR 298, be reluctant in the circumstances of this case to infer that Council's actions in continuing to direct water onto Mrs O'Brien's property, over which it has no easement, was an act done in good faith, or involved the good faith exercise of a power, in circumstances where no evidence was called by Council to establish this, and no evidence was called to explain this lack of evidence. The purposes for which the Council drain was installed (under s 59A of the Local Government Act 1993) are not established by any evidence.

(a) Injunction

1. Mrs O'Brien submits that the appropriate remedy is to block the pit or pipe so that the water continues along the high side of Norma Rd. She submits that the pit entry is sometimes blocked by leaf litter which results in Norma Rd property owners having to cope with the flow of water. To block the pipe permanently would have the same effect.
2. As noted earlier, Mr Williams gave evidence that the pit "does block fairly regularly" and Council takes action to remedy this problem "only under pressure from residents". This suggests to me that blocking the pit to allow water to travel down Norma Rd has an adverse effect on those property owners sufficient to cause them to "pressure" Council. There was reason to believe that heavy flows of water may cross to the southern side of Norma Rd further down (east) from the pit and flow onto properties on the low side. There were drains at the top of driveways near the roadway on that side of the road. Also, that section of Norma Rd, as seen on the view and as indicated on the contour plan east of Pacific Rd, appeared to have a slight depression in the centre of the roadway: at least there was no significant camber to prevent flows across the road. I think the Court should be cautious in making an order that has potentially detrimental effects on other property owners without hearing from them.
3. Mr Williams' gave evidence in respect of allowing water to continue down Norma Rd: "It does not appear that there has been a major issue downstream. So whatever the drainage system [downstream] is doing, it might not be perfect but it coping". This does not persuade me that I should make orders resulting in the water being redirected to flow down Norma Rd.
4. The decommissioning of the Norma Rd pit would regularly direct an additional amount of up to 121 to 133l/s of water easterly down Norma Rd. Although there is a further drainage system further down Norma Rd, it has a 300l/s capacity. When this is exceeded, water would flow to the southern side of Norma Rd, with possible adverse effects to downslope housing on both sides of Norma Rd. To direct more water to those properties than would normally flow upon them, by directing water from the upper catchment some of which would naturally flow to Mrs O'Brien's property, may be to create a nuisance to them of the same type which Mrs O'Brien complains of in these proceedings.
5. If the only significant interference with Mrs O'Brien's use and enjoyment of her property is the increased amount of debris that is deposited, then changing the course of the water flow seems an unnecessary and excessive step to remedy the problem.
6. The flow of debris onto Mrs O'Brien's land could be remedied by Council acting to place a grate or mesh over the Norma Rd pipe to prevent debris travelling down the pipe into the channel. The transport via the Council drain of debris such as bottles, plastic bags and the like produced by human activity could thus readily be prevented without reducing the water flow. Installing such a grate will marginally reduce the opening to the pipe but will not reduce the water flow because of the limited pit opening: the pipe capacity already well exceeds the capacity of the pit opening. It would need to be regularly inspected to clear away any build-up of debris, but that action already needs to be done in relation to the pit opening. And no issue of safety or other matter would seem to preclude a grate on the pipe. It would also seem relatively economical to install. On the material before me, it seems that a mandatory injunction to compel the installation of a grate would be appropriate.
7. In my view, the installation of a grate would remove the unreasonable interference with Mrs O'Brien's use and enjoyment of her land by precluding debris from being carried onto her land via the pit opening and channel, and thus removing the actionable nuisance to Mrs O'Brien. As this remedy should not increase the flow of water down Norma Rd, I need not consider any adverse impact on other residents or property owners.
8. An alternative method of eliminating the nuisance and reinstituting a flow equivalent to natural conditions would be to divert part (on my calculations 42%) of the water coming from the enlarged upper catchment so that it flowed past the opening to the pit. That may well be possible. But if natural water flows are to be restored to Mrs O'Brien's land, rather than merely channelling them in the direction of other property owners, the pit opening would also need to be enlarged to cope with the higher flows during infrequent high magnitude rainfall events which have been moderated by the Council drain. The result would be less water being directed down the pipe in frequent, lower magnitude storms, because of the diversion, but in heavier and infrequent (less than biennial) rainfall events the enlarged pit opening may result in a greater flow to Mrs O'Brien's property even though some water has been diverted. Neither party asked for this remedy nor do I think it cures the nuisance as economically and fairly as installing a grate to eliminate debris. By the installation of a grate, Mrs O'Brien would retain the advantage she possessed when she purchased her property, of having the upper catchment limited by the pit opening, no matter how heavy or extreme the storm.

(b) Damages

1. Mrs O'Brien claims damages in the alternative to an injunction.
2. The claim for damages is based upon the reduced value of Mrs O'Brien's property by reason of the increased water flow through the Council drain onto Mrs O'Brien's land (see Exhibit C, Report of Paul Chaloner dated 8 August 2011 at [1.1]). As I have not proposed to compel Council to block the Council drain, the question of damages remains. Further, diminution in the value of the property might evidence the extent of a nuisance: see Kerr on Injunctions at 138. Mrs O'Brien did not make this claim, however. Rather, she asserted that the diminution in value was relevant only as the proper measure of damage in the event that no injunction were granted.
3. The valuation expert relied upon Mr Williams' figures as to the extent of the water flow caused by the Council drain (see Exhibit C, Report of Paul Chaloner dated 8 August 2011 at [1.2]) and stated that the diminution in value is "by reason of the [Council drain] drainage system…continuing to discharge stormwater onto the land in excess of the natural flow that would otherwise flow upon it" (Exhibit C, Report of Paul Chaloner dated 8 August 2011 at [10], my underlining). I have not accepted Mr Williams' figures. In extreme events such as 1 in 100-year storms there is no "excess of the natural flow" but rather a reduction of the natural flow by reason of the limited pit opening. As the foundation of Mr Chaloner's opinion of reduced value is based upon the assumption of an increased water flow onto Mrs O'Brien's property, apparently in all storms regardless of magnitude, and that assumption is not established, the opinion is left without a factual foundation.
4. Mr Chaloner also assessed that the property value was diminished because "a much larger pipe and overland flow system has been installed than what would normally have been required" (see Exhibit C, Report of Paul Chaloner dated 8 August 2011 at [1.2]). But there is no basis to attribute this drainage system of Mrs O'Brien to the existence of the Council drain.
5. Mrs O'Brien utilised a 2m wide area for her drainage system reserved for the inclinator rather than a 1m wide area that may have been sufficient to accommodate the water flows. There was no evidence that this was due to the additional flows created by the Council drain. Nor could it be, since the drainage system was designed to accommodate a 1 in 100-year event as assessed by experts retained by Mrs O'Brien, and the Council drain would moderate or lessen flows in that event rather than magnify them. Accordingly, no diminished value by reason of the larger area reserved for Mrs O'Brien's drainage system can be attributed to the works of Council.
6. Mrs O'Brien correctly submitted that no contrary valuation evidence was served and Mr Chaloner was not challenged on his evidence. But this does not mean that Mr Chaloner's opinion must be accepted. His opinion evidence relied upon assumptions about water flow and that the size of Mrs O'Brien's drainage system resulted from the Council drain, assumptions which were not established by the evidence. In my view, any diminution in value based upon an increased water flow is mistaken, and any diminution in value based upon the size of Mrs O'Brien's drainage system cannot be attributed to the Council drain.
7. In my view, once the measures I have indicated are implemented to prevent debris from flowing through the Council drain, there is then no factor impacting on the value of Mrs O'Brien's home. There is a more regular, but less extreme flow of water through her drainage system, but I am unable to conclude that that represents a negative impact on the value of her property. That matter was not considered by Mr Chaloner.

C. Conclusion

1. I find that Council is liable in nuisance in directing an increased water flow onto Mrs O'Brien's land in frequent lower magnitude events. This impedes Mrs O'Brien's reasonable use and enjoyment of her land by depositing a significantly increased level of debris, but not in the other respects claimed by her.
2. My preliminary view is to order that Council, by the installation of a grate or other device on the pipe opening in the pit, preclude the transport through the pipe of plastic bottles, bags and other artificial refuse greater than approximately 25mm in diameter. I note that Mrs O'Brien did not seek that any injunction be enforced immediately. In any event, as this particular remedy has not been the subject of submissions, I propose to hear from the parties as to whether it may be inappropriate.

D. Orders and costs

1. Accordingly, the orders of the Court are: 1. Direct the parties to bring forward orders that reflect these reasons. 2. In the event of disagreement, the matter will be relisted in respect of orders. 3. In any event, the matter will be relisted in respect of costs.

Amendments 08 August 2016 - 31 July 2015 removed as a hearing date. Included erroneously. DISCLAIMER - Every effort has been made to comply with suppression orders or statutory provisions prohibiting publication that may apply to this judgment or decision. The onus remains on any person using material in the judgment or decision to ensure that the intended use of that material does not breach any such order or provision. Further enquiries may be directed to the Registry of the Court or Tribunal in which it was generated. Decision last updated: 08 August 2016