[2023] UKUT 00282 (LC)

Of the items of evidence on which Mr Evans relies, the first three, from the GL Martin investigation, and the fourth, about the pool, point to water levels having been lower in 2004 and 2007, and are positive evidence of pre-works water levels. There is no longitudinal survey over time– the best we have is the three weeks when the pool was empty in May 2004 (and not, therefore, during a period of drought). There is no survey that covers the whole garden – but the GL Martin evidence at the south end and the evidence about the pool at the north end are independent of each other. As to the pool, Mr Groves said nothing to counter Mr Hollingworth’s and Mr Brookhouse’s evidence. As to the GL Martin data, Mr Groves’ comments were speculative and unevidenced. It would have been helpful to have more information about the procedures used by GL Martin; but if procedures for taking reliable measurements (such as testing every five minutes over a 20 minute period) are as Mr Groves said “industry standard” then it is more likely than not that they were followed. And Mr Groves produced nothing to justify his view that a water level recorded at the point where made ground gives way to clay cannot be accurate. We are not persuaded that the data levels recorded by GL Martin were not accurate.

The conditions in the garden seen by Mr Morley indicate that water levels were higher after the works, because such conditions had not been seen before the works. The other three items on which Mr Evans relies are all consistent with his view.

None of this is top quality evidence about the whole garden, although we regard the GL Martin measurements as good quality evidence about the area concerned. And on the other hand there is no evidence whatsoever that water levels were around 2m AOD before the works were commenced, and in light of the surrounding topography and of what is known about the nearby watercourses levels of 2m AOD would call for explanation; there would need to be an unusual feature in the nearby land to be causing such an anomaly.

Such evidence as we have indicates that levels were as expected before work commenced, and that the 1.3m seen by GL Martin is likely to be typical if on the high side. Even if that measurement was wrong by 20cm, at the limit of the margin for error that Mr Groves postulated, that would be half a metre below that seen in the Eldred data, which agrees with one end of Mr Evans’ range since he believes levels were 0.5 to 0.9m lower.

Mr Evans has provided a hypothesis about how water levels could have risen.

The old wall at the property is, as we said above, not very old. There is a photograph of a previous wooden wall in 1936 (when the property was advertised for sale in Country Life), and landward of that a line on a nineteenth century OS map may represent a still earlier structure. The riverside boundary of the property has moved outwards over the years, certainly in the last 150 years. Mr Evans suggests that the remains of earlier walls remain buried in the garden.

The old wall, while not impermeable, provided a reasonable defence; before the works there was no flooding save for the isolated instance of storm Xaver in 2013 (see paragraph 17 above). However, in the course of the respondent’s work the old wall has been taken down to below ground level and has been structurally compromised below ground too as we have seen (paragraph 32 above). It does not present the same barrier to water as it did before the work.

Mr Evans hypothesises that water flows at high tides into the material between the new wall and the old wall, and further penetrates the old wall (in its damaged condition) into the ground between the old wall and what he called the “buried revetment” – the remains of the supposed still older wall below the ground. He surmises that water overtops the buried revetment only at spring tides; at neap tides it does not do so. But once over the buried revetment it cannot flow back freely. There is no tide coming towards the river to lift it over, and the ground riverward of the revetment is under pressure of water from the river so it is only going to drain back through the buried revetment and then the old wall very slowly at extremely dry periods such as the drought of summer 2022 – hence the low water levels at that date. Mr Evans drew some support for his hypothesis from the consistently elevated levels in pipe 2 in the Eldred data; he explained that while borehole 6 goes up to 2.4m AOD at high tides and back down again to below 2m, pipe 2 (nearer the house) only oscillates between 1.9m and 2.1 or 2.2m. That led him to the view that something was stopping pipe 2 going down further.

Mr Groves’ only answer to this hypothesis is to maintain that water that flows into the property also flows out again. We accept that that may be largely true, but that is not inconsistent with the build-up of water underground by the mechanism that Mr Evans has suggested. If that is what is happening then what flows in flows out, but what is in effect stuck behind underground structures stays there, and therefore the overall water level is higher.

Mr Evans’ hypothesis places a lot of weight, metaphorically, on the supposed buried revetment. We do not know if it is there but the respondent has not argued that it is not. But there is evidence that there used to be a different wall, at least in the 1930s. It makes sense to suppose that if the garden was extended, older material might remain underneath the newly extended garden. Mr Groves has not explained why Mr Evans’ hypothesis does not work if the buried revetment is present. We find that there is probably material underground. We think that Mr Evans’ explanation is plausible on that basis. We do not need to make a finding of fact about the mechanism by which the water levels have risen; but the fact that there is a plausible explanation gives us further confidence in the evidence that water levels have risen.

In closing Ms Ward KC made the point that the buried revetment has always been there. So it has, but before the works were done the old wall had not been reduced in height and had not been damaged by the work. Far more water is able to get past it than was previously the case, and so there is more scope now for the process Mr Evans postulates.

In conclusion, such evidence as we have, together with the expectations of professionals about groundwater levels in land in the position of The King’s Lodging, and the explanation provided by Mr Evans, all lead us to find on the balance of probabilities that groundwater levels at The King’s Lodging were significantly lower before the respondent’s works were carried out than they were when the Eldred data were recorded. We can infer that they have been at similar levels to those in the Eldred data in similar conditions since then, which are likely to have been typical save in times of drought (when we know that water levels were lower). We can infer that they were higher when the extra-high tidal inflow occurred in 2019. No cause for the raised levels has been suggested other than the respondent’s works and we infer that the raised levels were caused by the works.

The claimants have made out their case that water levels have risen at The King’s Lodging as a result of the respondent’s works by somewhere between 0.5m and 1m, and probably nearer to 1m.

The extra-high tidal inflows

In its statement of case the respondent said: “It is admitted that the [new wall] as originally constructed left a gap at the corner with the dock inlet at the Property. This was remedied by the insertion of the gravity plug referred to at paragraphs 15 and 16. It is denied that there is any ongoing tidal flooding of the garden.” Yet the experts agree that the extra-high tidal inflows will recur when the river level exceeds 3.1m AOD (which it has not done since January 2019) – unsurprisingly since no remedial work has been done since the last occurrence.

The respondent also pleaded that “… the Respondent does not believe that the appearance of groundwater in the garden of the Property is a result of the Works. It is a natural phenomenon and was likely always occurring, but only now visible as the topsoil of the garden has been removed.” We take that as a reference to the extra-high tidal inflows. It was a surprising assertion in light of the work the respondent has done to try to stop those inflows, and was at odds with the view of their own personnel and of CH2M during the period when the remedial works were carried out. In light of the hydrologists’ agreed position the respondent’s pleaded case was clearly incorrect on this point.

Mr Groves in his first report explained that there were “at least two leakage mechanisms” at work when these inflows occur:

“(a)

chronic failure of the concrete ‘seal’ between the outside of the old river wall and the new RC between it and the SSP (and, by implication, the reinforcing works that were undertaken to prevent inflows in 2017) along the line of the wall and (b) through construction joints within the Works perpendicular to the line of the wall.”

If we had concluded that groundwater levels at The King’s Lodging had not risen since the works were undertaken, we would still have to consider whether the extra-high tidal inflows were likely to cause damage to the house in the future. As it is we have found that water levels have risen. Insofar as those raised levels have caused or are likely to cause problems for the structure of the house, then the future extra-high tidal inflows can only exacerbate that problem. And they are likely to become more frequent; Mr Evans pointed out that sea levels are predicted to rise, and that by 2057 normal high spring tides will be at 3.25 AOD, so what is currently extra high will become normal.

Mr Groves produced a calculation which he said demonstrated that river water cannot reach the house because its velocity, of a few millimetres per hour, will never be sufficient for it to do so before it flows out again. One of the variables in the calculation is the consistency of the ground, and the difficulty with that calculation is that the consistency of the ground is unknown; Mr Groves explained that he had done the calculation using different values for the ground, assuming maximum and minimum permeability. But of course the ground is likely to contain subterranean structures between the house and the river and any calculation that assumes a uniform content is unlikely to be accurate. Another difficulty is that the calculation appears to be at odds with what has been observed at the property, both in the Eldred data which show water rising very fast indeed when tides are rising and in the videos of inflowing water which show the extra-high tidal inflows flooding in. Mr Groves’ response to that was that vertical velocity is different from horizontal velocity; but he agreed that even if river water does not itself reach the house it will displace groundwater which will rise in response (see paragraph 101 above).

Mr Groves’ calculations of horizontal velocity therefore offer no comfort; extra-high tidal inflows will continue to occur, will continue to introduce saline water into the garden, and will – however temporarily – further raise the groundwater levels in the garden and around and under the house. If Mr Evans’ hypothesis about the cause of the raised groundwater levels is correct then extra-high tidal inflows will overtop any buried structures, as the spring tides do but more so. Even when the ground dries out, as it did in summer 2022, the raised levels will gradually be restored as wetter conditions recur, and that process will be hastened and reinforced by extra-high tidal inflows when they recur. And recur they will, with increasing frequency as sea-levels rise.

Conclusions about the hydrology evidence

Our overall conclusions follow from the two previous sections and can be briefly stated; we have found that groundwater levels have risen at The King’s Lodging after, and as a result of, the respondent’s works. Any problems caused by the raised groundwater levels can only be exacerbated by extra-high tidal inflows.