There are three water mains along Lisson Grove in central London with diameters of 4',9' and 36' In February 1997, Diggenwell Plant, engaged in that ubiquitous activity of cable laying, was digging a trench across Lisson Grove from east to west. Just after midday water began to appear in the trench. Diggenwell called Thames Water. No one at that stage realised Diggenwell had hit the 36' main. At 3.45pm, the main, in the words of His Honour Judge Seymour QC, 'exploded'. Thames managed to shut it three hours later but by that time properties in the vicinity had been flooded, costing the water services company more than £750,000 in compensation.
Last year, the judge heard Thames' claim against Diggenwell, in which Thames said the flood damage was the contractor's fault. The judgment makes interesting reading, mapping out Thames' responsibilities in respect of its underground services, reciting the saga of what happened, and setting out the judge's condemnation of Thames' handling of the situation.
The Metropolis Water Act 1852 obliges Thames to maintain accurate maps of mains and pipes.
Thames' maps of Lisson Grove show the three mains, with the 36'main along the western kerb.
It is, in fact, in the middle of the road.
Diggenwell claimed Thames knew that the map was wrong; that the 36' main was in the middle of the road; and that the main was at no great depth. It said Thames knew because less than five months earlier, and about 5m further down the road, another contractor digging another trench had hit the same main. What is more, one of Thames' employees, Mr Frost, attended both incidents. Putting to one side what this says about how often we have to endure roads being dug up, Diggenwell pointed to this earlier event and said that the true cause of the damage was Thames' failure to know or quickly realise that it was the 36'main that had been damaged.
The judge pieced together the evidence carefully. Diggenwell had started working its way slowly across the road using jackhammers. The 4' main was exposed. The workmen then encountered a 'box'of hard concrete where they were expecting the 9'main to be. The jackhammers could not deal with the concrete, so they began to use a JCB to tackle the area of concrete from both the east and west sides, apparently working on the assumption that the width of the concrete was consistent with it containing a 9' main. The JCB, working at a shallow depth on what was assumed to be the far side of the concrete box, hit water.
Within about 30 minutes Thames arrived on site. It did not ask Diggenwell what mains had already been found. If it had, Thames would have realised the 4'main was already safely exposed.
Instead, Thames followed what the judge described as its 'rigid and inflexible approach' of successively shutting down the mains, starting with the smallest. It shut down the 4' main (which was plainly undamaged) and was still shutting down the 9'main when the damaged 36' main burst.
The judge decided Diggenwell had been negligent to use the JCB on what it assumed to be the far side of the concrete when it did not know what was beneath it. But he went on to find that it was Thames' failures that were the real cause of the flood damage.
Experts agreed that after the earlier incident Thames should have updated its plans or otherwise noted the position and depth of the largest main. On arriving at the site, it should have made a proper assessment. The judge concluded that if Thames'personnel had been equipped with all the relevant information known to the company, they would have appreciated, at once, that the main that had been hit was probably the 36'one, and shut it. Moreover, they could have done so without disrupting the water supply to the neighbourhood.
As to Mr Frost, the judge described it as 'wholly inexplicable'that he did not share his knowledge of the location of the 36' main with the other Thames personnel on site. Piecing together the timetable, the judge concluded that, had Thames acted as it should have done, the main could have been closed before it exploded, thereby avoiding the flood. What a shower.