Oldcorn & Anor v Southern Water Services Ltd

A statutory sewerage undertaker may owe a common-law duty where its positive act creates a foreseeable risk of flooding, provided the claim does not merely enforce statutory infrastructure duties through a process inconsistent with the Water Industry Act 1991. The measured duty applicable to natural nuisance and non-feasance does not govern negligent positive acts. In that situation, the standard is that of the reasonable water authority. A defendant must assess the competing risks created by a flood-prevention measure, including its effect on surface-water discharge. Causation must still be proved on the balance of probabilities, ordinarily by reliable hydraulic modelling.

The claimants owned a property at Felpham which flooded during exceptional rainfall in June 2012. They alleged that Southern Water negligently installed a Tideflex valve in its storm-water system, substantially restricting the discharge of surface water and causing the flooding. Claims in negligence and nuisance were defended on the grounds that the statutory scheme displaced any common-law duty, that the claimants had no relevant drainage right, that the common enemy principle applied, and that the Tideflex did not cause the flooding.

The court determined the applicable duty, the extent of the flooding, whether installation of the Tideflex was negligent, and whether the claimants had proved causation.

1. Duty. The court held that the claim was not an attempt to require Southern Water to construct new sewers or otherwise perform its statutory drainage obligations. It concerned a positive operational act: installing a valve which allegedly created a restriction. Such a claim was not inconsistent with the regulatory scheme under the Water Industry Act 1991. The reasoning in Hanifa Dobson v Thames Water Utilities Limited was followed. Barratt Homes Ltd v Dwr Cymru Cyfyngedig No 2 and Nicholson v Thames Water were distinguished.
2. The common enemy principle did not assist Southern Water. The Tideflex was not installed to protect the defendants’ own land from the sea, and the complaint concerned negligent interference with the drainage system. The relationship between easements and tortious duties was governed by modern nuisance and negligence principles, not exclusively by property law, applying Ward v Coope.
3. The measured duty described in Sedleigh-Denfield v O’Callaghan, Goldman v Hargrave, Leakey v The National Trust and Vernon Knight Associates v Cornwall Council applied to natural nuisance and non-feasance. The present case concerned misfeasance. Southern Water therefore had to meet the standard of the reasonable water authority.
4. Negligence. The Tideflex substantially restricted surface-water flows. Southern Water had failed to assess its likely hydraulic effect or to balance the risks of sea-water flooding and surface-water flooding. A reasonable statutory sewerage undertaker would have undertaken that assessment before installation. The installation was therefore negligent.
5. Causation and disposal. The claimants’ hydraulic model contained material uncertainties concerning impermeable areas, rainfall and the timing of flooding. The defendants’ model was also not sufficiently reliable to establish the counterfactual. The court was consequently not satisfied that, but for the Tideflex, the property would probably have avoided flooding. The claim was dismissed. Quantum was not determined, although the judge indicated the award that would have been made if causation had been proved.