Floods and expert evidence: Oldcorn v Southern Water Services Ltd

Oldcorn v Southern Water Services Ltd [2017] EWHC 62 TCC 

This case sets clear limits on the Marcic defence and confirms that where a sewerage undertaker’s owes a private law duty of care, it may not be able to rely upon the more limited Leakey “measured” duty of care.

C were freehold owners of a property that was the subject of surface water flooding in June 2012. The property is in Felpham near Bognor Regis, and located about 75 meters from the sea wall.

On the western boundary of the property, there was a ditch which connected upstream to surface water sewers and downstream to a piped outfall which discharged to the sea at low tide.  The ditch and connected oversize pipes were intended to store run-off at times of high tide. A flap in the piped outfall was intended to prevent seawater ingress.

Seawater flooding occurred in 2009 as a result of the failure of the flap. As a result D installed a new “Tideflex” valve in the outfall. This was intended to prevent a further incursion by the sea. However, it also had the effect of restricting surface water discharge at times of low tide.

In 2012 – at a time of very heavy rainfall – flooding occurred again. C blamed the restricting effect of the new valve.

 The key issues to be determined at trial were:

  • What relevant legal framework applied, if any?
  • Whether the installation of the tideflex valve was negligent
  • Whether the flooding would have avoided but for the presence of the tideflex valve.

 HH Judge McKenna (sitting as a High Court judge) found that D owed C a duty of care in nuisance and negligence. D had denied the existence of a duty of care on the basis of Marcic v Thames Water [3003] UKHL 66 where the House of Lords held that no duty was owed to a private landowner for flooding caused by inadequate sewers. The Judge closely examined the relevant authorities. Marcic was held to be inapplicable because D had by its positive act negligently installed a valve which restricted the flow in its own pipe.

The standard of care was that of a reasonable water authority. This was not a case to which the Leakey measured duty of care applied, because this was not a case of a “natural” nuisance, and because it was a case of misfeasance, not non-feasance.

D sought to rely on the “common enemy rule” in Arscott v Coal Authority & Another [2004] EWCA Civ 892, that is to say that when installing the Tideflex D was seeking to protect its own property from flooding. The Court rejected this on the facts.  By installing the valve, D was not erecting a defence for the protection of its own land, but protecting C’s land.

The Judge found that “to my mind, on the totality of the evidence, a reasonable statutory sewerage undertaker in the position of the Defendants would have carried out an assessment of the risk of installing a tideflex. Any such assessment would have established that it posed a substantial restriction to the surface water flows and should not have been installed unless and until a proper evaluation of the respective risks was undertaken and an informed judgment made. This was not done…”. Accordingly, the Judge found that, failing to carry out the assessment of the effect of installing the Tideflex was negligent.

Whilst C succeeded on duty and breach, it lost on causation. Both parties relied on expert hydraulic modeling to prove their cases on causation. The Judge found that the flooding of the property was not, on the balance of probabilities, caused by the installation of the Tideflex. This was because of a number of issues with the flood modelling evidence, such as discrepancies as to the severity of the rainfall and the extent of the catchment.

With an increased incidence of flooding in recent years and more such claims coming to trial, this case provides important clarifications as to the extent of a sewerage undertaker’s common law duty of care, the scope of the Marcic and “common enemy” defences, and the applicability of the Leakey duty in nuisance. It is also a timely reminder of the complexities of the causation issues which arise in this type of case.


Neil Moody QC was instructed by Kennedys for the Claimants.








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Filed under Causation, Duty of Care, Expert Evidence, Floods, Nuisance

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