Q: What duty does the upstream landowner owe to the downstream owner to prevent flooding nuisance?

A: A landowner owes a measured duty in both common law nuisance and negligence to take reasonable steps to prevent natural occurrences, such as floods, on its land from causing damage to neighbouring properties. The landowner’s liability is subject to the concepts of reasonableness between neighbours and reasonable foreseeability. It has also been suggested that the resources and abilities of both the claimant and the defendant are relevant. The measured duty applies to removing or reducing them for a neighbouring landowner or occupier.

Where the defendant is a public authority with substantial resources, the court must take into account the competing demands on those resources and the public purposes for which they are held. It may not be fair, just or reasonable to require a public authority to expend those resources on infrastructure works to protect a few individuals against a modest risk of property damage.

The upstream riparian owner is:

• Entitled to heighten the banks on its land to prevent floodwater from coming on to it, even if this diverts the flood water on to the land of another. This may be subject to obtaining an environmental permit for flood risk activities for those works. However, the landowner of lower land does not have a duty to receive the water generally outside a defined watercourse and can take reasonable steps to prevent the water entering its land.
• Under no common law duty to improve drainage capacity of its watercourse.
• Under a duty of care, to keep the bed of the stream and structures, such as culverts or trash screens, clear of obstructions.

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