Flood risk

How we're managing local flood risk

As a lead local flood authority (LLFA), we are responsible for leading the coordination of local flood risk management in Wandsworth. This includes ensuring that flood risk from surface runoff, groundwater and small watercourses and ditches, known as ordinary watercourses, is identified and managed as part of locally agreed work programmes.

Our long term management of local flood risk is underpinned by our legal duties under the Flood and Water Management Act 2010 and Flood Risk Regulations 2009.

Developing a Local Flood Risk Management Strategy

The Local Flood Risk Management Strategy sets out how local flood risk, defined as flood risk from surface water, groundwater and ordinary watercourses (small watercourses and ditches), will be managed in Wandsworth over future years. It is a legal requirement under the Flood and Water Management Act 2010 and must be consulted on with the public and other risk management authorities prior to being adopted.

We are currently in the process of producing the Strategy for Wandsworth.

Investigating significant flooding events

We have a duty to investigate and publish the findings of any significant flood events within Wandsworth. This includes identifying which authorities have flood risk management functions and what they have done or intend to do in exercising these with respect to the flooding incident.

There is no set guidance for what constitutes a 'significant flooding event'. We have developed a set of criteria and a procedure for when and how we will investigate any significant flood events. These are currently being finalised and will be published here following approval.

All reported flooding incidents, irrespective of whether they require a formal flood investigation, will be recorded in our Flood Incident Database. This allows us to improve our understanding of flood risk and flooding mechanisms across the borough and provide a robust evidence base for securing funding through external funding streams to implement flood mitigation measures.

Managing ordinary watercourse activities

We have overall responsibility for regulating the management of activities that create obstructions to flow in watercourses to ensure that flood risk is managed appropriately. It involves giving consent for acceptable work to be carried out and taking enforcement action if work is unacceptable. This is important as work that is carried out without consent has the potential to increase flood risk to people and property, including those unconnected with the works.

Ordinary watercourses are all watercourses, including rivers, streams, ditches, drains, cuts, culverts, dikes, sluices and passages through which water flows that are not identified as a Main River on the Environment Agency's Main River Map.

It is the responsibility of the riparian owner to ensure that the watercourse is maintained and all obstructions (natural or otherwise) are cleared so the normal flow of water is not impeded. If you wish to undertake any works, temporary or permanent, in or adjacent to an ordinary watercourse you will need to seek consent before commencing works.

Register of flood risk assets

We have a duty to maintain a register of structures or features that are considered to have an effect on flood risk, which includes details of ownership and condition.

Designation of features considered to be important for flood risk management

We have powers to designate structures that affect flooding in order to safeguard assets that are relied upon for flood risk management. Once a feature is designated, the owner must seek consent from Wandsworth to alter, remove or replace it.

Approval of Sustainable Drainage Systems (SuDS)

The Flood and Water Management Act 2010 has made provision to establish all LLFAs as the Sustainable Drainage Systems (SuDS) Approving Bodies (SABs), responsible for approving and adopting all SuDS for new developments and ensuring that these are provided in line with National Standards and best practice guidance.

SuDS are drainage systems that aim to mimic nature through managing surface water to take account of water quantity (flooding), water quality (pollution) and amenity issues. They can be designed to slow down water runoff before it enters rivers or other watercourses, provide areas to store water in natural contours and can be used to allow water to soak (infiltrate) into the ground. They could include measures such as green roofs, rainwater harvesting, permeable paving, rainwater gardens, swales or ponds. 

When enacted, Wandsworth Council will become the SAB for the London Borough of Wandsworth. At present, the date for commencement of this duty has not been confirmed.

We will review the requirements for SuDS approval and establishing the SAB as information is made available from Central Government.

Working with other flood risk management authorities

We have a duty to lead on local flood risk management, including establishing effective partnerships both within the Council and with external risk management authorities including neighbouring boroughs (as LLFAs), the Environment Agency and Thames Water.

South West London Flood Group

The South West London Flood Group was formed in 2011, comprising the LLFAs of Wandsworth, Merton, Sutton, Croydon, Kingston and Richmond, and the Environment Agency and Thames Water. The Group meets quarterly to discuss flood risk management activities across South West London to ensure a coordinated approach, sharing of best practice and identifying opportunities to undertake joint working.