Types of flooding

Surface water flooding 

Surface water or flash flooding occurs when heavy rainfall exceeds the capacity of the ground and local drainage networks to absorb it. It can lead to water flowing over the ground and pooling in low-lying areas. It is typically caused by short intense rainfall. This is identified as the biggest risk in London. 

Surface water flooding is more difficult to predict and pinpoint than river flooding. We estimate that around 2,090 properties in the borough are at a high risk from surface water flooding. 

You will most obviously see this as water ponding on roads. Most roads have roadside gully pots at the side of the road which captures the water, this then flows into Thames Water sewers in most cases or soakways. The local authority highways teams are responsible for clearing gullies and managing these soakaways. 

Report an issue with a drain

After heavy rain, it is expected to see some water in the road or on open land, despite work undertaken to prevent this. It may be because other parts of the drainage system are at full capacity and it will slowly recede. If water is still present after a few hours and you believe the issue is being caused by a blocked or damaged roadside gully, or if you wish to report another non-emergency drainage issue, please report a gully problem.

There are gullies or drainage systems that are present in private estates or roads which are the responsibility of the landowner or private management company, usually shared ownership between residents. Significant structures and their owners where the information is provided by the third party may be identified in the Flood Asset Register produced by the local authority.

Report instances of flooding

If your property has flooded, complete our report instances of flooding. We collect data on flooding to help us work with other authorities and agencies to prepare for and manage future flood risks in the borough.

River flooding 

River flooding (fluvial) happens when a water course cannot cope with the water draining into it from the surrounding land. River flooding Is usually caused by heavy rain falling on already waterlogged land. We estimate that around 5,074 properties in the borough are at risk from river flooding. 

Our responsibility to prevent flooding

We have a range of duties and powers to help reduce and manage flooding within the borough. 

We also work closely with external bodies such as the Environment Agency and Thames Water to provide a joined up approach. Unfortunately it is not always possible to prevent damage to properties in every flood. We do not have a legal obligation to protect individual properties. However, we will do all we can to reduce the risk of flooding and help residents following a flood. 

Main rivers 

Main rivers are mapped and registered by the Environment Agency. The Environment Agency undertakes some maintenance work in high-risk areas. If you notice a blockage or tree on a main river which is causing risk of flooding, call the Environment Agency hotline on 0800 80 70 60. 

Permits are also required from the Environment Agency for structures along main rivers. There are also structures and screens that are managed and cleared on rivers on a more regular basis in periods of adverse weather. This could be the Environment Agency, local authority or other organisation or private landowner. The significant structures will be highlighted in the Flood Asset Register. 

Ordinary watercourses 

Roadside ditches normally belong to the adjoining landowner and not the highway authority, except where land has been acquired for new road building. 

Consent is required from the Lead Local Flood Authority (LLFA) to undertake some works on an ordinary watercourse. If a landowner wishes to pipe, alter a pipe, or dam an ordinary watercourse, they should apply for consent from the LLFA by contacting 020 8871 7620.

Where there is local authority owned land, we have a programme for clearance and maintenance. Where they are piped or culverted, this does not change the responsibility. Please contact the LLFA on 020 8871 7620 to find out more. 

Groundwater

Groundwater flooding occurs because of the underground water table rising, which can result in water emerging through the ground and causing flooding in extreme circumstances. This source of flooding tends to occur after extensive periods of heavy rainfall. 

Reservoirs

A reservoir is, most commonly, an enlarged natural or artificial lake, pond or impoundment created using a dam or lock to store water. There are a number of these may be managed by different companies and landowners. 

Contact details of the responsible body will be displayed at each reservoir, who will have an onsite reservoir plan, however in an emergency please call the local authority on 020 8891 7999 who are responsible for offsite reservoir plans and alerting the wider public of the potential issue. 

Canals

The Canal and River Trust  is responsible for the canals. Contact them:

• For non-emergency related matters, call them on 0303 040 4040
• For emergencies, call the 24-hour number on 0800 479 9947