Types of flooding
Different sources of flooding can affect residents in Lambeth. These can often occur at the same time, such as when heavy rain causes combined surface water and sewer flooding.
Flooding from rivers
Also referred to as fluvial flooding, flooding from rivers alone is not a major concern in Lambeth. The only open rivers we have are the River Thames, forming the northern borough boundary, and a small section of the River Graveney in the southwest. The channels and banks of both rivers have been heavily modified over the years, and other rivers in the borough - including the lost River Effra running from West Norwood to meet the Thames at Vauxhall - have long been buried and used as sewers.
The Environment Agency is responsible for managing the risk of flooding from rivers and the sea, and you can view a map of flood risk on Gov.UK.
Tidal flooding and storm surges
The Environment Agency is also responsible for managing tidal flood risk. Much of London, including the northern part of Lambeth, relies on the Thames tidal defences for protection from this source. The River Thames is tidal and can rise and fall by up to 7 metres twice a day. The defences, consisting of the Thames Barrier and raised walls, are designed to protect the city from high tides and storm surges. There is a risk of flooding across the north of the borough in the unlikely event of water breaching the defences. The Environment Agency has modelled likely water levels in various breach scenarios, which can be viewed in our Strategic Flood Risk Assessment Addendum (PDF 3.9MB).
Due to climate change, sea levels are predicted to continue rising this century, and we expect more extreme storms across the North Sea, with surges that could raise the Thames beyond normal tide levels. The Environment Agency is implementing the Thames Estuary 2100 (TE2100) Plan to combat rising sea levels and to ensure London remains protected to the same standard as today.
Sewer flooding
The vast majority of Lambeth is served by Thames Water’s combined sewer network. A combined sewer mixes foul water from our buildings with rainwater that runs off roofs, streets, and parks. This means the system must carry more water when it rains, and because we still use Victorian-era sewers designed for a much smaller population, there is a risk of them overflowing and backing up into homes and businesses. To reduce the volume of rainwater entering our sewers, Lambeth Council has worked with Thames Water and others to install sustainable drainage systems (SuDS) across the borough.
Surface water flooding
Surface water flooding, also known as pluvial or flash flooding, can happen when heavy rainfall overwhelms our drainage system. It can happen quickly and unpredictably, but generally, people in low-lying areas and basements are most vulnerable. You can view the Environment Agency’s to check your risk of flooding from surface water map or to see which areas are likely to be affected now and in future.
Due to climate change, we expect Lambeth to become hotter and drier in summer and warmer and wetter in winter. This will lead to more extreme storms, with intense rainfall over a short period. In July 2021, parts of London experienced a month’s worth of rainfall in just 2 hours, flooding an estimated 2000 properties. This is the type of storm we expect to see more often now than in the past.
Lambeth is a highly urbanised area, with most of the surface area taken up by buildings and roads that can’t absorb water. This means water runs off quickly when it rains, overwhelming old drainage systems not designed for today’s population or climate.
To better understand and adapt to these issues, Lambeth Council has conducted a Surface Water Management Plan (PDF 5.3MB) and is installing sustainable drainage systems (SuDS) across the borough.
Groundwater flooding
Groundwater flooding is much less predictable than other types of flooding. The main water table beneath Lambeth lies deep underground in the chalk bedrock, and a thick layer of clay between it and the surface effectively acts as a plug.
Closer to the surface, there are layers of gravel and sandier soils, which can hold some water. These pockets of perched water usually rise and fall seasonally, so if we’ve had a particularly wet winter, we may expect some groundwater to emerge in basements in spring. Groundwater generally flows towards the River Thames, so areas close to the river are also susceptible.
To manage the risk of groundwater flooding, the council’s planning and flood risk teams assess the risk posed to, and from, new development in the borough.