The catchment of the brook is somewhat in reverse, with the upper half, south of Wimbledon Common being heavily urbanised and concreted and the lower half being more verdant and open. This can lead to pluvial and fluvial flood risk in our area, writes our Project Manager, Tarun Ingvorsen.
Pluvial flooding comes from the rain and is exacerbated by poor surface water drainage. If an area is concreted over, the water can not go anywhere, causing flooding. When this enters a watercourse, causing it to burst its banks, we have fluvial flooding – flooding from a watercourse, where there is too much water for the river channel to hold.
As the Beverley Brook sits within the tidal Thames it, too, is affected by the tides, as far up as around Rocks Lane. When the tide goes upstream, it effectively acts as a wall for water coming downstream. This is called tide lock and can cause fluvial flooding as the water has nowhere to go, apart from out of bank. When all three of these events happen at the same time, as in July 2021, devastating flooding can result.
A fourth type of flooding exists – this is called ground water flooding. This is when the water table is so high, that water seeps upwards and can cause localised saturation and inundation.
It is important to remember that floodplains and floods are natural habitats and processes that benefit river ecosystems and the land around them. However, as populations have grown, flood plains have been built upon and altered, resulting in more dangerous and damaging floods than would otherwise have occurred. BCL aims to develop community recognition of flood plains as a vital and necessary ecosystem in natural river management and flood resilience. However, because we have heavily developed the floodplain of the Beverley Brook, flooding where it is meant to happen can now have devastating results for our local area.
Flood resilience can be defined in two ways: with hard engineering flood defences (Thames Barrier, tide walls, etc.) and without. Flood defences typically work against nature and can cause problems themselves: if the Thames Barrier stops working, high tides will surge upstream. If water breaches flood walls, it will be trapped on land for much longer that if it was allowed to return to the river without a wall.
Definitions of flood resilience without hard engineering can be described as:
- Building capacity within communities to manage water before, during and after flood risk events,
- Managing the risk of damage from flood events to people, property and community,
- Reducing the impact of climate change and enabling a swifter and less costly recovery.
Here at BCL our focus is to work with nature and as such, we tend to steer away from flood defences.
Much of Barnes, Mortlake and East Sheen are at risk of one of these forms of flooding. We sit in Flood Risk Zones 2 and 3 and are at risk of flooding if the Thames Barrier fails. We need to manage how we use the land and water around us to help us cope with the impact of this increasing risk.
With predicted increases in sea levels (and tides) from climate change, we must prepare ourselves for the fact that our local areas will continue to flood, likely with increasing frequency. Using a more holistic approach to flood resilience we can alter our habits in little, typically inexpensive ways that will have big impacts on our lives after flood events. After the high waters recede, we will hopefully face less damage to property, fewer lost memories and hopefully, a quicker recouperation from the flood.
Quite a lot of houses in our area – even those further away from the brook and river – are at risk of internal flooding during high tide, pluvial, fluvial and ground water flood events. Even small changes like not draining the bath or not running the washing machine during heavy rains, moving your treasured possessions upstairs, or onto a higher shelf decreases the likelihood of this.
Remembering the ‘Three Ps’ – poo, pee and paper, the only things that should be flushed down the loo, will help keep drains from blocking, reducing the chances of your toilet backing up when it rains. If we all do these little things, we can help make ourselves and each other more resilient to flooding in the future.