Question: What have you found to be the most effective way of stopping flooding in the UK?

Josh Wolstenholme answered on 6 May 2020:

This is a great question!

Rivers and water flowing under the ground can only handle a certain amount of water at a time, this is determined by many different things such as the local rocks, shape of the landscape and the size of a river. When water comes down as rain, that rain is looking for the fastest and easiest way back to the lowest height – the sea! It can travel over or through the ground and soil, and the ability for the ground to absorb water determines how quickly water can make it back to the sea. If you have rocks or surfaces that water finds it difficult to pass through (they have a low permeability) such as shale or most concrete, then the water can’t go any deeper into the ground. This causes it to make its way to a river more quickly. If you’ve got steep slopes as well, the water can move even faster as it doesn’t have time to drain into the soil. Each part of the world is different, whether by the amount of buildings, shape of the land or river network, so each river catchment will respond differently. When you get lots of rain like we did in February, all that water is either filling up the space in the ground so no more can get in, or travelling towards the river.

Flooding happens when there is too much water in the catchment than the river or groundwater can store, so the water in the river rises until it bursts its banks. Flooding will always happen as it’s a natural process, we can only protect against it to a certain level based off a ratio of cost to benefits, availability of material and predictions based on past events. You can protect against flooding using big expensive concrete walls in an area to increase how much water the river can hold, but this only moves that water downstream, the problem goes elsewhere. This type of approach is called ‘hard’ engineering, is often designed to protect high value places such as city centres and power stations from a flood of a given size.

You can also manage the land better, by planting trees in the right places, allowing room for the river to flood by connecting it to the floodplain, and making the river longer by increasing the amount of bends in it. All these measures try to give the river space to flood, sacrificing ‘low value’ land such as parks to increase the storage capacity of the river. My work looks at a type of flood management measure called a leaky dam, where the aim is to store as much water as possible in the hills and slowly release it towards the sea, reducing the speed at which the water travels!

In a nutshell, there is no one effective way to stop flooding, as flooding can’t be stopped! It can be managed, to an extent, but each area is different and will have a different most effective method, or more likely a group of methods. Areas like Hull which is very flat and by the sea are more vulnerable to flooding from the sea, and therefore has a tidal barrier, to hold water back and reduce the chance of it entering the city. In somewhere more inland like Leeds, there are many methods to reduce flooding, including allowing the river to flood in low value lands, and making the river less straight and more wiggly in places.

The best way to reduce flooding in my opinion is to take care of our uplands, allow peat bogs to soak up all that water and slowly release it into the catchment, and we need to accept that we can’t stop all floods! Focus on resilient housing, buildings and community plans for emergencies are needed, it’s a problem that affects everyone, even in ways we don’t realise.