In this blog we hear from DCRT Natural Flood Management Officer, Debbie Coldwell. Read on to find out how the natural approach to flood defence could help to better protect us in the future.
November 2019 was a devastating month for many within the Don Catchment. More rainfall fell in 24 hours in some areas than normally falls over the entire month at this time of year. Hundreds of people have been flooded out of their homes and vast expanses of land left underwater for prolonged periods. Unsurprisingly, this has led to a lot of questions about the causes of flooding, and what can be done to reduce the risk in future. A good summary by the BBC is available here. Issues around dredging and hard engineered flood defences (e.g. flood barriers) in particular have received a lot of attention, as has the role of more natural flood management methods.
One of the main issues with both hard engineered solutions and dredging is that they are not sustainable. With climate change, we are expected to experience both more, and higher intensity storms and we cannot simply keep dredging deeper channels and building bigger walls. A much wider approach needs to be taken that includes these traditional measures of flood defence, in combination with management throughout the whole catchment that helps to capture and “slow the flow” of flood waters. There are a variety of ways that this can be done, and it is generally referred to as Natural Flood Management. This includes measures such as tree planting, which can help to increase evaporation of rainfall and allows more water to be absorbed into the soils beneath them. Temporary storage pools can be created in the landscape that fill during heavy rainfall and drain away slowly, delaying the time it takes for this water to reach our river networks. Leaky woody dams can be placed within streams and rivers, helping to slow the speed of water both in the channels as well as causing it to spill out on to vegetated banks that also slow flows. Soils on farms can be improved to better act as sponges, capturing more water and reducing the amount of top soil washed away with knock on benefits for agriculture. If this kind of management is done at a great enough scale throughout the landscape, then it can help to reduce both the maximum height of flood waters and the time it takes for those flood peaks to reach downstream populated areas, allowing more time to prepare.
There are lots of other benefits of NFM too. For starters, it is generally much cheaper than more traditional flood defences and by taking some of the pressure off these walls and barriers, NFM can also help to increase their lifespans, providing further cost savings. NFM can also help to better water quality by filtering out sediment and pollutants, improving our rivers and reducing water treatment costs. NFM can also provide lots of habitat for wildlife and help capture carbon dioxide through the planting of trees and improving soil health, for example.
This is why DCRT support the NFM movement and took me on in April this year. I’ve been looking into the potential for NFM schemes in and around the Chesterfield area in the Upper Rother Catchment and there is an awful lot of opportunity! Development of plans on council owned land is underway and we’re also hoping to work with many private landowners and managers throughout the catchment. NFM works best by having as many features as possible throughout the landscape to help capture and slow down the movement of water as it travels downstream. Each individual measure doesn’t have to be very big, it’s the cumulative effect of water being slowed down and held back across a wide area that helps to reduce flood risk.
It is important to recognise that NFM cannot stop flooding. After prolonged periods of heavy rainfall, NFM features will be overwhelmed and no longer able to hold back further rainfall, which is when more traditional flood barriers come into play, and these too can be overtopped in the severest of cases. Ultimately tackling climate change, which is increasing the number and severity of storms is essential in reducing flood risk. NFM, however, if done over a large enough area, has an important part to play in reducing the risk from many storms that would have otherwise lead to flooding. So if you own or manage land in the area and would like some advice on how you can help contribute to slowing the flow, do get in touch!