What is Natural Flood Management?
Organisation: The Rivers Trust
Location: European
Type: Technical Support & Training
Healthy river catchments store water in the landscape and slow the flow of water downstream.
Our modern river landscape is very different from what nature intended. We have lost water storage in wetlands, created hard surfaces that water rushes off, and changed our river channels so they move water very quickly. Our rivers are less able to cope with the rain we expect in the future, making flooding more likely to impact communities.
Natural Flood Management (NFM) or Working with Natural Processes (WWNP), as it is also known, to reduce flood and coastal erosion risk involves implementing measures that help to protect, restore and emulate the natural functions of catchments, floodplains, rivers and the coast.
WWNP takes many different forms and can be applied in urban and rural areas, and on rivers, estuaries and coasts. Different terminology such as soft engineering, green infrastructure, sustainable drainage and runoff attenuation may also be used to describe the techniques used.
NFM aims to reduce the maximum water volume of a flood (the peak flood flow) and/or delay the arrival of the flood peak downstream increasing the time available to prepare for floods.
There are 4 key, underlying mechanisms by which this can be achieved:
- Increasing storage: creating temporary storage which will fill up during a flood event and empty slowly (e.g. reconnecting functioning floodplains and creating storage ponds)
- Increasing catchment and channel roughness: this ‘slows the flow’ by increasing the resistance to surface and in-channel water flow (e.g. planting trees and hedgerows, restoring meandering rivers and installing leaky dams)
- Increasing losses: this increases the amount of water that drains (infiltrates) into the ground or is lost back into the atmosphere via evapo-transpiration (e.g. changing agricultural practices to improve soil structure and reduce soil compaction and installing sustainable urban drainage systems (SUDS))
- De- syncronising peak flows from tributaries: Slowing down one tributary compared to another can significantly reduce flood peaks downstream.
NFM measures work by affecting one or more of these key mechanisms. The primary aim should be to restore the natural functioning of river catchments as much as possible, but where natural recovery is not possible, measures can be used to emulate natural processes to manage flood risk. The Environment Agency’s WWNP Evidence Base provides a series of one-page high-level summaries about different NFM techniques HERE.
Natural flood management is not the complete solution to flooding but is one of many tools needed to manage flood events. Used in conjunction with other flood management solutions, like hard engineering and community resilience measures, natural flood management can have a beneficial impact on reducing flood risk downstream. Natural Flood Risk Management is a key part of a catchment-based approach, reducing the impact of floods and droughts as well as improving water quality and biodiversity. These benefits will make catchments more resilient to the impacts of climate change if we get the ‘design’ right. It may take a decade or more before we start to see the true benefits NFM.
This page is supported by the Flood Resilient Areas by multi-layEr Safety (FRAMES) project under the Interreg North Sea Region VB programme, funded by the European Regional Development Fund. For more information please visit http://northsearegion.eu/frames/