Catchment Management Techniques
Hot topic – Natural Flood Management
Natural Flood Management (NFM) is a buzz word at the moment, but what is it and what does it mean for our catchments in UBOCP?
The intention of NFM is to:
• Work with natural processes
• Increase infiltration by following best practice for soils and land management
• Store water within the catchment
• Reconnecting with the natural floodplain
• Slow the flow in the river
• (On the coastal this can include salt marsh / realignment)
The concept of NFM is not new. For millennia humans have recognized, respected and utilized the power of flooding. The reason for its recent revival as a viable management option are many. NFM isn’t just a temporary fad – it’s integral to flood management:
• There are many rural communities where there are only a few properties at risk and it can be both technically challenging and financially disproportionate to use hard engineering solutions.
• NFM is good for the environment. Features such as leaky log-jams provide habitat as well as reducing flood-risk, whilst trees have a plethora of benefits in the natural world. By holding water on land and increasing infiltration rates it can contribute to reduced diffuse pollution into our rivers, and therefore reducing the need to apply more agri chemicals as they are not washed away, creating a cost saving in some cases.
• NFM is several orders of magnitude less expensive than hard-engineer solutions. It is cost-effective.
• The ability of NFM to evolve and develop as the world evolves and develops is an important selling point. People often talk about climate change in loose terms, but what it means is more unpredictability in the natural environment and more extremes. NFM can cope with that – it isn’t about setting a wall to a certain height – it’s about working with nature and changing with it.
• it is often about working with the traditional forms of flood management
• Designed to ensure land drainage is maintained
It is important to stress that NFM better suited to smaller, more frequent flood events. It is NOT about providing protection from flooding in the big events, but to reduce the impact of flooding.
Tree planting in floodplain as a method to slow surface water runoff into the river (once trees have grown)
How NFM measures affect the flow of water :
– Slowing the flow in stream – Reducing the speed at which water travels through the river system can provide communities with more time to prepare for flooding. Attenuating flow can also reduce the overall flow peak. In one example where NFM has been implemented, the measures increased the time to peak flows by 60 minutes. That’s 60 minutes more time for vulnerable people and emergency services to prepare and act.
– Water storage – Creating areas for rainfall, surface runoff and floodwater to be retained, away from people and property, can reduce flood-risk. Typically such storage reduces the flood peak by taking more time for the water to move through the catchment.
– Desynchronisation of flows – Where tributaries meet within a river system there can be substantial flood-risk. NFM interventions can force floodwater to arrive at different points within the catchment at different times, causing multiple small peaks in flow rather than one large one.
– Interception of water – Reducing the amount of water reaching the floodplain by intercepting it within the wider catchment can significantly reduce peak flows.
Series of woody dams can help slow the flow of water in the channel by holding back the water in times of high flow
In catchments where there are NFM measures being put in place they are working with the EA or the relevant Lead local flood authority to ensure that relevant permissions are sought and wider flood risk is accommodated. Anyone seeking to explore NFM on their land should contact the EA for more information regarding permissions and to explore any options.
There are currently projects funded within our UBOCP catchment to develop our understanding of NFM and which measures are most feasible where. These include: Leckhampstead – Bucks CC / Alconbury, EA / upstream of Buckingham on the Ouse, River Thame conservation trust with Alyesbury Vale District Council. You can find updates and more information about these from our partners and through your volunteer host.
You can find out more details about NFM by following these links:
Jeremy Purseglove alluded to NFM in his 1988 book “Taming the Flood”,
Government working with Natural Processes
Catchement Based Approach (CaBA) Natural Flood Management
Rhone Mediterranean Corsica Water River Management
–Helen Chapman (Catchment Coordinator, Environment Agency)