Natural Flood Management
Natural Flood Management (NFM) harnesses the landscape itself to reduce the impact of heavy rainfall events, reduce flood peaks and help protect smaller, flood-prone communities.
Farmers and land managers can use a number of low-cost NFM solutions help the land act as a ‘sponge’ to absorb – then slowly release – water until after a flood peak has passed. These methods include constructing leaky wooden dams, improving soil health and restoring flood plains.
The main aim is to ‘slow the flow’ of water – a challenge that is growing across the High Weald AONB as the impacts of climate change and development increase.
Natural Flood Management in the High Weald
The waterways, rolling hills and steep-sided valleys of the High Weald mean there are several hotspots for flooding in the AONB.
We are working in partnership with the Environment Agency and several organisations on pilot projects to mitigate flooding in particularly vulnerable areas.
We recently led on the Sussex Flow (Cuckmere and Combe) NFM project. This focused on the Upper Cuckmere and Powdermill Stream to help communities at Horam, Hellingly and Crowhurst.
We are particularly keen to work with landowners in these target areas and are developing funding packages to support this work.
If you are in one of these target areas and would like to find out more, please contact our NFM Project Officer Dean Morrison on firstname.lastname@example.org.
How does it work?
There are a number of different Natural Flood Management methods currently in use across the High Weald:
Leaky wooden dams
These are timber structures created in small upstream tributaries with the aim of temporarily holding back water during periods of high flow. They can be thought of as mimicking the effect of naturally fallen timber in truly wild forests, or beaver dams.
The heavily-wooded landscape of the High Weald – with its steep-sided gill streams – offers ample locations for this approach.
The aim is not to create permanent pools of water, but to store it for a few hours while it slowly drains away. These structures need to be carefully designed using long timbers which will not wash away and cause problems downstream.
A gap is left underneath them so as not to disturb the function of the river in normal flows, and to allow free passage for fish. Often willow is incorporated into the structure, this takes root in water and helps create a long-lasting sustainable barrier.
Soil and crop management
The condition of the land which rain falls upon can make a major difference to whether flooding occurs. Over time, intensive farming practices in the UK have compacted and sterilised soils, reducing the land’s ability to absorb and retain water,
In ideal circumstances the rain falls on land which is able to soak it up and store it (infiltration). If there is a cover crop then even if the ground is saturated, flows of water are slowed down by the vegetation (interception and surface roughness).
Increasing soil organic matter, and encouraging a variety of deep-rooting plants through practices such as regenerative agriculture can greatly increase the soil’s ability to absorb and retain water.
Maintaining crop cover through permanent pasture or winter cover crops helps slow run-off. These practices also have many other benefits such as capturing carbon, preventing soil erosion and improving water quality.
It is sometimes possible to create offline storage ponds to temporarily hold excess water.
These take water in flood conditions and store it before slowly releasing it back over time.
They can be designed to permanently retain some water for wildlife, or to drain completely allowing grazing in the summer months.
Rivers and flood plain restoration
Many of our rivers have been deepened and straightened to speed away the flow of water. They become disconnected from their natural floodplains which means reduced capacity to store water away from residential areas downstream.
There are many good examples of projects which reverse the process by creating meanders or resetting the system towards a more natural condition.
This has the potential to create wonderful habitats for wildlife as well as storing water in the floodplain to feed the river in drought conditions.
Photo credit: National trust, Sheffield Park and Garden