Managing trees and river blockages: Finding the right balance
A fallen tree across a river often sparks concern. Will it cause flooding? Should it be removed immediately? And who is responsible for dealing with it?
These are questions our teams receive regularly, particularly during periods of heavy rainfall or following storms. While it might seem obvious that every blockage should be cleared as quickly as possible, the reality is often more complex. In many situations, trees and woody material in rivers can provide important environmental benefits, and in some locations, they can even help reduce flood risk.
That is why Natural Resources Wales (NRW) takes a balanced, risk-based approach when deciding whether intervention is needed.
Understanding NRW's role
Many people are surprised to learn that NRW is only one of several organisations responsible for managing flood risk in Wales. Alongside local authorities, highway authorities, water companies, infrastructure owners and private landowners, we all have different responsibilities for watercourses and flood risk management.
NRW's Flood Risk Management powers apply to statutory ‘Main Rivers’ which you can see a map of using the links below. However, our powers are generally permissive rather than mandatory. This means that, while we can undertake work where appropriate, we are not legally required to remove every blockage or carry out maintenance at every location.
Our decisions therefore focus on managing risk where intervention will have the greatest benefit for people, communities and critical infrastructure. You can read more about this approach of prioritising funding for communities at greatest risk in Welsh Government’s National Strategy for Flood and Coastal Erosion Risk Management,
Why river blockages matter
Trees, branches and other debris can sometimes obstruct the flow of water. In areas, where homes, businesses and key infrastructure are often located close to rivers, a significant blockage has the potential to increase flood risk.
For example, a large fallen tree that narrows a river channel could restrict flow and increase water levels upstream during heavy rainfall. Where nearby properties are already vulnerable to flooding, this may justify further investigation or action.
However, not every blockage creates a problem. The location, surrounding land use, river characteristics and potential consequences all need to be considered before a decision is made.
When NRW may intervene
Our priority is protecting people and communities from flooding.
We will typically consider intervention when a blockage:
- Creates an immediate flood risk to homes, businesses or communities.
- Threatens critical flood risk infrastructure, such as flood defences that NRW maintains.
- Could damage assets that play an important role in managing flood risk.
- Forms part of a wider flood response during an active flood incident.
Safety is also an important factor. Although a blockage may warrant removal, it is often unsafe to undertake works during high river flows or flood conditions. In these situations, attempting removal can place staff, contractors and equipment at unnecessary risk.
In certain emergency circumstances, NRW may need to act on land owned by others to manage an immediate flood risk, while ensuring landowners are informed as soon as possible afterwards.
When we may choose not to act
It is equally important to recognise that not all river blockages are harmful.
In the right place, fallen trees and woody debris are a natural part of river systems. These features can slow water movement, temporarily store water, reduce downstream flood peaks and create valuable habitats for fish, insects and other wildlife.
You can watch this short video to find out a little more - Healthy rivers - Wood is good.
Removing every tree or obstruction from every watercourse would not only be costly but could also remove many of the natural processes that contribute to healthier and more resilient river environments.
As a publicly funded organisation, NRW must also make best use of available resources. We therefore prioritise work where the risks and benefits are greatest, rather than attempting to remove every blockage regardless of its impact.
The role of landowners and asset owners
Managing flood risk is a shared responsibility.
Landowners often have responsibilities under the common law principles of riparian ownership to maintain watercourses flowing through or alongside their land. Similarly, organisations that own structures such as bridges, culverts and other in-channel assets are generally expected to manage and maintain those features and keep them clear where appropriate.
Where blockages affect privately owned structures or land and pose an immediate flood risk to people and / or communities, the most effective solution is often for the responsible owner to take action, as they are usually best placed to understand local conditions and ongoing management requirements.
This approach is reflected in the Welsh Government's Flood and Coastal Erosion Risk Management Strategy, which highlights the important role that asset owners and operators play in helping manage local flood risk.
Balancing flood risk and nature recovery
Every decision NRW makes is evidence-based and involves balancing a range of factors.
Our specialist teams use flood maps, modelling, asset information, local knowledge and risk assessments to determine whether intervention is necessary. We also consider environmental impacts and opportunities to work with natural river processes wherever appropriate.
In many cases, allowing suitable woody material to remain within a river can support both flood resilience and biodiversity objectives. This reflects NRW's wider commitment to the sustainable management of natural resources and to building resilience in both communities and ecosystems.
A risk-based approach for Wales
There is rarely a one-size-fits-all answer when it comes to managing trees and blockages in rivers.
Sometimes intervention is essential to protect people and communities. At other times, the most sustainable solution is to allow natural processes to continue. By taking a risk-based approach, NRW aims to focus resources where they will have the greatest impact while also supporting healthier river environments for future generations.
Understanding these decisions helps explain why a fallen tree that prompts action in one location may be left in place elsewhere. Each site is assessed individually, with flood risk, safety, environmental benefit and value for public money from finite resources all playing a part in the final decision.
Want to know more?
If you own land next to a river or stream, or would like to learn more about flood risk management responsibilities in Wales, useful guidance is available through:
National Strategy for Flood and Coastal Erosion Risk Management (Welsh Government) - Roles and Responsibilities Page 17 onwards
Riparian Ownership: Maintaining Watercourses (Welsh Government)
Responsibility for rivers, streams, culverts, and canals (NRW) (includes main river map)
Find flood defence structures near you - The National Flood Asset Database (NRW)
Check if you need a flood risk activity permit or FRAP (NRW)
Understanding who is responsible for what helps ensure rivers are managed effectively, flood risk is reduced where necessary, and Wales’s waterways continue to support both communities and nature.