Managing Trees and Blockages in Rivers: NRW’s Risk-Based Approach
Natural Resources Wales (NRW) plays a key role in managing flood risk across Wales. One area that often raises questions is how we deal with trees, natural blockages, and debris in rivers. These features can influence flood risk, but they can also have ecological benefits. So, when does NRW intervene; when do we expect others to act; and when might nature be allowed to take its course? This blog from the National Flood Risk Services team explains our approach.
NRW is just one Risk Management Authority (RMA) in Wales whose remit includes Flood Risk Management (FRM). We work with local authorities, highway authorities, private landowners and other organisations who have responsibilities to keep channels, and in channel structures they own or manage, clear to help manage flood risk.
NRW has FRM powers on statutory Main Rivers only. Roles and Responsibilities are set out in Welsh Government’s National Strategy for Flood and Coastal Erosion Risk Management in Wales. You can get more information on our Flooding web pages including your responsibilities if you own a watercourse. You can check if you own or are close to a ‘main river’ here.
Why Blockages Matter
Fallen trees, woody debris, and other obstructions can restrict river flow, potentially increasing flood risk to nearby communities. In urban areas, where space is limited and properties are close to watercourses, a blockage can quickly become a hazard. For example, if a fallen tree reduces a river channel’s width by more than 50% and flood maps show a risk to adjacent properties, then there is potentially an increased flood risk.
Our Legal Powers
Under the Water Resources Act 1991, NRW has permissive powers to carry out flood risk management work on main rivers and the coast. These powers are discretionary, meaning we can decide when and where to use them, based on risk. In a very small number of locations, we may have duties as a landowner but otherwise we are not legally obliged to clear any blockages from main rivers, so our decision to do so must balance flood risk reduction with environmental considerations and relative affordability. We must also consider others’ legal responsibilities.
When We Intervene
NRW will typically consider removing blockages when:
- They pose an immediate flood risk to people and communities[WJ1] .
- They occur in urban areas or near [WJ2] critical infrastructure we maintain, such as flood defences.
- They threaten the integrity of flood defence assets we have built, or we maintain. You can check who is responsible for many FRM assets by looking up their location in this link.
Even if the above criteria is met, we can only act when it is safe to do so – it is not usually safe to remove blockages during flood/high flow events. Trying to do so can put staff and equipment at serious risk, and can also have safety implications for any structure impacted by or creating a blockage.
In emergencies, we may act even on third-party land, notifying owners after. We may also respond during flood events as part of our incident management procedures or General FRM Oversight Role, ensuring channels remain clear where blockages could worsen flooding.
When We Don’t
Not all blockages increase flood risk. In rural settings, woody debris can slow water flow, reduce downstream flood peaks, and create valuable habitats for wildlife. For this reason, NRW often does not remove natural blockages when they do not increase flood risk to communities/homes. This approach supports our commitment to sustainable management of natural resources and biodiversity.
As a publicly funded organisation, we must take our funding allocation into account as part of our decision making. We must operate within our allocated budget and resource levels and accordingly have to make risk-based decisions to get the best value from our funding. So it is not feasible to remove all blockages.
We expect other organisations and landowners to maintain river channels on their land, including blockages on structures that they own or manage, for example bridges. Welsh Government’s FCERM Strategy outlines how asset owners and operators have a role to play and it may be them who are best placed to understand the local management of land, water and flood risk facing their community.
Unless critical infrastructure such as flood defences are threatened by erosion caused by blockages, we generally expect landowners to take appropriate action in accordance with the principles of riparian ownership, established in common law.
NRW’s Flood Risk Management staff do not routinely remove fly-tipped waste or dead animals from watercourses unless they obstruct access for flood risk work or pose an immediate flood or pollution risk. This includes abandoned vehicles. In most cases, responsibility lies with landowners, local authorities, insurance companies or private owners. You can find more information on this on our web pages.
Balancing risk and nature
Our decisions are guided by evidence and local knowledge. We use flood maps, modelling, asset data, and consequence ratings to assess whether intervention is necessary. Where possible, we work with natural processes—such as encouraging appropriate woody debris in rivers—to deliver flood resilience and ecological benefits. You can watch this short video to find out a little more - Healthy rivers - Wood is good.
Want to know more? See the links below for guidance on flood risk management and your responsibilities as a riparian owner.
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)