Flood risk and responsibilities

If you live or work close to a watercourse and within the natural floodplain, there is a risk that river flooding may threaten your property or workplace. Flooding can also affect areas away from the natural flood plain. Intense and prolonged storms can exceed the capacity of the local drainage system or saturate the ground and put many more homes, businesses and people at risk from surface water, groundwater and watercourse flooding. There are a number of sources of flooding that may present a risk to residents which include:

  • Coastal flooding - occurs when normally dry, low-lying land is inundated by seawater either during high tidal conditions or/and due to wave overtopping
  • Fluvial  flooding - occurs when excessive rainfall over an extended period of time causes a river to exceed its capacity and spill out onto the adjacent floodplain
  • Surface water flooding - is caused by the build-up of storm water on surfaces, often when these surfaces are hard paved, or where there is too much rainfall for the soil to handle.
  • Groundwater flooding - when the water table; the water level below ground, rises above the ground surface. During heavy rainfall, the water level in the ground may rise to so much that it floods basements, or emergence of groundwater at the surface may cause damage to properties and infrastructure.
  • Reservoir flooding - follows the failure of structures holding back reservoir water (for example dams, retaining walls). It is the most unlikely source of danger to any property due to the strict regulations and maintenance schedules used by reservoir operators

NRW’s interactive map allows you to check risk of flooding and explore in-depth flood risk information.

Gwynedd Council work with partner organisations to manage the risk of flooding within its communities, and minimise the effects and damage caused.


Flood risk responsibilities

There are a number of organisations with statutory responsibilities for managing flood risk in Gwynedd in accordance with the Flood and Water Management Act 2010; these organisations are known as risk management authorities (RMAs), and consist of:

Natural Resources Wales (NRW) is the risk management authority with responsibility for matters relating to flooding from main rivers and the sea. NRW has powers to work on main rivers and the coastline to manage flood risk.

NRW’s flood risk management works can include: 

  • constructing and maintaining flood risk management assets, for example flood banks, and works on main rivers to manage water levels and make sure flood water can flow freely
  • operating flood risk management assets during a flood
  • dredging the river
  • issuing flood warnings 

NRW has a strategic role for all sources of flooding in Wales. It has worked with the Welsh Government on a national strategy for Wales. The strategy shows how communities, the public sector and other organisations can work together to manage the risk. This includes the development of local flood risk management strategies by lead local flood authorities. NRW also undertake a statutory consultee role providing technical advice on main river and coastal flood risk to Gwynedd and Snowdonia National Park planning authorities 

Under the Flood and Water Management Act 2010, Gwynedd Council became the Lead Local Flood Authority (LLFA), with the role of overseeing the management of flood risk from local sources in Gwynedd. Local sources of flooding include surface water, ordinary watercourses (including lakes and ponds or other areas of water flowing into an ordinary watercourse) and groundwater, and where there is interaction between these sources and main rivers or the sea. The Flood and Coastal Erosion Risk Management (FCERM) Unit within the Council’s Consultancy Service (YGC) fulfils the LLFA role on behalf of the Council. 

The Flood and Water Management Act 2010 places a number of statutory duties on Local Authorities in their role as LLFA including: 

  • the preparation of local flood risk management strategies
  • a duty to investigate all flooding within its area insofar as a LLFA consider it necessary or appropriate 
  • a duty to maintain a register of structures and features likely to affect flood risk
  • authorising consent to individuals, companies, group of individuals and public bodies, who wish to carry out changes to an ordinary watercourse that may affect flow or flood risk
  • undertake a statutory consultee role providing technical advice on local flood risk to Gwynedd and Snowdonia National Park planning authorities
  • Evaluate and approve drainage applications for new developments where construction work has drainage implications, and adopt and maintain sustainable drainage schemes 


In addition to these, each LLFA has a number of what are called permissive powers. These include: 

  • powers to designate certain structures or features that affect flood or coastal erosion risk
  • the power to undertake works to manage flood risk from surface runoff or groundwater, consistent with the local flood risk management strategy 

Dŵr Cymru Welsh Water (DCWW) has two key responsibilities: to provide a high quality water supply to customers and to take away wastewater and return it to the environment safely. 

In providing their basic function of containing, carrying and treating water and wastewater, DCWW’s assets may present flood risks which can result from system failures, burst pipes and mains, or similar escapes from the sewer network and other assets, for which Welsh Water are responsible. 

In order to reduce the risks associated with these assets Welsh Water has a number of risk management systems in place, which include historical incident reviews, proactive risk capturing and prioritisation, catchment investment planning and emergency incident planning. 

Gwynedd Council are responsible for the network of non-trunk roads in the county, whilst NMWTRA are responsible for the network of trunk roads acting on behalf of the Welsh Government. Under the Highways Act, the highway authority has a duty to maintain the highway, including ensuring highway drainage systems are clear. As part of this duty, all roads in the county are subject to a programme of inspection and maintenance, and problems are dealt with as they arise. 


Other responsibilities

It should be noted that although RMAs are responsible for managing flood risk from various sources, they are not liable for any damages caused by flooding. Property owners are responsible for protecting their property from flooding along with their responsibilities as riparian owners. 


Riparian owners are the owners of land adjoining a watercourse and have an important role in flood risk management within a river catchment. Riparian owners have a variety of responsibilities, including the following: 

  • maintaining river beds and banks
  • allowing the flow of water to pass without obstruction
  • controlling invasive alien species such as Japanese Knotweed

Riparian owners should also ensure that nothing on their land could be washed away by a high flow of water and cause an obstruction further downstream. 

Find out more through NRW’s guide to your rights and responsibilities of riverside ownership in Wales


As flood risk can never be completely eliminated individuals have a personal responsibility to be aware of the level of flood risk where they live, to effectively plan to protect themselves and their property from flooding damage. 

Advice regarding flood preparedness can be found here.