River Dee Flooding & Flood Risk, Wales and Cheshire

River Dee flooding in Wales and Cheshire comes in three forms along one river. In the Welsh hills above Llangollen the Dee rises within hours; across the flat border country from Bangor-on-Dee to Farndon it spreads over the meadows and stays out for days; below Chester Weir it is tidal, and Chester, Deeside and the estuary shore flood from the tide and storm surge as well as from the river. This is the Afon Dyfrdwy, the Dee of Bala and Chester, not the Aberdeenshire river of the same name. We prepare flood risk assessments, Flood Consequence Assessments and drainage strategies for sites on both banks.

In the early hours of 21 January 2021 Storm Christoph pushed the River Dee to 575 cubic metres a second at Manley Hall and to 16.46 metres at Bangor-on-Dee, both the highest ever recorded there.

To talk through a site near the Dee, call 01293 214444 or email enquiries@unda.co.uk.

• Course. From the slopes of Dduallt above Llanuwchllyn, through Bala Lake, Corwen and Llangollen, across the border plain to Chester, then out through the Dee Estuary to the Irish Sea.
• Two countries. The upper and middle river is in Wales; for long stretches below Bangor-on-Dee the channel is the border itself; Chester, Parkgate and the Wirral shore are in England, Deeside and Flint in Wales.
• Who regulates it. Natural Resources Wales on the Welsh reaches and the Environment Agency on the English ones. It is a Main River throughout.
• Where the tide starts. At Chester Weir. The Environment Agency's tidal flood warning areas begin at Grosvenor Bridge, and its flood plan notes that high tides regularly reach up the river below Farndon.

What happened on the River Dee in Storm Christoph?

Storm Christoph set the River Dee's modern records over the night of 20 to 21 January 2021. Two days of heavy rain on the Welsh hills sent a flood down the valley that reached Manley Hall at about 2am on 21 January, at 575 cubic metres a second, more than a quarter above the previous highest peak there in October 2000. Downstream the same water arrived at Bangor-on-Dee and Farndon hours later, and both villages had people out of their homes before dawn.

• Bangor-on-Dee. The river reached 16.457 metres above Ordnance Datum, its highest recorded level, beating the February 2011 peak. A major incident was declared just before 1.42am, and residents of Abbey Gardens, Overton Road and the High Street were taken to Ysgol Sant Dunawd, with concern that the defences had never been tested that high (Wrexham.com, 21 January 2021).
• Farndon. The Environment Agency recorded 9.6 metres AOD, 240 millimetres above the previous record of 9.36 metres set in 2000. A flood warning went out at 00:10 and a severe flood warning at 10:19. Cheshire West and Chester's investigation counted 24 homes affected, four evacuated and three flooded, on River Lane and at Farndon Hay, where Townfield Lane was cut off.
• Across the English borough. The council's Storm Christoph report recorded 195 properties flooded inside and 141 evacuated across Cheshire West and Chester, most of them from smaller watercourses; in Blacon, where Finchett's Gutter drains into the Dee, 27 properties flooded.
• Since then. The Environment Agency's flood plan for the basin names Christoph as the only flood since 2015 to reach more than 20 homes in the English part of the Dee catchment. For a Dee-side site, the January 2021 levels are the flood of record an assessment now has to account for.

Why does the River Dee flood?

The Dee floods because a wet, steep Welsh catchment drains onto a long, nearly level floodplain that ends in a tidal channel. Above Manley Hall the catchment averages 1,367 millimetres of rain a year and climbs to 878 metres, and almost none of it is built on, so a storm reaches the river quickly. Below Erbistock the valley floor widens and flattens, the water spreads, and the Environment Agency says the river at Chester can take three to four days to peak after the rain.

Reservoirs blunt the upper river but do not stop it. Llyn Celyn, Llyn Brenig and the sluices at Bala Lake form the Dee Regulation Scheme, which Natural Resources Wales says controls 16 per cent of the catchment above Chester Weir and has greatly reduced flooding in the valley below Bala (NRW). The other 84 per cent, including the Alwen, Ceiriog and Alyn, is not controlled, and in 2021 the gauges downstream still broke their records.

• The Welsh hills. Fast response, steep channel, the Llangollen to Trevalyn Meadows warning area first in line.
• The border plain. The National River Flow Archive notes that flood attenuation on the lower Dee floodplain is notable: the water slows, spreads and lingers, which is why Farndon and Holt stay flooded long after Llangollen has cleared.
• The tidal channel. From Chester Weir the river runs in a straight, embanked channel past Saltney, Sandycroft and Queensferry to Connah's Quay. A high tide can hold the river back here and shut the outfalls of the drains that empty into it.

Check flood risk along the River Dee

The map below draws the River Dee in coral from its source above Llanuwchllyn to the head of the estuary, with the live gauges on the main river. Enter a postcode to screen a site against the Environment Agency's flood data, use our flood risk map to check its flood zone, or open the live river levels map to follow the Dee alongside its tributaries.

Each gauge reads against its own datum, so a level compares with that gauge's own history and not with the next one downstream. Natural Resources Wales runs the gauges on the main river, including the English one at Farndon.

Flows from the National River Flow Archive; Farndon from Cheshire West and Chester's Section 19 report; Bangor-on-Dee from contemporary reporting of the Natural Resources Wales gauge.

When has the River Dee flooded before?

Christoph topped a long run of Dee floods. The gauge at Manley Hall has measured flows since 1937, and its ranked annual peaks put 2000 and 2011 next after 2021, almost all of them between October and March.

1. 1928. A flood destroyed the original Chain Bridge at Llangollen; it was rebuilt the following year.
2. December 1964. Manley Hall recorded a daily mean flow of 521 cubic metres a second on 14 December, still the highest daily figure in its record.
3. Autumn 2000. 455 cubic metres a second at Manley Hall on 30 October and a record 9.36 metres at Farndon; a week later Chester Suspension Bridge logged its highest daily flow.
4. February 2011. Bangor-on-Dee reached 16.35 metres, its record until 2021, with 449 cubic metres a second at Manley Hall.
5. December 2013. Tidal flooding reached West Kirby on the Dee Estuary.
6. 2015 to 2023. Peaks of 365 cubic metres a second in December 2015, 428 in Storm Dennis in February 2020 and 322 in October 2023.

Where does the River Dee flood, from Bala to the estuary?

From Bala to Bangor-on-Dee the risk is river flooding and Natural Resources Wales issues the warnings. From Holt and Farndon to Chester it is still the river, now slow and wide, under Environment Agency warnings. Below Chester Weir it is tide and surge on both shores, with defended land behind the embankments at Chester and along Deeside.

In the English part of the basin the Environment Agency counts around 3,000 people living where rivers or the sea could flood them (Dee flood risk management plan). On the Welsh side, Natural Resources Wales lists Queensferry, Sandycroft and Manor Lane, Connah's Quay and Shotton, and Garden City with Deeside Industrial Estate as flood risk areas for the sea, and keeps Bangor-on-Dee and Holt on its register of communities at risk. Our Cheshire page sets the Dee beside the Weaver, the Gowy and the Mersey.

Is the River Dee a Main River, and who regulates it?

Yes. The Dee is a Main River along its whole course, and which body regulates it depends on which side of the border the work is. Natural Resources Wales covers the Welsh reaches and the Environment Agency the English ones. On either side, building within 8 metres of the bank, or 16 metres where the river is tidal, may need a flood risk activity permit from that regulator before work starts, in addition to planning permission.

• The border reach. Below Bangor-on-Dee the river is the boundary for long stretches, so the regulator can change from one bank to the other. Check which country the red line sits in first.
• The streams that feed it. Most smaller tributaries and field drains are ordinary watercourses, looked after by their riparian owners and consented by the council; our guide to main rivers and ordinary watercourses sets out the difference, and ordinary watercourse consent covers culverts and outfalls.
• Defended land. Embankments at Chester and along Deeside lower the chance of tidal flooding without removing it, so an assessment behind them has to show what happens if they are overtopped or breached.

England or Wales: which planning rules apply to a site near the Dee?

The bank the site is on decides the policy, the report and who reviews it. On the English side, chapter 18 of the National Planning Policy Framework applies: a site in Flood Zone 2 or 3, or a hectare or more in Flood Zone 1, needs a site-specific assessment, and more vulnerable uses in the higher zones face the sequential test and often the exception test. On the Welsh side, the version of TAN15 in force since 31 March 2025 and the Flood Map for Planning Wales apply, and the report is a Flood Consequence Assessment, reviewed with Natural Resources Wales.

• English bank. Cheshire West and Chester decides most applications, with the Environment Agency as consultee; our notes on NPPF flood risk policy cover the tests in turn.
• Welsh bank. Gwynedd, Denbighshire, Wrexham and Flintshire decide applications against TAN15; the Flood Map for Planning Wales sets the zones, and the 2025 changes to TAN15 widened when an assessment is needed.
• Drainage on each side. English sites answer to the lead local flood authority and the 2025 National Standards for sustainable drainage; most new development in Wales needs separate approval from the council's SuDS Approval Body before construction, which has applied since January 2019.

Flood and drainage reports for sites along the Dee, on either bank

Each report answers its own question about a Dee site. A flood risk assessment, or a Flood Consequence Assessment in Wales, asks whether the development is safe and keeps flood risk from rising elsewhere. A sequential test asks whether a lower-risk site was available instead. A drainage strategy works out where the rain falling on the new roofs and roads goes when the Dee is high and the tide holds the outfalls shut.

• Any site on the Dee floodplain. Our flood risk assessment work starts from the gauged levels at Manley Hall, Bangor-on-Dee and Farndon and from the defences in front of the site.
• Planning applications in England. From Farndon and Aldford down to Chester, Parkgate and the Wirral shore, a flood risk assessment for planning answers the questions Cheshire West and Chester and the Environment Agency will ask.
• Planning applications in Wales. From Bala to Bangor-on-Dee and along Deeside, a Flood Consequence Assessment shows the council and Natural Resources Wales that the scheme meets TAN15's acceptability criteria.
• Welsh policy questions. Our TAN15 advice explains how the 2025 version treats land behind flood defences, such as the embankments along Deeside.
• Buying near the river. A flood risk survey for property purchase gives a buyer at Farndon, Bangor-on-Dee or behind Chester's embankments the 2021 flood record and the flood zone before exchange.
• English sites in Flood Zones 2 and 3. New homes on the Dee floodplain at Chester or Farndon usually need the sequential and exception test to show why this site, and how it stays safe.
• Surface water and new development. A drainage strategy shows the council how a Dee-side site drains during a three- or four-day river peak.
• Runoff limits and SuDS. A surface water drainage strategy sets the discharge rate and storage for a site whose outfall below Chester Weir may be tide-locked.
• Permissions with a drainage condition. Where Cheshire West and Chester has approved a scheme subject to a drainage condition, our discharge of drainage conditions work provides the detail needed to clear it.
• Sites near the channel or behind a defence. Flood modelling gives a site its own flood levels and breach depths on the long, flat reach from Bangor-on-Dee to Chester and on the tidal embankments, where national maps are too coarse.
• Homes that have flooded. After River Lane in Farndon and parts of Blacon flooded in 2021, a flood risk assessment for insurance sets out the real risk for an owner or insurer.
• Getting people out. Where a Chester or Deeside site stays dry only while the embankments hold, a flood warning and evacuation plan sets out how occupants are warned and leave.
• Businesses on the floodplain. The retail and industrial estates off Sealand Road in Chester and Deeside Industrial Estate sit in tidal warning and flood risk areas, and a business continuity flood assessment looks at keeping a site trading.

Who manages flood risk on the River Dee?

Responsibility splits by country and by source of water. The two national regulators run the main river, its warnings and their own defences; the councils handle surface water, groundwater and ordinary watercourses as lead local flood authorities; and the water companies deal with flooding from sewers.

• The river. Natural Resources Wales on the Welsh reaches and the Environment Agency in England, under the Environment Agency's Dee flood risk management plan for the English basin and Natural Resources Wales' plan for Wales.
• Councils. Gwynedd, Denbighshire, Wrexham and Flintshire in Wales; Cheshire West and Chester, Shropshire on the border reach, and Wirral on the estuary shore.
• Committees and resilience forums. The North West Regional Flood and Coastal Committee oversees the English schemes; emergency planning runs through the Cheshire Local Resilience Forum and the North Wales Resilience Forum.
• Sewers. Flooding from a public sewer goes to the water company for the address: Dŵr Cymru Welsh Water serves Chester and much of the Welsh side, and United Utilities the Wirral.
• Warnings. Sign up free with the Environment Agency or Natural Resources Wales, or call Floodline on 0345 988 1188, which covers both countries.
• In an emergency. Call 999 if life is at risk, and 105 for a power cut.

River Dee flooding: what people ask

For a site anywhere on the Dee, from Bala to the Wirral shore, call 01293 214444 or email enquiries@unda.co.uk. The chartered consultants at Unda Consulting Limited can tell you what your application or purchase needs on either side of the border. Reports for sites along the River Dee come from Unda Consulting Limited, a CIWEM Business Partner.