River Irwell Flooding & Flood Risk

Rain that falls on the moors above Bacup can be in Salford the same afternoon, and that speed is what sets River Irwell flooding apart. The river drops about 375 metres in 63 km, through Rawtenstall, Ramsbottom, Bury, Radcliffe and Kearsley to Salford and the centre of Manchester. Mill towns line the valley floor the whole way, so when the Irwell comes out of its channel it comes out into streets.

On 26 December 2015 the Irwell reached the highest level on record at ten of its eleven gauges, from Waterfoot down to Adelphi Weir in Salford. The peak flow at Manchester Racecourse, 560 cubic metres a second, is the largest in a record that starts in 1941.

Unda Consulting Limited, a CIWEM Business Partner with chartered consultants, prepares flood risk assessments and drainage strategies for sites along the Irwell. To talk through a site, call 01293 214444 or email enquiries@unda.co.uk.

• Where it starts and ends. Irwell Springs on Deerplay Moor, about 400 m up above Bacup. Ordnance Survey mapping uses the name for 63 km, as far as Woden Street in Manchester, where the Manchester Ship Canal begins. The canal follows the river's old course west to Irlam, and the River Mersey joins it there.
• Catchment. 552 km² at the Adelphi Weir gauge in Salford, on the National River Flow Archive's figures. With the Irk, the Medlock and the brooks that join below the weir, the Environment Agency's catchment flood management plan puts the whole catchment at over 700 km² and more than two million people.
• Main River status. Main River from about 750 m below the springs to the River Irk confluence beside Victoria Station.
• Tide. None. At Adelphi Weir the river is still some 24 m above sea level, and locks hold the Ship Canal below it.
• Warning service. 20 Environment Agency flood warning areas, from Bacup to Regent Bridge, inside two flood alert areas.

Why does the River Irwell flood so quickly?

Because the top of the catchment is steep, wet and thin-soiled, and almost nothing slows the water on its way down. The moors above Irwell Vale get about 1,440 mm of rain a year on peat over Millstone Grit and Coal Measures, the valleys below them are deeply cut, and the National River Flow Archive, which is not given to strong language, describes the regime at Salford as very responsive. Four to five hours is the time to peak that the Environment Agency's catchment plan gives for the middle Irwell.

Boxing Day 2015 shows the speed. The Irwell Vale gauge peaked at 12.30pm, Bury Ground at 1.45pm, Kearsley at 2.15pm and Adelphi Weir in Salford at 5pm. A site in Lower Broughton had four and a half hours between the peak in Rossendale and the peak outside the door, and a site in Ramsbottom had less than one. Nobody on this river gets a day's notice.

• The Rossendale brooks. Whitewell Brook, Limy Water and the River Ogden fall off the same moors into the upper valley. The Ogden joins at Irwell Vale, which is why that village floods from two rivers.
• The Roch. Joins between Bury and Radcliffe with the water from Rochdale and Littleborough. In 2015 the Roch at the confluence ran 1.1 m above anything in its 64-year record, according to the Greater Manchester flood investigation.
• The Croal. Brings Bolton's water in at Kearsley. By the Kearsley gauge the river drains 520 km², nearly all of its catchment.
• The Irk and the Medlock. Both come in through the centre of Manchester, the Irk beside Victoria Station and the Medlock at Castlefield, much of their length in walled channel or culvert.
• Towns and hard surfaces. About 16% of the catchment above Adelphi Weir is urban on the archive's URBEXT measure, and Bury, Bolton and Rochdale drain to the river through sewers and culverted brooks.

Reservoirs do little to help. The headwater groups at Haslingden Grane and Ogden change low flows far more than floods, on the archive's account, and the mean flow at Adelphi Weir is under 18 m³/s where the 2015 peak a short way upstream was more than thirty times that.

When has the River Irwell flooded?

Five floods stand out since gauging began: 1946, 1954, 1980, 2015 and 2020. The largest was 2015. The combined flow record for Salford, which the National River Flow Archive holds under Manchester Racecourse, begins in 1941, and its three largest peaks are 26 December 2015, 20 September 1946 and 1 January 2025.

1. September 1946. About 500 m³/s through Salford. The Environment Agency's catchment plan counts more than 5,000 properties flooded from the Irwell, and a later flood reached 600. Afterwards the channel below Adelphi Weir was widened and a new cut dug, which first carried water in September 1970.
2. January 1954 and October 1980. Peaks of 432 and 466 m³/s in the Salford record. The Agency lists both, with 1946, as Salford's significant floods.
3. June 2012. A summer storm on 22 June produced what were then the largest flows the Irwell Vale and Bury Ground gauges had recorded. Irwell Vale, Strongstry and Chatterton flooded, as they had in 2007.
4. Boxing Day 2015. Up to 128 mm of rain fell on the upper catchment in 36 hours. The Greater Manchester investigation counts around 750 properties flooded inside in Lower Broughton, about 671 in Radcliffe and Redvales, 57 at Prestolee and Stoneclough, 54 in Ramsbottom and 13 in Summerseat, where the Waterside restaurant fell into the river. Lancashire County Council's Rossendale report adds 62 in Irwell Vale, 50 in Rawtenstall, 24 in Strongstry and Chatterton and 21 in Waterfoot.
5. February 2020, Storm Ciara. The second-largest peak at every flow gauge from Irwell Vale to Kearsley, and the record, 2.28 m, at the newer Throstle Mill gauge in Bacup. A combined authority report gives 70 mm of rain in 12 hours at Holden Wood, 32 homes and four businesses flooded in Bury borough, and water over the temporary defences into Close Park at Radcliffe.
6. November 2024 and New Year 2025. Storm Bert, on 23 November 2024, gave Bury Ground its third-largest peak. Under six weeks later, on 1 January 2025, the Salford record took its third-largest, 497 m³/s.

Sources: National River Flow Archive pages for Irwell Vale, Bury Ground, Kearsley and Manchester Racecourse. The archive publishes one peak for each water year, which is why two cells in each of the 2024 and 2025 rows hold no figure.

Three of the four largest peaks through Salford in an 84-year record have come since 2015. A flood risk assessment for a site here starts from the 2015 levels, then adds the climate change allowance the Environment Agency sets for the Irwell catchment.

River Irwell map and live gauges, Bacup to Salford

The map draws the Irwell in coral from Irwell Springs to the head of the Ship Canal, with the Environment Agency's eleven gauges on it; click a pin for the latest reading. Enter a postcode to screen that spot against the national flood data. Our flood risk map runs the same check anywhere in England, and the live river levels map shows these gauges beside every other river's.

A gauge reading only means something against that gauge's own history, because each one measures from its own zero, so 6.33 m at Kearsley and 3.87 m at Adelphi Weir describe the same flood. The table runs downstream. The last column is the level above which the Agency says property flooding is possible, where it publishes one.

Take the last column from the one before it to see how far over a flood went. In 2015 Pioneer Mills stood 2.12 m above its property level and Kearsley 1.98 m above. The Greater Manchester report puts the Kearsley peak 1.6 m higher than any other reading in the gauge's 13 years, and estimates it as a level reached once in 100 to 150 years.

Places the River Irwell floods, town by town

Wherever a town sits on the valley floor, which is nearly everywhere. The Environment Agency's catchment plan counted 7,500 properties in the wider Irwell catchment with a 1% chance of river flooding each year, rising to about 10,000 by 2100, with Salford and central Manchester the largest groups. The 20 warning areas on the Irwell itself fall inside two alert areas: the Upper River Irwell, which takes in Rossendale, Bury and Radcliffe, and the Lower River Irwell through Salford and Manchester.

The pages linked in the table cover each council's own rules. On the river, the upper valley and the lower valley are different problems. In Rossendale the flood arrives fast and from several directions at once: on Boxing Day 2015 Lancashire County Council found overwhelmed drains at Bacup, surface water and Cowpe Brook at Waterfoot, and river, groundwater and surface water together at Rawtenstall and Irwell Vale. From Radcliffe down the river is larger and a little slower, the Roch and the Croal have joined it, and the sites that matter most sit behind walls and basins which the river has already overtopped once, in 2015.

What do the Salford basins and the Radcliffe defences change for a site?

They lower the chance of flooding without changing the flood zone. The Environment Agency's flood map for planning draws Flood Zones 2 and 3 as if no defences existed, so land in Lower Broughton or Redvales that would flood without its wall is still Flood Zone 3 for a planning application. The assessment changes instead. It has to deal with the walls and basins being overtopped or failing, with a depth and a route for the water in each case.

• Littleton Road basin, Salford. Finished in 2005. It stores 650,000 m³ beside the river at Kersal and, on the Agency's catchment plan figures, was built for a flood with a 1.3% chance in any year. On Boxing Day 2015 it began filling at about 9.25am, and later that day the river still overtopped the left-bank defences between Wallness Bridge and Hough Lane Bridge.
• Castle Irwell basin, Salford. Opened on 2 February 2018 on the old racecourse: 28 hectares, £10 million and room for 650 million litres. With Littleton Road it protects more than 1,900 homes and businesses in Lower Broughton and Lower Kersal. In 2015 it was a building site. The river filled it anyway.
• Radcliffe and Redvales. A £40 million scheme by the Agency and Bury Council, with more than 2.5 km of walls and embankments for up to 870 properties. The first phase, at Close Park and Dumers Lane, was finished in autumn 2020. During Storm Ciara that February, temporary works at Morris Street kept water out of about 100 properties while Redvales, not yet defended, flooded.
• Irwell Vale, Strongstry and Chatterton. No scheme. The Agency halted its plans in winter 2023 when the estimate rose from £14.7 million to £23 million and left a gap of about £9 million.

So a site in Lower Broughton needs the overtopping case worked through: how deep, how fast, and by which route water arrives if the basins fill and the walls are passed, as happened in 2015. That is residual risk, and it sets floor levels and escape routes as surely as the flood zone does. A site at Irwell Vale has no defence to argue about. There the question is the river itself, a gauge that passed its property level by 1.23 m in 2015, and how much warning anyone gets.

Is the River Irwell a Main River?

For almost all of its length, yes. The Environment Agency's Statutory Main River Map shows the Irwell as Main River from about 750 m below Irwell Springs to the point where the Irk joins beside Victoria Station. On that length the Agency regulates the channel, and work in the river or within 8 metres of the bank may need a flood risk activity permit from the Agency as well as planning permission; the Irwell has no tidal reach, so the 16-metre distance that applies beside tidal Main Rivers does not arise.

Two stretches are different. The first 750 m below the springs is an ordinary watercourse, where consent for works comes from Lancashire County Council. And the last 2 km, through the city centre from the Irk to Woden Street, was not on the Main River map when we checked it on 10 November 2026, although the Agency runs a flood warning area there. For a site on that reach, ask the Agency and the council which consent applies before any work near the bank is drawn up.

• Who owns the banks. Usually whoever owns the land beside the river. Riparian owners have to let water pass and keep their bank and any culvert clear, which matters in a valley with as many old mill structures as this one.
• Main River or ordinary watercourse. The label decides who regulates work and who is consulted on an application. Our guide to Main Rivers and ordinary watercourses explains the two, and the other river pages show how it varies from river to river.
• When an assessment is needed. Chapter 18 of the NPPF (policy F4) asks for a site-specific assessment for any site in Flood Zone 2 or 3, a site of a hectare or more in Flood Zone 1, and land at risk from another source such as surface water.

Reports for sites beside the Irwell, from Rossendale to Salford

Three separate reports come up on Irwell sites, and a scheme may need one or all of them. A flood risk assessment shows the development will be safe and will not make flooding worse for the neighbours; a sequential test asks whether it could have gone on lower-risk land; a drainage strategy says where the site's own rain goes. Modelling and groundwater work feed into an assessment when the site calls for them.

• Sites in the valley-floor flood zones. A flood risk assessment on the Irwell works from the 2015 gauge records, the Agency's modelled levels and flood zones drawn without the Salford and Radcliffe defences.
• Planning applications. Rossendale, Bury, Bolton, Salford and Manchester councils each expect a flood risk assessment for planning with an application in Flood Zone 2 or 3 beside the river.
• Buying a house near the river. In streets that flooded on Boxing Day 2015, a flood risk survey for property purchase sets out one property's flood history, zone and defences before exchange.
• Whether the site is the right one. Where a site in Lower Broughton or beside the river in Radcliffe lies in Flood Zone 2 or 3, the sequential and exception test has to show no lower-risk site was reasonably available and that the scheme will be safe for its lifetime.
• Surface water on steep ground. On the Rossendale hillsides runoff is a flood source in its own right, and a drainage strategy shows the lead local flood authority how a major site will hold it back.
• Discharge rates and storage. A surface water drainage strategy fixes how much the site may release and how much it stores, including what happens when the Irwell is high and an outfall to it cannot flow freely.
• After permission. Permissions along the river commonly carry a drainage condition, and discharge of drainage conditions supplies the detail the council needs to sign it off.
• Levels behind the defences. Flood modelling gives depths and flow routes for one plot when the Salford basins fill or the Radcliffe walls are overtopped, which the national maps do not show.
• Hours of warning. With the peak taking under five hours from Irwell Vale to Salford and 20 warning areas on the river, a flood warning and evacuation plan sets out what occupiers do when a warning is issued.
• Groundwater in the valley gravels. The Agency notes a groundwater flood risk at Meadow Park in Irwell Vale, and the county council found it at Rawtenstall in 2015, so a groundwater flood risk assessment is sometimes needed on the valley floor.
• Insurance. After about 750 properties flooded in Lower Broughton and 671 in Radcliffe and Redvales in 2015, an insurance flood risk assessment gives an underwriter evidence about one building.
• Works and trading estates. Industrial units flooded at Bridge Trading Estate in Bury and Pioneer Mills in Radcliffe in 2015, and a business continuity flood risk assessment helps an occupier plan for the next time.
• Buying commercial property. A lender or buyer taking on a converted mill or a trading estate beside the Irwell can use commercial due diligence to see what the 2015 flood means for that asset.

The Agency's catchment plan calls much of the valley's geology and soil relatively impermeable, which limits where a soakaway will work. Our ground conditions and soakaway checker gives a first view of what lies under a site.

Who deals with flooding on the River Irwell?

It depends on where the water comes from. The Environment Agency's Greater Manchester, Merseyside and Cheshire area looks after the Main River, the Salford basins, the Radcliffe defences and the warnings. Surface water, groundwater and the smaller brooks fall to the lead local flood authority, which is Lancashire County Council in Rossendale and the borough or city council in Bury, Bolton, Salford and Manchester. Sewers belong to United Utilities.

The Agency's North West flood risk management plan sets the measures for the catchment to 2027. Works near a Main River are covered by its permit rules.

Questions about flooding from the River Irwell

For any site on the Irwell, from the Rossendale valley to central Salford, call 01293 214444 or email enquiries@unda.co.uk.