Flood Risk Assessment in Blackburn

A flood risk assessment in Blackburn starts with a river that disappears under the town centre. The River Blakewater comes off the moors above Guide as Knuzden Brook and runs open through Whitebirk, Little Harwood and Brookhouse. It then drops into a culvert beneath the town centre and comes out again at Whalley Banks before it meets the River Darwen beside Witton Country Park. Above the town, steep gritstone slopes and a ring of reservoirs feed both rivers, and heavy rain reaches them within a few hours.

We prepare flood risk assessments in Blackburn for planning applications, house purchases, mortgages and insurance, along with sequential and exception tests and surface water drainage strategies. That covers the town centre and the Wranglings, and districts such as Ewood, Witton, Mill Hill, Feniscowles, Cherry Tree, Lower Darwen, Shadsworth, Intack, Roe Lee and Brownhill. Most lie in the BB1 and BB2 postcode districts. Blackburn with Darwen Council is a unitary authority, so it decides the planning application and acts as lead local flood authority. The same council covers Darwen (BB3), six kilometres up the Darwen valley, and this page covers Darwen sites too. Rishton, Accrington and Clitheroe sit under Lancashire County Council and appear on our Lancashire page.

On Boxing Day 2015 the River Darwen at Blackburn Waterfall reached 3.42 m, more than 1.6 m above the level at which the Environment Agency says property flooding becomes possible. The same day the Blakewater at Harrison Street, in the Wranglings, peaked just 3 cm short of its own property flooding level.

To talk through a site in Blackburn or Darwen, call 01293 214444 or email enquiries@unda.co.uk and one of our flood risk consultants will take it from there.

What river runs through Blackburn, and where does it go underground?

Two rivers do. The Blakewater crosses the old town from east to west, much of it in culvert. The Darwen runs north past Ewood and Witton on the western side and carries the water of both towns on to the Ribble at Walton-le-Dale. The council's 2020 strategic flood risk assessment lists six main rivers in the borough. Below them are many smaller brooks, a good number of them piped under streets and mills.

Whoever owns land over a piped brook usually owns the culvert as well, with a duty to keep it flowing. Our notes on what a culvert is and who answers for it and on riparian ownership set out those duties. Because the moors drain so quickly, the 2020 study puts the critical storm duration for the Darwen, the Blakewater and their tributaries at between 1.25 and 4.75 hours.

Screen a Blackburn address on the flood map

A postcode typed into the box below brings up the planning flood zone, surface water and reservoir risk and the climate change outlook at that point; our full flood risk map does the same anywhere in England. The coral outline is the town's built-up area as the Office for National Statistics drew it in 2022. It reaches from Feniscowles and Cherry Tree in the west to Shadsworth and Guide in the east, and north to Wilpshire and Ramsgreave, which lie in Ribble Valley borough with Lancashire County Council as their flood authority. Darwen is mapped as a separate built-up area, so it falls outside the line even though the same council and river serve it.

Gauges and warnings on the Blakewater and the Darwen

Four Environment Agency gauges in the town show how close the rivers have come to homes. Three set their records on 26 December 2015, when Storm Eva followed Storm Desmond across the North West; Ewood's record dates from the summer storm of June 2012. All four can be followed on our live river levels map.

Seven Environment Agency flood warning areas cover parts of Blackburn. On the Darwen, one takes in Ewood Park, Stancliffe Street, Griffin Mill and River Mill, a second runs from Lower Darwen Bridge along Bolton Road to Griffin and Witton, and the Ewood Mill Race has its own. On the Blakewater, warnings cover Cob Wall and Brookhouse down to the town centre, Whitebirk and Green Bank (with Knuzden Brook), and the Wranglings in two parts: Railway Road to Whalley Banks, and the streets around George Street West and Pleasington Street. Darwen has four more of its own, at Livesey Fold, Hollins Grove, Hardman Way and the Cross Street area.

Floods recorded in Blackburn and Darwen, from the 1960s to 2018

The record here is a mix of river floods, storms that overwhelmed drains and failures of the canal. The council keeps its own database of incidents going back to 1905, and United Utilities logged sewer flooding at property level between 2009 and 2018. The dated events below come from the council's flood study, its news releases and the Environment Agency's gauges.

1. Mid-1960s, Gorse Street. Water leaking through the bed of the Leeds and Liverpool Canal flooded property near Gorse Street, the first recorded canal incident in the town.
2. 2002 and 2004. Blackburn flooded from the River Blakewater in both years, with localised surface water flooding alongside; the council later counted a run of near misses on the river.
3. 22 June 2012. About a month's rain fell in 24 hours over East Lancashire. Lancashire Fire and Rescue took more than 400 flooding calls. In Darwen the river burst its banks, the A666 was closed and residents left their homes; downstream, the Ewood gauge set the record it still holds.
4. March 2015. The Environment Agency and the council set out a £3.5 million plan for the Blakewater between the Youth Zone and the ambulance station on George Street West. The design raised river walls from Byrom Street to Freckleton Street and made a new bridge on the Freckleton Street link road part of the defences, to protect more than 200 homes and businesses.
5. 26 December 2015. Storm Eva sent the Darwen at Waterfall to 3.42 m and the Blakewater at Harrison Street to within 3 cm of its property flooding level, both still the highest readings on record.
6. December 2018. Vandals breached the Leeds and Liverpool Canal, damaging several businesses and flooding roads. Tighter precautions followed, but the council's study still treats a breach as a real, if unlikely, risk.

Councillors described 2015 and 2019 as close calls in Darwen. In March 2026 the council set out plans for the Darwen Surface Water Resilience Scheme: about £1.2 million to cut the risk to around 200 homes along the A666. A site with any of this history nearby should expect the council and the Environment Agency to ask how it would cope with a repeat.

Reservoirs and the canal: the water held above the town

The council's study counts 22 large reservoirs that could affect the borough, two-thirds of them owned by United Utilities. The Leeds and Liverpool Canal adds 7.5 km of water held behind banks, raised on embankments in places. Failure of either is unlikely. Both still define flood extents that a site-specific assessment has to look at.

• Fishmoor and Guide. Fishmoor, the largest in the town at 1.4 million cubic metres, and Guide stand above the eastern edge of Blackburn. The Local Plan asks schemes on Haslingden Road and Issa Way North to consider flooding from them.
• The highest consequences. The study names Fishmoor, Guide, Hoddlesden and Earnsdale as the reservoirs with the greatest consequences for Blackburn in the unlikely event of a failure; for Darwen, Earnsdale poses the greatest.
• Ramsgreave and Rishton. These two could affect the Blakewater, Knuzden Brook and the canal upstream of the town centre.
• The Ewood Aqueduct. The canal crosses the Darwen on a high embankment at Ewood, the biggest raised structure on its route through the borough.
• Three overflows. Surplus canal water spills into Knuzden Brook at Whitebirk, into an unnamed brook that reaches the Darwen at Mill Hill, and into another Darwen tributary at Feniscowles.

The study rates the overall reservoir risk as medium, low in probability but high in consequence, and asks for any development beside the canal to assess what a breach would do to the site. Our explainers on reservoir flooding and planning and on residual flood risk cover how that is handled in a report.

Rain, combined sewers and gritstone: draining a site in Blackburn

Surface water is as important here as the rivers, and the council's study says so in terms. The ground is poor at taking water, most of the town drains to combined sewers, and many small streams were long ago diverted into pipes. When those pipes fill, the water that once ran in an open channel looks for a route across the surface.

Infiltration is tested to BRE 365 first, and our note on when infiltration testing is needed explains the process. Our free ground conditions and soakaway checker gives an early read on the geology, and the drainage calculators help size storage. Skip these steps and the strategy invites an LLFA objection.

Planning policy for a flood risk assessment in Blackburn

Since 25 January 2024 the council has decided applications against the Blackburn with Darwen Local Plan 2021 to 2037. Policy DM13 deals with flooding and sustainable drainage, and Policy DM28 with building beside watercourses and reservoirs. Both lean on the borough's strategic flood risk assessments, and as lead local flood authority the council reviews the drainage of major schemes itself.

One gap in the evidence matters: in 2020 the Environment Agency had no climate change flood outlines for any river model in the borough. The study therefore treated Flood Zone 1 land within 20 m of Flood Zone 2 as possibly at future risk, and a site-specific assessment now has to apply the current allowances itself. What the 2025 National Standards for sustainable drainage add to that is set out in our explainer.

Allocated sites with flood conditions written into the Local Plan

The plan seeks at least 447 new homes a year, 7,152 over its 16 years, plus new employment land. Its 2020 flood study screened 66 possible sites and judged 11 potentially unsuitable: two because they lay in the functional floodplain and nine because of serious surface water risk. Of the 23 sites where it asked for layout to be designed around flood risk, 14 were more than 97% in Flood Zone 1, so surface water drove the advice there. Several adopted allocations carry flood requirements in their own policy wording.

• Former Markets site, Penny Street. The Blakewater runs through the middle of this 1.57 ha town centre site in culvert. A mitigation strategy has been agreed with the Environment Agency, but further flood modelling is required before building, and the river is to be opened up where possible or given an 8 m easement.
• North East Blackburn. A 97.5 ha urban extension at Roe Lee, Little Harwood and Whitebirk for 1,500 homes, 690 of them by 2037. A small area of Flood Zone 3b is left undeveloped, and the policy asks for ways to open up the culverted brook that crosses the south of the site before it passes under Brownhill Drive.
• Bank Hey. A Flood Zone 3b strip stays open and the ponds and drains crossing the site are kept, with a drainage strategy agreed before the application goes in.
• Roe Lee Mills and Queen's Park. The Level 2 study asks for a drainage strategy at the assessment stage and an 8 m buffer along the open watercourse on the southern boundary.
• Issa Way North and South. Culverts cross both sites, so development keeps an easement or protects the pipe, and the plan asks for flooding from Fishmoor (and on the northern site, Guide) to be considered.
• The former Thwaites site on Starkie Street, and Carl Fogarty Way. Land in Flood Zone 2 is kept out of the developable area on both.

On land like this, assessing flood risk on a site and planning its drainage are best scoped together, because the same culvert, easement or flow path decides both the layout and the outfall.

Does a Blackburn proposal need a flood risk assessment?

It depends on the flood zone, the size of the site and the use. National policy asks for one in Flood Zones 2 and 3 and on sites of a hectare or more in Flood Zone 1. It also asks for one wherever surface water, a culvert or a reservoir puts the site at risk. In Blackburn, Policy DM13 extends the sequential test to flood risk from any source.

On a windfall site, the sequential test means comparing it with other sites across an agreed area of search, and that work is easier to finish before the scheme is drawn up than after.

Flood and drainage reports for sites from the Wranglings to Witton

Each report below answers a question that comes up on sites in Blackburn and Darwen. They are written by our chartered consultants, and a senior consultant reviews and signs off each one before it goes out; Unda is a CIWEM Business Partner.

• Homes and mills by the rivers. New housing, mill conversions and commercial buildings in the Darwen and Blakewater flood zones go to the council with a flood risk assessment for planning, showing occupants kept safe for the building's life and nobody downstream made worse off.
• Every source weighed. Runoff from the moors, culverts, combined sewers, reservoirs and the canal all sit alongside the rivers in a flood risk assessment here, since the river flood map shows only some of them.
• Buying near the water. A search or a lender may query a terrace at Ewood or a house by the Blakewater at Green Bank. A flood risk survey for property purchase then checks the threshold heights, the routes water would take to the door and any past flooding at that address.
• Sites the plan did not allocate. Windfall housing in a flood risk location has to pass the sequential and exception test, and in Blackburn Policy DM13 applies that to surface water and reservoir risk as well as the rivers.
• Ten homes or more. The council reviews the drainage of every major application as flood authority, so schemes of that size submit drainage strategy evidence with the plans.
• Gritstone, till and old sewers. Where the ground will not soak water away, a surface water drainage strategy holds runoff in tanks, ponds or permeable paving and lets it out slowly to a brook, keeping it off the combined sewer wherever it can.
• Conditions on the permission. Where a Blackburn approval comes with a drainage condition, discharge of drainage conditions supplies the final calculations, construction details and the lifetime maintenance plan DM13 asks for.
• The town centre culvert. On the former Markets site the plan requires more modelling of the culverted Blakewater before building, and flood modelling is how a blockage is tested or a design flood level fixed where national outlines are too coarse.
• Seven warning areas. Warnings are issued for Ewood, Waterfall, Witton, the Wranglings, Cob Wall, Brookhouse, Whitebirk and Green Bank, and a flood warning and evacuation plan sets out who acts on them in a building and where people go.
• Cover after a flood. Owners near the rivers that rose in 2002, 2004, June 2012 and on Boxing Day 2015 can use a flood risk assessment for insurance to give an underwriter facts about their own building.
• Shallow groundwater. British Geological Survey mapping shows groundwater near the surface under the town centre, Mill Hill, Bank Top and Little Harwood, so a cellar, basement or soakaway there may need a groundwater flood risk assessment.
• A combined network. Several allocation policies flag an identified drainage area nearby and ask for early talks with United Utilities, and a foul drainage strategy shows where a scheme's waste water can join a network that mostly carries rain as well.
• Firms beside the Darwen. Griffin Mill, River Mill and the premises around Ewood Park lie inside a warning area, and a business continuity flood risk assessment works out what a flood would stop and how quickly a firm could reopen.
• New employment floorspace. Where commercial buildings, such as those planned on the 72,000 square metre site at junction 5 of the M65, seek a BREEAM rating, a BREEAM flood risk assessment supports the Pol 03 credits.
• Land before it is bought. Where a site includes a Flood Zone 3b strip or a culvert, as on North East Blackburn, a flood risk feasibility study tests how many plots it can take before a price or a layout is agreed.

Who to contact about flooding in Blackburn and Darwen

Ring 999 straight away if floodwater is putting people in danger; 105 is the number for a power cut. Otherwise, the right body depends on the source of the water.

Flood warnings for any of Blackburn's seven warning areas, and Darwen's four, are free when you sign up with the Environment Agency. Out on the Fylde coast, our Blackpool page covers a town where the sea and surface water lead, and across the moors to the south-east our Rochdale page covers another Pennine mill town with a river under its centre.

Questions about flood risk and drainage in Blackburn

To discuss a site anywhere in Blackburn or Darwen, call one of our experienced flood risk consultants on 01293 214444 or email enquiries@unda.co.uk.