Flood Risk Assessment in Dartford

A flood risk assessment in Dartford, Kent starts with two rivers and a barrier. The River Darent runs through the town centre from Brooklands to Dartford Creek, and at the creek mouth the Dartford Creek Barrier holds back the tidal Thames. Our consultants assess sites here for planning applications, house purchases, lenders and insurers, and prepare the sequential and exception tests and surface water drainage strategies that often sit alongside them.

The page covers Dartford, Kent as the Office for National Statistics maps the town: the town centre, Temple Hill and the riverside north of the railway, West Hill to the west and Wilmington to the south, across the DA1 and DA2 postcode districts. Stone, Greenhithe, Swanscombe and the Dartford side of Ebbsfleet Garden City lie east of that outline. They share the same council, Local Plan and flood evidence, but Stone is mapped as a separate built-up area and none of them is drawn here.

Closing the Dartford Creek Barrier against a high tide stops the Thames, but it also stops the Darent draining, and the council warns that this can make river flooding in the town worse.

To talk through a site with one of our flood risk consultants, call 01293 214444 or email enquiries@unda.co.uk.

What does the Dartford Creek Barrier protect?

The barrier stands where Dartford Creek, the tidal mouth of the Darent, meets the Thames on the marshes north of the town. It was built in 1981 as part of the Thames tidal defences and is run by the Environment Agency, which lowers it to stop high tides backing up the lower Darent and Cray. With the walls and embankments along the Thames, it keeps the north of the town dry in a surge.

Kent County Council's 2017 profile, Flood risk to communities in Dartford, rates the tidal line at a 1-in-1,000-year standard along 15 km of frontage from Dartford Creek to Denton Wharf in Gravesend, protecting more than 2,000 homes and 400 other properties. Even with those defences, it counted 290 homes in the Dartford Town area at medium or high risk from rivers and the sea, and 931 at some level of risk.

• Defended land stays in the flood zone. The Flood Map for Planning draws Flood Zones 2 and 3 as if the defences were not there, and the Dartford Plan describes the area north of the railway line as at high risk of tidal flooding. Our guide to residual flood risk explains what an assessment has to show on land like this.
• Breach has to be tested. The borough's Strategic Flood Risk Assessment draws on the Environment Agency's 2018 Thames Estuary Breach Assessment and a 2020 Dartford and Crayford model with four breach locations, and asks sites behind defences to plan for rapid inundation with little warning.
• A shut barrier traps the river. When the tide is high, gravity outfalls on the lower Darent and Cray cannot discharge. The SFRA calls this tide-locking, and it can coincide with heavy rain on the town.
• The defences will be raised. Under the Thames Estuary 2100 plan the Dartford and Erith policy unit is under policy P4, and by 2040 defence owners are expected to work with the Environment Agency to raise defences where required. Before 2070 the options include improving the Thames Barrier or building a new barrier at Long Reach, inside the borough; our article on the Thames Barrier covers the wider system.

Rivers, rain, sewers and chalk: the other flood sources in Dartford

The 2021 SFRA ranks the tide as the largest source of flood risk in the borough, and a Dartford site usually has to answer three or four others as well. The Darent floods the valley floor through the town, surface water follows roads and dry valleys, and beside the rivers the groundwater in the chalk sits close to the surface.

In the north of the town these sources overlap. A drainage scheme near the marshes has to hold water for the length of a high tide as well as a storm, because its outfall may be shut when the rain falls. Our explainers on tidal flooding and planning and on surface water flooding and planning go through each source in more depth.

Look up a postcode in Dartford, Temple Hill or Wilmington

Enter a postcode below to screen a site against Environment Agency data for rivers and the sea, surface water and reservoirs, or open the full flood risk map for anywhere in England. The coral line follows the ONS built-up area, so the Creek Barrier and most of the marshes north of the town fall outside it, as do Stone and Greenhithe to the east.

A record of floods in Dartford since 1953

The SFRA lists the tidal surges of 1953 and 1978 and the river floods of 1968, 1993 and the winter of 2002 to 2003 as the notable events in the borough. Kent County Council's own database adds 33 flooding incidents across the borough, without recording their source.

1. 31 January 1953. A storm surge on a spring tide flooded the Dartford and Crayford Marshes, Crossways and Greenhithe. Around 1,300 properties in Dartford and Swanscombe were affected and tidal defences in the borough were breached. The surge along the rest of the east coast is told in our piece on the 1953 North Sea flood.
2. September 1968. The Darent and the Cray overtopped their channels, and the Environment Agency's recorded outlines show river flooding through Dartford and at Sutton at Hone, with smaller watercourses flooding the marshes and Crossways.
3. January 1978. A surge of similar size to 1953 reached the estuary, but the defences built along the north Kent coast in the meantime reduced its impact.
4. December 1993. An operational failure or breach of a defence let the Darent flood Dartford Trade Park, south of the town centre.
5. December 2002 to January 2003. The Darent flooded again over the winter; the Environment Agency reported 126 properties flooded across Kent.
6. 18 December 2013. The Environment Agency's gauge on the Darent at Hawley, just south of the town, recorded its highest level, 0.64 m.

The Hawley gauge and the Erith tide gauges are on our live river levels map, which puts every Environment Agency station in England on one screen.

Central Dartford: new homes on the Darent floodplain

Dartford grew up beside the Darent, and the Dartford Plan accepts that much of the town centre is at high risk of river flooding as a result. It builds its strategy around regenerating Central Dartford all the same, with 2,200 new homes expected there through allocations and existing permissions. The justification is national policy, which allows development where the wider benefits outweigh the risk and the scheme stays safe for its lifetime.

The SFRA records what happened when the council and the Environment Agency looked for a scheme to shrink the town-centre floodplain in the 1% annual chance flood with climate change. More storage at Brooklands Lake, more flow down the flood relief channel through Central Park and flapped outfalls through the tidal walls were all tested. The gains were small: Overy Liberty Bridge stays a constriction, and a low point in the bank between Bridge House and the bridge would still overtop first. No scheme is being pursued.

So each development has to bring its own mitigation. The SFRA expects more vulnerable uses above the climate change flood level with freeboard, no displaced water or blocked flow routes, and an approach agreed with the Environment Agency. The council's Lower Darent Riverside Strategy, adopted in May 2024, sets the riverside approach from the Thames to the south of the town, and a supplementary planning document built on it went to Cabinet for adoption in June 2026.

The Dartford Plan, the 2021 SFRA and Kent's drainage rules

Dartford Borough Council decides planning applications against the Dartford Plan, adopted on 22 April 2024 and running to 2037. Kent County Council is the Lead Local Flood Authority and is consulted on surface water for major development, while the Environment Agency advises on the Darent, the Cray and the tidal Thames. Policy M4, Flood Risk and Riverside Design, is the local test:

• Riverside frontages. Sites on the Thames or the Darent are expected to explore better landscape, habitat, access and river recreation, planned together with any defence works.
• The defence raising zone. Development in the tidal flood defence raising zone must not constrain the future maintenance and raising of the defences and, where feasible, should help deliver the Thames Estuary 2100 Plan.
• Safe for its lifetime. Permission is granted only where a site is safe from all types of flooding for the lifetime of the development, allowing for climate change, without displacing flood water or worsening risk elsewhere.
• The national tests. Sites at risk from any source are required to pass the sequential test and, where needed, the exception test, reduce risk where possible, provide safe access and escape, and build in protection and resilience.
• SuDS on every major scheme. Major development must include multi-functional sustainable drainage, and infiltration is acceptable only where it will not harm groundwater in a source protection zone.

The evidence behind M4 is the Dartford Borough Level 1 and 2 Strategic Flood Risk Assessment, prepared by JBA Consulting and issued as a final report in February 2021; our explainer sets out what an SFRA does. For floor levels it asks for at least 300 mm above the 1% annual chance river flood or the 0.5% annual chance tide, each with climate change, for non-sleeping uses, and 600 mm where people sleep on the ground floor. Emergency vehicles should be able to reach the site during a flood.

Nationally, the flood risk policies sit in chapter 18 of the August 2026 NPPF. Policy F4 sets when an assessment is needed, F5 and F6 hold the sequential and exception tests, and F8 now expects all development to follow the 2025 National Standards for sustainable drainage.

Kent's Drainage and Planning Policy sets the county's SuDS rules, including greenfield runoff rates, a 2 l/s minimum discharge for small sites and no infiltration into made ground. Large parts of the borough lie in groundwater source protection zones; in zone 1 only clean roof water may go to ground. Our ground conditions and soakaway checker gives a first read on the chalk and the superficial deposits before any testing.

When does a site need a flood risk assessment in Dartford?

Most sites in the town centre and north of the railway need one. So do plenty of Flood Zone 1 sites. The table covers the usual cases; for any one site, its levels and its use settle the rest.

Housing on the Darent floodplain or behind the tidal walls is also judged under the sequential test, which policy M4 repeats, with the exception test to follow where national policy requires it.

Reports for Dartford sites, from Brooklands to the Creek

Which report a site needs depends on where it sits between Brooklands and the Creek and on who is asking. Our consultants are chartered, Unda is a CIWEM Business Partner, and a senior consultant signs off every report.

• Applications on the Darent or behind the walls. Schemes on the town-centre floodplain and on the riverside north of the railway need a flood risk assessment for planning that meets policy M4.
• Every source on one plot. Here a flood risk assessment weighs the river, the tide, surface water, chalk groundwater and the sewers together.
• Before exchange. Homes near Brooklands Lake, the Trade Park or the A206 confluence raise lender questions that a flood risk survey for property purchase settles.
• Housing in Flood Zone 3. New homes on the Darent floodplain or behind the tidal defences meet the sequential and exception test before anyone discusses floor levels.
• Runoff from new building. Policy M4 asks every major scheme for multi-functional SuDS, which our drainage strategy work sets out for the council and Kent County Council.
• Chalk, made ground or a tide-locked outfall. Infiltration is limited in the source protection zones and refused into made ground, so a surface water drainage strategy here often has to find another route or store water for a tide.
• After consent. Where Dartford Borough Council attaches a drainage condition to a permission, we prepare the evidence for the discharge of drainage conditions.
• Breach depths and floor levels. Behind the Thames walls the SFRA asks for breach hazard to be assessed, and flood modelling can quantify it where the 2018 breach outputs do not reach a site.
• Getting out before the water arrives. Riverside homes in the Dartford, Crayford and Greenhithe tidal warning area need a flood warning and evacuation plan, because a breach gives little warning.
• Water in the chalk. Beside the Darent and Cray up to three-quarters of the ground is susceptible to groundwater flooding, so basement and soakaway schemes benefit from a groundwater flood risk assessment.
• Insurance on the floodplain. Kent County Council counted 290 homes in the Dartford Town area at medium or high risk, and a flood risk assessment for insurance gives an underwriter evidence about the building itself.
• Buying riverside employment land. Part of the Littlebrook employment area lies in the zone the Dartford Plan reserves for a possible Long Reach barrier, so flood risk due diligence belongs before the deal.
• Keeping a business trading. Dartford Trade Park flooded from the Darent in December 1993, and a business continuity flood assessment helps occupiers there plan for the next event.
• Sewer capacity. Thames Water records put 12 of the borough's 59 sewer flooding incidents in the DA1 1 town-centre postcode, so a foul drainage strategy should confirm capacity early.
• Town-centre commercial floorspace. The Priory Centre allocation alone expects 10,000 m² or more of retail, leisure and office space, where a BREEAM flood risk assessment supports the Pol 03 credit.

Flood warnings, gauges and the bodies responsible for Dartford

If a flood puts anyone's life at risk, call 999. For a power cut, call 105. For everything else, the responsibility is split between these bodies.

Three Environment Agency warning areas cover the town: River Darent at Dartford Trade Park, Brooklands and Dartford to the Thames estuary, Dartford, Crayford and Greenhithe for the tide, and the Tidal Thames from Dartford Creek to Erith High Street East. The river gauge at Hawley is the nearest on the Darent, and the Check for flooding page for Dartford shows anything in force.

Upstream, the Darent valley is covered on our River Darent page, and the estuary on our River Thames page. Erith shares the TE2100 policy unit, Gravesend lies downstream on the same defended frontage, and Grays faces the town across the river. For the rest of the county, start from our Kent county page or the full list of areas.

Dartford flood risk: questions from buyers, owners and developers

From the Creek to Wilmington, Unda Consulting Limited prepares flood risk assessments, sequential and exception tests and drainage strategies for homes, businesses and development land. To discuss a site in Dartford, Temple Hill or West Hill, call 01293 214444 or email enquiries@unda.co.uk.