Flood Risk Assessment in Gravesend

A flood risk assessment in Gravesend usually starts at the river wall. The town faces the tidal Thames downstream of the Thames Barrier, behind defences the Environment Agency plans to raise by 2040, and inland its dry chalk valleys and combined sewers flood streets in heavy rain. For sites here we prepare flood risk assessments for planning, purchase and insurance, sequential and exception tests, and surface water drainage strategies.

This page covers Gravesend as the Office for National Statistics draws its built-up area: the town centre and the riverside between the Town Pier and the Canal Basin, Milton and Denton to the east, Pelham and Windmill Hill, and Westcourt, Kings Farm, Riverview Park, Singlewell and Chalk to the south, across the DA11 and DA12 postcode districts. Northfleet, Perry Street and Rosherville to the west form a separate built-up area outside the coral outline, but they share Gravesham Borough Council's planning policies, the same tidal walls and the same Environment Agency flood warning area, so most of what follows applies there too.

The Thames Barrier stands upstream at Woolwich and does nothing for Gravesend. The town relies on its own river walls, and the Environment Agency has named Gravesend Reach as one of two possible sites for the barrier that may one day replace it.

To talk a site through with one of our flood risk consultants, call 01293 214444 or email enquiries@unda.co.uk. Reports for sites in Gravesend come from Unda Consulting Limited, a CIWEM Business Partner.

Why does Gravesend rely on its own tidal walls?

Because the Thames Barrier protects London upstream of Woolwich, and everything seaward of it depends on the walls along its own bank. The Gravesend frontage is held by a tidal wall and floodgates whose crest stands at about 6.7 to 6.8 m AOD through the main urban area, according to Gravesham Borough Council's Water and Flood Risk Background Paper. Kent County Council's 2017 flood risk profile for Gravesham describes a 1 in 1,000 year standard of protection and notes that many of the floodgates are operated privately, which is why the council's evidence lists a gate left open in a surge as one of the ways the town could still flood.

Those walls are why the riverside can look low risk on the long-term flood risk map, which counts defences, and also why it stays in Flood Zone 3 on the Flood Map for Planning, which ignores them; our note on why defended land stays in a flood zone explains the gap. An assessment for a riverside site has to test what happens if a wall is overtopped or breached, or a gate is left open, which is the residual flood risk the council's evidence warns about. A few small parts of the town stand in front of the walls, where protection is limited or absent.

What the Environment Agency plans for the Gravesend riverside

The walls will not stay at today's height. The Thames Estuary 2100 plan sets dates for raising the defences downstream of the Thames Barrier, and its 2023 review brought the decision on the estuary's end-of-century defence forward from 2050 to 2040. For Gravesend the timetable runs:

1. By 2030. Councils are asked to work with communities on a riverside strategy; none yet exists for this frontage.
2. December 2025. The Environment Agency published possible barrier locations, including a 7 km² area of interest at Gravesend running from the Tilbury area to Shorne Marshes.
3. By 2040. The first raising of the downstream walls, about 30 to 60 cm in places, and a decision on the end-of-century option, which could mean upgrading the existing barrier or building a new one at Gravesend Reach or Long Reach.
4. By 2070. A second stage of downstream raising, a further 100 to 150 cm, with the chosen end-of-century option in operation.

That timetable sets the levels a riverside design has to reach. The council's background paper gives the 1 in 1,000 year tide near the Imperial Estate as 5.81 m AOD in 2000 and estimates 7.12 m AOD by 2137 on the higher central sea level allowance, or 7.57 m AOD on the upper end, against walls of about 6.7 to 6.8 m AOD today. The council says its own figures were not verified by the Environment Agency, so an assessment uses the levels the Agency supplies for the site and the current climate change allowances. The draft Local Plan 2042 asks riverside schemes not to compromise future raising of the defences. The estuary as a whole is covered on our River Thames page, and our guide to planning for sea level rise beyond 2100 explains the longer view.

Look up an address between the Town Pier and Riverview Park

Enter a postcode below to screen a site in the town, or open our full flood risk map for anywhere in England. The coral outline is the ONS built-up area of Gravesend, so Northfleet, Perry Street and Rosherville lie just beyond its western edge, and Shorne and the marshes beyond its eastern edge.

When the Thames came over the wall in Gravesend

The written record for the riverside is short: two surges before the modern defences were built, and a wet night on the promenade in 2019.

1. March 1949. North-easterly gales pushed the Thames over its banks into Gravesend and Northfleet, and the Promenade, West Street, East Street and the canal area were under water, according to the Discover Gravesham chronology.
2. 31 January to 1 February 1953. The North Sea surge badly flooded West Street and Gordon Gardens and the cellars of the Ship and Lobster at Denton, partly submerged the Northfleet riverside and the Northfleet FC ground, and broke the sea wall on Higham Marshes in six places. The Queen visited Gravesend a week later to see the damage, as KentOnline's account recalls. Our article on the 1953 North Sea flood covers the night along the whole east coast.
3. Early 1980s. The Thames Barrier at Woolwich and the higher walls downstream, the programme that followed 1953, became fully operational.
4. 30 September 2019. Heavy rain overnight and a high tide left the Dell beside Fort Gardens largely under water and flooded the garden of the Clarendon Royal Hotel. A warning for the Thames between Greenhithe and Gravesend was issued and later withdrawn, and the council handed out sandbags, KentOnline reported.

Rain on the chalk: surface water, sewers and groundwater

Away from the river, Gravesend floods from rain. The town climbs south from the Thames onto chalk cut by dry valleys, and in a heavy storm those valleys carry water faster than the drains can take it. The Core Strategy lists the borough's dry river valleys, alongside the Thames and the Ebbsfleet, as places at risk. The River Ebbsfleet, a main river on the Dartford boundary, is the borough's only natural watercourse where river flooding is expected, and it runs through Northfleet, outside the Gravesend outline.

Kent County Council's Thameside surface water management plan, prepared with Dartford and Gravesham councils, describes the drainage area around Gravesend, Milton, Westcourt and Denton as served by a combined foul and surface water sewer network, with known surcharging at numerous locations. It records:

• Ponding and flow paths on Thames Way, Milton Hall Road, Parrock Avenue, Pine Avenue, Norfolk Road, Valley Drive and Roehampton Close.
• Overloaded sewers behind flooding in Gravesend South, Gravesend East and Westcourt South, and at Wombwell Park in Northfleet.
• Blocked drains and gullies flooding the carriageway in Gravesend North and a number of properties in Gravesend East.

Groundwater is the third source. The draft Local Plan 2042 lists groundwater emerging from the underlying chalk aquifer among the borough's flood risks, and the council's background paper links it to water levels rebounding where quarry and industrial pumping has stopped. The same chalk holds the aquifer that supplies the area's drinking water, with Source Protection Zones that draft policy LP10 singles out, so infiltration needs care: our ground conditions and soakaway checker and BRE 365 infiltration rate calculator give a first read before anyone digs a trial pit. How planning treats rain-driven flooding is set out in our guide to surface water flooding and planning.

Which Gravesend sites need a flood risk assessment?

Any development in Flood Zone 2 or 3 does, and in Gravesend that means the riverside strip from West Street and the Town Pier past the Canal Basin to Denton, with the low ground behind it along Milton Road. Gravesend town centre around the Civic Centre, Windmill Hill, Riverview Park and Singlewell sit in Flood Zone 1 for rivers and the sea, where the triggers are site size, surface water and the dry valleys. Our guide to flood zones 1, 2 and 3 explains how the zones are drawn.

Housing in Flood Zones 2 and 3 also faces the sequential test unless the site is allocated in a plan that has already applied it; our explainer covers how the sequential and exception tests work.

Gravesham planning policy: CS18 today, LP10 next

Gravesham Borough Council decides most applications in Gravesend. Kent County Council is the Lead Local Flood Authority for surface water, groundwater and ordinary watercourses, and the Environment Agency advises on the tidal Thames. Around Ebbsfleet and on parts of the Northfleet riverside, the Ebbsfleet Development Corporation is the planning authority instead.

The adopted plan is the Gravesham Local Plan Core Strategy of September 2014. Its policy CS18 on climate change:

• Steers development to the areas at least risk of flooding, except the previously developed Thames riverside sites in policies CS03, CS04 and CS05.
• Requires a flood risk assessment and, where needed, a flood risk management plan showing a scheme is adequately defended and safe for its lifetime.
• Refuses permission for schemes that do not pass the sequential and exception tests.
• Puts the defences first, prioritising their maintenance, improvement or replacement over other land uses.
• Asks for SuDS on all development where technically and financially feasible, with runoff no worse than the existing use.

Its replacement, the Gravesham Local Plan 2042, finished its Regulation 19 consultation on 18 August 2026, and the council aims to submit it for examination in autumn 2026. Draft policy LP10 keeps the riverside exception and asks every assessment to show the development is safe for its lifetime with climate change allowances and will not increase flood risk elsewhere. It requires SuDS on all major development, with surface water going to the ground first, then a watercourse, then a surface water sewer, and a combined sewer only as a last resort. Where Southern Water's network lacks capacity, the council will condition the upgrades before occupation.

The strategic flood evidence is still the Kent Thameside Strategic Flood Risk Assessment prepared with Dartford in 2005 and updated in 2009, which the council's 2020 background paper reviewed against current sea level guidance. Kent County Council reviews drainage on major schemes against its Drainage and Planning Policy Statement, and its Local Flood Risk Management Strategy 2024 to 2034 lists Gravesend among the places at particular risk of coastal and tidal flooding. Nationally, the NPPF's flood risk chapter (chapter 18) and the 2025 national standards for sustainable drainage also apply.

Regeneration on the riverside and in the town centre

Most of the new housing planned for Gravesend is on former industrial land by the river, and the sustainability appraisal of the draft plan finds that the four Gravesend riverside allocations lie mostly in Flood Zone 3.

• Albion Waterside (LP3A). About 650 homes and 4,500 m² of commercial space on 7.22 ha around the Canal Basin, with an upgrade of the tidal defences and SuDS written into the policy.
• Canal Basin broad location (LP3B). Around 590 homes across 33 ha east of the basin, where defences, finished floor levels and safe access and egress have to work together.
• Lion Business Park and Dalefield Way (LP3C, LP3D). About 1.25 ha of new employment land each at the eastern end of the town.
• Town centre sites (LP4A to LP4F). Denser schemes such as St George's phase 2, which the appraisal places partly in Flood Zone 3, and infill where surface water and sewer capacity decide the drainage.

The Core Strategy accepts that some of the riverside opportunity sites cannot meet the sequential approach and must pass the exception test instead, so the weight at application falls on the site's own safety case: floor levels above the design tide, a dry route out, and evidence of what happens if a wall fails. Below-standard or privately owned defences are a common snag, as our article on defences that protect on paper but not in practice explains.

Our reports for sites in and around Gravesend

A flood risk assessment asks whether a site is safe, a sequential test whether it should be there at all, and a drainage strategy where the rain goes. Which of them a Gravesend site needs depends on the plot and the plan, and our consultants prepare each of these:

• Riverside and town-centre applications. Albion Waterside, the Canal Basin and any Flood Zone 2 or 3 plot behind the river wall need a flood risk assessment for planning.
• Tide, rain and chalk on one plot. Behind the Gravesend walls, a flood risk assessment has to weigh residual tidal risk, the dry valleys, groundwater and the combined sewers together.
• Before you exchange. Homes near West Street, the Promenade or Denton draw lender and insurer questions that a flood risk survey for property purchase answers.
• Homes in the tidal zone. Windfall housing on the riverside that is not allocated faces the sequential and exception test under policy CS18 before anyone looks at floor levels.
• Runoff from new development. Draft policy LP10 asks for SuDS on all major schemes and a discharge hierarchy that ends at the combined sewer, which our drainage strategy work sets out for Kent County Council.
• Ground or sewer. On chalk where Source Protection Zones may limit infiltration, a surface water drainage strategy shows whether the ground will take the water before a sewer connection is proposed.
• After consent. Where Gravesham attaches a drainage condition, we prepare the evidence for the discharge of drainage conditions.
• Getting people out. Riverside homes inside the Environment Agency's Gravesend and Northfleet warning area often need a flood warning and evacuation plan, the kind of flood risk management plan policy CS18 asks for.
• Overtopping and breach. With walls at about 6.7 to 6.8 m AOD and the borough's breach modelling dating from 2009, flood modelling gives the depths and hazards for a failed defence on a riverside site.
• Water in the chalk. Draft policy LP10 protects the chalk aquifer and its Source Protection Zones, and a groundwater flood risk assessment looks at emergence and rebound where basements or infiltration are planned.
• Insuring an existing home. The Thameside surface water plan records properties flooded by blocked drains in Gravesend East, and a flood risk assessment for insurance gives an underwriter evidence for the building itself.
• Buying riverside land. Former industrial sites at Albion Waterside and the Canal Basin lie mostly in Flood Zone 3 behind privately operated floodgates, so flood risk due diligence belongs before the deal.
• Keeping a business running. Policy CS04 retains the Canal Road industrial site and the riverside industrial area east of the Canal Basin, both behind the walls, where a business continuity flood assessment helps occupiers plan for a surge.
• Sewer capacity. Draft policy LP10 lets the council hold back occupation until Southern Water's network is upgraded, so a foul drainage strategy should confirm capacity early.
• Commercial floorspace. LP10 expects BREEAM Excellent water performance from non-residential buildings of 1,000 m² or more, so commercial schemes at Lion Business Park or Dalefield Way that seek BREEAM certification can use a BREEAM flood risk assessment to support the Pol 03 credit.
• Testing a broad location. The 33 ha Canal Basin broad location is earmarked for intensification without individual site allocations, so a flood risk feasibility study shows what the tidal zone allows before land is assembled.
• National policy. The August 2026 NPPF rewrote the flood chapter that Gravesend's riverside schemes are judged against, and our NPPF flood risk guidance explains each policy.

Flood contacts for Gravesend, from Floodline to Southern Water

If anyone's life is in danger in a flood, call 999, and report a power cut on 105. For everything else, these are the bodies that look after flood risk in the town.

The nearest Environment Agency sea level gauge is the River Thames at Tilbury, across the water, and the Gravesend and Northfleet flood warning area page shows any live warning for the tidal areas of both towns and Swanscombe. Our live river levels map puts the estuary gauges on one screen.

Across the river, Tilbury and Grays face the same surges from the north bank, Dartford shares the Kent Thameside evidence upstream, and Rochester sits on the tidal Medway to the east. For the wider picture, see flood risk assessments across Kent and every area we cover.

What Gravesend clients ask before instructing a report

For a site anywhere from the Gravesend riverside to Singlewell, or in Northfleet next door, call 01293 214444 or email enquiries@unda.co.uk and a flood risk consultant from Unda Consulting Limited will talk it through.