Flood Risk Assessment in Gillingham

Unda prepares flood risk assessments in Gillingham for developers, planning consultants, architects, homebuyers and businesses. A flood risk assessment in Gillingham shows Medway Council and the Environment Agency that a development will stay safe from flooding for its whole lifetime, and will not push flood risk onto neighbouring land. We prepare these assessments for planning, for property purchase and mortgage, for insurance and for BREEAM, alongside the sequential and exception tests and the surface-water drainage strategies (SuDS) that schemes here so often need.

Gillingham sits on the tidal Medway estuary, so the picture is rarely simple. Tidal risk from the river, surface water that overwhelms the drains in heavy rain, and groundwater rising through the chalk all have to be read together for an assessment to stand up to scrutiny. Our consultants know Medway's flood history and planning policy well, and write reports built to be approved the first time.

Gillingham's lower ground drains to a defended tidal estuary, and its town centre relies on a combined sewer that can be overwhelmed in a downpour — so the same site can face the sea, surface water and groundwater at once, and only an assessment that reads all three together will satisfy the Environment Agency and Medway Council.

To talk through a site, call Unda on +44 (0) 1293 214444 or email enquiries@unda.co.uk, and one of our experienced flood risk consultants will come back to you within 60 minutes.

Flood risk assessment in Gillingham at a glance

The essentials a developer, agent or homeowner needs before bringing a Gillingham site forward.

• Medway Council is the Lead Local Flood Authority. Medway is a unitary authority, so the council — not Kent County Council — leads on surface water, groundwater and ordinary watercourses, while the Environment Agency leads on the tidal River Medway.
• The tidal Medway estuary is the dominant river risk. Gillingham's riverside, including Pier Road and the Riverside area, lies within the tidal floodplain protected by raised defences; much of the higher town sits in Flood Zone 1.
• Surface water is the most widespread risk inland. Heavy rain regularly overwhelms the combined sewer network, with Pier Road a recognised hotspot.
• An assessment is normally required for development in Flood Zones 2 or 3, for sites of one hectare or more anywhere, and for smaller sites where the Flood Map for Planning shows surface water risk.
• We cover every reason you might need one — planning, property purchase, mortgage and insurance, and BREEAM — plus sequential and exception tests and drainage strategies.

Check flood risk anywhere in Gillingham

Medway is outlined below, with Gillingham on the tidal estuary in the north-east of the authority. Screen any postcode against Environment Agency data for rivers and sea, surface water and the planning flood zones, with a climate outlook to 2125. It is an indicative first pass, not a substitute for a site-specific assessment.

Is Gillingham at risk of flooding?

Yes, in more ways than its position might suggest. Gillingham faces tidal flooding from the Medway estuary along its northern riverside, surface water flooding across the built-up town when intense rain overwhelms the drains, and groundwater flooding where the chalk water table rises. The town's higher ground largely sits in Flood Zone 1, but a low-risk river-and-sea result never rules out surface water or groundwater, both of which Medway Council assesses separately.

The tidal River Medway is the source the Environment Agency leads on. Gillingham's waterfront — Pier Road, the Strand, Gillingham Riverside and the former St Mary's Island and dockyard fringe at the boundary with Chatham — lies behind raised tidal defences, which is why those areas remain within the mapped tidal floodplain even though they are defended. Inland, the risk shifts to surface water and the drainage network: Gillingham's Victorian combined sewers carry foul water and rainwater together, and in a downpour the rainwater cannot drain away quickly enough.

Because most Gillingham sites face more than one source, an assessment that looks only at the river will not hold up. A robust report reads the tidal, surface water and groundwater picture together, applies the right Environment Agency data, and where mapping is not detailed enough brings in flood modelling to establish levels accurately.

A history of flooding in Gillingham and Medway

Dated events are why Medway scrutinises riverside and low-lying development so closely, and why a flood risk assessment in Gillingham has to be evidence-led rather than generic. The tidal Medway has a long memory.

• 1953 — the North Sea flood. On the night of 31 January to 1 February 1953 a storm surge drove up the Medway: homes in Pier Road, Gillingham were flooded, the Empire Theatre and shops in Chatham's Medway Street and Military Road went under, and the sewage works at Motney Hill near Rainham was submerged. The disaster led directly to the modern tidal defences along the estuary.
• December 2013 — the St Jude tidal surge. The 5–6 December 2013 surge was the most serious for decades. Around 300 people were evacuated across Medway and two emergency shelters were opened, with isolated flooding reported at Pier Road in Gillingham and Canal Road in Strood, where a flood wall was briefly breached.
• Recurrent surface water flooding. Pier Road near Lower Rainham Road and the Asda junction floods in heavy rain when the combined sewer is overwhelmed, causing closures and delays — a reminder that the risk here is not only tidal.
• The wider Medway picture. The tidal Medway and estuary — covering the Medway Towns, Lower Halstow, Upnor and the Hoo Peninsula — carry standing Environment Agency flood warning and alert areas that are activated on high spring tides and surges.

Which flood zone is Gillingham in, and do you need a flood risk assessment?

Most of built-up Gillingham sits in Flood Zone 1 (low river-and-sea probability), while the tidal riverside — Pier Road, the Strand and the waterfront — falls within Flood Zones 2 and 3. But the flood zone is only the starting point: since the September 2025 Planning Practice Guidance update, the risk-based approach applies to all sources of flooding, so a Flood Zone 1 site flagged for surface water can still need an assessment.

• Flood Zones 2 or 3. Development on Gillingham's tidal riverside almost always needs a flood risk assessment for planning, and often a sequential and exception test.
• Sites of one hectare or more. An assessment is required even in Flood Zone 1, to address surface water and runoff.
• Surface water risk on the map. Smaller Flood Zone 1 sites increasingly need one where the Flood Map for Planning shows surface water risk — common across Gillingham's older streets.
• A more vulnerable use. Converting commercial premises to homes on or near the waterfront introduces residential use into a higher-risk area and triggers assessment.
• Property purchase, mortgage or insurance. A lender or insurer may ask for a site-specific flood risk survey for a property purchase where an environmental search flags risk.

If you are not sure whether your scheme needs one, send us the site address and we will tell you quickly. Our guidance follows the NPPF and its Planning Practice Guidance, and we have seen how a thin or self-prepared report can cost more in delay than it saves.

Planning and drainage policy for development in Gillingham

Two kinds of authority set the rules in Gillingham. The Environment Agency leads on the tidal River Medway and the estuary. Medway Council — as a unitary authority, it is its own Lead Local Flood Authority — leads on surface water, groundwater and ordinary watercourses, and is a statutory consultee on surface water drainage for major development. This is a point competitors routinely get wrong: Gillingham is not covered by Kent County Council.

For surface water, Medway expects schemes to follow the drainage hierarchy — reuse and infiltration before discharge to a watercourse, and the public sewer only as a last resort — and to limit runoff to greenfield rates with an allowance for climate change. Where infiltration is proposed, testing to BRE Digest 365 is normally expected; you can get an early read on ground conditions with our geology and soakaway checker and size features with the drainage calculators and BRE 365 calculator. A drainage strategy that defaults to the sewer without ruling out infiltration is a common reason an LLFA objects to an application.

What your flood risk assessment in Gillingham must show

On the tidal estuary, the assessment has to engage the defences honestly. Defences reduce the chance of flooding but never remove it, so the report must address residual risk — what happens in a breach or overtopping — alongside the standard requirements.

• The design flood level. The relevant tidal or surface water event plus the appropriate climate change allowance over the development's lifetime, taken as 100 years for housing.
• Finished floor levels. Generally at least 600mm above the design flood level, referenced to Ordnance Datum, reducible only with high certainty.
• Safe access and egress, and residual risk. Breach and overtopping behaviour for defended riverside sites, with safe routes and, where needed, a flood warning and evacuation plan.
• All sources together. Tidal, surface water, groundwater and sewer flooding assessed as one picture, not in isolation.

Development in Gillingham and what it means for flood risk

Gillingham and the wider Medway Towns are among the busiest growth areas in north Kent, and the kind of site you bring forward shapes the assessment you need. Getting the scope right is the difference between a clean approval and a drainage objection that holds an application up for months.

• Riverside and waterfront regeneration. Schemes along Gillingham Riverside, the Strand and towards the Chatham waterfront sit in the tidal floodplain, so they turn on defences, finished floor levels and residual-risk modelling.
• Town-centre infill and change of use. Converting shops or offices to flats in the older town introduces residential use onto combined sewers, where surface water and a surface water drainage strategy usually drive the assessment.
• Suburban and edge sites. Development towards Rainham, Twydall and Hempstead often turns on surface water, ordinary watercourses and infiltration rather than the tidal river.
• Strategic growth across Medway. The emerging Local Plan 2041 directs major growth to the riverside and the Hoo Peninsula, with flood infrastructure built into the masterplanning — raising the bar on drainage and flood evidence for sites across the authority.

Climate change is not optional here. A Gillingham assessment must apply the Environment Agency's allowances for higher tides, river flows and rainfall over the development's lifetime — generally 100 years for housing — which sets floor levels, freeboard and how much attenuation a drainage scheme needs.

How Unda helps with flood risk assessment in Gillingham

We act as the accurate translation layer between your scheme and the requirements set by the Environment Agency, Medway Council as the Lead Local Flood Authority, and national planning policy. We are experts on Medway's flooding, not a generic report mill, and a senior consultant signs off every report. Unda has completed more than 5,000 flood risk assessments since 2014 and is a CIWEM Business Partner; you can read more about us and our work in the media.

Our flood risk consultants stay involved past the report to answer the Environment Agency or Medway Council if questions arise, so an application keeps moving. Start with our free flood risk map and live river levels map to screen a Gillingham postcode, then talk to us about a site-specific assessment.

Flood risk assessments and related reports for every situation in Gillingham

A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports. They often travel together in a planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go. We prepare all of them for sites across Gillingham and Medway.

• Flood risk assessment for planning. Site-specific and prepared to satisfy the NPPF, the Environment Agency and Medway Council. Groundwater and, where needed, flood modelling are assessed within it rather than as separate reports.
• Flood risk survey for property purchase. For homebuyers and their advisers when a conveyancing search flags risk — common along the Gillingham waterfront. Flood risk can affect value and mortgageability.
• Flood risk assessment for insurance. Property-specific evidence where premiums rise or cover is restricted after a tidal or surface water event.
• Flood risk assessment for BREEAM. Structured around the Pol 03 flood and surface water criteria for schemes pursuing certification.
• Sequential and exception tests. The locational justification when development is proposed in Gillingham's tidal Flood Zones 2 or 3.
• Surface water drainage strategy and SuDS. Managing runoff to greenfield rates using the four pillars of SuDS, with discharge of drainage conditions and preliminary drainage design at the right stage.
• Groundwater flood risk. Assessed within the FRA, and as a focused study where Gillingham's chalk and a rising water table need closer attention.

Local flood risk management and emergency contacts in Gillingham

The most reliable Gillingham flood information comes from the lead authorities. For an immediate threat to life during a flood, always call 999; for a power cut during flooding, call 105.

• Check for flooding in Gillingham. Environment Agency live warnings, river and tide levels and maps at check-for-flooding.service.gov.uk; sign up for flood warnings or call Floodline on 0345 988 1188.
• Medway Council flood team. Surface water, groundwater, ordinary watercourses, reporting flooding and the SFRA at Medway Council flood and water management.
• Medway drainage guidance. The Medway sustainable drainage (SuDS) guidance and the Local Flood Risk Management Strategy.
• Sewer flooding. Report to Southern Water, the sewerage company for Medway, which deals with combined-sewer surcharge.
• Future planning policy. The emerging Medway Local Plan 2041 sets out riverside regeneration and strategic flood infrastructure.

Flood risk assessment in Gillingham: frequently asked questions