Flood Risk Assessment in Woolwich

Woolwich sits on the south bank of the tidal Thames, a short way downstream of the Thames Barrier, on ground that has taken water from the river within living memory. That setting shapes every flood risk assessment in Woolwich: the town lies inside the tidal floodplain and stays dry because of the capital's engineered defences, so the question a planning authority really wants answered is what happens to a site if those defences are ever overtopped or breached.

We prepare flood risk assessments in Woolwich for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface-water drainage strategies. We assess every source that matters here — the tidal Thames, the surface water that overwhelms drains on the low ground below Shooters Hill, the culverted watercourses draining Plumstead and Charlton, and the groundwater that sits close to the surface near the river — then deal directly with the Environment Agency and the Royal Borough of Greenwich on your behalf. Our flood risk consultants know the Woolwich waterfront and its regeneration sites well, and guide architects, developers, planning consultants, home buyers and businesses through to a decision.

For a quote or to talk a site through, contact one of our experienced flood risk consultants on 01293 214444 or enquiries@unda.co.uk.

Woolwich owes its dry streets to the Thames Barrier and the walls behind it, which means almost every riverside site here sits behind defences — so the flood risk that decides a planning application is the residual risk of what reaches the site if those defences are overtopped or fail.

Flood risk assessment in Woolwich at a glance

• Woolwich is on the tidal Thames. The Environment Agency's tidal flood warning area runs from Woolwich Arsenal to Deptford Creek, and broadly marks the land where the chance of tidal flooding is greater than 1% in any year.
• The Thames Barrier is on Woolwich's doorstep. Its 520-metre span crosses the river at New Charlton, in the Royal Borough of Greenwich, and forms part of a system protecting around 1.42 million people and roughly £321 billion of property.
• Most of riverside Woolwich is in Flood Zone 3. Behind defences, but still tidal floodplain — which is why residual risk, safe finished floor levels and safe access and escape drive the assessment.
• The Royal Borough of Greenwich is the Lead Local Flood Authority. It handles surface water, groundwater and ordinary watercourses, and is the statutory consultee on drainage for major development.

Flood risk in Woolwich: the tidal Thames, surface water and what lies beneath

Tidal flooding from the Thames is the dominant risk in Woolwich, but it is not the only one. Surface water floods the low ground where the drainage network runs out of capacity, culverted watercourses carry run-off down from Shooters Hill and Plumstead, and groundwater sits close to the surface in the alluvium near the river. Most sites here face more than one source at once, which is why a single national map never settles the question.

The town lies on the flat river terrace and estuary alluvium beside the Thames, with the ground climbing steeply south to more than 130 metres at Shooters Hill, capped by London Clay. That range gives Woolwich two very different drainage worlds within a short distance: fast run-off shedding off the clay heights, and low, poorly-draining land by the river where water has nowhere to go by gravity. Reading which source drives the risk on a given plot is the heart of a credible tidal and surface water assessment.

• Tidal (the Thames). The defining risk. Woolwich sits within the tidal Thames floodplain; the riverside is defended, but a surge combined with a high spring tide is the scenario the defences — and every FRA behind them — are built around.
• Surface water (pluvial). Now the most widespread source of flood risk in England. Intense rain overwhelms the urban drainage network on the low ground around Woolwich, Plumstead and Charlton, and can trigger an assessment even where the river risk is defended. See our note on surface water and planning.
• Ordinary watercourses. The Wogebourne (the old Plumstead or Wickham Valley watercourse) and other small channels draining Shooters Hill are largely culverted beneath the built-up area, where they can surcharge in heavy rain — a Lead Local Flood Authority matter rather than the Environment Agency's.
• Groundwater. In the river terrace and estuary alluvium the water table sits close to the surface, so riverside sites often report water ingress and struggle to infiltrate — critical for basements and any soakaway. See groundwater flooding.
• Sewers. In a dense, largely combined-sewer catchment, surcharging drains add to the picture in extreme rain. Our guide to sewer flooding explains how this is assessed.

The Royal Borough of Greenwich's Strategic Flood Risk Assessment, prepared by AECOM, maps all of these sources — the tidal Thames, fluvial watercourses including the River Ravensbourne to the west, ordinary watercourses, surface water, groundwater and reservoirs — and is the starting point for reading any site in the borough. The Environment Agency's flood map and free check-for-flooding service give the screening picture; a site-specific FRA turns that into a real answer for a building.

A history of flooding in Woolwich and the Thames Estuary

Woolwich's flood defences exist because the river has flooded this stretch before. Two twentieth-century disasters on the tidal Thames — in 1928 and 1953 — drove the decision to build the Thames Barrier, and they still define how flood risk is assessed here today.

On 7 January 1928 a high spring tide met a North Sea storm surge and the Thames poured over its embankments. Fourteen people drowned across riverside London and thousands were made homeless, with serious flooding reported at Greenwich, Woolwich and further downriver. The far larger North Sea flood of 31 January to 1 February 1953 killed more than 300 people along the east coast and the Thames Estuary; London itself escaped loss of life, but the water rose by close to three metres and flooded low-lying riverside districts including Plumstead. The 1953 catastrophe led the Waverley Committee to recommend a closable barrier across the Thames rather than ever-higher walls.

• 1928 Thames flood. A surge on a spring tide overtopped the embankments; 14 died in riverside London, with flooding recorded at Woolwich and Greenwich.
• 1953 North Sea flood. More than 300 deaths along the coast and estuary; riverside Plumstead among the areas flooded as the tide rose almost three metres. The event that made the case for the Barrier.
• 1982 — the Thames Barrier becomes operational. Built at Woolwich Reach and first used against a tidal surge shortly after, it has been closed to protect London hundreds of times since.

That history is why a modern assessment cannot simply record that a Woolwich site is "defended". The defences work — but planning policy requires an FRA to show what would happen in the event they are overtopped or breached, and to keep people and property safe for the development's whole lifetime. Our explainer on residual flood risk sets out exactly this point.

The Thames Barrier, Thames Estuary 2100 and residual risk in Woolwich

The Thames Barrier and the walls behind it protect Woolwich today, but they do not remove the need for a flood risk assessment. The land is still tidal floodplain, the defences carry a residual chance of failure, and the long-term plan for the estuary assumes those defences will have to be raised as sea levels rise.

Woolwich falls within the Environment Agency's Greenwich policy unit under the Thames Estuary 2100 plan — the adaptive strategy that manages tidal flood risk across the estuary to the end of the century. In this unit a "P5" policy applies, meaning the Agency and its partners must take further action over the coming decades to reduce flood risk, including raising the tidal defences to keep pace with rising sea levels and bigger, more frequent storm tides. The tidal defence system as a whole — the Barrier, eight other major barriers and more than 330 kilometres of walls and embankments — protects around 1.42 million people and an estimated £321 billion of property. You can read more in our overview of the Thames Barrier and of sea level rise and coastal flooding.

For a development this means the FRA has to look beyond the defended-today position: it must account for climate-change allowances on tidal levels over the site's lifetime, set finished floor levels and safe access and escape accordingly, and — where the site is more vulnerable — demonstrate that occupants can be kept safe if a breach occurs. Where national mapping is not enough to answer those questions, detailed flood modelling derives the levels, depths and flow routes an assessment relies on.

Planning and drainage policy for development in Woolwich

A flood risk assessment in Woolwich has to satisfy three layers of policy at once: national planning policy and its guidance, the London Plan, and the Royal Borough of Greenwich's own flood and drainage requirements. Getting all three right the first time is what keeps an application moving.

Nationally, an FRA is required for development in Flood Zones 2 and 3, on sites of one hectare or more even in Flood Zone 1, and where surface water risk or a critical drainage area applies. Because most of riverside Woolwich is in Flood Zone 3, that threshold is met on the majority of sites. Our guides to when you need an FRA and to the NPPF set out the national test in full.

• Lead Local Flood Authority. The Royal Borough of Greenwich is the LLFA and the statutory consultee on surface water drainage for major development. Its Strategic Flood Risk Assessment, Local Flood Risk Management Strategy and surface water studies set the local expectations. See the role the LLFA plays.
• London Plan Policy SI 12. Development must manage flood risk and support the Thames Estuary 2100 approach, working with rather than against the tidal defences.
• London Plan Policy SI 13 and the drainage hierarchy. Schemes must aim for greenfield run-off rates and follow the London drainage hierarchy — rainwater reuse, then infiltration, then green attenuation, then a watercourse, and only then a sewer. See our summary of the London Surface Water Strategy.
• London Sustainable Drainage Proforma. Every London borough requires this GLA proforma to accompany a drainage strategy for major development. Our explainer on the SuDS proforma covers what it needs.
• Sequential and Exception Tests. In higher-risk zones a scheme may need to pass the sequential and exception tests, showing why it should be on that land and that it is safe without increasing risk elsewhere.

Because Woolwich is low-lying and largely built on clay and alluvium, infiltration drainage is often difficult, so schemes usually rely on attenuation and controlled discharge — which the LLFA will expect to see evidenced. Ground conditions can be screened early with our geology and ground conditions map, and where infiltration is proposed it is tested to BRE Digest 365 using our BRE 365 infiltration calculator and sized with our drainage calculators.

Development in Woolwich and what it means for flood risk

Woolwich is one of London's largest regeneration stories, and almost all of it is happening on defended tidal floodplain and former industrial land beside the river. That combination — high-density, more-vulnerable residential use on Flood Zone 3 brownfield ground — is exactly the situation that makes flood risk and drainage central to getting permission.

The former Royal Arsenal is one of the capital's largest brownfield regeneration sites: an 88-acre riverside estate where several thousand new homes are being delivered over a programme running towards 2030, alongside new streets, public space and the town-centre renewal around the Elizabeth line station. Sites like these sit squarely within the tidal floodplain, so the flood risk assessment and drainage strategy do real work — proving the development is safe for its lifetime, that people can leave safely in an extreme event, and that surface water is managed to the standard the borough and the GLA require.

• Riverside brownfield regeneration. Former industrial and munitions land by the Thames, typically in Flood Zone 3, where finished floor levels, safe access and escape, and breach scenarios must all be addressed.
• High-density residential. Flats and mixed-use blocks are a "more vulnerable" land use, raising the bar the FRA and any exception test must clear.
• Groundwater and basements. With the water table close to the surface near the river, below-ground parking and plant need careful groundwater assessment and drainage design.
• Constrained drainage. Clay and alluvium limit infiltration, so most schemes attenuate and discharge at a controlled rate under the London drainage hierarchy.

Larger regeneration schemes carry wider sustainability benefits that can help satisfy part of the exception test, but that never removes the need to demonstrate the site itself is safe. Whether the job is a single riverside plot or a phase of a masterplan, the same principles apply — read the tidal risk correctly, respect the defences and their residual risk, and design drainage that the Royal Borough of Greenwich will accept.

How Unda helps with flood risk assessment in Woolwich

We are flood risk and drainage specialists who know the tidal Thames and its planning framework well. We have prepared flood risk assessments and drainage strategies for defended riverside sites across London and the estuary, and we deal with the Environment Agency and Lead Local Flood Authorities directly so you do not have to.

For a Woolwich site that usually means establishing the tidal flood levels and their climate-change allowance, setting finished floor levels and safe access and escape, testing the residual breach risk behind the defences, and building a drainage strategy that follows the London hierarchy and passes the borough's requirements. Where the national maps are not enough, we model the site; where infiltration is doubtful, we test and design around it. The aim is always the same — an assessment robust enough to clear the first time.

Our flood risk consultants work for architects, developers, planning consultants, home buyers and businesses, and you can see the wider areas we cover on our flood risk assessment areas hub, including neighbouring Thames-side towns such as Dartford, Gravesend, Grays and Tilbury.

Flood risk assessments for every situation in Woolwich

A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports. They often travel together in a Woolwich planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go. We produce all three, along with the assessments people need outside the planning system.

• Flood risk assessment for planning. The core report for a planning application, showing a site is safe for its lifetime without increasing risk elsewhere. See FRA for planning.
• Flood risk assessment for property purchase. A site-specific answer for buyers and lenders when a search or survey flags flood risk. See flood risk for property purchase.
• Flood risk assessment for insurance. Evidence for brokers and underwriters where cover is restricted, declined or priced on the broad national data. See FRA for insurance.
• Flood risk assessment for BREEAM. Structured around BREEAM Pol 03, framed differently from a planning FRA. See BREEAM flood risk assessment.
• Sequential and exception tests. The locational justification for building on higher-risk land. See sequential and exception tests.
• Surface-water drainage strategy and SuDS. Managing run-off under the London drainage hierarchy, with a preliminary drainage design early and discharge of drainage conditions later. See drainage strategy.
• Groundwater assessment. Groundwater is assessed within the FRA as one of its sources, and matters especially near the river. See groundwater.

Local flood risk management and emergency contacts in Woolwich

Several bodies share responsibility for flooding in Woolwich. The Environment Agency manages the tidal Thames and issues flood warnings; the Royal Borough of Greenwich, as Lead Local Flood Authority, handles surface water, groundwater and ordinary watercourses; and Thames Water is responsible for the public sewers. In an emergency, the routes below are the ones that matter.

If you are checking a specific property, start with the Environment Agency's free flood warning service for the Woolwich Arsenal to Deptford Creek area and the Royal Borough of Greenwich's what to do in a flood guidance, and keep an eye on levels through our live river levels map. For the planning framework that London-wide drainage sits in, see the London Sustainable Drainage Proforma and the London Plan. Ageing sewer capacity across the capital is a live issue too, as our note on the Thames Water crisis and the new Thames Tideway Tunnel explains.

Frequently asked questions about flood risk assessment in Woolwich

Prefer to talk it through first? Call one of our experienced flood risk consultants on 01293 214444 or email enquiries@unda.co.uk, and we will help you work out exactly what your Woolwich site needs.