Flood Risk Assessment in Greenwich

Greenwich is a borough shaped by the tidal Thames. From Deptford Creek in the west, past the great sweep of the Greenwich Peninsula, and on to Charlton Riverside, Woolwich and Thamesmead in the east, much of its riverside sits on land that would flood at high tide were it not for the walls and gates that hold the water back. Preparing a flood risk assessment in Greenwich means understanding that defended landscape in detail: which land lies in Flood Zone 3, how the Thames Barrier protects it, and what happens in the residual case where a defence is overtopped or breached.

We prepare flood risk assessments in Greenwich for planning, property purchase and mortgage lending, insurance, and BREEAM, alongside sequential and exception tests and surface-water drainage strategies (SuDS). Each is a different report answering a different question, and every one is built on the same detailed reading of how the tidal Thames, the borough's rivers and its surface water behave around a specific site.

The southern end of the Thames Barrier stands in the borough itself, at New Charlton — and much of Greenwich's river frontage lies in Flood Zone 3, kept dry only by tidal defences. That residual risk is what a flood risk assessment in Greenwich has to confront head-on.

• Dominant risk is tidal. The Thames along Greenwich is tidal and much of the frontage is in Flood Zone 3, protected by flood walls and the Thames Barrier rather than being naturally dry.
• Residual (breach) risk drives planning here. Because so much of the borough sits behind defences, the key question is what happens if those defences are overtopped or fail — assessed using the Environment Agency's Thames tidal breach modelling.
• Rivers and surface water matter too. The Ravensbourne, its tributary the Quaggy and Deptford Creek affect the borough's western edge, and surface-water flooding is recorded across Eltham, Kidbrooke, Plumstead and Abbey Wood.
• Regeneration sites need careful work. The Greenwich Peninsula, Charlton Riverside, Royal Arsenal and Thamesmead are major growth areas in defended, residual-risk locations, where the sequential and exception tests and finished floor levels are decisive.
• Call 01293 214444. Speak to one of our experienced flood risk consultants on 01293 214444 or enquiries@unda.co.uk for a no-obligation quote.

Flood risk in Greenwich: the tidal Thames comes first

The main flood risk in Greenwich is tidal flooding from the River Thames. The river is tidal all the way through the borough, and a large part of the land beside it — including much of the Greenwich Peninsula, Charlton Riverside, Woolwich and Thamesmead — sits within Flood Zone 3, the Environment Agency's highest-probability zone. That land is not naturally above the tide; it is kept dry by a continuous line of flood walls and embankments and, above all, by the Thames Barrier downstream at Woolwich Reach. Surface water, the Ravensbourne catchment and groundwater add to the picture, but the tidal Thames is the story a flood risk assessment in Greenwich must lead with.

Screening a Greenwich site starts with the Environment Agency's flood map for planning and the check for flooding service for rivers, sea and surface water. You can get an indicative first read for any postcode using Unda's own free tools — the Flood Risk Map, the Live River Levels Map and the Geology & Ground Conditions map — but for a defended borough like Greenwich the national maps are only the starting point. It is worth understanding the difference between the long-term flood risk map and the flood map for planning before drawing any conclusion about a site.

The Thames Barrier, TE2100 and residual flood risk in Greenwich

The Thames Barrier is the single defence that makes development in riverside Greenwich possible. Spanning the river between Silvertown in Newham and New Charlton in the Royal Borough of Greenwich, it became operational in 1982 and is closed under storm-surge conditions to hold back the tide and protect London. Because so much of Greenwich lies behind it and behind the local flood walls, the borough's Strategic Flood Risk Assessment treats the defended land as being at residual risk — the flooding that would occur in the unlikely event that a defence is overtopped or breached.

• Residual risk is modelled, not assumed. The Environment Agency's Thames tidal breach modelling — undertaken at 13 locations along the Thames frontage in 2015, and extended upstream of the Barrier in 2017 — underpins how the borough assesses breach depths and hazard for individual sites.
• A breach would reach well inland. The SFRA identifies that, in a worst-case tidal breach, parts of Thamesmead, Charlton Riverside and the Greenwich Peninsula would flood — which is why finished floor levels, safe access and flood-resilient design are so important here.
• TE2100 sets the long game. Under the Environment Agency's Thames Estuary 2100 Greenwich Policy Unit, tidal defences on this reach are covered by a policy to take further action over time — raising and adapting defences to keep pace with sea-level rise.
• Land is being safeguarded for the future. If a new tidal barrier is built downstream, it is likely to sit in the Greenwich area, and land is being kept available against a 2050 horizon.

Greenwich is not a place where a site is simply "in Flood Zone 3" or "in Flood Zone 1". It is a defended floodplain, and the real question your assessment must answer is how safe the development stays if a defence fails — now and as the sea rises.

That is why sea-level rise and tidal flooding and the NPPF climate-change allowances feature so heavily in Greenwich assessments: the design has to work not just for today's tide but for the raised tides expected across the lifetime of the development. Where the national mapping cannot resolve breach behaviour on a particular site, flood modelling is used to derive the depths, velocities and hazard ratings the local planning authority and the Environment Agency will expect to see.

The Ravensbourne, the Quaggy and surface water in Greenwich

Away from the Thames, the borough's flood risk is driven by its rivers and by surface water. The River Ravensbourne and its tributary the Quaggy drain the higher ground of Bromley and Lewisham and reach the Thames through Deptford Creek, on Greenwich's western boundary. The Quaggy rises as the Kyd Brook in Bromley and runs some 13 kilometres through Bromley, Greenwich and Lewisham before joining the Ravensbourne, and both rivers have a history of overtopping in heavy rain — the Environment Agency operates a flood alert area for the Ravensbourne catchment covering Lewisham, Bromley, Greenwich and Croydon.

• Deptford Creek. The tidal mouth of the Ravensbourne on the western edge of the borough combines tidal and fluvial influences, and is a focus for regeneration around Greenwich Reach and Creekside.
• The Quaggy and Kidbrooke. The Quaggy corridor through Kidbrooke and towards Sutcliffe Park has been the subject of major flood-alleviation and river-restoration work, creating landscaped flood storage to reduce downstream risk.
• Surface-water hotspots. As Lead Local Flood Authority, the council records surface-water flood risk across Eltham, Kidbrooke, Plumstead and Abbey Wood, where intense rainfall can overwhelm the drainage network.
• Groundwater. In the river gravels and made ground along the valley floors and riverside, groundwater flooding can affect basements and undermine soakaway assumptions — a source every flood risk assessment has to consider even though it appears on no national map.

For most Greenwich developments the surface-water question is inseparable from the flood risk question: because the ground is often low-lying, heavily built and underlain by variable geology, keeping runoff within strict discharge limits is a real design constraint. Our drainage calculators and BRE 365 infiltration-rate calculator help test whether infiltration is even feasible before a scheme commits to it. Where it is not — which is common on Greenwich's clay and made-ground sites — the strategy has to rely on attenuation and controlled discharge instead. You can read more on surface water flooding and planning and on property flood resilience.

A history of flooding in Greenwich

Greenwich's flood defences exist because London has been flooded by the sea before. The tidal Thames has produced some of the capital's worst disasters, and the modern system of walls and the Barrier is the direct answer to them.

• 1928 — the last flood of central London. On 7 January 1928 a storm surge drove a wall of water up the Thames, overtopping embankments and killing fourteen people in central London — a warning of what an undefended tidal Thames could do.
• 1953 — the North Sea flood. On the night of 31 January to 1 February 1953 a catastrophic surge struck the east coast and the Thames estuary; on the river's north bank Silvertown, North Woolwich, Canning Town and Custom House were badly hit. The disaster led directly to the decision to build the Thames Barrier.
• The Barrier era. Since it became operational in 1982 the Thames Barrier has been closed hundreds of times to protect London from tidal surges, and the frequency of closures has increased over the decades — a visible measure of rising risk.
• Recent river alerts. The Ravensbourne and Quaggy are placed on flood alert during heavy rainfall, most recently in storm conditions, reflecting the continuing fluvial risk on the borough's western side.

Planning policy and flood risk assessment in Greenwich

For a planning application in Greenwich, the flood risk assessment has to satisfy national policy and the borough's own local policy at the same time. Nationally, the National Planning Policy Framework and its Planning Practice Guidance set the framework; locally, the Royal Borough of Greenwich is the Lead Local Flood Authority and the Environment Agency is the statutory consultee for the tidal Thames.

• When you need one. A flood risk assessment is required for development in Flood Zones 2 and 3, for sites of one hectare or more in Flood Zone 1, and where surface water, critical drainage or a change to a more vulnerable use is involved — see when do I need an FRA.
• The Local Plan. The Royal Greenwich Local Plan: Core Strategy (adopted 2014) carries the flood-risk and sustainable-design policies — Policies E2 and E3 — that require applicants to address flood risk, reference the borough's SFRA, and reduce residual risk on high-risk sites. A new Local Plan is being prepared to replace it.
• The SFRA. The borough's Strategic Flood Risk Assessment (Levels 1 and 2) sets out the breach modelling, the residual-risk mapping and the developer guidance your site-specific assessment must build on.
• The Local Flood Risk Management Strategy. The council's Local Flood Risk Strategy, reviewed in 2022, sets its objectives for managing surface-water, groundwater and ordinary-watercourse flooding.
• Sequential and exception tests. Where a site lies in a higher flood zone, the sequential and, where needed, exception tests must be satisfied before permission can be granted — a live and closely-argued area of planning practice.
• Drainage and SuDS. Major development must manage surface water sustainably, following the SuDS hierarchy and keeping discharge within the required rate; the council reviews drainage as part of the application.

Development and flood risk assessment in Greenwich

Greenwich is one of London's most active regeneration boroughs, and almost all of its largest growth sites sit on defended, residual-risk land beside the Thames. That combination — high development pressure and a defended floodplain — is exactly where flood risk work becomes decisive, because a scheme has to demonstrate it can be made safe for its lifetime without increasing risk elsewhere.

• Greenwich Peninsula. A large-scale mixed-use regeneration on former industrial land within Flood Zone 3, where floor levels, safe access and residual-risk mitigation are central to every application.
• Charlton Riverside. A major housing-led opportunity area on low-lying riverside land, identified as being within the area that would flood in a tidal breach.
• Woolwich and Royal Arsenal. High-density riverside regeneration where tidal defences and finished floor levels govern the design of new homes and commercial space.
• Thamesmead. Extensive regeneration on some of the lowest-lying land in the borough, historically reclaimed marsh, where drainage and tidal residual risk are fundamental.
• Deptford Creek and Kidbrooke. Sites influenced by the Ravensbourne and Quaggy, where fluvial and surface-water risk sit alongside the tidal picture.
• Smaller sites and conversions. Extensions, changes of use and infill across the borough still frequently trigger the need for an assessment where they fall in a flood zone or introduce a more vulnerable use.

How Unda helps with flood risk assessment in Greenwich

We are flood risk consultants with extensive experience of the tidal Thames and of London's defended floodplain, and we know Greenwich well — how the Barrier and the local defences work, how the borough's SFRA treats residual risk, and what the Environment Agency and the council's flood team expect from an application here. We are specialists in flood risk assessment in Greenwich, working on sites right across the borough from planning through to the discharge of drainage conditions.

Every assessment we produce is site-specific and led by the questions that actually decide a Greenwich application: which defences protect the site, what the breach modelling shows, whether the sequential and exception tests are engaged, and how surface water will be managed within the discharge limits. Where flood levels cannot be read from national mapping we build a hydraulic model; where the case turns on location we prepare the sequential and exception tests; and our consultants are here to talk a scheme through before you commit to it. You can read more about why expertise matters on flood risk applications, and about the wider Thames flood-defence programme.

Flood risk assessments for every situation in Greenwich

A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports. They often travel together in a Greenwich 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 each of them, as well as assessments for reasons that have nothing to do with planning at all.

• Flood risk assessment for planning. The site-specific report that satisfies the NPPF and the Royal Greenwich Local Plan, demonstrating a development is safe for its lifetime and does not increase risk elsewhere.
• Flood risk for property purchase. For buyers, owners and lenders who need to understand the flood risk to a specific building, beyond the broad datasets in a conveyancing search.
• Flood risk assessment for insurance. Site-specific evidence for brokers and underwriters where cover has been restricted, declined or priced on the national picture alone.
• BREEAM flood risk assessment. Structured around BREEAM Pol 03, which classifies flood risk differently from a planning assessment and often needs its own report.
• Sequential and exception tests. The locational case that steers development to lower-risk land first and, where needed, justifies proceeding on a higher-risk Greenwich site.
• Drainage strategy and SuDS. The surface-water design that keeps runoff within limits, from preliminary drainage design through to the discharge of drainage conditions.
• Groundwater and flood modelling. Groundwater is a source every assessment considers, and hydraulic modelling is the technique we use where national mapping cannot resolve the flood levels on a site.

Local flood risk management and emergency contacts in Greenwich

Responsibility for flooding in Greenwich is shared between several bodies. The council leads on surface water, groundwater and ordinary watercourses; the Environment Agency manages the tidal Thames and the main rivers; and Thames Water is responsible for the public sewers. The contacts below are useful both for developers and for anyone who needs to report or prepare for flooding.

To sign up for flood warnings for the tidal Thames or the Ravensbourne, register with the Environment Agency's flood warning service or call Floodline on 0345 988 1188. For live conditions you can also use Unda's Live River Levels Map.

Frequently asked questions about flood risk assessment in Greenwich