Flood Risk Assessment in Greenwich

A Flood Risk Assessment is a site-specific technical study, submitted in support of a planning application, that identifies and evaluates the flood risk to and from a proposed development and demonstrates how that risk will be managed. Its central task is to answer a set of connected questions: what are all the sources of flooding that could affect this site; how likely is each, and how severe would it be, now and over the lifetime of the development once climate change is taken into account; will the proposed development be safe from those risks; and — just as important — will it avoid increasing flood risk anywhere else, and where possible reduce it? A well-written FRA answers each of those questions with evidence, not assertion.

The document exists because the planning system takes a precautionary, evidence-led approach to flooding. National policy requires that flood risk is understood and taken into account at every stage of the planning process, and the FRA is the mechanism by which that happens for an individual site. It is proportionate to the scale, nature and location of the development: a minor householder proposal in a low-risk part of the borough needs far less than a new block of flats on the Thames-side floodplain, but where an FRA is required, it must be robust enough for the council and, on higher-risk sites, the Environment Agency to rely on.

An FRA is not the same thing as the Environment Agency's Flood Map for Planning, though people often confuse the two. The flood map is a strategic, national-scale product that shows the flood zones and ignores the presence of flood defences; it tells you the broad probability of river and sea flooding at a location but not the detailed, defended, site-specific risk. The FRA takes that starting point and goes much further — bringing in the effect of the defences, the borough's Strategic Flood Risk Assessment, breach and overtopping modelling where relevant, surface-water and other sources, the finished floor levels and layout of the actual proposal, and the climate-change allowances. It turns a broad-brush map into a specific, defensible case for a specific scheme.

Crucially, an FRA is a design document as much as a technical report. Its recommendations — finished floor levels set above the design flood level, safe access and escape, flood-resilient and flood-resistant construction, compensatory flood storage, and a surface-water drainage strategy — feed directly back into the architecture and engineering of the scheme. That is precisely why we prepare or coordinate the FRA alongside the design rather than treating it as a report bolted on at the end: the flood-risk response and the building have to be designed together to work.

The requirement for an FRA is set by national policy and applied through the local validation checklist, and it turns mainly on which Environment Agency flood zone the site sits in and how large it is. A site-specific Flood Risk Assessment is required for all development proposals in Flood Zones 2 and 3 — the medium and high-probability zones. Because so much of riverside and eastern Greenwich lies within Flood Zone 3, an FRA is a routine requirement for development across large parts of the borough, and it should be assumed necessary on any site near the Thames or in the low-lying east until the flood map and the borough's mapping show otherwise.

An FRA is also required even in Flood Zone 1 — the lowest-probability zone — in several important situations. It is needed for any proposal on a site of one hectare or more, regardless of the flood zone. It is needed where the site is identified by the Environment Agency as having critical drainage problems, or is shown in the borough's Strategic Flood Risk Assessment as being at increased flood risk now or in the future. And it is needed where the site may be affected by other sources of flooding — surface water, groundwater, sewers or reservoirs — particularly where the development would introduce a more vulnerable use. In dense, low-lying urban Greenwich, surface-water flood risk is a genuine and increasingly recognised issue even away from the river.

For minor development and householder applications, the requirements are lighter but not absent. A small extension in Flood Zone 1 will usually need no FRA at all; the same extension in Flood Zone 2 or 3 will generally need at least a proportionate flood-risk statement addressing the risk and how the proposal responds to it, even if a full modelling exercise is not warranted. Basement and lower-ground development is a special case that draws particular scrutiny, because basements are highly vulnerable to flooding and, in the wrong location, are strongly resisted. The safe course is always to check the flood zone and the borough's validation requirements for the specific site before assuming an FRA is not needed.

The practical point is that the FRA requirement is checked at the very start of the local validation process. If a scheme that needs an FRA is submitted without one, the council will simply refuse to validate the application, and it will sit in limbo until the missing document is provided — one of the most common and most avoidable causes of delay. We establish at feasibility whether your Greenwich site needs an FRA (and if so, what depth of assessment), so the document is prepared in step with the design and the application is complete and validatable when it goes in.

The Environment Agency divides land into flood zones according to the probability of river (fluvial) and sea (tidal) flooding, and these zones are the starting point for every flood-risk decision. It is important to understand that the flood zones deliberately ignore the presence of flood defences — they show the risk as if the defences were not there — which is why a site can be shown as high-risk on the flood map yet be well protected in reality by the Thames Barrier and the river walls. The zones are shown on the Environment Agency's Flood Map for Planning; the FRA then refines this into the actual, defended, site-specific risk.

Flood Zone 1 is land at low probability: assessed as having less than a 1 in 1,000 annual probability of river or sea flooding — that is, less than a 0.1 per cent chance in any given year. Most development is acceptable in Flood Zone 1 without a sequential or exception test, though an FRA is still needed on sites of a hectare or more or where other sources of flooding are in play. Flood Zone 2 is land at medium probability: between a 1 in 100 and 1 in 1,000 annual probability of river flooding (1 per cent to 0.1 per cent), or between a 1 in 200 and 1 in 1,000 annual probability of sea flooding (0.5 per cent to 0.1 per cent) in any year.

Flood Zone 3 is land at high probability, and national guidance divides it into two parts, though the Flood Map for Planning itself does not distinguish between them — that distinction is drawn by the borough's Strategic Flood Risk Assessment and by site-specific evidence. Flood Zone 3a is land assessed as having a 1 in 100 or greater annual probability of river flooding (1 per cent or more), or a 1 in 200 or greater annual probability of sea flooding (0.5 per cent or more). Some development can take place in Zone 3a, but it depends on the vulnerability of the use and on passing the planning tests. Flood Zone 3b is the functional floodplain — nominally land with a 1 in 20 or greater annual probability of flooding (5 per cent or more), or land the SFRA identifies as needed to store or convey flood water. Development in the functional floodplain is very heavily restricted, because that land does an active job in a flood.

For a Greenwich site, the flood zone is the essential first fact. Much of the borough's riverside and eastern land — around the Greenwich Peninsula, parts of Charlton, Woolwich, Thamesmead and Abbey Wood — falls within Flood Zone 3 on the undefended flood map, precisely because it is low-lying land on the tidal Thames. But because that land sits behind the Thames Barrier and substantial river defences, the real, defended risk is far lower than the raw zone suggests. Reconciling the undefended flood zone with the true defended (and residual) risk is one of the central tasks of a Greenwich FRA, and it is why the borough's own detailed flood mapping matters so much.

The first of the two national planning tests is the sequential test, and it embodies the whole philosophy of flood-risk planning: to steer new development towards areas with the lowest probability of flooding. In practice the test asks a simple question — is there a reasonably available site, suitable for the proposed development, that carries a lower flood risk? If there is, the development should go there rather than on the higher-risk site. Only if no such lower-risk site is reasonably available can development on the higher-risk land proceed to the next stage.

The sequential test applies to development in areas known to be at risk from any form of flooding, not just from the river or the sea — surface-water flooding counts, as do groundwater, sewer and other sources. It is applied where any part of the proposal falls within a flood-risk area, including not just the buildings themselves but access and escape routes, land raising, parking and other elements. The test is applied first at the plan-making stage, when the council allocates land, and then again at the application stage for individual proposals on unallocated or windfall sites.

For a small residential scheme on a specific plot, the sequential test can be a nuanced exercise, because the 'area of search' for reasonably available alternative sites, and what counts as 'suitable', have to be judged sensibly. Recent updates to national policy and the Planning Practice Guidance have refined how the test is applied and have introduced an important route by which it can be satisfied on a single site: where a site-specific Flood Risk Assessment demonstrates that no built development within the site — including access and escape, land raising and other vulnerable elements — would be located on land at risk of flooding from any source, now or in the future, the sequential test can be regarded as passed for that site. This can unlock otherwise constrained plots where the developable footprint can be kept clear of the flood risk.

In Greenwich, the sequential test has a particular character because so much of the borough's regeneration land is on the floodplain. The borough's Strategic Flood Risk Assessment is the tool that supports the test — it maps the risk across the whole borough so that the council and applicants can see where the lower-risk land lies. For an applicant, the practical answer is usually to demonstrate, with the SFRA and a site-specific FRA, either that no reasonably available lower-risk site exists for the development, or that the scheme's footprint can be arranged to sit clear of the risk. We advise on the sequential-test position for your site at the outset, because it is pointless to design a scheme that cannot pass it.

Where the sequential test has shown that development cannot reasonably be steered to lower-risk land, some proposals must then pass a second, tougher test before they can proceed: the exception test. It is not needed for every scheme on higher-risk land — it depends on the vulnerability of the proposed use and the flood zone — but where it applies, it is a demanding bar, and clearing it is the central purpose of the FRA that supports the application.

The exception test has two limbs, and both must be passed. The first is that the development must provide wider sustainability benefits to the community that outweigh the flood risk. The second — and this is where the FRA does its heavy lifting — is that the development must be demonstrated to be safe for its lifetime, taking account of the vulnerability of its users, without increasing flood risk elsewhere and, where possible, reducing flood risk overall. In other words, it is not enough to show that a scheme is desirable; you must also prove, with technical evidence, that the people who will live there will be safe throughout the building's life, including as the climate changes, and that building there will not make flooding worse for anyone else.

The exception test is mandatory in specific combinations of use and flood zone. Most ordinary housing is classified as 'more vulnerable' development, and more vulnerable development in Flood Zone 3a requires the exception test to be passed. 'Highly vulnerable' development — which includes basement dwellings — requires the exception test in Flood Zone 2 and is not permitted at all in Flood Zone 3. More vulnerable development is not permitted in the functional floodplain (Flood Zone 3b) at all. Understanding exactly which test your combination of proposed use and flood zone triggers is fundamental, because it determines what the FRA has to prove and, sometimes, whether the scheme is viable at all.

For a residential scheme on the Greenwich floodplain, the exception test is often the decisive hurdle, and the safety limb is met through design: finished floor levels set safely above the design flood level (including a climate-change allowance and a freeboard margin), safe access and escape that remains available during a flood or, where dry access cannot be achieved, a flood warning and evacuation plan agreed with the emergency services, flood-resilient and flood-resistant construction so any water that does enter causes limited damage and the building can be reoccupied quickly, and no net loss of flood-storage capacity. We design these measures into the scheme and evidence them in the FRA, so the exception test is passed on the strength of the design rather than argued after the fact.

National policy groups development into five flood-risk vulnerability classifications according to how serious the consequences of flooding would be, especially for people, and the classification of your proposed use — combined with the flood zone — determines which tests apply and whether the development is acceptable at all. Getting the classification right is therefore one of the first things an FRA establishes.

The five categories, from most to least sensitive, are: essential infrastructure (such as essential transport and utility infrastructure that has to cross or be located in a flood-risk area to function, including some that must stay operational during a flood); highly vulnerable development (including basement dwellings, police, ambulance and fire stations and command and telecommunications installations needed during a flood, and caravans and mobile homes for permanent residential use); more vulnerable development (which covers most housing — dwellinghouses and flats — as well as hospitals, residential institutions such as care and children's homes, hostels, hotels and health services); less vulnerable development (most commercial, retail, offices and light industry, and land and buildings used for agriculture); and water-compatible development (such as docks and marinas, water-based recreation, and flood-control infrastructure).

For residential development — the core of Crown's work — the key facts follow from housing being 'more vulnerable'. In Flood Zone 1, more vulnerable development is acceptable without a flood test (though an FRA may still be needed for the reasons set out earlier). In Flood Zone 2, more vulnerable development is generally appropriate subject to a site-specific FRA. In Flood Zone 3a, more vulnerable development requires the exception test to be passed. In Flood Zone 3b, the functional floodplain, more vulnerable development is not permitted. The single most important nuance for house design is basements: a basement dwelling is 'highly vulnerable', which means it needs the exception test even in Flood Zone 2 and is not permitted in Flood Zone 3 — a critical point on the Greenwich floodplain, where basement and lower-ground accommodation is treated with real caution.

This matrix of use against zone is the framework within which every flood-risk decision is made, and it explains why the same site can be perfectly acceptable for one kind of development and unacceptable for another. Part of our job at feasibility is to establish where your proposed use sits in the classification and what that means in your flood zone, so the scheme is shaped from the outset to a use-and-location combination that can actually be consented — and so, for example, a basement is only proposed where the flood zone genuinely allows it.

The Royal Borough of Greenwich is one of the most historically significant places in Britain, and its history is inseparable from the river that gives so much of it a flood-risk story. At its heart is Maritime Greenwich, inscribed as a UNESCO World Heritage Site in 1997: the Old Royal Naval College, the baroque masterpiece begun by Sir Christopher Wren on the site of the old Greenwich Palace where Henry VIII and Elizabeth I were born; the Queen's House by Inigo Jones; the National Maritime Museum; the Royal Observatory; and Greenwich Park rising behind them. It was here that the world's time was fixed — in 1884 the Greenwich Meridian was adopted as the Prime Meridian, zero degrees longitude, and Greenwich Mean Time became the global standard. Down at the riverside sits the Cutty Sark, the last surviving tea clipper, launched in 1869 and preserved in dry dock beside the Thames.

The borough is far larger than the historic town. The Royal Borough of Greenwich was formed in 1965 from the old metropolitan boroughs of Greenwich and Woolwich, and it was granted royal borough status on 3 February 2012 — the fourth in the country — to mark the Diamond Jubilee and in recognition of its royal history, the Prime Meridian and its World Heritage status. It runs along the south bank of the Thames from Deptford in the west, through Greenwich, the Peninsula, Charlton and Woolwich, out to Plumstead, Thamesmead and Abbey Wood in the east. It is that long river frontage — and the low-lying land behind it — that puts flood risk at the centre of so much development here.

The relationship between Greenwich and the tidal Thames has always been a working one, and the borough's great regeneration sites are almost all on former riverside industrial land: the Greenwich Peninsula around The O2, built on the vast former East Greenwich Gas Works; Charlton Riverside; the Royal Arsenal at Woolwich; and the renewal of Thamesmead. This is exactly the low-lying, formerly industrial floodplain land that national and London policy directs towards housing — and exactly the land where flood risk has to be assessed and designed for. The history of development in the east of the borough is, in large part, a history of building on the floodplain behind engineered defences.

The defining piece of that engineered defence is the Thames Barrier, which sits across the river at New Charlton, in the Royal Borough of Greenwich, with its northern end at Silvertown in Newham. Completed in the early 1980s, the Barrier protects central and east London from tidal surges by closing against high tides so that the defended land upstream is not overwhelmed; the defences downstream of the Barrier are markedly higher than those upstream to account for the difference in levels. The Barrier and the river walls are the reason that land shown as Flood Zone 3 on the undefended flood map is, in practice, well protected — but they also introduce the concept of 'residual risk': the risk that remains in the unlikely event that a defence is overtopped or breached, which a Greenwich FRA on defended floodplain land has to address head-on.

For a flood risk assessment, then, Greenwich's geography is planning-relevant at every turn. Where a site sits relative to the Thames, the flood zones and the borough's own flood mapping; whether it is on defended floodplain and therefore carries a residual breach or overtopping risk; whether it is affected by surface-water flooding in the denser inland areas; and how the site relates to the long-term management of the estuary all shape what the FRA must assess and what the design must deliver. Knowing precisely where your site sits in this river-shaped borough is the foundation of a credible flood-risk case.

Flooding is not an abstract policy question in Greenwich; it is written into the borough's history. The low-lying Thames-side marshes east of Greenwich — the land that became Thamesmead and the industrial river frontage — were reclaimed and drained over centuries, protected by embankments and river walls that had to be constantly maintained against the tide. The catastrophic North Sea flood of 1953, which inundated large parts of the east coast and the Thames Estuary and killed hundreds, was the event that ultimately drove the decision to build a permanent tidal barrier for London, and so the modern flood-defence framework that governs development in Greenwich today grew directly out of that disaster.

The building of the Thames Barrier in the late 1970s and early 1980s, closing across the river at New Charlton, transformed the flood-risk picture for the whole of central and east London. By allowing the surge tides to be held back, it made it possible to develop and regenerate the low-lying land behind the defences that would otherwise have been at serious tidal risk. Much of the borough's subsequent regeneration — the Peninsula, Charlton Riverside, the Royal Arsenal, Thamesmead — has been made possible by the protection the Barrier and the river walls provide, and is, in flood-risk terms, development on defended floodplain.

That legacy is exactly why flood risk is such a central and well-understood issue in Greenwich planning. The council and the Environment Agency have invested heavily in understanding the borough's flood risk in detail, culminating in a Strategic Flood Risk Assessment (including a detailed Level 2 assessment) that draws on Environment Agency Thames tidal breach modelling to map not just the headline flood zones but the residual risk from a defence breach or overtopping across the developable land. This detailed local evidence base is a genuine asset to applicants, because it allows a site-specific FRA to reason precisely about the defended and residual risk rather than relying on the crude national flood map.

Looking forward, the management of flood risk in Greenwich is governed by one of the most sophisticated long-term flood plans in the world: the Environment Agency's Thames Estuary 2100 plan (TE2100), which sets out how London's tidal defences — including the Thames Barrier itself — will be maintained, raised and, in time, replaced to keep pace with rising sea levels through the rest of this century. TE2100 divides the estuary into policy units, with central London from Hammersmith to Greenwich covered by its own policy, and it is the strategic backdrop against which the climate-change allowances in any Greenwich FRA are set. Flood management here is not a static defence but a planned, adaptive programme — and development is expected to be designed with that long horizon in mind.

Every planning application in the borough is decided against the development plan, which for Greenwich means the Royal Greenwich Local Plan: Core Strategy with Detailed Policies (adopted 30 July 2014), together with the London Plan (2021) and national policy in the National Planning Policy Framework. The Local Plan carries the borough's flood-risk and sustainable-drainage policies, which apply the national sequential and exception-test framework locally and set the borough's expectations for how development addresses flood risk, manages surface water and contributes to reducing risk over time. The council is also preparing a new Local Plan, so it is always worth checking the current adopted position for your site at the point of application.

Sitting behind the Local Plan is the borough's Strategic Flood Risk Assessment — the evidence base that maps flood risk from all sources across the whole borough. Greenwich has both a Level 1 SFRA (a broad assessment of risk across the borough) and a more detailed Level 2 SFRA for the areas where development pressure and flood risk coincide, which uses Environment Agency Thames tidal breach modelling to assess the residual risk on the developable floodplain in detail. The SFRA is the document that underpins the sequential test at the local level, that distinguishes Flood Zone 3a from the functional floodplain (3b), and that a site-specific FRA should be consistent with. We use the SFRA as a starting point for every Greenwich FRA.

The London Plan adds a further, strongly worded layer. Its flood-risk and drainage policies require development to comply with the national sequential approach, to be safe from flooding over its lifetime, and to manage surface water through sustainable drainage systems following the drainage hierarchy — with demanding targets for reducing surface-water run-off towards greenfield rates. The London Plan's approach to the tidal Thames also recognises the role of the defences and TE2100, and expects development on the floodplain to be designed accordingly. For a Greenwich scheme, the flood-risk case therefore has to satisfy the borough's Local Plan, the London Plan and national policy simultaneously, and we structure the FRA and the accompanying planning statement to walk the case officer through all three.

In addition to the borough as local planning authority, the Royal Borough of Greenwich acts as the Lead Local Flood Authority (LLFA) for local flood risk — surface water, groundwater and ordinary watercourses — and is a statutory consultee on surface-water drainage for major development. The Environment Agency is the statutory consultee on main-river and tidal flood risk. A Greenwich FRA therefore has to satisfy potentially two different flood authorities, each with its own focus, and the FRA and drainage strategy have to be robust enough for both. We prepare the documents with both audiences in mind so the application is not held up by an objection from either.

A robust Flood Risk Assessment does not look only at the river. National guidance requires the FRA to consider flooding from all sources, and in Greenwich each of them is genuinely relevant somewhere in the borough. The FRA identifies which sources affect the specific site, assesses the probability and consequences of each, and shows how the design responds — because a scheme that manages tidal risk beautifully but ignores surface water, or vice versa, is incomplete.

Tidal flooding from the Thames is the headline source for much of the borough. It is the reason the riverside and eastern land falls within Flood Zone 3 on the undefended map, and it is managed by the Thames Barrier and the river walls. For a defended floodplain site, the FRA has to consider both the very low probability of the defences being overtopped or breached (the residual risk) and the depth, velocity and hazard of the water that would result — which is where the borough's breach modelling and the SFRA come in. Fluvial (river) flooding from smaller watercourses is less significant in most of Greenwich than the tidal Thames, but has to be considered where relevant.

Surface-water (pluvial) flooding — rainwater that cannot drain away quickly enough during intense storms and ponds or flows across the ground — is an increasingly important source in dense, heavily paved urban areas, and it affects inland parts of Greenwich well away from the river. It is the source most exacerbated by development (paving over green land increases run-off) and the one the drainage strategy has to answer directly. Groundwater flooding can occur where the water table rises to the surface, a real issue in low-lying areas with a high water table like parts of the Thames-side east. Sewer flooding — where the drainage network is overwhelmed or blocked — and, in a residual sense, flooding from reservoirs and artificial water bodies, complete the list of sources the FRA screens for.

For a Greenwich site the balance of these sources depends entirely on location. A riverside plot on the Peninsula is dominated by tidal residual risk; an inland plot in a dense part of Woolwich or Plumstead may be driven far more by surface water and the capacity of the local sewers; a low-lying site with a high water table has to think about groundwater. We identify at the outset which sources genuinely bear on your site — using the flood map, the borough's SFRA, historic flood records and site investigation — so the FRA focuses its effort where the real risk lies and does not miss a source that would otherwise sink the application.

A Flood Risk Assessment has a recognised structure, and a good one tells the reader — the case officer, the Lead Local Flood Authority and, on higher-risk sites, the Environment Agency — a clear and complete story. The Environment Agency now publishes a standard FRA template and guidance to encourage consistency, and while the depth is proportionate to the site, the essential ingredients are the same. We prepare the FRA to that standard so it is easy for each consultee to assess and hard for anyone to reject on grounds of incompleteness.

The core of the report is the assessment of flood risk itself: a clear description of the site and the proposed development; the flood zone and the flood risk from every relevant source, now and over the development's lifetime with climate change taken into account; the effect of the defences and, on defended floodplain, the residual risk from breach or overtopping (drawing on the SFRA and any modelling); and the design flood level against which the scheme has to be made safe. This is the evidence base on which everything else rests, and its quality is what makes an FRA persuasive rather than merely present.

The report then sets out how the development responds — the flood-risk management measures that make the scheme safe and that avoid increasing risk elsewhere. Typically these include: finished floor levels set above the design flood level plus a freeboard allowance; safe access and egress arrangements (dry access wherever possible, and where it cannot be achieved, a flood warning and evacuation plan agreed with the emergency planners); flood-resistant construction to keep water out and flood-resilient construction to limit damage and speed recovery where it gets in; the provision of compensatory flood storage where any is lost; and the surface-water drainage strategy that ensures the development does not worsen flooding downstream. Where the exception test applies, the FRA marshals this evidence to demonstrate that the safety limb is met.

Finally, the FRA addresses the sequential and exception tests explicitly where they apply, sets out the surface-water drainage and SuDS strategy (often as an integral part of the FRA or as a companion document), and draws its conclusions in terms the decision-maker can adopt. A well-structured Greenwich FRA is internally consistent with the drawings — the finished floor levels in the report match the levels on the sections, the drainage strategy matches the site layout, the flood-storage figures match the ground levels — so that the case officer and the flood consultees can rely on it without finding the documents quietly contradicting one another.

A defining feature of modern flood-risk assessment is that it must look decades ahead, not just at today's risk. National policy requires development to be safe not merely now but over its whole lifetime — conventionally taken as 100 years for residential development — which means the FRA has to allow for the way flood risk will increase as the climate changes. The Environment Agency publishes climate-change allowances that set out, by river basin and epoch, how much peak river flows, sea levels and rainfall intensities are expected to rise, and the FRA applies the appropriate allowance to the design flood level for the site.

For a tidal Thames site, the dominant allowance is the projected rise in sea level over the design lifetime, which raises the level the defences and the development must be able to cope with. For surface-water and drainage design, the relevant allowance is the projected increase in rainfall intensity, which means drainage systems have to be sized for heavier future storms, not just today's. Applying the right allowance for the right epoch and the right vulnerability of development is a technical judgement, and getting it wrong — using too small an allowance — is a common reason an FRA is challenged by the Environment Agency.

In Greenwich, the climate-change picture is inseparable from the Thames Estuary 2100 plan. TE2100 is the Environment Agency's adaptive long-term strategy for managing tidal flood risk in the estuary as sea levels rise — maintaining, raising and eventually replacing the Thames Barrier and the river defences through this century in a planned sequence. It provides the strategic context within which a Greenwich FRA reasons about future defended levels and residual risk, and it means that development on the floodplain is expected to be designed with the long-term adaptation of the defences in mind. A site-specific FRA on the Greenwich floodplain should sit comfortably within, and not cut across, that long-term plan.

The practical implication for design is that finished floor levels, the layout of vulnerable accommodation, escape routes and the drainage system all have to be set for the future, climate-adjusted flood level, not just the present-day one. That can mean raising floor levels, arranging the most vulnerable uses (like bedrooms) on upper floors, keeping habitable rooms out of basements, and sizing drainage for future rainfall. We build these lifetime allowances into the design from the start, because a scheme designed only for today's risk will either fail the exception test or need expensive redesign when the flood consultees insist on the correct allowance.

A Flood Risk Assessment and a surface-water drainage strategy go hand in hand, and on many Greenwich sites they are prepared together, because managing the rainwater the development generates is central both to avoiding surface-water flooding on the site and to not increasing flood risk elsewhere. London and national policy require new development to manage surface water through sustainable drainage systems (SuDS) and to follow the drainage hierarchy — discharging rainwater to the ground by infiltration or to a watercourse in preference to the sewer, and only to the sewer as a last resort and at a strictly restricted rate.

The London Plan sets demanding targets for reducing surface-water run-off, aiming towards greenfield run-off rates where feasible, which on a previously developed or paved site means the development has to leave the site draining more slowly than it did before. In practice, a residential scheme achieves this with a combination of measures: permeable paving, green and blue roofs, rain gardens, soakaways where the ground infiltrates, rainwater harvesting, and attenuation tanks or basins that store storm water and release it slowly. The drainage strategy sets out which of these the scheme uses, calculates the storage and discharge rates, and demonstrates that the development will not worsen flooding downstream — including for the future, climate-adjusted storm.

Greenwich's ground conditions make this a genuine design constraint rather than a formality. The low-lying east sits on alluvium and made ground over the London Clay, often with a high water table, so infiltration drainage (soakaways) frequently does not work well and the strategy has to rely more on attenuation and controlled discharge. On tight infill and backland sites there may be limited room for below-ground storage, which forces the drainage design to be integrated into the layout and the landscape from the outset. As Lead Local Flood Authority, the borough scrutinises the surface-water strategy on major schemes, so it has to be realistic and properly calculated.

Because the drainage strategy affects levels, layout, landscape and even the structure (attenuation tanks and their access), it is far better resolved as part of the design than discovered as a problem when the council or the LLFA asks how the surface water will be managed. We coordinate the drainage strategy with the FRA and the architecture so the SuDS are realistic, the levels and falls actually work, and the whole water-management case — flood risk in and flood risk out — is coherent and defensible in one package.

The most important thing to understand about a Flood Risk Assessment is that its conclusions are design instructions, and the real work of managing flood risk happens in the building, not the report. The FRA identifies the design flood level; the design then has to place the accommodation, set the floor levels, arrange the escape routes and specify the construction so that the development is genuinely safe for its lifetime. On the Greenwich floodplain, this is where an integrated architecture-and-engineering approach earns its keep.

Finished floor levels are the first line of defence: habitable floor levels are set above the design flood level (including the climate-change allowance) plus a freeboard margin, so that even in the design flood the living accommodation stays dry. Where the required level is high, this shapes the whole building — raised ground floors, undercroft parking or non-habitable uses at the lowest level, and the most vulnerable rooms (particularly bedrooms) placed on upper floors so that people can move up and stay safe. Basements and habitable lower-ground rooms are avoided on higher-risk sites precisely because they are highly vulnerable and, in Flood Zone 3, not permitted.

Safe access and escape is the second essential. The ideal is dry access — a route in and out that stays above the flood level so that occupants and emergency services can come and go safely during a flood. Where the surrounding land means dry access cannot be fully achieved, the FRA relies on a flood warning and evacuation plan, agreed with the emergency planners, coupled with safe refuge within the building (habitable space above the flood level). The layout of the site and the buildings is designed to make this work, because access and escape are matters the Environment Agency examines closely.

The third element is resilient and resistant construction. Flood-resistant (or 'dry-proofing') measures aim to keep water out — flood barriers, raised thresholds, sealed construction up to a design level. Flood-resilient (or 'wet-proofing') measures accept that water may get in during an extreme event and limit the damage and speed the recovery — water-resistant materials, raised electrics and services, and layouts that can be cleaned and reoccupied quickly. On defended floodplain in Greenwich, where the residual breach risk is very low probability but potentially deep, resilient construction is often the pragmatic response to that residual risk. We specify these measures in the design and evidence them in the FRA so the safety case is built, not merely asserted.

A Flood Risk Assessment rarely travels alone. It sits within the wider suite of drawings and supporting documents that make up a planning application, and it has to be consistent with all of them. The most immediate relationship is with the drawings themselves — the site layout, floor plans, elevations and, especially, the sections and levels — because the finished floor levels, the arrangement of vulnerable accommodation and the escape routes that the FRA relies on all have to be shown correctly on the drawings. An FRA that recommends a floor level the drawings do not achieve is worse than no FRA at all.

The FRA works closely with the surface-water drainage strategy and, on many sites, with a SuDS or sustainable drainage report — often prepared together because flood risk in and flood risk out are two sides of the same coin. It also connects to the ground investigation and contamination assessment (relevant on the borough's former industrial floodplain land, where the ground conditions drive both the drainage and the foundations), to the energy and sustainability strategy, and to any biodiversity or landscape work where SuDS features double as green infrastructure. On some sites the FRA even bears on the heritage and design case, where raising floor levels affects the appearance of the building in a sensitive setting.

For the planning case itself, the FRA underpins the flood-risk section of the planning statement, and where the sequential or exception test applies, the statement and the FRA together carry the argument. On major schemes the FRA may need to sit alongside a formal sequential-test statement and, for the exception test, the wider-sustainability-benefits case that the FRA's safety evidence complements. The design and access statement, where one is required, should reflect how flood risk has shaped the design. The whole application has to tell one coherent story.

Because these documents are so interdependent, the value of preparing or coordinating them together is real. When the same team that designs the building also prepares or manages the FRA and the drainage strategy, the levels match, the layout reflects the flood-risk response, and the planning statement argues a case the technical documents actually support. That coherence is exactly what makes an application straightforward for the council and the flood consultees to approve, and it is the opposite of the piecemeal, contradictory bundle that invites objections and delay.

We treat the Flood Risk Assessment as an integral part of the design process for any Greenwich scheme on or near the floodplain, not as a report to be commissioned at the end. The starting point is a flood-risk screening at feasibility: we check the Environment Agency flood zone and Flood Map for Planning for the site, consult the borough's Strategic Flood Risk Assessment (including the detailed Level 2 mapping where relevant), review historic flood records and the local surface-water risk, and establish which sources of flooding bear on the site and which tests will apply. That screening tells us, before any design work, whether an FRA is needed, how deep it has to be, and whether the flood-risk position is workable for the development you have in mind.

From there, the flood-risk response and the design develop together. We establish the design flood level with the appropriate climate-change allowance, set finished floor levels and arrange the accommodation and escape routes accordingly, work up the surface-water drainage and SuDS strategy alongside the layout and levels, and specify resilient and resistant construction where the residual risk warrants it. Because Crown provides the architecture, the structural design and the building-services design together, the FRA's recommendations are engineered into a buildable scheme rather than imposed on a design that then has to be reworked.

We then prepare (or, on the most technically demanding modelling-led sites, coordinate with a specialist flood consultant) a site-specific FRA to the Environment Agency's standard structure, addressing all sources, the residual risk, the design flood level and the management measures, and — where they apply — the sequential and exception tests. The document is written to be consistent with the drawings and the drainage strategy and to answer, in advance, the questions the case officer, the Lead Local Flood Authority and the Environment Agency will ask. On higher-risk sites we engage with the Environment Agency early, so that any concerns are surfaced and resolved before submission rather than after.

The result is an application in which the flood-risk case and the design stand together: the FRA proves the scheme is safe and does not worsen flooding elsewhere, and the drawings deliver exactly what the FRA describes. That integration is the difference between a flood-risk document that unlocks a difficult floodplain site and one that merely records a problem — and on the Greenwich floodplain, it is very often the deciding factor in whether a scheme is consented.

The reasons flood risk stalls or sinks a Greenwich application are remarkably consistent, and understanding them is the best way to avoid them. The most basic — and most avoidable — is submitting an application that needs an FRA without one, or with an FRA that is plainly inadequate for the site. Because the FRA is a validation requirement, the council will not even start assessing the application until the document is provided, so the omission simply parks the scheme. Assuming a site does not need an FRA when it sits in Flood Zone 2 or 3, or is over a hectare, is a frequent and costly error.

The next cluster of mistakes is technical. Using the wrong climate-change allowance, or none at all, so that the design flood level is too low and the scheme is not actually safe for its lifetime, is one the Environment Agency spots immediately. Relying on the undefended flood zone without properly reasoning about the defences and the residual breach risk — or, conversely, ignoring the residual risk altogether because the site is defended — both draw objections. Setting finished floor levels that the drawings do not actually achieve, or that leave habitable rooms below the flood level, undermines the whole safety case. And treating surface-water drainage as an afterthought, so that the scheme increases run-off and worsens flooding downstream, will draw an objection from the Lead Local Flood Authority.

A third group of mistakes is about the tests. Proposing a highly vulnerable use — most often a basement dwelling — on a site where the flood zone does not permit it is a fundamental error that no amount of good design can rescue. Failing to address the sequential test at all, or addressing it inadequately, leaves the application without the foundation on which the whole flood-risk case rests. And attempting the exception test with a weak safety limb — vague on access and escape, silent on residual risk, thin on resilient construction — invites refusal, because the exception test is a genuinely high bar.

Our approach is to design each of these problems out. We establish the FRA requirement and the applicable tests at feasibility, use the correct climate-change allowances, reason carefully about the defences and the residual risk using the borough's SFRA, set floor levels the design actually delivers, integrate the drainage from the start, and keep highly vulnerable uses off sites where they are not permitted. Where a site genuinely cannot support the development safely, we say so early — because there is no value in submitting a scheme the flood consultees are bound to resist.

The cost of a Flood Risk Assessment depends heavily on the site and the depth of assessment it needs. A proportionate flood-risk statement for a modest proposal in a lower-risk part of the borough is a relatively small piece of work; a full, modelling-informed FRA for a residential scheme on the defended Thames floodplain — addressing residual breach risk, climate-change allowances, the exception test and a detailed drainage strategy — is a more substantial undertaking, sometimes involving a specialist flood-modelling consultant. We scope the FRA to your specific site and give you a clear view of the cost before the work begins, and we tell you honestly which depth of assessment your site genuinely requires so you are not paying for modelling a simpler site does not need.

The FRA sits within the wider fee picture for a scheme. Separate from our design and FRA work, you should budget for the council's planning application fee (set nationally), any pre-application advice fee, and — where the scheme needs them — other specialist inputs such as a ground investigation, an arboricultural report, a daylight and sunlight assessment or an ecology and biodiversity net gain assessment. On the floodplain, the ground investigation is often closely tied to the flood and drainage work, because the ground conditions drive both the foundations and the infiltration potential, so it is efficient to plan them together.

On timescales, the flood-risk screening is part of the feasibility stage and adds little time on its own; the full FRA is prepared alongside the design, so it runs in parallel rather than adding a separate block of time at the end — provided it is started early. Where the site is higher-risk and warrants early engagement with the Environment Agency, that engagement is worth allowing time for, because resolving the Agency's concerns before submission is far quicker than doing so after an objection during determination. The planning application itself then runs against the standard targets — eight weeks for minor schemes, thirteen for major — from validation.

The honest truth of flood risk, as with the rest of a planning application, is that money and time are lost on the problems that surface late: the invalid application that needs an FRA it did not have, the objection from the Environment Agency about the wrong climate allowance, the redesign forced by floor levels set too low. Getting the flood-risk screening and the FRA right, in step with the design, is what avoids all of that — and it is the most cost-effective way to take a floodplain site through planning.

The process starts with feasibility and flood-risk screening. We survey the site, check its planning history and constraints, and carry out the flood-risk screening described above — establishing the flood zone, the relevant sources, the applicable tests and the depth of FRA needed. This is where we give you an honest early view of whether flood risk is a manageable design constraint on your site or a fundamental obstacle, before you commit to a full application.

The Royal Borough of Greenwich offers a pre-application advice service, and on floodplain sites it is usually worth using — especially where the scheme is finely balanced or where the Environment Agency's view will be decisive. A written pre-application response gives you the council's early position on the principle and the flood-risk approach, and on higher-risk sites it is often sensible to engage the Environment Agency in parallel, so that the design flood level, the climate allowance and the acceptability of the access and escape strategy are agreed before the full application is prepared. Surfacing the flood consultees' concerns early is far cheaper than discovering them during determination.

We then develop the design with the flood-risk response built in, prepare the FRA and drainage strategy alongside the drawings, and submit the complete application to the council through the Planning Portal, managing it through validation and determination. Because the FRA is a validation requirement, a complete, well-prepared submission validates without a hitch; the council consults the Environment Agency and, on drainage, the Lead Local Flood Authority, and we respond to any queries or requests for clarification from either. Minor residential applications run against an eight-week target, major schemes against thirteen weeks, from validation.

Once planning permission is granted, flood-related conditions are common — for example securing the finished floor levels, the drainage scheme, the flood-resilience measures or a flood warning and evacuation plan — and we help discharge them so the scheme can move to construction without delay. Because the same coordinated team that prepared the FRA prepares the Building Regulations and construction information, the flood-risk measures that won the permission are carried through faithfully into the built scheme, rather than being lost in a handover.

To make it concrete, consider a common Greenwich scenario: a developer has a cleared plot on former industrial land near the river — say towards Charlton Riverside or the Peninsula — and wants to build a small block of flats. The Environment Agency flood map shows the site in Flood Zone 3, because it is low-lying tidal land shown as if undefended; in reality it sits behind the Thames Barrier and the river walls. Flats are 'more vulnerable' development, so in Flood Zone 3a the exception test applies, and the whole scheme's viability turns on getting the flood-risk case right.

At feasibility, we screen the site: we confirm the flood zone, consult the borough's Strategic Flood Risk Assessment (including the Level 2 breach modelling for the developable floodplain) to understand the defended and residual risk, check the surface-water and groundwater position on the made ground, and confirm which tests apply. We establish the sequential-test position — usually, on regeneration floodplain land where the whole area is at similar risk, that no reasonably available lower-risk site exists for the development, supported by the SFRA — so the exception test is the real hurdle to clear.

The design and the FRA then develop together. We establish the design flood level with the appropriate sea-level climate-change allowance for the development's lifetime, and set the finished floor levels of the habitable accommodation above it with freeboard — which on this site means a raised ground floor with parking, plant or non-habitable uses at the lowest level and homes above. Bedrooms and the most vulnerable accommodation are placed on upper floors; safe refuge above the flood level is provided; and, because dry access across the surrounding land may not be fully achievable in a residual breach, a flood warning and evacuation plan is prepared with the emergency planners. Resilient construction limits the damage from the very low-probability residual event. A SuDS-led drainage strategy, relying on attenuation given the poor infiltration of the made ground, ensures the scheme does not worsen surface-water flooding.

On the planning side, we prepare the site-specific FRA to the Environment Agency's standard structure — assessing all sources, the residual risk from the SFRA modelling, the design flood level and every management measure — and it carries the safety limb of the exception test, while the planning statement carries the wider-sustainability-benefits limb (much-needed housing on brownfield regeneration land). We engage the Environment Agency before submission so the design flood level, climate allowance and access strategy are agreed. With the sequential test satisfied, the exception test passed on the strength of the design, and the drainage resolved, the application goes in as a complete, coherent case the council and the flood consultees can approve.

Managed through the council's validation and determination, with the flood consultees on side because their concerns were resolved up front, a scheme like this has a genuine prospect of consent. Once permission and the flood-related conditions are dealt with, the same coordinated team carries the finished floor levels, the drainage and the resilience measures through into the Building Regulations and construction drawings — so the building that gets built is the safe building the FRA promised.

Crown Architecture designs residential schemes across the Royal Borough of Greenwich and the surrounding boroughs, and on the borough's extensive floodplain we treat flood risk as an integral part of the design — not a report bolted on at the end. We prepare or coordinate the Flood Risk Assessment and the surface-water drainage strategy alongside the architecture, the structural design and the building-services design, so the flood-risk response is engineered into a buildable scheme and the FRA describes exactly what the drawings deliver.

We know the Greenwich flood context in detail: the tidal Thames and the Thames Barrier at New Charlton; the borough's regeneration land on defended floodplain and the residual breach risk that carries; the Strategic Flood Risk Assessment and its Level 2 breach modelling; the Local Plan and London Plan flood and drainage policies; the surface-water risk in the denser inland areas; and the long-term backdrop of the Thames Estuary 2100 plan. We use that knowledge to give honest advice at feasibility — including telling you when a site's flood risk is a genuine obstacle — and to build flood-risk cases designed to satisfy the council, the Lead Local Flood Authority and the Environment Agency.

Just as importantly, we are straightforward to work with. We screen the flood risk early and honestly, scope the FRA to what your site genuinely needs, quote clearly, and prepare a coordinated, self-consistent application that the case officer and the flood consultees can approve without having to fill in gaps or reconcile contradictions. Where a site warrants early engagement with the Environment Agency, we manage it, so concerns are resolved before submission rather than after.

We also stay with the project after planning. Once permission is granted we help discharge the flood-related conditions — floor levels, drainage, resilience, evacuation planning — and carry the flood-risk measures through into the Building Regulations and construction information, so the safe building the FRA describes is the building that actually gets built. The aim is a single, accountable point of contact from the first flood-risk screening to a consented, buildable scheme, on land that flood risk makes genuinely challenging.

If you are planning a residential scheme on or near the floodplain in Greenwich — a riverside plot, a regeneration site, an infill or backland plot, or a replacement dwelling — send us the address and what you have in mind, and we will screen the flood risk, tell you honestly what is achievable, and set out the FRA and design work needed to get there.