Flood Risk Assessments & Drainage Strategies in London
Independent flood risk consultants serving London and surrounding areas. Planning-ready FRAs and SuDS drainage strategies from £295, delivered within 3–5 working days.
Flood Risk Assessments in London
Flood Risk Environmental provides Flood Risk Assessments, SuDS drainage strategies and detailed drainage design for planning applications across all 33 London boroughs and surrounding areas.
London has significant tidal flood risk from the Thames, substantial surface water flooding in many inner-city boroughs, and complex drainage requirements. The Thames Barrier protects central London from tidal flooding, but residual risk behind defences must still be addressed in FRAs. Surface water flooding affects many boroughs including Lewisham, Croydon and Southwark.
Our reports are prepared by a qualified consultant with over 17 years' experience and written specifically to satisfy the requirements of your London Borough and the Thames Regional Flood and Coastal Committee as the Lead Local Flood Authority.
Services in London
- Flood Risk Assessments — from £295
- SuDS drainage strategies for planning
- Detailed SuDS and drainage design
- LLFA SuDS proforma completion (London Boroughs)
- Sequential and Exception Test submissions
- S23 Ordinary Watercourse Consent
- EA Flood Risk Activity Permit applications
- LLFA drainage objection responses
Flood risk in London
London's headline flood risk is tidal. Large areas of central and east London — from Westminster and the South Bank out to the Isle of Dogs, Thamesmead and beyond — sit within the Thames tidal floodplain (Flood Zone 3) but are defended to a very high standard by the Thames Barrier and the tidal defences. For most sites the issue is therefore not whether the site floods today, but residual and breach risk over the development's lifetime as sea levels rise, which an FRA must address with finished floor levels, safe access and flood resilience.
Away from the river, dense surface water (pluvial) flooding is the biggest day-to-day problem — intense summer storms overwhelm the combined sewer network and pond in streets, basements and lower-ground flats across almost every borough. Basements and lightwell flats are treated as highly vulnerable, so conversions and new basements routinely need a flood risk (and often a Basement Impact) assessment.
Because every London borough is its own Lead Local Flood Authority, drainage and validation requirements vary from borough to borough. We prepare FRAs and drainage strategies to each borough's specific standards, and address the Thames tidal, ordinary watercourse and surface water issues the EA and borough drainage teams look for.
Local flood facts — London
- Main watercourses: River Thames (tidal), plus the Lea, Wandle, Ravensbourne, Brent and Roding
- Lead Local Flood Authority: Each London borough (33 in total, including the City of London)
- Main flood sources: Tidal (defended), fluvial and widespread surface water
- Key FRA consideration: Defended tidal Flood Zone 3, residual/breach risk and basement vulnerability
When Do You Need a Flood Risk Assessment in London?
Planning applications in London require a Flood Risk Assessment in the following circumstances:
Development in Flood Zone 2 or 3
Any development in London's Flood Zone 2 or 3 areas requires an FRA. The LLFA will object to applications in flood risk areas without a robust FRA and drainage strategy.
Major Applications (10+ dwellings)
Major planning applications in London — 10 or more dwellings, sites over 0.5ha, or non-residential floorspace over 1,000m² — require an FRA in any flood zone.
Sites Over 1 Hectare in FZ1
Large sites in Flood Zone 1 may require an FRA if over 1 hectare, to demonstrate that drainage is adequate and runoff won't increase downstream flood risk.
LLFA Drainage Conditions
Where a London Borough has imposed a pre-commencement drainage condition, we prepare the detailed SuDS design package needed to satisfy the condition and secure approval.
LLFA Drainage Objections
If your London planning application has received a flood risk or drainage objection from the LLFA, we can review it and prepare a technical response to resolve it fast.
Change of Use
Converting commercial buildings to residential use in a flood risk area in London typically requires a new Flood Risk Assessment to confirm future occupiers will be safe.
Frequently Asked Questions
Trusted by Developers, Architects & Planning Consultants
★★★★★ 5.0 from 6 Google reviews
“Antony was great to work with when we needed a Flood Risk Assessment and Emergency Flood Plan. As an architect I would definitely use FRE Consultants again… his report went a good way in helping us get planning permission on a tricky site. Highly recommended.”
“Antony carried out my Flood Risk Assessment and has done a great job. My architect commented that the report was professionally drafted and very easy to follow. I highly recommend Antony's services.”
“Antony carried out a SuDS report for one of our projects and provided an excellent service throughout — quick to respond, clear communication, and a thorough, detailed report within the agreed timescale. We will certainly be using his services on all future projects!”
“Extremely helpful, prompt and friendly service carrying out a Flood Risk Assessment for a home project that required planning permission in a flood risk area… the price was reasonable and given up-front, and the final report was highly professional and exactly as required.”
“I had an extension completed on my house and needed a Flood Risk Assessment for planning. The service received was great and at a competitive cost. We were granted planning after first submission.”
“Nice and quick service. Recommend A++”
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