Timeline depends on site complexity and information availability. For straightforward sites in Flood Zone 2 or 3 with good topographic data and no significant site-specific constraints, we typically deliver FRAs within 2-3 weeks.

​

More complex assessments—those requiring hydraulic modelling, detailed sequential testing, or addressing multiple flood sources—may take 4-6 weeks. The critical path is usually obtaining detailed topographic survey and any required hydraulic model data from the Environment Agency or Lead Local Flood Authority.

If you're working to tight planning submission deadlines, let us know at the outset. We can often fast-track assessments or provide preliminary advice whilst detailed analysis progresses.

Essential information includes:

• Site location plan and red line boundary

• Topographic survey with spot levels or contours

• Proposed site layout showing buildings, access roads, and finished ground levels

• Details of proposed use and vulnerability classification

• Any previous flood risk studies or site investigation reports

Additional information that helps but isn't always essential:

• Ground investigation data (particularly for groundwater flood assessment)

• Hydraulic model data from Environment Agency or LLFA

• Details of existing drainage infrastructure and watercourses

• Historical flooding records or anecdotal evidence from site owners

If you don't have everything, that's fine—we can advise what's needed at different project stages and work with outline information initially.

Not always. Many FRAs rely on published Environment Agency flood mapping, which is based on national-scale hydraulic modelling. This is acceptable where:

• The published mapping adequately represents site-specific conditions

• The development doesn't significantly alter flood flow paths

• You're not proposing land raising or structures in the floodplain

• The site sits comfortably outside the modelled flood extent

Bespoke hydraulic modelling becomes necessary where:

• Published mapping doesn't cover your area or is outdated

• You're proposing flood defences or compensatory storage

• The development involves significant earthworks in the floodplain

• Local authorities or Environment Agency require site-specific modelling to inform decisions

• You need to demonstrate no loss of floodplain storage or demonstrate appropriate mitigation

We'll advise whether modelling is required based on initial desk study and consultation with regulators.

The flood zones reflect the probability of river or sea flooding:

Flood Zone 2 – Between 0.1% and 1% annual chance of river flooding (1 in 1000 to 1 in 100 year event), or 0.1% to 0.5% for tidal flooding. This is "medium probability" in planning terms.

Flood Zone 3 – Greater than 1% annual chance (more frequent than 1 in 100 years for rivers). This is "high probability" and splits into:

• Flood Zone 3a – High probability area where development is possible subject to Sequential and potentially Exception Tests

• Flood Zone 3b – Functional floodplain where water flows or is stored during flood events. Most development inappropriate here.

The flood zone determines what development types are acceptable and what tests must be passed. More vulnerable development (residential) faces tougher tests in higher zones. Highly vulnerable development (e.g., basement dwellings) should not be permitted in Flood Zone 3.

Yes, but it's more challenging and depends on the vulnerability classification of your proposed use. The NPPF's vulnerability classification ranges from:

• Water-compatible (flood control infrastructure, amenity open space) – acceptable in all zones

• Less vulnerable (general industrial, retail) – acceptable in Zones 1, 2 and 3a

• More vulnerable (residential, schools, hospitals) – require Exception Test in Zone 3a, not permitted in 3b

• Highly vulnerable (basement dwellings, mobile homes, emergency services) – not permitted in Zone 3

Even where development is theoretically acceptable, you must:

1. Pass the Sequential Test (demonstrate no reasonable alternatives at lower risk)

2. Pass the Exception Test where required (show sustainability benefits and that development will be safe)

3. Incorporate appropriate mitigation (raised floor levels, flood-resistant construction, safe access)

Many residential schemes successfully gain consent in Flood Zone 3a, but it requires robust justification and carefully designed mitigation.

The Sequential Test aims to steer development to areas at lowest flood risk. It requires demonstrating there are no reasonably available sites at lower risk that would meet the development need. "Reasonably available" considers:

• Availability and deliverability of alternative sites

• Appropriateness for the proposed use

• Consistency with wider planning objectives

• Whether alternatives would meet development need

Local authorities undertake sequential testing at plan-making stage, but applicants must still demonstrate compliance at application stage—particularly for windfall sites not allocated in Local Plans.

The Exception Test applies where development must proceed in higher-risk areas despite the Sequential Test.

It has two parts:

1. Part a: The development provides wider sustainability benefits that outweigh flood risk

2. Part b: The development will be safe over its lifetime without increasing risk elsewhere, and where possible reduce flood risk overall

Both parts must be satisfied for consent. We prepare Exception Test evidence addressing these requirements with robust technical justification.

Groundwater flooding occurs where water tables rise above ground level, typically in permeable chalk or limestone areas. It's often prolonged (lasting weeks or months) and difficult to predict.

We assess groundwater flood risk through:

​

Desk Study
BGS mapping of susceptibility, Environment Agency groundwater flooding records, and hydrogeological conceptual models.

​

Site Investigation
Review of borehole logs from ground investigation, identifying encountered groundwater levels and seasonal variation.

​

Consultation
Discussion with local authorities about historical groundwater flooding incidents, and review of anecdotal evidence from site owners and neighbours.

​

Mitigation Design
Where groundwater flood risk is identified, we specify appropriate measures—raised floor levels, waterproofing, land drainage, or foundation design that accommodates inundation.

Groundwater flooding is often overlooked in FRAs, but it can be a show-stopper for basement construction or developments with underground parking in susceptible areas.

Yes—effective engagement with statutory consultees is often the difference between smooth planning approval and protracted objections. We routinely:

• Seek pre-application advice from Environment Agency and Lead Local Flood Authorities

• Discuss proposed mitigation approaches and agree acceptable finished floor levels before formal submission

• Respond to consultee comments during planning determination

• Attend meetings to resolve technical queries

• Negotiate planning conditions wording to ensure requirements are reasonable and achievable

This proactive approach means fewer surprises at determination stage and reduces the risk of delay or refusal.

Mitigation varies by site, but common measures include:

​

1. Finished Floor Levels
   Setting ground floors a minimum 300-600mm above design flood level (often 100-year plus climate change event). This is the most fundamental and effective mitigation.

2. Flood-Resistant Construction
   Specification of water-resistant materials below flood level—solid floors instead of suspended timber, cement render rather than gypsum plaster, flood-resistant doors and airbricks.

3. Flood Resilience Measures
   For sites where raising floor levels isn't feasible, active resilience measures like removable flood barriers, automatic flood doors, or sump pumps may be considered—though these are generally less preferred than passive measures.

4. Compensatory Storage
   Where development reduces floodplain storage volume (through buildings or land raising), "level-for-level" compensatory storage elsewhere on site prevents increased flood risk downstream.

5. Safe Access and Egress
   Demonstration that site access remains passable during design flood events, or that alternative evacuation routes exist if primary access is inundated.

6. Flood Warning and Evacuation Plans
   For more vulnerable development in higher-risk areas, preparation of flood response plans specifying warning arrangements and evacuation procedures.

The aim is to make the development safe without resort to temporary or unreliable measures that might not be deployed when needed.

Cost varies significantly depending on site complexity, size, and assessment requirements:

• Simple FRAs (sites >1 hectare in Flood Zone 1 with no significant constraints) – typically £350

• Standard FRAs (sites in Flood Zone 2, or Zone 1 with surface water flooding issues) – typically £450

• Complex FRAs (Flood Zone 3 sites requiring Sequential/Exception Tests, or any site requiring hydraulic modelling) – typically £1,000-1,500+

• Strategic FRAs (large masterplans, infrastructure projects, or sites requiring extensive modelling) – £8,000-20,000+

​

These are indicative ranges. We provide fixed-price quotes once we understand site-specific requirements. Early engagement helps avoid unnecessary work—if we can demonstrate flood risk is low with a proportionate desktop assessment, that's what we'll propose rather than gold-plating the study.

Our primary focus is England where we're most familiar with Environment Agency procedures and NPPF requirements. However, we can undertake assessments in Wales where flood risk mechanisms and technical requirements are similar, though we'd liaise with Natural Resources Wales rather than Environment Agency.

For sites in Scotland or Northern Ireland, flood risk policy and assessment procedures differ more significantly. We'd recommend consultants with specific expertise in those jurisdictions to ensure compliance with SEPA or Rivers Agency requirements.

Historical flooding is obviously a concern, but it doesn't automatically prevent development. What matters is:

1. Understanding the flood mechanism – Was it river flooding, surface water, groundwater, or a combination? What was the return period?

2. Assessing current and future risk – Has anything changed since (new defences, upstream storage, channel improvements)? What's the risk under current and future climate?

3. Designing appropriate mitigation – Can the development be made safe through floor levels, resilience measures, or site layout that avoids highest-risk areas?

We review Environment Agency historic flood maps, local authority records, and any anecdotal evidence. If the site has flooded to significant depth during recent events, that obviously makes consent more challenging—but with robust mitigation design, many sites with flooding history successfully gain planning approval.

The key is transparency. Attempting to downplay or ignore known flooding history undermines credibility with regulators. Far better to acknowledge the hazard and demonstrate you've properly addressed it.

If you need a Flood Risk Assessment for a planning application, or want to discuss whether your site requires one, get in touch. We're happy to provide initial advice on requirements and likely costs at no charge—it helps us give you an accurate quote and means you get site-specific guidance rather than generic information.

We work with sites across England, from small residential extensions to major mixed-use developments and infrastructure projects. Our assessments are prepared by experienced consultants familiar with Environment Agency procedures and local planning policy requirements.

​

Contact us to request a quote or discuss your development site's flood risk.