What Makes a Good Flood Risk Assessment?

By Simon Crowther BEng (Hons) FCIWEM C.WEM MIET, Director at FPS Environmental Ltd

Flood Risk Assessments are no longer a tick-box at the end of a project

This article is intended for planners, planning consultants, architects, developers and homeowners who are extending or redeveloping property, because the way Flood Risk Assessments (FRAs) are procured and used is still, in many cases, out of step with what planning policy, insurers, and good engineering practice now require.

Across the market they are too often treated as a compliance document that appears towards the end of a project. That approach belongs to a different era. A good Flood Risk Assessment is not a report that justifies a design after the event, it is a technical input that helps shape the design from the outset. The difference between those two positions is significant, both in terms of risk and in terms of the long-term value of a site.

This was brought into sharp focus recently when we were sent an enquiry including a Flood Risk Assessment prepared for a retrospective application in Flood Zone 3 and asked whether we could respond to the Environment Agency’s objections. Having read both the objections and the report, I was not surprised they had objected. I would have objected too.

The FRA document was six pages long and consisted largely of screenshots from the Flood Risk for Planning website accompanied by sweeping statements that had no technical justification. River model data had not been requested, yet the report concluded there would be no loss of floodplain storage. That is not something that can be asserted without reviewing levels and without interrogating how the site interacts with the modelled flood extents and depths.

Mapping is a starting point, not an assessment

Without model data it is difficult to understand how water behaves across the site, what the hazard is, how access and egress is affected or whether people and users would be safe during a flood event.

In this example case there was also a newly installed access roadway. That immediately raises questions about how infiltration characteristics have changed, whether runoff rates have increased and how the natural drainage of the site has been altered. None of that had been considered.

Given the proposed use, I would also have expected to see a Flood Warning and Evacuation Plan so that there was a clear strategy for both people and animals in the event of a flood warning. With no model data, even understanding likely depths at the site becomes difficult.

That is the difference between a document that describes a flood zone and an assessment that understands flood risk.

The issue of competence in the UK market

One of the points I made at a recent Public Policy Exchange event on FRAs and Sustainable Drainage (SuDs) was that competence in this sector is largely assumed. There is no formal requirement for a specific professional qualification to produce a Flood Risk Assessment, and the title “engineer” is not protected like lawyer or doctor. From a client perspective that makes it very difficult to differentiate between a robust, site-specific assessment and a templated report.

There will be examples of good work, and there will also be examples that slip through planning because of resourcing pressures within the planning system. I was recently told, quite proudly, by a prospective client that their AI-generated drainage strategy had achieved planning permission, despite them not fully understanding it. The purpose of this process, however, is not to obtain a decision notice. It is to understand and manage risk for the lifetime of the development and for the surrounding area.

The market is still being driven by price and speed

Many Flood Risk Assessments are procured on the basis of lowest cost or fastest turnaround. A short report that does not request model data will always perform well against that criteria, but that simply defers the cost and the programme risk to a later stage when the Environment Agency raises an objection, and the work has to be redone properly.

At that point you are commissioning model data, perhaps undertaking a cut and fill exercise, preparing compensatory storage calculations and often introducing a Surface Water Drainage Strategy that could have been considered much earlier when the layout and levels were still flexible.

What appears to be a saving at the start becomes abortive work later.

A good FRA is bespoke and integrated into the design process

A robust Flood Risk Assessment is tailored to a specific site and a specific proposal. It requires the consultant to understand planning policy, to understand the flood mechanisms that affect the site and to prepare a scope of work that reflects those factors. That might include an Exception Test, a Sequential Test, a Flood Warning and Evacuation Plan or compensatory storage calculations. It may also require engagement with the wider design team.

That is why the most effective appointments happen early. When the Flood Risk Consultant is involved at concept stage, the design can respond to the site rather than trying to justify something that has already been fixed. In many cases that leads to better outcomes, not only in terms of risk reduction but also in terms of development potential.

With most developments now requiring a Surface Water Drainage Strategy as well, there is also a clear efficiency in having a consultant who understands the flood risk context and can take that knowledge forward into the drainage design. DEFRA released a major update in mid-2025, with new National Standards for Sustainable Drainage Systems (SuDS). You can read more in our blog here: Update to the National Standards for Sustainable Drainage Systems (SuDS)

The role of the client in achieving a good outcome

The quality of a Flood Risk Assessment is not solely down to the consultant.

It is very difficult to produce good work when the instruction arrives late in the process with the sole objective of obtaining a compliant report.

The best projects are those where the client is engaged, open to discussion and willing to explore how the development can respond to the site. That does not necessarily mean higher overall cost. In many cases it means better long term value and better outcomes.

For instance, when preparing Surface Water Drainage Strategies, there is often a reluctance from clients to undertake site investigations such as infiltration testing because of the extra fees. In the absence of that information the design has to assume worst case conditions, which frequently leads to larger and more expensive drainage infrastructure during construction.

Under the Construction (Design and Management) Regulations, CDM, the client should not be driving designer fees down to a level that compromises the ability to carry out the work properly. A Flood Risk Consultant is not there to be a yes person. Their role is to understand the risk and, where necessary, to challenge the brief.

The value of visiting the site and meeting the design team

For more complex or constrained sites, a site visit is invaluable. It allows levels, thresholds, existing drainage arrangements and the surrounding context to be properly understood. It also gives the client the opportunity to meet the person who is advising them and to have a meaningful discussion about what good looks like for that particular development.

Those conversations rarely happen when the appointment is based purely on a low fee and a remote report.

Looking beyond policy and into long-term performance

If I give a recent site example, it was almost the complete opposite of the compliance-led template report approach that still lingers from a bygone era.

The existing property had flooded historically, it sat within a mapped flood zone, and the brief was for an extension, that required planning permission. On the face of it that could have been treated as a straightforward planning exercise. Produce the report, set a floor level, move on. But when you look at it through the lens of managing risk rather than just achieving consent, it became clear there was an opportunity not only to accommodate the extension but to improve the performance of the existing house.

The first step was understanding the client goals, and then a site visit. That immediately changes the quality of the conversation because you are no longer talking in abstract terms. You are walking the site with the residents, understanding how they actually use the building, where the low points are in the garden, how water currently behaves during heavy rainfall, and how they access and move through the space day to day. That context never comes through properly in a purely desktop exercise.

From there we obtained the model data and interrogated it. Not just flood extents, but depths, hazard, rate of onset and how the flow routes interacted with the plot. That then allowed an initial advice note to be prepared so that we could sit down with the client and talk about what good looked like for them.

That discussion covered far more than a finished floor level for the extension. It became a conversation about whether they even wanted the extension at the same internal level as the existing house, what the number and position of door openings should be, and whether the construction itself could be used as part of a wider resilience strategy.

For example, if a sump system was incorporated within the extension footprint, that could provide an additional layer of resistance for the existing property. Not because it was required for planning, but because it could improve the way the whole building would perform during an event, and be simple and low cost to include at this stage – whereas breaking through a floor slab late would introduce risk, and much higher cost.

I also reviewed the existing drainage in detail, both surface water and foul. Several downpipes were discharging to the ground, with no formal connection, exacerbating localised ponding. That is exactly the sort of issue that never appears in a standard report, yet it has a direct impact on how the site behaves in heavy rainfall. By picking that up early we could look at reconfiguring the drainage properly, introducing non-return valves to address backflow risk, and understanding how those measures would interact with the flood levels from the model.

Once you are in that mindset, you are no longer working to achieve a tick-box outcome. You are looking at whether there is an opportunity to introduce shallow swales, SuDS features or even subtle land regrading so that there is no loss of floodplain storage and, in some cases, a betterment in how water is managed across the plot.

It is not the cheapest way to approach an extension in terms of initial fees, but it is what good looks like, and it would be more cost effective long term. It is an engaged client who wants to understand the long-term performance of their home and is prepared to invest in a solution that reduces risk rather than just satisfying a policy requirement.

There is also a very real value point to that. A better designed building with a demonstrably lower flood risk is more insurable, more mortgageable and ultimately more valuable. That upfront engineering input pays dividends over the life of the property.

It links directly to another case study I recently wrote on a warehouse that was mapped at high surface water risk and was effectively uninsurable. By properly understanding the topography using LiDAR, reviewing the flow paths and introducing land regrading and an on-site detention basin, there is a strong likelihood that when the mapping is next updated the building will sit outside the high risk classification, with the flood storage deliberately located within the basin. You can read the case study here: Civil Engineering Flood Review – Commercial Site, Leicestershire.

That is a long-term view of risk and value. It is also a good example of how an assessment that starts with data and site understanding can influence not just a planning outcome but the future insurability and usability of a property.

This is where the conversation moves beyond simply quoting Planning Practice Guidance and into the territory of flood resilient construction and whole-life performance. With Flood Re due to end in 2039, and with any property built after 2009 already excluded from the scheme, the insurability of new development is a critical consideration. You can build something that is architecturally excellent and policy compliant, but if the flood risk has not been properly managed it may still be difficult to insure.

At that point the quality of the original Flood Risk Assessment becomes fundamental.

A personal perspective

Part of the reason I feel strongly about this is personal. My family home was a 2005 new build. It passed all the checks that existed at the time. The floor level was set above external ground, and the soakaway was constructed in accordance with the guidance then available. In 2007 it flooded.

Mapping has improved significantly since then, but the principle remains the same. If risk is not properly understood and managed, the consequences for homeowners and developers are severe.

This was brought into the public domain very clearly in the recent ITV programme Floods: New Build Nightmares, which showed what happens when new developments flood. The outcome is not just a technical issue. It is an emotional and financial one for the homeowner and a reputational and commercial one for the developer. By the time those issues are visible on national television it is far too late to retrofit the right decisions.

What do we actually mean by “good”?

The definition of good is “having the required qualities; of a high standard”. Whilst of a high standard naturally makes people think about detail and technical content, the required qualities are more open to interpretation.

For some, good means cheap and quick. For others it means a consultant who produces the document without asking too many questions or challenging the brief. In that sense the market has, for a long time, rewarded the wrong behaviours.

My view is that good is the opposite of that. It is a fee that reflects the level of detail required, enough time spent to properly consider all of the requirements, and an engaged consultant who understands the site, understands the risk and is prepared to have the difficult conversations early. That is where value is created and where risk is reduced.

A phased approach may suit some sites

Not every project is viable to have a single fixed fee for a full assessment at the outset. For some sites a phased approach is more appropriate, starting with an initial advice note or feasibility review that defines the scope of the next stage. That allows the work to be targeted.

Our approach at FPS Environmental

As an engineering advisory firm, we are aware that we lose enquiries because we do not offer templated reports or tiered bronze, silver and gold packages, as others may do.

Our fees reflect the time required to obtain and analyse data, to understand the site and to produce a detailed, defensible assessment.

We are a team of engineers and consultants who care about the quality of our work and about the outcomes for the developments we are involved in. Our aim is not to produce the shortest report, it is to produce the right one.

A good Flood Risk Assessment is:

• Bespoke to the site
• Informed by model data
• Integrated into the design process
• Focused on long-term performance and safety

That is what good looks like now.

If you are looking to discuss a site, whether at an early feasibility stage or as part of an ongoing planning application, you can contact us at FPS Environmental and we will help you define the right next step.