Case Study: Environment Agency Objection Resolved Without Modelling — 8 Dwellings, Sileby

Written by Antony Riozzi BEng (Hons) — Director & Principal Consultant, Flood Risk Environmental. 17+ years in flood risk & drainage, with experience at a Lead Local Flood Authority, a national housebuilder and in consultancy. About the author →

Location

Sileby, Leicestershire

Development

8 dwellings — reserved matters (outline granted 2023)

Authorities

Charnwood Borough Council · Environment Agency

What we delivered

Flood risk technical note · finished floor level strategy drawing · flood warning & evacuation plan

Outcome

EA confirmed it would accept the raised floor levels; no bespoke modelling, no floodplain compensation, all eight plots retained

The challenge

Outline permission for eight dwellings on a 0.49 ha site behind Barrow Road was granted in December 2023. At that time the site was wholly in Flood Zone 1 — no flood risk assessment was needed and no flood condition was imposed. Then, in March 2025, the Environment Agency published its updated national flood map (NaFRA2), and the lower north-western part of the site was suddenly shown in Flood Zone 3.

Environment Agency Flood Map for Planning extract dated August 2021 showing the Sileby site in Flood Zone 1 — **August 2021** — the site (marker) sits in Flood Zone 1 when outline permission was sought. © Environment Agency copyright and/or database rights; © Crown copyright and database rights, Ordnance Survey — reproduced from the Flood Map for Planning service.

Environment Agency Flood Map for Planning extract dated July 2026 showing the same Sileby site partly in Flood Zone 3 — **July 2026** — the same site after the NaFRA2 update: the lower north-western corner is now shown in Flood Zone 3. © Environment Agency copyright and/or database rights; © Crown copyright and database rights, Ordnance Survey — reproduced from the Flood Map for Planning service.

When the reserved matters application went in, the Environment Agency issued a holding objection. The developer faced the prospect of commissioning bespoke hydraulic modelling and providing on-site floodplain compensation — which, on a site this size, would have cost plots and made an eight-dwelling layout unworkable. The architect asked us to find a proportionate way through.

What we did

We started with the planning position rather than the hydraulics. Within a week of instruction we had written to the case officer and the Environment Agency setting out three points: the principle of development, including flood risk, had been established at outline when the site was in Flood Zone 1 and could not be reopened at reserved matters; the NaFRA2 mapping is a broad-brush national dataset that in this location represents an ordinary watercourse within the Lead Local Flood Authority's remit; and the Flood Zone 3b outline it had initially shown had already been withdrawn by the Agency owing to anomalies in the national data. Critically, the national model does not include the culvert that carries the watercourse away from the site under the adjoining industrial estate — so the mapped extent effectively shows a culvert-blockage scenario, a residual risk rather than a design flood.

Alongside that argument we offered a constructive way out: precautionary finished floor levels, set with freeboard above the maximum mapped flood extent. Two weeks later the Environment Agency confirmed, via the council, that it was willing to accept the raised floor levels provided they were expressed in metres above Ordnance Datum.

FRE drawing 238B_1001 Proposed Finished Floor Level Strategy showing the mapped flood extent overlaid on the topographical survey with interpolated flood levels and a finished floor level scheduled for each of the eight plots — FRE drawing 238B_1001 — Proposed Finished Floor Level Strategy. The maximum mapped extent (Flood Zone 3, Flood Zone 3 plus climate change and Flood Zone 2) is overlaid on the client's topographical survey; flood levels are interpolated at 5 m stations along the boundary and a finished floor level, mean ground level and cut/fill depth are scheduled for every plot.

Deriving those levels is where the engineering sits. We georeferenced the maximum mapped extent — Flood Zone 3, Flood Zone 3 with the 2070–2125 climate change allowance, and Flood Zone 2 — onto the site topographical survey, which gave us around 290 spot levels to work with. The flood level along the extent was then read off as the surveyed ground level at the mapped water's edge, at 5 m intervals, with stations that tracked raised boundary features rather than open ground excluded. Across the site the interpolated flood level ranged from 46.14 to 46.85 mAOD.

For each plot we adopted the governing flood level at and immediately adjacent to it and set the finished floor level a minimum of 300 mm above — giving levels between 46.975 and 47.150 mAOD. Where existing ground or drainage levels were already higher, the higher level governed and gave extra freeboard. The result was an 11-page technical note and a single drawing that told the Agency exactly what it had asked for.

An eleventh-hour request

Two days before the decision was due, the case officer asked whether a flood evacuation plan existed. It did not — the Agency had not asked for one — so we produced a Flood Warning and Evacuation Plan the same day. It assessed the evacuation route along the private drive and Barrow Road against the mapped extent using the EA LiDAR terrain model, node by node: the maximum depth on the route was 0.23 m, every node scored a hazard rating below 0.75 ('low hazard — caution') and dry ground in Flood Zone 1 is reached about 120 m from the site exit. Because access and egress had been within the scope of our original fixed fee, there was no additional charge.

Figure from the flood warning and evacuation plan showing the eight plots with their finished floor levels, the mapped flood extent, and the evacuation route along the private drive to Barrow Road with assessment node N1 — Evacuation route, refuge and access flood depths from the Flood Warning and Evacuation Plan — the dwellings are the primary refuge, with floor levels at least 300 mm above the maximum flood level; the route reaches dry ground in Flood Zone 1 about 120 m from the site exit. {OSM}

Wider map of the evacuation route along Barrow Road towards Sileby village with assessment nodes N1 to N6 and the point where the route clears all mapped flood zones — The wider evacuation context along Barrow Road to Sileby village. Assessment nodes N1–N6 mark every place the mapped extent laps onto the carriageway; the deepest is 0.23 m at N1 and the route is clear of all mapped flood zones beyond roughly 450 m. {OSM}

The outcome

The Environment Agency agreed to accept the precautionary floor levels as the means of resolving its objection, and the technical note supplied the levels it needed to withdraw it. No hydraulic modelling. No floodplain compensation. No lost plots. The applicant's exposure went from an open-ended modelling exercise to a fixed-fee note, a drawing and an evacuation plan, delivered inside the reserved matters timetable.

If you are in the same position. The March 2025 NaFRA2 map moved thousands of sites into Flood Zone 2 or 3, and objections like this one are now common on applications that were once straightforward. The answer is rarely bespoke modelling. It is usually a clear account of the flood mechanism, a proportionate mitigation the Agency can accept, and levels it can check. We have done this before and we can usually tell you within a day whether it will work for your site.

Talk to us about an Environment Agency objection →

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Frequently Asked Questions

Can the Environment Agency object at reserved matters if the site was in Flood Zone 1 at outline?

It can raise a holding objection because it consults on the current flood map, but the principle of development — including its acceptability in flood risk terms — is established at outline and reserved matters are confined to layout, scale, appearance and landscaping. Setting that out clearly, and offering a proportionate mitigation, is usually enough to resolve the objection without reopening the principle.

What is a precautionary finished floor level strategy?

It sets the ground floor of every dwelling a fixed freeboard — here 300 mm — above the highest mapped flood level at that plot, derived by overlaying the flood extent on a topographical survey. The levels are given in metres above Ordnance Datum so the Environment Agency and the council can check them, and they can be secured by condition.

Do you always need hydraulic modelling to answer an Environment Agency objection?

No. Modelling is only proportionate where the flood mechanism is uncertain or the mitigation depends on it. Where the mapped flooding is a residual risk — as it was here, from an unmodelled culvert — a level-based mitigation derived from the mapped extent and a survey is quicker, cheaper and often more persuasive.

How long did this take?

From instruction to the Environment Agency confirming it would accept the approach was about three weeks, including the correspondence. The technical note and drawing followed once the survey overlay was complete, and the evacuation plan was turned around in a day when the case officer asked for it.

Environment Agency Objection Resolved Without Modelling — Eight Dwellings, Sileby