Construction Stage Flood Risk and the Lessons from Attleborough

Far less attention is usually paid to what happens in between – the construction stage. During this phase, sites are highly dynamic. Temporary access routes are formed, ground is reprofiled in stages, permanent drainage systems may be incomplete or not yet operational, and temporary works are often introduced close to watercourses. These interventions can be short-lived, but during periods of extreme rainfall they can have significant hydraulic consequences.

The flooding experienced in Attleborough during Storm Babet in October 2023 has brought that overlooked phase into sharp focus. In this case, official investigations, political scrutiny, and first-hand accounts from residents all point to construction-stage activity as a meaningful part of the story, alongside wider catchment constraints and extreme weather conditions.

This article sets out what happened in Attleborough, what has been said by residents and decision-makers since, and why the construction phase of development now demands far greater attention in flood risk management.

Storm Babet and flooding in Attleborough

Storm Babet brought a period of intense and prolonged rainfall across large parts of Norfolk in October 2023. In Attleborough, the volume and duration of rainfall overwhelmed parts of the local drainage, sewerage, and watercourse network, resulting in floodwater entering residential streets and properties at speed and depth.

For many residents, the flooding was not a short-term inconvenience but a life-altering event involving contaminated water, rapid onset, and long displacement. Barry Herber, who has lived in Attleborough for more than 50 years, described how quickly conditions deteriorated:

For households close to Mill Lane, flooding was compounded by sewer surcharge as drains backfilled under pressure. Geoff Freston recalled how internal flooding escalated as systems failed:

For the Herbers, the flooding brought both immediate danger and long-term harm. Barry Herber described being unable to reach home as water levels rose, and the moment he realised the severity of the situation:

The consequences extended well beyond property damage. Floodwater was contaminated with sewage, and the physical and psychological effects have been lasting.

For many households, the flooding meant months away from home, repeated repairs, and a lasting sense of vulnerability. As one resident put it:

Flood risk at planning stage – and what it often misses

Under the planning system, flood risk is typically assessed with reference to the completed development. Flood Risk Assessments model how a site is expected to behave once construction is finished, permanent drainage infrastructure is in place, and mitigation measures are fully operational.

What is often less thoroughly examined is how a site behaves during construction. At this stage, surface water routes can be interrupted, temporary structures may cross ordinary watercourses, and ground levels can change incrementally rather than in a single, controlled operation. Drainage systems may be partially installed, leaving parts of a site reliant on temporary measures that are not designed to manage extreme events.

Jesy Ferry, Flood Risk Consultant at Unda, explains why this distinction matters:

Construction-phase impacts are frequently addressed through Construction Environmental Management Plans or method statements, but these are rarely subjected to the same level of scrutiny as planning-stage flood assessments. Jesy adds:

The events in Attleborough illustrate why the assumption that construction impacts are always minor or manageable can be misplaced.

The Norwich Road development – setting out the context

At the time of Storm Babet, a major housing development was under construction on the north side of Norwich Road in Attleborough. The scheme, known as the Gables development, was planned to deliver 165 homes and occupied land in close proximity to the Besthorpe Stream.

The location of the site is significant. The development sits upstream of existing residential areas that later experienced flooding, within a catchment already subject to known constraints and historic flood risk. The relationship between the site, the watercourse, and surrounding development meant that any changes to flow conveyance or floodplain storage had the potential to affect neighbouring areas.

Jesy explains why such locations demand heightened scrutiny:

The planning history of the site also forms part of the wider context. Breckland Council initially refused planning permission for the development because the land lay within a floodplain. That decision was later overturned on appeal, allowing the scheme to proceed. While that outcome established the acceptability of the development in planning terms, it did not remove the need for careful management of flood risk during construction.

Construction-stage works and the Besthorpe Stream

Concerns about construction activity near the Besthorpe Stream were raised locally in the aftermath of the flooding, particularly in relation to how quickly water levels rose and how little capacity appeared to remain within the channel.

Residents were acutely aware that changes had taken place near the watercourse during the build phase of the Norwich Road development. One resident questioned how such works had been allowed to proceed:

Subsequent investigation confirmed that a temporary road providing access to the development had been constructed across the Besthorpe Stream. During Storm Babet, this crossing restricted the movement of water along the channel.

From a hydraulic perspective, the mechanism is well understood. Temporary crossings can reduce channel width, introduce debris traps, and create localised head losses. As flows increase during intense rainfall, these restrictions reduce conveyance capacity, causing water levels to rise upstream. Once capacity is exceeded, water spills out of the channel and seeks alternative flow paths through adjacent streets and properties.

Jesy notes that the proximity of works to watercourses significantly increases risk:

In Attleborough, this process occurred against a backdrop of already constrained infrastructure. Residents observed the result in real time, with floodwater spreading rapidly across the area and overwhelming both surface drainage and foul sewer systems.

The critical issue is not simply that a structure existed, but that it was introduced during construction, outside the configuration assessed at planning stage, at a point when the catchment was least resilient to additional restriction.

Raised land and floodplain behaviour

The investigation also examined how changes in land levels associated with the development influenced flood behaviour during the storm.

The Gables development was being constructed on raised land on the northern side of Norwich Road. As floodwater spread across the area during Storm Babet, this raised ground altered natural flow paths and limited the ability of water to disperse across the floodplain.

Investigators concluded that the higher elevation effectively held water back against lower ground to the south. This led to increased flood depths and a wider extent of flooding affecting existing homes. The effect was described as water being “impounded” against the raised land.

From a flood risk perspective, this highlights how incremental changes in ground levels during construction can have a disproportionate impact during extreme events, particularly where development takes place close to ordinary watercourses and established communities.

Multiple contributing factors – not a single cause

It is important to be clear that construction activity was not identified as the sole cause of flooding in Attleborough. Official statements and investigations have consistently emphasised that multiple factors combined to produce the outcome experienced during Storm Babet.

These factors included the intensity and duration of rainfall, saturated ground conditions, historic alterations to watercourses, and existing constraints within the local drainage and sewerage network. In particular, the interaction between fluvial flooding and sewer surcharge played a significant role in the severity of internal flooding experienced by residents.

Jesy stresses the importance of looking beyond individual sites:

Barry Herber’s experience illustrates this interaction starkly. Floodwater entering his home was contaminated with sewage, leading to serious health consequences. This reflects a wider issue in areas where surface water, ordinary watercourses, and combined sewer systems are closely interconnected.

Residents themselves have framed the issue in broader, catchment-wide terms rather than attributing blame to a single cause. As one resident explained:

This perspective reflects an understanding that flood risk is cumulative, shaped by the interaction of development, infrastructure capacity, land management, and extreme weather, rather than any single failure in isolation.

Governance, responsibility, and the difficulty of intervention

One of the clearest themes to emerge from the Attleborough case is the complexity of responsibility for flood risk assets and infrastructure. George Freeman, the Conservative MP for Mid Norfolk, has highlighted a longstanding issue:

This historic arrangement meant that no single public body held clear long-term responsibility for maintenance or upgrade of key structures. When flooding occurred, this lack of clarity complicated both immediate response and longer-term planning.

Freeman acknowledged that interim measures were not a substitute for structural change, stating:

The Attleborough experience demonstrates how governance gaps can leave communities exposed, particularly when extreme weather tests the limits of existing systems.

Emergency action and interim measures

In the wake of the flooding, a range of short-term actions were agreed by the organisations involved. These focused on reducing immediate risk while longer-term responsibilities were clarified.

Anglian Water became involved on an interim basis, despite not holding long-term ownership of the affected assets. As Freeman explained:

He went on to confirm:

In the meantime, maintenance activity was increased to reduce the likelihood of blockages during further periods of heavy rainfall. While these measures have improved resilience, they have not eliminated risk entirely.

Residents have recognised the benefits of the work carried out, while remaining realistic about its limits. One resident noted:

But added:

Developer accountability and the wider policy debate

The flooding in Attleborough has fed into a wider debate about developer responsibility, infrastructure capacity, and the adequacy of current planning controls, particularly in areas experiencing sustained housing growth.

Freeman has been vocal in linking local experience in Attleborough to wider national policy questions. Speaking about development patterns and infrastructure investment, he said:

He has also highlighted the strain placed on ageing sewerage networks as new development is brought forward:

From a policy perspective, this raises questions about how flood risk is managed across the full lifecycle of development. While planning permission may establish the acceptability of a scheme in principle, it does not guarantee that surrounding infrastructure has the capacity to accommodate additional loading during construction or occupation.

Freeman has questioned how the system can encourage earlier and more comprehensive investment in drainage and flood mitigation, asking:

And has argued for stronger accountability where development contributes to flooding impacts:

These comments reflect growing concern that current arrangements do not adequately address cumulative impacts, construction phasing, or the timing of infrastructure upgrades relative to housing delivery.

Why construction-stage flood risk can no longer be overlooked

The events in Attleborough are unlikely to be unique. As rainfall becomes more intense and less predictable, temporary changes to land, watercourses, and drainage systems are increasingly exposed to conditions they were never designed to withstand.

For residents, the consequences are immediate and deeply personal. As one put it:

From a professional perspective, flood events also provide an opportunity to reflect and improve. Jesy notes:

For planning authorities, developers, and technical advisors, the lesson is clear. Flood risk management does not end when planning permission is granted. Temporary works need to be transparent, appropriately designed, and properly scrutinised.

As Jesy puts it:

For Unda, the Attleborough case reinforces the importance of evidence-led flood risk advice that looks beyond static drawings and considers how sites behave throughout their full lifecycle. That includes advising on construction-stage risk, temporary works, and catchment interactions, not just the final layout shown on a planning drawing.