How surveyors can help to mitigate flooding

As we are all too aware, major incidents, severe weather warnings and flooding events are not rare occurrences.

Storms Agnes, Babet and Ciarán have so far battered the UK in the 2023/24 winter season – with thousands of homes and other properties flooded as record amounts of rain fell across parts of the country.

It is heartbreaking for anyone to experience flooding in their home or business: it can cause structural and electrical damage, possessions are ruined or lost forever, it is uninhabitable for months as the building dries out, not to mention the stress and distress of dealing with the aftermath.
Of course, flooding can occur in many different ways – from surface water flooding to groundwater breaches and from coastal flooding to river flooding.

However it happens, the devastating results are the same and while flooding can affect any property, some have a higher risk than others, depending on where they are located.

It is why surveyors have a critical role to play in the pre-planning process. As climate change is now a bigger concern for property owners, landlords and developers (not to mention financial services providers), undertaking a thorough and robust flood risk assessment is non-negotiable.

A flood risk assessment is required for any planning application where the site of the proposed development is located within flood zones 2 or 3, defined by the Environment Agency (EA). These sites are considered to be at risk of flooding and therefore the EA and local planning authorities can challenge planning applications that have not taken into account all of the flood risks involved.

It is also mandatory to complete a flood risk assessment for any site over one hectare or more in flood zone 1, and for any site that is located within a critical drainage area.

It is incumbent on any surveyor to set out the flooding risks of any site so that the developer can make an informed decision about its plans. Thinking long term is key.

Other work, such as geotechnical investigation that assess soil conditions in the proposed development site, a topographical survey to show natural and manmade features, and utility survey, which maps underground utilities and buried services and is needed to design flood defences, may also be needed to determine any flood risks.

If the developer decides the risks are too high, and that any building would not generate a return on its investment, plans to build may change.

It is vital to prioritise flood risks in the initial stages of any scheme design. It is important to note, however, that it is still possible to build on a floodplain, such as when it could enhance the floodplain or reduce flooding risks to lower than previous and when a site has insufficient space to allow development outside the “at risk” areas.

If a developer is determined to continue with construction, despite any known flooding risk, the surveyor should recommend ways to mitigate it. This could be by changing the site layout, moving buildings and essential infrastructure outside the floodplains, and reducing the density of a development.

The surveyor could also recommend raising the property threshold to prevent flood water entering into it. The Environment Agency, Scottish Environmental Protection Agency and Natural Resources Wales usually ask for the finished floor level to be raised above the 1 in 100-year (fluvial) and 1 in 200-year (tidal) flood levels.

But if this cannot be achieved, other flood resistant measures should be considered, such as barrier systems, automatically closing airbrick covers and none-return valve systems. Sustainable Drainage Schemes (SuDS), which slow water down before they enter a water course or sewer, are also recommended, as are wetlands, swales or basins.

Doing the groundwork (literally and metaphorically) at the earliest stages of a development proposal can save time, money and future heartache. If a flood were to occur, hopefully the measures recommended by the surveyor will limit the disruption.

For more information on flood risk assessments and how GeoSmart reports can support planning applications, property transactions and insurance, contact us today to speak to one of our expert team.