One billion people globally are at risk of experiencing a flood. In the UK alone, an estimated 5.2 million homes and businesses are at risk. And the probability of flooding is increasing with climate change. Increased winter rainfall — projected to increase 35% by 2070 — and more severe weather events will exacerbate an already untenable set of circumstances.

The impact of flood risk on businesses is also troubling. In the UK, once a flood hits and affects a business, only 60% of them ever re-open their doors. And for businesses that do, each flood claim entails, on average, 50 lost days of business. Meanwhile, government strategy is shifting, with a newfound acceptance that ‘we can only reduce the risk in some places,’ rather than eliminate the risk altogether.

Now, more than ever, we must harness solutions to proactively mitigate flood risks wherever possible.

Do you know the flood risk for your assets?

Investing in flood resilience is driven by an awareness of the flood risk by the key stakeholders (e.g. building owner / occupier / insurer / lender). For property owners, that means assessing a wide range of factors.

What sources of flooding are in the vicinity of the building? What are the flow routes and hazards i.e., how would the water flow to reach the building or asset you’re trying to protect? What’s the history of flooding at the property? Would potential floodwater likely be contaminated i.e., is a water source nearby fresh, or contaminated with sewage or farm waste? What’s the estimated frequency, duration and depth of potential floods specific to the property?

The basics of flooding

Each type of flooding has unique implications. Pluvial, or surface water flooding, occurs when the ground can’t absorb the water fast enough, so it runs over the surface. Fluvial, on the other hand, occurs when streams, rivers or small ditches overflow. Groundwater flooding occurs when the ground is completely saturated with water, and the water has nowhere to go. Finally, tidal flooding is the temporary inundation of coastal areas or areas around rivers during exceptionally high-tide events. An area not often considered is the risk of sewage backflow into a property when the combined foul and surface water system is overwhelmed. Compound flooding is a combination of any of the above flood types.

It may be counterintuitive, but more properties are at risk from surface water flooding than that flowing from a river or sea. If rainfall is prolonged or intense enough, and the ground can’t absorb the water it will flow over the surface and may flood properties which are often thought to be at low flood risk.

Property flood resilience in practice

Property flood resilience (PFR) is a broad term capturing measures which minimise the impact of flood water on a property or asset — these can be both permanent measures built into the property or temporary measures deployed in a flood.

PFR is two-fold: resistance measures, or those that reduce the amount of water entering a building (e.g. flood doors/barriers/automatic air bricks), or recoverability measures that limit the damage caused if water does enter a building (e.g. kitchens / floor and wall finishes not damaged when they get wet). The trick is in balancing both measures, and determining which are most effective and timely for a specific property.

When delivering flood resilience, there’s an important and clear methodology UK professionals follow: the code of practice (CoP) for property flood resilience (C790F), published by the Construction Industry Research and Information Association (CIRIA), an independent not-for-profit organisation.

The CoP lays out a six-stage approach that qualified surveyors should follow for effective delivery.

• Flood hazard assessment – an assessment that reviews flood risk for the property; determines likely frequency, depth, severity and overall susceptibility to flood.
• Property survey – a property survey and assessment of existing resilience (conducted by a qualified skilled surveyor).
• Options development – deciding on PFR strategy and creating associated, detailed flood resilient design.
• Construction – installing PFR products by appropriately skilled contractors or specialists.
• Commissioning and handover – a post-installation audit conducted by an independent third-party surveyor confirming that measures operate effectively.
• Maintenance – assigning responsibility for ongoing operation and explaining to customers how to maintain measures.

A separate document, ‘making your property more flood resilient’ (CIRIA C70C) is a helpful resource for home owners or business owners interested in at-home flood resilience guidance.

The importance of winning over customers

Much of the at-risk population in the UK doesn’t actively adopt mitigation measures even when they’ve been impacted by multiple flood events. Recent research found there are several psycho-behavioural barriers that subconsciously influence a person’s likelihood to pursue flood risk mitigation.

According to research commissioned by the Environment Agency, there’s a widespread lack of awareness among the public of the true extent of risk facing their properties.

Many participants view themselves as being insufficiently at risk to justify any sort of flood mitigation investment. To that end, many misunderstand risk rates entirely. If a surveyor identifies a 1 in 33 annual flood probability, for example, many assume this means the property will experience a flood once in every 33 years on average. It actually means there’s a 3.3% chance of flooding each year — revealing the true risk to be much higher than perceived. This is made worse by homeowners and businesses not wanting to accept that there’s an ongoing risk.

Additionally, most participants didn’t feel empowered to act and had poor knowledge of which PFR measures were available to install. Self-efficacy also proved important in participant decision-making; those who felt confident in their ability to carry out PFR measures were more likely to do so.

It’s critical to help customers understand their risk and further establish their appetite for risk. Customers must be able to understand the cost-benefit analysis of how much risk they might be willing to accept, and how much they’re willing to invest to protect their property. We must collectively distance ourselves from the belief that only properties near a river, or only properties in certain environments are at risk. All properties can be at risk — and the time to mitigate, using a holistic and strategic approach, is now.

Some of these concepts were previously shared in a recent webinar presented by Ian Gibbs.