Flooding is one of the biggest risks to our built environment. Andy Brierley explains how data analysis is helping sound out a solution

Climate change is making the UK a flood risk hotspot. A study by 24 European scientific institutions, published in 2019, found changing weather patterns are making floods more frequent and severe.

The data showed the north and west of England and Scotland are being particularly hardest hit. This trend has major implications for how we manage the built environment, and the sewers that serve it.

In towns and cities, sewer surcharging – which happens when water flows exceed system capacity – can cause severe local flooding. This can damage homes and businesses, disrupt transport and cause pollution.

Prolonged bursts of heavy rain, already associated with climate change, increase surcharging risks. At Lanes, an increasingly important focus of our work is to help water utility and commercial clients prevent this from happening.

Acoustic sewer inspection
A strong focus for us is to make better use of data and digital technologies. An example is the use of acoustic sewer inspection. Working with our specialist service provider, Water Intelligence, we are now deploying a new system called Orca on behalf of Thames Water.

It uses sound waves to analyse the inside of sewer pipes, locating to within less than one metre defects or blockages. Using a traffic light system, it tells us with a high degree of accuracy if a sewer is in good condition (green), if there may be a problem that needs further investigation (amber), or if the pipe is defective (red).

The device can be operated by one person. We have used it to diagnose up to 5.5km of sewer pipe in one day, an astonishing achievement. A CCTV survey crew has two personnel and can manage 1km at most.

Orca is allowing us to rapidly locate sewers that present increased flood risks. More precisely, though, it locates sewers that do not. With wastewater systems, the risk is that resources will be committed where they are not needed.

If Orca tells us a sewer is fit for purpose, we can move on to one that needs our attention. By not committing additional resources to surveying or ‘just-in-case’ cleaning, the potential operational and capital savings are very significant.

Orca is a key tool in a wider operational strategy that makes full use of Thames Water’s advanced sewer modelling capability.

Remote flood monitoring
Maintenance data gathered by Lanes and Water Intelligence teams is continuously fed into a virtual model of strategically important sections of the region’s 108,000km network of sewers.

This predicts the location of blockage hotspots and allows us to deploy planned and reactive resources where they are needed most. The upshot, over the last three years, has been an extraordinary increase in planned sewer maintenance with a key objective of mitigating flood risks.

By the end of March, our teams had achieved a target set by Thames Water of cleaning 900km of sewers in one year – a 50 per cent increase on the previous year’s 600km target. It is equivalent to cleaning a sewer stretching 75km from London to Brighton every month.

Another area where digital technology is making a big difference is remote sensing, using sewer flood monitors. These are devices installed in manholes that trigger an alarm if water levels rise above a certain level.

Such devices have been used for quite a few years. In the past, they have been used as permanent fixtures across a network. However, the logistics and cost of maintaining large numbers of monitors at fixed points meant they often fell out of favour.

Agile flood prevention
Our approach has been to incorporate remote sensing with a much more agile and responsive approach to flood prevention on behalf of Thames Water.

Working with Water Intelligence, we can deploy more 60 flood monitors to keep a special watch on flooding hotspots for shorter periods. Aided by our enhanced understanding of the network from modelling, our app-based digital work platform FieldViewer, and Orca, this has become a powerful tool with none of the drawbacks described above.

The sensors can be installed in less than 15 minutes, so we do not need to get local authority permits or use traffic management, saving costs and improving productivity. If the alarm is triggered, our response is an emergency so, again, does not need a permit.

Using sensors has released operational teams from lift and look duties to check that manholes are not surcharging. It allows us to monitor high risk sewers around the clock. We can build up our understanding of how they behave in varying conditions, so we only response if there is a real emergency.

This is important because responding effectively to a sewer flood often involves mobilising a lot of resource – CCTV survey teams, jet vac units, tankers, civils teams and specialist engineering support both from us and the client.

We can use the monitors during special projects to protect events, such as music festivals, sporting events – Royal Ascot and Wimbledon – and Royal Weddings, or sensitive wildlife sites during heavy rain.

Major flood cost savings
An example was a programme to install multiple monitors across a 40-hectare site in Epping Forest, Essex. The initiative prevented more than 50 flood incidents and allowed work to solve the underlying problems to be brought forward.

We began our sewer monitoring programme in 2017 Since then, it has allowed us to prevent or significantly mitigate hundreds of flood incidents. This has enhanced environmental protection and allowed resource, both operational and capital, valued at many millions of pounds to be put to better use.

These kinds of initiatives, combined with the expertise and dedication of our personnel, such as our flooding and escalation team, are allowing us to transform our approach to sewer flooding. We are transitioning from firefighting problems to getting on top of them in planned way.

Other measures at our disposal include sewer lining. We have the very latest ultraviolet cured in place pipe (CIPP) technology that allows us to line pipes up to 1.6m in diameter. Pipes at risk of collapse, infiltration by tree roots or snag blocking can be strengthened and smoothed, eliminating future flood risks.

Flood risk education
We also work with clients and the wider public to reduce sewer flood risks. That involves continued public education about the damage caused by fatbergs – large blockages made up of cooking fats, oils and grease (FOG) mixed with millions of items like wipes that should never be disposed of down toilets.

Construction contractors can also contribute to sewer flooding risks by inadvertently, or sometimes deliberately, allowing building products to get into sewers. A notorious example in central London in 2019, discovered by one of our maintenance teams, resulted in 100 tonnes of piling concrete, dubbed a concreteberg, blocking a main sewer.

Cutting corners with site investigations, such as CCTV drainage surveys and sewer tracing, is a risky and potentially costly business. Utility companies will always look to reclaim the cost of removing blockages. It always pays to seek advice from a reputable drainage specialist.

In 2019, Lanes devised and led a campaign called Unblocktober to highlight problems caused by misuse of sewers – including river and marine pollution, plastic pollution and flooding. The campaign gained widespread support both in the UK and internationally.

Unblocktober returns in 2020. We would welcome the support and involvement of construction and civil engineering companies that want to take a proactive approach to protecting sewers and the environment, and to reducing the risk of flooding.

Andy Brierley is Technical Director of water utilities and drainage specialist Lanes Group plc, the UK’s largest independent drainage and utility specialist. Key sectors are construction, rail, energy, highways, insurance, and commercial maintenance. Water utility companies it works for include Thames Water, Severn Trent, Yorkshire Water, Anglian Water and Scottish Water. Its services include sewer lining and professional engineering services

For more information, please see: www.lanesgroup.com