Businesses and householders need to review the condition of their drainage systems as the extremely dry summer weather increases the risk of flash flooding, warns Kevin Moon, Managing Director of drainage and wastewater specialist Lanes Group plc.
The record heatwave over the last month has left ground baked so hard that rain from thunderstorms forecast for the days leading to the end of August 2022 will not be able to easily soak into the soil.
This means the water will remain on the surface and is likely to build up through surface water run-off, creating localised floods.
Water that would, in normal conditions, percolate into the ground will also surge into surface water drains and sewers that might not be able to cope with the sudden surge, said Kevin Moon.
Urgent drainage review
He added: “This could make flooding risks worse and result in flooding happening in unexpected places. Rainwater could also be combined with sewage, creating a serious hygiene risk as well as property being flooded.
“Businesses should consider these risks as part of an urgent review of their business continuity plans at a time when extreme weather events are likely to put extreme strain on their sewer systems.
“Making sure that site drainage systems are as in a good condition as possible, in terms of being free of debris that can disrupt water flows and reduce capacity and in good repair, should be a priority in situations like this.”
Lanes Group is the UK’s largest drainage and wastewater specialist. It helps thousands of businesses across the UK protect their properties through planned and reactive site drainage cleaning and maintenance services.
The company also delivers sewer unblocking, repair and rehabilitation services for many water companies, including Thames Water, Severn Trent, Northumbrian Water and Scottish Water.
Water main bursts
The dramatic impact on soil that has been baked bone hard has been demonstrated in a simple experiment by Professor Rob Thompson, of Reading University.
He filled three upturned plastic cups with water over normal grass, wet grass, and grass on ground baked hard by the sun.
The water in the cup on the wet grass rapidly soaks into the ground. The water in the cup on the normal summer grass soaks away more slowly. But the level of the water in the cup on the ground hardened by weeks of hot weather barely fell.
Periods of extreme heat and low rainfall, as experienced across the UK in July and August, can create a “perfect storm” of circumstances that can make flooding risks, when the rains return, much worse.
Extremely dry conditions, especially in areas with clay soils, causes the ground to heave, damaging buried pipes.
This has already resulted in an increase in water main bursts, just at a time when drinking water is at its most precious. In some cases, it has resulted in flash flooding.
On Sunday morning, August 14, thousands of homes had water supplies disrupted in the West End area of Southampton after a water main burst, flooding a road and many gardens.
The week before, a wall of water 4ft high flooded a large area in Islington, North London. Two adults and two children had to be rescued, as the flood water created two sink holes and damaged 50 properties.
Mayor of London Sadiq Khan has spoken of his worries about flash flooding in the capital.
He said: “Just over a year ago we saw flash flooding in London that affected people’s homes, businesses, Tube stations. I’m really concerned that we could see extreme hot weather followed by short periods of massive rain.”
Sewer pipe damage
Just like mains water pipes, sewer pipes can also be affected by the movement of clay soils, resulting in pipe joints being displaced, pipes cracking or even collapsing.
Sarah Dodd, Chair of the UK Subsidence Forum, has warned that this effect – clay soils moving as a result of drying out and contracting in summer and becoming wet and expanding again in winter – will intensify and spread across the UK.
She said: “Climate change will result in areas with clay soils further north in the UK being affected by ground movement for the first time, in some cases, and more frequently in all. This has significant implications for the maintenance of structures and underground assets.”
During prolonged periods of dry weather, tree root systems grow more aggressively as they search for water and nutrients, increasing the risk of root infestation of drainage pipes.
This can result in pipes becoming partially or even fully blocked by root mass, an occurrence that may only come to light when the rains return and the blockage results in localised flooding.
During long periods of dry weather, flow rates in sewers are reduced, allowing heavier, solid material and debris washed into the system to build up, compromising its capacity.
Severe disruption
Again, this is only discovered when the rains return and a sewer surcharges, with water coming to the surface, or it backs up into properties, causing an internal sewage flood.
Kevin Moon said: “The continued abuse of combined sewers, with people flushing items like wet wipes and sanitary products down toilets, and disposing of fats, oils and grease down sinks, also has a worse effect at times like this, because the material isn’t flushed through the system by regular rainfall.
“Businesses need to consider all these factors over the coming days and weeks as they review the resilience of their drainage systems in the light of heightened risks of flooding.
“They should also bear in mind that statistics show that most businesses that go through the shock of an extreme flooding event at their property do not survive the experience, even if they are insured. The disruption caused is too severe.”
Drainage resilience review
7 urgent issues to consider when carrying out a site drainage resilience review include:
- Is your property location at particular risk of localised flooding?
- Do you have an accurate and up to date map of your site drainage system and assessments of its condition and capacity? These can only be obtained by a drainage specialist carrying out a full site CCTV drainage survey.
- Is the planned preventative maintenance schedule for the property’s drainage system up to date? Has the drainage system been cleaned in the last 12 months?
- Are you already experiencing any problems with your drainage system? Does water pool on surfaces around your property after it rains? Do sinks drain and toilets flush properly?
- Are water courses around your property in optimum condition? Are storm culverts serving your site regularly inspected and cleaning?
- Has there been any extensive building carried out recently that might affect your site drainage system?
- Do you have emergency preparations in place if a flood occurs? This may include access to an emergency response service from a reputable drainage specialist and plans to protect assets and deliver services from a different location.
