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Businesses and householders need to urgently 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 summer heatwave has left ground baked so hard rainwater cannot soak away and is likely to rapidly build up through surface water run-off to cause localised flooding, with logistics and retail parks, factory sites, and schools often most at risk.
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 Moon.
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 is urging businesses to consider 7 urgent issues when carrying out a site drainage resilience review:
- 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.
Periods of extreme heat and low rainfall, as experienced across the UK in July and August 2022, can create a “perfect storm” of circumstances that can make flooding risks 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.
Just like mains water pipes, sewer pipes can also be affected by the seasonal contraction and expansion of clay soils, resulting in pipe joints being displaced, pipes cracking or even collapsing.
Climate change will result in areas with clay soils further north in the UK being affected by this type of ground movement for the first time. 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.
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.
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.”
