PARTNER CONTENT
What Lies Beneath
Lifting the lid on storm overflows and the UK s sewerage system
Whether you see them as the destroyer of the UK’s waterways or a necessary precaution in an increasingly unpredictable climate, there’s no doubt that storm overflows are a thorny topic. But what exactly are they, why are they used, and how can we reduce their impact on the environment?
nless you’ve been deliberately avoiding recent headlines, you won’t have failed to see or read the troubling news that the UK’s sewerage system is seriously under strain. Increased rainfall as a result of climate change has put the sewers at a growing risk of overflowing, meaning storm overflows are
How do sewerage systems work?
Underground a hidden world of drains and sewers works day and night to transport and treat wastewater from toilets and sinks, showers and baths.
What are storm overflows?
U
being used on a more regular basis.
And where normally, a combination of waste and rainwater flows down drains into a single pipe before heading to sewers to be treated, during storm events, overflows release untreated, diluted wastewater into rivers, lakes and seas. Yes, this does the important job of protecting properties and roads from flooding and prevents sewage from overflowing into our streets and homes. But it also, clearly, has a negative impact on the UK’s water.
So how do we solve this quandary? A fundamental way to address the problem is through collaboration. Water companies, house owners and developers, local communities, regulators and the government must work together to ensure the sewerage system has sufficient capacity to reduce the use of storm overflows and protect the health of our waters.
In order to improve the efficiency of these safety valves, they, of course, need to be monitored. In March, The Environment Agency published “event monitoring duration data” from all 10 water and sewerage companies across the UK, which revealed crucial information on the frequency and duration of storm overflow spills.
This data was collected from 13,323 overflows. A total 91% of all overflows were monitored last year, but to increase the clarity of that overview further, water companies in England will install monitors on all storm overflows by the end of 2023. This is comparatively impressive: very few other countries have this extent of monitoring. In Scotland, for example, less than 4% of overflows are monitored.
The data also revealed that in Wessex Water’s area, discharge numbers had decreased by 45% between 2020 and 2022. This was despite an increase in the number of overflows being monitored, and mainly attributed to lower winter groundwater levels and a long dry summer.
Picture the little drain at the top of your bathtub, which stops water sloshing onto your bathroom floor and leaking into your downstairs neighbours’ bedroom. Storm
When you turn your tap or flush the toilet, water flows down your drain and travels along a network of pipes before arriving at treatment works, where it’s cleaned and returned to rivers. Many of them also take the rain away from your roof in the same pipe.
overflows work in the same way. There are 1,297 of them across the Wessex Water region and they kick into action during storm events, when sewers fill up fast. To avoid the sewers filling up and spilling into streets and homes, storm overflows act as a safety valve and automatically divert dirty water that hasn’t been treated into open waters.
2022
2021
2020
Nr. Monitored Overflows:
Av. Discharge Count Sum:
Discharge Count Av.:
Discharge Hrs Sum:
Discharge Hrs:
% reduction from 2020:
935
31
28,888
255
238,049
-
Nr. Monitored Overflows:
Av. Discharge Count Sum:
Discharge Count Av.:
Discharge Hrs Sum:
Discharge Hrs:
% reduction from 2020:
1,049
23
23,635
144
150,978
37%
Nr. Monitored Overflows:
Av. Discharge Count Sum:
Discharge Count Av.:
Discharge Hrs Sum:
Discharge Hrs:
% reduction from 2020:
1,182
19
21,878
110
129,957
45%
So what else is going on here? It isn’t just storm overflow discharge polluting our waters. Industrial and other human activities, and agricultural run off - water from farm fields that enters rivers because of rain, irrigation or melted snow - can have similarly detrimental impacts on the environment. Run-off often contains pesticides and fertiliser chemicals, which are absorbed by aquatic plants and impact the ability of animals to find food and reproduce.
What impact is this having on the water environment?
The UK government has set itself the target of eliminating 40% of raw sewage overflows into rivers by 2040 as part of its Storm Overflows Discharge Reduction Plan.
It’s generally accepted that getting rid of storm overflows in the UK would be a lengthy, disruptive and wildly expensive undertaking. Roads would have to be dug up, and the entire sewerage network would require replumbing. This would cause disruption to communities and lead to an increase in water bills. For Wessex Water to achieve this it would cost an estimated £12-18 billion.
Instead, water companies are implementing a series of innovative solutions to modernise their sewerage systems. Last year Wessex Water invested £69 million to protect the region’s rivers and beaches. This involved multi-million pound schemes to deal with heavy deluges of rainwater to reduce storm overflows. From 2025, it will triple its investment from £3 million per month to £9 million per month.
Looking to the future
Making storm recycling centres bigger so more storm water can be treated
Building underground tanks to store rainwater for post-storm treatment, preventing immediate untreated discharge.
Create new reedbeds and nature-based solutions to treat overflows from inundated drains
and sewers.
Sealing ageing pipes to prevent groundwater seeping into sewers.
Real-time monitoring to inform locals of overflow operation and water conditions.
This money will be spent on a host of solutions, including:
1
Storm overflows account for
of the reasons why rivers in the area fail to meet good ecological status.
There's no denying the fact that during heavy rainfall, the rivers in places like Wessex Water’s region can be affected by storm overflows. But this isn’t by any means the full picture. Environment Agency data reveals that there are actually 1074 reasons why rivers in the area fail to meet good ecological status. Storm overflows account for a mere nine of them.
Water companies have a key role to play in reducing the number of storm overflows and their impact on the environment - but they can’t solve the problem on their own.
A new law will come into force next year ensuring that housing developers use sustainable drainage solutions on their new properties.
These will minimise the amount of water that runs off rooftops and driveways and into the sewerage system.
Wessex Water has been working with its customers and communities to help them separate the rainwater before it enters the sewers.
In it together
Working with local homeowners, churches and community organisations, Wessex Water’s Rainsavers programme helps find solutions to rainwater in the sewerage system problem.
Each household is assessed for suitable solutions – from rain gardens to soakaways – and provided with one or more water butts and a soaker hose system, where possible. Not only does a water butt divert rainwater from the sewer, it also encourages water efficiency in the garden.
Wessex Water Project Rainsaver
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Project Director: Tom Warner | Editor: George Clode | Senior Designer: Zimi Peche
Produced by Independent Ignite
PARTNER CONTENT
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storm overflows across the Wessex Water region
1,297
Wessex Water region
45%
discharges decreased by
between 2020 and 2022
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