Phillip Clisham explains why sewage is ending up in UK seas.
The topic of sewage discharges onto UK beaches and rivers has attracted a lot of attention lately.
While it’s fair to say that the views expressed by the press, public and our politicians is universally negative, it’s important to make sure that there’s understanding also, so we can find a solution to the problem.
Did you know...
The sewerage system is by far the biggest of the water and sewerage companies' asset sets, including 546,000km of drains and sewers – enough to wrap around the Earth 13 times.
What are storm overflows?
Until well into the second half of the 20th century, it was standard practice in the UK and most of the developed world to provide ‘combined sewers’.
Combined sewers carry dirty water from toilets, sinks and showers, and rainwater (surface water), combining both into a single pipe.
When it rains very heavily, the volume of rainwater can become too great for the pipes and some sort of overflow arrangement is needed to ensure that properties aren’t flooded.
There are approximately 15,000 storm overflows in England discharging to inland rivers, estuaries, the sea, and other water bodies.
Many of these have been in operation since the first sewers were built over 150 years ago.
Across Europe, there are 650,000 storm overflows.
As such, storm overflows aren’t new and exist in all developed countries.
Are storm overflows a problem?
While the effluent (liquid waste or sewage) that’s discharged from storm overflows should be mainly rainwater, there will still be a quantity of untreated sewage.
This can affect the health of rivers as the discharges can introduce ammonia and reduce the levels of dissolved oxygen in the rivers.
Storm discharges can also contain high levels of bacteria, which can cause harm to public health.
These discharges can also have a ‘social impact’ as the effect of seeing untreated flows from sewers being discharged into rivers causes concern.
If the storm overflow spills too often or discharges to a sensitive location, then the overflow can cause harm.
What factors influence storm overflow discharges?
In recent years, discharges from storm overflows have increased in many areas.
In some locations this is due to increased population and ‘urban creep’.
What is urban creep?
Urban creep describes the impact of issues such as gardens being paved over to provide space to park cars or the addition of conservatories and patios in gardens that were previously grass, resulting in more rainwater passing into the combined sewers rather than soaking into the ground.
Changing weather patterns are bringing more intense storms and droughts which are also harmful to rivers and lakes.
In other areas, aging sewers allow more infiltration (groundwater) to enter the pipes, increasing the flows within them and causing them to spill more frequently.
These trends are likely to continue unless more is done to reduce the problem.
Recognising the issue, the water companies and their regulators agreed to install event monitors in sewer overflows so the frequency of operation could be accurately recorded, and trends and impacts studied.
The installation of monitoring equipment is a work in progress and is set to be completed by 2025.
What can be done?
While there are a variety of things that can be done to reduce the problem, the main solutions include storing the sewage in huge underground tanks, rather than discharging to the environment.
However, there are limits to how much can be stored within a catchment before other problems are created.
Another approach is to separate the surface water and the sewage at source, but this is difficult in congested urban areas and can become very expensive.
What is the Storm Overflow Evidence Project?
A government-led storm overflow taskforce, including water regulator Ofwat, the Environment Agency, water companies, Consumer Council for Water, and other environmental groups was established.
The taskforce commissioned Stantec to explore policy options for reducing storm overflow spills and the harm that’s caused.
Stantec issued its report, the Storm Overflow Evidence Project. A range of options were considered, and costs and benefits assessed.
The report concluded that eliminating storm overflows would cost between £350 billion and £600 billion, resulting in an increase in household bills of between £569 and £999 per year.
A whole range of options which involved retaining storm overflows but reducing the spill frequency were also evaluated and presented.
What are the major challenges?
The UK water industry is facing a series of major and often conflicting challenges over the next 30 years.
The sector must find ways to reach net-zero carbon to mitigate the effects of climate change. All while keeping the taps on, helping to improve river quality and reducing flooding in the face of changing weather patterns.
At the same time, the population of the UK is set to grow, particularly in areas that will have less water as a result of climate change.
Key challenges include:
- Reducing leakage by 50% by 2050.
- The UK will need to be able to move large quantities of water between regions to supply water to regions which are water stressed.
- More reservoirs will need to be built to store water for the first time in 40 years (and other water sources considered).
- The impact of discharges from the sewerage system is likely to increase as the population grows and climate changes drives the need to separate foul and surface water.
- We must find ways to achieve cleaner rivers, and supply water over greater distances while consuming much less energy.
What solutions are available?
Engineers are trialling nature-based solutions and examining how clean, healthy rivers can be achieved by considering the catchment as a whole.
Gas, electricity and other products are being produced from sewage sludges to provide green energy to homes and create useful products from waste.
If we all work together, there’s the potential to overcome these challenges in a way that doesn’t harm the planet.
Policymakers must be very careful as we find a route to the cleaner, greener future that’s needed.
As such, it’s important that the storm overflow issue is debated based on sound principles and an understanding of the implications of the decisions made, rather than being driven by the press and populist policies.
It’s vital that all parties collaborate to find the solutions which are right for the UK.
The public is rightly concerned, but some of the emotion and finger-pointing needs to be stripped out of the debate.
The industry cannot afford to carry the burden of a huge unnecessary programme of construction works.
What steps have been taken?
On 26 August 2022, the UK government published its storm overflows discharge reduction plan which commits the water companies to spending £56Billion between 2025 and 2050.
This is in addition to the work that has already been committed to, which is on-going. By 2025, water companies will have reduced overflow discharge from 2020 levels by 25%.
The civil engineering profession must now help to ensure that the investment of £2Billion/year delivers the improvements to the rivers and waterways intended.
Over time I would hope that we can work together to engineer clever, efficient and environmentally friendly solutions.
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