Clean Rivers and Seas Plan

The government’s Storm Overflows Discharge Reduction Plan was published in August 2022 and sets clear and specific targets for water companies, regulators and the government to work towards the long-term ambition of eliminating harm from storm overflows. Water companies will be required to meet the targets set out in the plan, and the government expects our regulators – Ofwat and the Environment Agency (EA) – to support and challenge water companies to meet these targets.

The key targets are:

• By 2035, water companies will have improved all overflows discharging into or near every designated bathing water, and improved 75% of overflows discharging to high-priority sites.
• By 2050, no storm overflows will be permitted to operate outside of unusually heavy rainfall or to cause any adverse ecological harm.
• Water companies will only be permitted to discharge from a storm overflow where they can show that there is no local adverse ecological impact.
• Water companies must significantly reduce harmful pathogens, such as bacteria, from storm overflows discharging into and near designated bathing waters, by disinfection or reducing the frequency of discharges to meet EA spill standards by 2035.
• Storm overflows will not be permitted to discharge above an average of 10 rainfall events per year by 2050.
• Water companies will be required to ensure all storm overflows have screening controls.

Water companies will also be expected to adhere to a number of principals when achieving these targets, including complying with set regulations, planning for the future, driving better solutions and better management of rainwater. The ultimate purpose of the plan, its targets and its principals is to ensure the necessary steps are taken to reduce storm overflows by 2050.

Our plan may need to be adjusted following:

1. Government recommendation: Defra and the EA provide water companies with feedback on their plans. We may make improvements or amendments following any target changes or recommendations.
2. Customer and stakeholder feedback: We’re always mindful of any impact to our customers and their bills, so we regularly ask for feedback from customers and stakeholders about the work we’ve planned.
3. New data and technology: We’ve introduced new monitoring equipment at scale alongside artificial intelligence (AI) and other new technology. These technologies will help us to future-proof our solutions and gather valuable new data. The more we learn, the more we can improve and refine our plan to make sure we are always delivering the most effective and efficient interventions.
4. Speed of delivery: We balance several factors when calculating the appropriate speed of delivery. This includes available supply chain options, the cost of delivering schemes and the potential impact on customer bills, partnership working agreements and time-sensitive regulatory targets.
5. Changes to the government plan: Under the Environment Act 2021, the government must produce a report every five years (to match the five-year programming periods called ‘AMPs’ that we work in as a water company) detailing the implementation of the plan and the effect of any progress.

The government will use their findings to establish if companies can go further and faster to achieve the storm overflow targets set out for them, without having a disproportionate impact on customer bills.

We are not starting from scratch. We're building on the progress we have made since privatisation, where £10 billion has been spent to increase the volume of wastewater that is fully treated before being released back into the environment (previously only approximately 50% treated to around 95% today). This has helped improve the quality of our bathing waters from only 28% meeting public health standards pre-privatisation, to 84% now rated as ‘good’ or ‘excellent’.  

To support this, our shareholders have invested £1.6 billion into the company in recent years, to enable us to deliver a significant programme of improvement, especially around solving storm overflows sustainably and for the long term.  

We created our interactive map so our customers can easily see storm overflow improvement projects in their area. The map shows active and planned projects, complete with an at-a-glance overview of all the relevant details including:

• the main cause of releases activating from the storm overflow
• average annual releases (2020/21 data) from the storm overflow
• estimated investment required to complete the proposed improvements
• if the storm overflow releases into a site of interest such as shellfish waters and bathing waters
• when we aim to begin the work
• what solutions we’re proposing to reduce the storm overflow.

The map shows our dedication to transparency and keeping our customers and stakeholders informed about our plans and our progress.

The plan is split into five-year Asset Management Periods (AMPs).

Purple pins indicate projects we’re planning to complete in the Asset Management Period (AMP) between 2025-2030. Blue pins indicate projects we’ll be undertaking after 2030. Green pins indicate storm overflows where work is currently not in scope as they’re already achieving the government's target (the overflow is not activating greater than 10 times per year on average).

We’ve prioritised overflows by targets set by our regulators and in the Storm Overflows Discharge Reduction Plan to first reduce the impact on shellfish waters, environmentally sensitive sites and bathing waters.

However, we want to work with our communities to get this right, so we’ll be gathering feedback from our customers to understand if the plan is going at the right speed and focusing on the right areas.

We have what’s called Event Duration Monitors (EDMs) on our storm overflows. These EDMs detect when there’s a release and measure the duration of it, giving us instant updates and much greater accuracy when determining which storm overflows are releasing and how often.

We used EDM data from 2020 and 2021 to determine the average number of releases from each individual storm overflow. We also use EDM data to log all releases on our near real-time storm overflow monitoring service, Rivers and Seas Watch.

We analysed the data from our EDMs by comparing it with historical rainfall data, river levels and groundwater levels to understand the primary cause of releases from each storm overflow.

We then categorised the main cause of releases into:

1. those caused primarily by too much rainfall getting into the network
2. those caused primarily by groundwater getting into public and private sewers
3. those with multiple primary causes.

We have estimated the cost for each storm overflow by determining the size and type of solutions required and the primary cause for that overflow releasing. These decisions have been informed by what we’ve learned in our Pathfinder Projects, which aim to test a variety of different solutions to ensure our programme is effective and efficient in our next financial programming period (often referred to as AMP 8).

Example 1 - for an overflow with a primary root cause of too much rainwater (surface water run-off). We estimate the size of the non-permeable area (hardstanding) to be managed, the range of solutions required to manage it, and whether a storage component is required. Once we’ve done this, we use standard cost coefficient/curves to determine cost.

Example 2 - for an overflow with a primary root cause of groundwater (infiltration). We estimate the size of the necessary wetland treatment step, alongside an estimate for the total relining/sealing of private and public sewers in the area. Once we’ve done this, we use standard cost coefficient/curves to determine cost.

Example 3 - for an overflow where the primary cause is complex (there are multiple potential causes). We’ve estimated the cost of the solution using storage as the only intervention. However, it’s likely that once detailed area investigations start, a combination of green (SuDS) and grey solutions may be delivered.

Many of our solutions rely on SuDS (Sustainable Drainage Systems) to allow more sustainable and effective drainage of rainwater and surface water, so it doesn’t just flow into the sewer system.

There are many types of SuDS. Here are a few that we’re either currently using or planning to roll out as part of our mission to ‘slow the flow’:

• Slow-drain water butts: Like a regular water butt, slow-drain water butts collect rainwater run-off from roofs and store it to be used by the homeowner. However, they also feature a small drainage pipe installed halfway down, so the bottom half of the water is saved, and the top half drains out slowly at a pace which doesn’t contribute to the system being overwhelmed.
  
• Raingarden planters: Raingarden planters are planter boxes that sit underneath your gutters to slow the flow of water coming out of them and prevent it from overwhelming the sewer system. Excess rainwater flows from the gutter into the planter and is soaked up by the soil and plants within.
• Raingardens: Similar to raingarden planters, raingardens use the water that would normally flow from your gutter system into the drain, but instead of redirecting it to a raised planter, it is redirected to a specially planted area.
• Soakaways: A soakaway is an innovative way to increase drainage, that’s invisible due to being hidden underground. Their construction involves digging a hole in the ground and stacking crates or other material within it. The crates have spaces inside them which give large volumes of water sufficient surface area to seep back into the ground.
• Permeable paving: An alternative to concrete and brick, permeable paving offers much better drainage and can be used in car parks, driveways, playgrounds and more. With permeable paving, the rainwater drains rather than leaving pools of water, as happens on concreted areas. As well as preventing  pooling and flooding, it helps to control excess storm, surface and groundwater.

Where there is groundwater infiltration into the sewer, we’re proposing to construct wetlands alongside the relining of public and private (customer pipes) sewer sealing.

A constructed wetland can be used in various parts of the wastewater treatment process. They form part of a natural landscape and support biodiversity, making them preferable to traditional grey solutions such as storm tanks. Where storm tanks simply hold excess water, wetlands absorb, hold and treat the water, as well as slowly releasing it back into the environment.

Unfortunately, there is no fast and simple solution. If we stopped storm overflow releases tomorrow, the excess water would have nowhere to go and as a result would overflow onto the streets and come back up the pipes into houses and businesses.

Much of the UK sewer system we still use today is a combined sewer system. Increases in ‘urban creep’ (such as paving over green spaces) and an increase of extreme weather events adds pressure to this existing infrastructure.

Separating the combined sewer system isn’t feasible. It would cost up to £600 billion and take several decades to do this, during which time there would be consistent and significant disruption.

Building enough tanks to cope with all the excess water would cost up to £240 billion, and we believe building bigger or additional infrastructure should only be considered when other long-term solutions have been exhausted.

So instead, we’re focusing on;

• Controlling the source of the excess water: Shifting to sustainable and nature-based solutions such as regreening – or restoring land, constructing wetlands, and installing sustainable drainage systems to slow the flow of water into the system. This is the most effective way to reduce storm overflows; by redirecting or slowing the flow of water into the sewer.

• Optimising existing infrastructure: Correcting misconnections, controlling the network in a more dynamic way, and using artificial intelligence and monitoring technology to anticipate and act on problems before they cause disruption.

• Partnerships: We can’t do this alone. A lot of the network is privately owned, so we need local authorities, businesses, and our customers to work with us to allow us to put these solutions in place. We’re also working hard to educate our customers and the whole supply chain on what they can do to help slow the flow, and ultimately reduce storm overflows.

We’ve entered our delivery and testing phase after careful planning, surveying and initial pilot work for our Pathfinder Projects. These projects allow us to trial various solutions in a small area to determine the best solution for the wider area.

The next two years are critical for the future of the water sector. What we learn during this time will shape not our direction, but the direction of the entire industry when it comes to using sustainable drainage systems and optimising resources.

Once we know which interventions are the most effective in certain circumstances, we can roll these out on a larger scale, and our progress will accelerate dramatically with immediate and noticeable results.

We know people are looking to us for instant solutions, but it takes time to plan, test and deliver these projects. However, with careful planning and trialling, there are many mutual benefits including;

• funding and resources are reserved for solutions we are certain will work
• reduced environmental impact
• wider benefits from delivering green solutions such as increased biodiversity, carbon reduction and
  increased amenity value of the site
• reduced cost to our customers, partners and stakeholders
• faster and more effective overall results

If you have any feedback on the functionality of the map or to report an error with the page, please let us
know by emailing cso.maps@southernwater.co.uk.