Meeting our targets
Our Storm Overflow Action Plan (SOAP) sets out our plans to ensure every storm overflow we’re responsible for meets the targets set out in the Government’s Storm Overflows Discharge Reduction Plan (SODRP). Through discussions with the Government, Defra, the Environment Agency, Ofwat, and other key stakeholders we’ve developed our plan and we’ll refresh this as we deliver the required improvements.
Once our more detailed Storm Overflow Action Plan is ready, it will be published here alongside a live map of all of our overflows and how they are performing. We hope this will be in the coming months.
We’ve already started to improve the impact storm overflows have on the environment through our Get River Positive commitments which you can read more about here.
We’re working hard on our current £384m programme of capital investment supporting spill reduction, as well as moving faster with predictive technologies as part of our additional £41m invested in new Artificial Intelligence (AI) capabilities, and improved the operability of our EDMs
Our next steps
We recognise there is still much to do, and over the coming years, we will be investing in significant upgrades to improve overflow performance to ensure we do not cause harm to the rivers and watercourses across our region. As our programme develops and evolves, we will update the detail in our action plans on an annual basis as we believe transparency and accountability are important.
Periods of significant rainfall are likely to become less exceptional and more typical in the future and our plan sets out how we’re further accelerating improvement activities so that we can respond to this.
We take the delivery of our storm overflow commitments incredibly seriously and know we need to be as open as possible about this, so we will provide an annual update on progress. We believe this level of public transparency and accountability is important to demonstrate progress against what is likely to be a very challenging investment programme.
The improvements we need to deliver are forecast to cost in the region of £4.4 billion between now and 2050. We are on track to spend over £384million on improvements through current investment plans while our proposed AMP8 plan is looking to spend around £1.1 billion on storm overflow improvements alone.
Storm Overflows
We have 2,428 operational storm overflows across the Severn Trent region – more than any other water company. These are made up of a mix of overflows on the sewer network (often referred to as combined sewer overflows, or CSOs) and those located within our wastewater treatment works (known as settled storm overflows, or SSOs).
Historically, many sewerage systems were built with a single piped network which collected wastewater from inside homes and businesses, as well as rainwater from roads, roofs, and other hardstanding areas. Draining rainwater into sewers helped flush the pipes during storms to keep them flowing clear and helping reduce odours. In more recent years, sewerage systems have been designed with separate wastewater and storm sewers, but we are left with the legacy of tens of thousands of kilometers of combined sewerage systems.
To mitigate the risk of sewer capacity being overwhelmed by excessive rainwater, storm overflows were incorporated into the design to act as a relief point, allowing diluted flows to be discharged into rivers and watercourses.
These safety valves help prevent customers’ homes and businesses from being flooded. Each overflow is allowed by the Environment Agency, with the terms of their permits set to ensure activations do not have a detrimental environmental impact on the receiving watercourse.
Most overflows have in-built storage to delay their activation to give time for flow in the receiving watercourse to increase, so further improving dilution and reducing any potential for environmental impact. All of that said, we recognise that the use of storm overflows is no longer considered acceptable and so we have been working with our regulators and government to reduce the use of them.
It is important to realise that all overflows operate within the terms of their permits and, since 2005, we have made significant improvements in our performance by installing monitors and responding effectively to the data we receive from them.
These monitors are installed in sewer pipes to give early warning of flow levels building up, which can indicate potential blockages that need to be cleared. To improve the data we receive, we completed our comprehensive EDM (Event Duration Monitoring) programme to install monitors on every one of our storm overflows at the end of last year.
This EDM information (which sends data every 15 minutes), tells us when overflows have been activated and the duration of their operation. Every year this data is reported to the Environment Agency after it has been checked and scrutinised by external auditors.
You can see our latest EDM data here.
By their very nature, storm overflows are designed to activate only during periods of heavy rainfall. This can occur during summer months when torrential rainfall from thunderstorms overwhelms the capacity of our combined pipes, or in winter, when prolonged rainfall over many days can also fill combined pipes.
As rainfall also causes increased flows in receiving watercourses, this provides further dilution to storm activations which are already heavily diluted with rainwater.
All our storm overflows have EDMs installed which report the number of times our storm overflows activate, when they are activating, and for how long each overflow discharged. How we monitor and report overflow performance is strictly set out by the Environment Agency, and every year all water and sewerage companies are required to formally submit this information to them. As storm overflow activations are inherently linked to weather patterns across each year, this inevitably results in variations in EDM data from company to company and year to year.
In addition to our EDMs, we also have thousands of early warning monitors fitted across our sewer network which continually analyse changes in depth and/or flow in the sewer so we can identify potential problems as they are forming, allowing us to react before a problem occurs. The information from these monitors is tracked by our Control Centre and allows our operational teams to react proactively to any potential issues.
This has helped us significantly reduce pollution incidents from our storm overflows, as well as reducing the risk of blockages across our network. We are proud to have delivered our pollution targets set by our regulators for each one of the last eight years.
Storm overflows are designed to minimise their impact on the environment by only activating once flows in the sewers get too high. By delaying activation, this gives time for flows in the sewer to become more diluted with rainwater.
This also allows time for flows in the receiving watercourse to react to rainfall run-off from surface water drainage and fields to provide further dilution. These factors were all considered whenever the Environment Agency granted a permit, so as to ensure that there is limited/no environmental damage.