How do we monitor our storm overflows?
Over the past few years, we’ve been installing monitors on our overflows to help us gain a better understanding of our network and any impact the overflows might be having on the environment. Here in Yorkshire, 100% of our overflows are now monitored.
There are two ways you can view data on our storm overflows
- Our interactive map that shows in near real-time whether our storm overflows are operating
- Our annual storm overflow data which is published on this page.
Our EDM annual report
We share our EDM data with the Environment Agency annually and the 2023 returns are also published here to ensure customers have all the information they need about storm overflows.
For 2023, we are publishing our Environment Act Storm Overflow Report which includes our annual EDM return data. To go beyond this, we have also included some additional data about whether the asset is a discharge that is permitted by the EA, the grid reference of the discharge and the waterbody that it discharges into. We have also included details of the investigations and improvement schemes we have undertaken as part of the Water Industry National Environment Programme (WINEP).
You can also have a read through the reports we’ve published in previous years as well as seeing our interactive map of the 2023 data.
Environment Act Storm Overflow Report 2023
.xlsx download
Environment Act Storm Overflow Report 2022
.xlsx download
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Environment Act Storm Overflow Report 2021
.xlsx download
Bathing Water Regulatory Annual Return 2022
.xlsx download
Bathing Water Regulatory Annual Return 2021
.xlsx download
How is the data pulled together and validated?
We’ve collected over 150 million data points during 2023 and spent time validating the data to make sure it is as accurate as possible. We do have some data quality issues which we are investigating such as where data is missing, negative or flatlining.
We have investigated over 650 overflows which discharge the most to understand if the data is representative of performance, with resolution activity and further investigations ongoing.
If there’s been an issue with the monitor, such as a failure or an environmental factor that’s caused a false reading, we’ve flagged the data and manually corrected it. We have a full audit trail for all corrected data.
Our 2023 data – a summary
|
|
2019 |
2020 |
2021 |
2022 |
2023 |
|---|---|---|---|---|---|
|
Average rainfall (over the year, regionally) |
1028mm |
1078mm |
989mm |
915mm |
1193mm |
|
Days >6mm rainfall |
51 |
64 |
51 |
50 |
71 |
|
|
2019 |
2020 |
2021 |
2022 |
2023 |
|---|---|---|---|---|---|
|
Number of storm overflows (with data) |
697 |
2105 |
2087 |
2118 |
2190 |
|
Total number of discharges |
22,821 |
65,083 |
70,062 |
54,273 |
77,761 |
|
Total duration of discharges (hours) |
107,836* |
420,419 |
406,131 |
232,054 |
516,386 |
* 2019 duration corrected following Annual Return submission.
|
|
2019 |
2020 |
2021 |
2022 |
2023 |
|---|---|---|---|---|---|
|
Average number of discharges for an overflow |
33 |
30 |
33.6 |
25.6 |
35.9 |
|
Average duration of discharge (hrs) |
5 |
6 |
5.8 |
4.3 |
6.6 |
We experienced a very wet 2023, with the highest level of rainfall since 2013 and the second half of the year was one of the wettest on record. We had 11 named storms in the region as well as a very wet summer and prolonged heavy rainfall towards the end of the year which meant groundwater levels were elevated and there was infiltration into our sewer network. All this rainfall ultimately means that our storm overflows discharged more this year than we would’ve liked. Overflows operate during prolonged or heavy rainfall and the multiple storms in close succession lead to an increase in discharges as excess flows held in storm tanks can’t be treated before the next rainfall event.
We’ve been working really hard to reduce discharges from our storm overflows. Our modelling indicates investment in our network and changes to our operations since 2021 equate to an improvement of 12,980 discharges when normalised against rainfall – so we know we’re heading in the right direction but there’s more to do. All of our storm overflows are now monitored, and we’re making headway with our £180million programme to reduce discharges from some of the most frequently operating overflows. This work is due to finish by April 2025, and then we’ll be working on our exciting programme of work between 2025 and 2030 to reduce discharges even further.
What we’re doing to improve
We are seeing a combination of factors, from urbanisation to climate change, frequently testing the design and capacity of our network. At the same time, increased awareness of the operation of storm overflows is driving an important debate on what society sees as acceptable. We’re committed to going above and beyond the DEFRA Storm Overflow Taskforce activity in ending pollution from storm overflows.
In Yorkshire, we have 2,190 overflows and we know replumbing the whole of Yorkshire is an enormous task that would be both disruptive and costly to customers, and we need to ensure water bills remain affordable, but we are committed to playing our part to improve Yorkshire’s rivers and coastline.
To help drive improvements, with support from our shareholders, we’ve started a £180million investment programme to reduce discharges from the overflows we know are operating more frequently.
Storm overflows are a priority for us and the programme will be looking at four ways of reducing overflows - creating storage in the system for the stormwater, separating surface water out, stopping infiltration, or making changes to other assets like our pumping stations so we’re passing forward the right flows.
Separating surface water out could include creating SUDs, so we’re slowing the flow of water. We’re also looking at water butts so we can disconnect drainpipes from roofs and store the water for watering gardens instead of it going into our sewer system.
All of the work we’re undertaking will take us beyond the government’s storm overflow reduction plan and we’re already planning our largest ever environmental investment programme between 2025 and 2030.