Information about monitors
We use event duration monitoring (EDM) to record storm discharge activity. EDM monitors indicate when and where a storm discharge is happening. We use this data on our storm discharge map.
Here are some of the frequently asked questions we get about EDM monitors and our map. If your question isn't answered here, contact us.
Why are some monitors showing as offline?
We'll take a monitor offline to investigate if:
- It stops communicating with our systems
- We believe the monitor is producing inaccurate data
- We identify an issue with the device
We apologise for any missing information and aim to get offline monitors working again as soon as we can. This may take some time if the installation location is difficult to get to, for example, in manholes on busy roads.
Monitors may also be offline if significant investment works is taking place on-site. For example, upgrading one of our sewage treatment works, or a more complex solution to rectify tidal influence on the monitors.
How accurate are the monitors?
The data received from our EDM monitors isn’t always accurate. It doesn’t confirm discharges, it only indicates them.
EDM data on the website is unvalidated. It's sometimes driven by interference with the monitor or monitor communication issues. These issues take time for us to investigate and update the map.
Do offline monitors record any information?
Some offline monitors do still record storm discharge activity but the data isn't reliable. Whilst a monitor is offline, we won't display any further details about it. The monitor could be broken and unable to record active discharges. Or, it could falsely indicate active discharges when there aren't any. We take the monitor offline to investigate exactly what's happened.
We apologise for any missing information and aim to get offline monitors working again as soon as we can.
Why is there no record of any previous discharges at this location on the map?
The storm overflow may not have discharged since this location was added to the map.
Occasionally our OpenData platform doesn't hold records of the most recent discharge. This could be due to an EDM device reconfiguration, replacement or new installation. We join these data sets for our annual return, but sometimes can't correctly show these on our map. The live data is correct, and once a discharge has occurred since the re-configuration this will be stored as the last discharge time and duration.
Historic information for the majority of our EDM monitors is available for the previous year. You can access our annual storm overflow activity reports showing you data from previous years. This is updated by mid-March with data from the previous calendar year. If the monitor you’re looking for doesn’t feature in this report, it would not have been installed during that period. The report does show a date of installation.
Why is your map 'near real time' and not 'real time'?
We make the data available as soon as currently possible. Any delays are due to sensor, communication and system limitations.
The data has to flow through different systems before it's published on the website:
- EDM monitors take measurements every 15 minutes. If two consecutive readings show that the water levels are too high, it triggers an alert.
- We use cloud-based data storage to save every alert. This runs an automatic check for new alerts every 30 minutes.
- New alerts are then sent to our mapping software using an API integration. This updates our storm discharge map every 10 minutes with the latest alerts.
This means data is usually available within an hour of a discharge starting. If there are communication issues, the data is safely stored until connection is re-established. In these instances, data is available later than usual. In rural settings, we rely on mobile phone technology to send the data.
Why is the information on your map different to the data in your annual report?
Our annual EDM report to the EA uses the 12/24 counted spills method. We also supply full start/stop times as part of information requests.
Within the annual report, one or more overflow events within a period of 12 hours or less will be considered to be one spill. One or more overflow events over a period of between 12 and 36 hours will be considered to be two spills. Each subsequent 24 hour duration counts as one additional spill and the whole of the 24 hour block is included.
Find more information on how the Environment Agency regulates storm overflows.
Some of our discharge locations have more than one discharge point with an EDM fitted. In the 2022 annual EDM report, we listed these individually rather than together. To keep the map simple, we're combining them as one 'pin' on the map. This is because the discharge points are so close together, they impact the same location. If any of the EDMs indicate a discharge, the pin will go red. It will only go green once all the discharge points at that location have stopped discharging for over 48 hours.
In 2022, the annual report also included additional combined sewer overflows (CSOs). There are ongoing investigations to establish if monitoring is required at these new locations. Where monitoring is required, we'll fit EDMs and add locations to the map.
To find out more about changes within our annual report, read the EDM annual return guide.
Why do some of the pins overlap on the map?
The pins on our map show discharge locations. In some cases, different storm overflows use the same discharge location. This means that their pins overlap on the map. This currently affects five of our locations.
We order pins so that the most important information is visible on top. Monitors showing active storm discharge have priority. They're followed by monitors that indicate a discharge within the last 48 hours, and so on. You can see all information for the location by using the arrows in the bottom right corner of the status pop-up.
Why isn't my local pumping station showing on the map?
We've installed monitors at our storm overflows which are currently in use. These sites are agreed with the Environment Agency.
There will be some locations where sewage escapes due to a breakdown, power failure or blockage. These locations include manholes and pumping stations, which are not monitored. We'll be adding more locations to our list as EDM monitors are installed.
Contact us to let us know about an overflowing pumping station.
Why doesn't my local treatment works appear on your map?
Some of our sewage treatment works are designed to treat all the flow which arrives at the site. These don't have the ability to discharge storm sewage but are permitted to discharge treated sewage. Some of our smaller treatment works discharge flow to ground (similar to a septic tank), not into rivers.
These sites don't have any storm discharge to be monitored so aren't shown on the map. We'll be adding more locations to our list as EDM monitors are installed.
Why isn't the monitor on the watercourse itself?
EDM monitors are normally located at the point of the overflow, rather than the point the discharge enters the watercourse. There will be a pipe that connects the overflow to the discharge point on the watercourse.