dataset · England
Event Duration Monitoring - Storm Overflows - Annual Returns
This Event Duration Monitoring (EDM) dataset relates to the performance of storm overflows in England. Data are provided by Water and Sewerage Companies (WaSCs) to the Environment Agency each year as part of their regulatory Annual Return, to fulfil their permitted conditions to discharge from these storm overflows under the Environmental Permitting Regulations. Data files are provided by year (2025, 2024, 2023, 2022, 2021 & 2020) and include a sheet for each of the 10 WaSCs with storm overflows
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Licence: ["There are no public access constraints to this data. Use of this data is subject to the licence identified.", "There are no public access constraints to this data. Use of this data is subject to the
Evidence quality: 47.7
Listed in data.gov.uk public catalogue API on 2026-10-16; relevance/value screened (haiku).
Metadata checked: 2026-10-14T13:20:00.000Z
What's in it
- Data offered docs-verified
- storm overflow spill frequency (how often each monitored overflow discharged) · storm overflow spill duration (how long each monitored overflow discharged) · number of storm overflows with EDM · number of storm overflows returning spill counts · average spill duration and average spill count per WaSC · EDM operability reasons (from 2021 onwards) · long-term spill trends 2016-2025
- Coverage docs-verified
- England · 2020-2025 annual returns; long-term trends 2016-2025
- Resolution llm-inferred
- Per monitored storm overflow, grouped by WaSC sheet; annual
- Update frequency docs-verified
- Annually
- Formats docs-verified
- ZIP
- Access docs-verified
- Free and open; no public access constraints; Open Government Licence v3.0; no API or auth
Useful for
- Use cases llm-inferred
- Baseline storm overflow spill frequency and duration for a catchment in a drainage or water-quality assessment · Benchmarking a WaSC's spill performance for a discharge-compliance or permit review · Long-term (2016-2025) spill trend context for an environmental impact or water-quality assessment
- Audience llm-inferred
- water quality consultants · drainage engineers · environmental consultants · hydrologists · planners
Limitations
- Constraints docs-verified
- England only, covering the 10 WaSCs with storm overflows · Annual returns only; updated once a year · Data as submitted by WaSCs, reflecting the best available information at time of submission · Revised 2025 figures (Anglian Water, Northumbrian Water): LTA and EDM Operability may not align with revised spill figures · Reasons for EDM coverage below 90% are included only from 2021 onwards
Evidence
- https://environment.data.gov.uk/api/file/download?fileDataSetId=c55e170e-3c75-49a5-8026-a961ff94c8e0&fileName=EDM Storm Overflow Annual Return - Long-term Trends.zip
- https://www.data.gov.uk/dataset/19f6064d-7356-466f-844e-d20ea10ae9fd/event-duration-monitoring-storm-overflows-annual-returns
Check upstream coverage, uncertainty and licence before use. Station observations are not forecasts or design levels.