This Event Duration Monitoring (EDM) dataset relates to the performance of storm overflows in England. Water and Sewerage Companies (WaSC) submit this data to the Environment Agency each year as part of the Bathing Season Return, in order to fulfil their permitted conditions to discharge from these storm overflows under the Environmental Permitting Regulations.
Data files are provided by year and, where applicable, include a separate sheet for each WaSC with storm overflows in England. Each WaSC sheet shows how often and for how long each monitored storm overflow discharged during the EDM Bathing Season (1 May – 30 September). The dataset also explains why EDM may have provided information for less than 90% of the relevant return period, and why an overflow may have high spill counts during that time. These datasets reflect the best information available to the WaSC at the time of submission.
The datasets from 2023 onwards also include key summary data tables. These summary tables provide information such as the number of storm overflows with EDM, the number returning spill counts, and the average spill duration and average spill count for each WaSC.
A dataset README guide is also provided from the 2025 dataset onwards, offering further information to help users understand and interpret the data. Attribution statement: © Environment Agency copyright and/or database right 2025. All rights reserved.