Why it keeps happening
Three things we can measure in the data. None of them proves a cause on its own, but each points at a different kind of infrastructure problem.
A discharge in dry weather is not an exceptional circumstance, so it is not permitted on any reading of regulation 4.
See the 0 →A strong signal, not a finding. We cannot see whether flow is transferred to another works for treatment, and the permitted figure is not always published.
See the 4 →Rainfall across the catchment does not explain a discharge that an overflow's own treatment works did not share.
See the 0 →Where the indicators concentrate
| Overflow | Hours | Dry | What it points to | Verdict |
|---|
Hours are the last full year; dry spills are since 2020. Verdict is whether a measure is linked to the overflow — see the gaps.
What this analysis cannot see
These indicators are measured from spill timing and rainfall alone. They cannot see misconnections, the quality of effluent from a works that is running normally, flow transferred between works for treatment, a company's maintenance history, or the periods when a monitor was offline. Because a quiet monitor records nothing, every count here is a floor, not a total.