Extreme Weather & Wastewater: Managing the Surge Without Losing the Signal

The UK is dealing with Storm Goretti—a rare “weather bomb” bringing severe winds, heavy rain and snow, and widespread disruption (including red/amber warnings and travel impacts). It’s a timely reminder that extreme events are now routine and they stress wastewater networks everywhere.

Globally, science points to a clear trajectory: intense rainfall and compound extremes are increasing, driving rapid surges in level and flow, infiltration during prolonged wet periods, and delayed melt surges after snow and ice. For operators, that means more noise in telemetry and a flood of alerts—just when decisions need to be fast and defensible.

A quick word on legislation (and why it matters operationally)

Around the world, regulators are tightening expectations on storm overflows and transparency—UK Section 81 & WINEP, US EPA’s NPDES CSO Control Policy, and similar regional frameworks. You already know the details; the point is this: with more extreme weather, networks must show they can manage surge conditions and maintain credible incident records.

What storms, snow and ice do to networks

• Rapid storm surges: surcharge and backflow, atypical pump cycling, and CSO risk—alert volumes spike.
• Snow melt: a deceptive lull during accumulation, followed by melt-driven inflow surges; cold conditions can impact batteries/telemetry and site access.
• Wind/coastal surge: distorts expected diurnal patterns; incident attribution benefits from catchment‑level context.

Cutting through alert noise—without muting critical signals

It’s easy to drown in alarms or, worse, to suppress everything. The goal is smart triage that keeps visibility high and avoids alert fatigue:

1. Multi‑signal confirmation
   Don’t escalate on a single spike. Combine level + rate‑of‑change + duration, and verify hydraulic cause with pump state or local rainfall where available.
2. Hysteresis on thresholds
   Separate on/off conditions to prevent oscillations from generating repetitive alarms.
   Example: Trigger ≥95% capacity sustained ≥5 min; clear only when <85% for ≥10 min.
3. Storm‑mode logic
   During named storms or national warning periods, focus on ROC outliers that exceed historical storm envelopes—these often flag blockages or abnormal behaviour, rather than expected surge.
4. Temporal bundling (keep timestamps)
   Group alerts landing within 10–15 minutes to reduce fragmentation while retaining original timestamps for audit and post‑event analysis.
5. Geospatial clustering
   Elevate catchment/sub‑catchment clusters over isolated nodes to expose trunk‑system issues and support meaningful incident narratives.

Five quick wins for winter operations

• Tie storm‑mode activation to national weather warnings (e.g., Met Office red/amber).
• Review persistence and hysteresis on high‑risk assets (syphons, trunk mains).
• Implement catchment clustering in dashboards; escalate cluster incidents first.
• Run cold‑weather checks on batteries, seals, and telemetry; pre‑empt ice impacts.
• Maintain a simple overflow event template (inputs → decision → action → outcome) to keep incident records credible under scrutiny.

Why this matters—beyond today’s storm

From the UK to North America and APAC, extreme precipitation and compound weather are raising the baseline for operational resilience. Keeping signals clear—and records robust—during surge conditions is now central to performance, public trust, and programme delivery.

Track the UK situation today:
Met Office warnings and updates on Storm Goretti (multi‑hazard, snow, high winds):
https://www.metoffice.gov.uk/weather/warnings-and-advice [metoffice.gov.uk]