Storm overflow register · Northumbrian Water

Seaton Carew sewage works: storm overflow spills 2025

Seaton Carew sewage treatment works, run by Northumbrian Water, has 1 monitored storm overflow discharging to North Sea. In 2025 it recorded 68 spills totalling 235 hours, against 85 spills and 314 hours in 2024. By hours spilling, it ranks 84 of 183 Northumbrian Water works, where 1 spilled longest.

Every spill in 2025

Each blue mark is one spill, placed by when it started and sized by how long it lasted. Hover over a mark for the date and duration.

JanFebMarAprMayJunJulAugSepOctNovDecSeaton Carew Sewage…87 spills, 11.6 h, 1 Jan to 1 Jan182 spills, 38.8 h, 5 Jan to 7 Jan6 spills, 0.4 h, 10 Jan to 10 Jan10 spills, 0.8 h, 24 Jan to 24 Jan10 spills, 2.2 h, 27 Jan to 27 Jan9 spills, 1.7 h, 20 Feb to 20 Feb9 spills, 1.3 h, 23 Feb to 23 Feb39 spills, 4.1 h, 12 Mar to 13 Mar26 spills, 5.3 h, 22 Mar to 23 Mar3 spills, 1.3 h, 24 May to 24 May9 spills, 0.6 h, 29 May to 29 May6 spills, 0.9 h, 5 Jun to 5 Jun9 spills, 0.4 h, 7 Jun to 7 Jun11 spills, 0.7 h, 8 Jun to 8 Jun22 spills, 1.3 h, 9 Jun to 9 Jun2 Jul 2025 03:12 GMT, 45 min8 spills, 0.6 h, 14 Jul to 14 Jul9 spills, 2.2 h, 15 Jul to 15 Jul13 spills, 6.1 h, 18 Jul to 19 Jul2 spills, 0.1 h, 4 Aug to 4 Aug2 spills, 0.6 h, 27 Aug to 27 Aug2 spills, 1 h, 31 Aug to 31 Aug2 spills, 0.2 h, 1 Sep to 1 Sep5 spills, 0.8 h, 3 Sep to 3 Sep3 spills, 1.6 h, 4 Sep to 4 Sep10 Sep 2025 21:13 GMT, 3 min13 spills, 1.9 h, 14 Sep to 15 Sep2 spills, 0.1 h, 17 Sep to 17 Sep38 spills, 22 h, 20 Sep to 21 Sep4 spills, 0.5 h, 28 Sep to 28 Sep37 spills, 4.9 h, 2 Oct to 3 Oct24 spills, 10.6 h, 19 Oct to 20 Oct10 spills, 1.7 h, 4 Nov to 5 Nov23 spills, 2.8 h, 10 Nov to 12 Nov161 spills, 29.5 h, 12 Nov to 15 Nov102 spills, 12.2 h, 18 Nov to 19 Nov4 spills, 0.3 h, 23 Nov to 23 Nov19 spills, 2.3 h, 24 Nov to 24 Nov5 spills, 1.5 h, 25 Nov to 25 Nov11 spills, 0.6 h, 26 Nov to 26 Nov9 spills, 1.4 h, 28 Nov to 28 Nov162 spills, 21.6 h, 29 Nov to 1 Dec54 spills, 5 h, 4 Dec to 5 Dec19 spills, 2.9 h, 7 Dec to 7 Dec78 spills, 9.3 h, 9 Dec to 9 Dec81 spills, 16.6 h, 15 Dec to 16 Dec15 spills, 2 h, 18 Dec to 18 Dec

Hours spilling by month, 2025

020406080Jan 2025: 54 hours spillingJanFeb 2025: 3.0 hours spillingFebMar 2025: 9.3 hours spillingMarApr 2025: 0.0 hours spillingAprMay 2025: 2.0 hours spillingMayJun 2025: 3.3 hours spillingJunJul 2025: 9.7 hours spillingJulAug 2025: 1.8 hours spillingAugSep 2025: 27 hours spillingSepOct 2025: 16 hours spillingOctNov 2025: 70 hours spillingNovDec 2025: 39 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
20 Sep 2025, 12:53Seaton Carew Sewage Treatment Works16.0 h
29 Nov 2025, 14:40Seaton Carew Sewage Treatment Works10.6 h
13 Nov 2025, 02:09Seaton Carew Sewage Treatment Works9.1 h
19 Oct 2025, 18:17Seaton Carew Sewage Treatment Works8.9 h
15 Dec 2025, 11:37Seaton Carew Sewage Treatment Works8.7 h

Estimated 2025 spill volume and pollution

Estimate, not a measurement. Monitors record how long an overflow spills, not how much. This calculator back-calculates a spill rate from the size of the works, using the Environment Agency's permit formulae, and multiplies it by published storm-sewage concentrations. How it works.

This works serves fewer than 2,000 people, or was not matched to a UWWTD report, so its size is not published. The population equivalent above is a placeholder of 1,000. Enter the population served if you know it.

Volume, central estimate4,028 m³range 1,605 - 10,113 m³
In litres4.0 millionrange 1.6 million - 10.1 million L
Olympic swimming pools1.6at 2,500 m³ each
Organic load, as people's raw sewage6,042person-days of untreated BOD

Assumed spill rate while spilling: 1.9 - 11.9 L/s (central 4.8 L/s), from a dry-weather flow of 1.9 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 64 kg363 kg2,023 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 168 kg1,712 kg7,292 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 3.0 kg25 kg94 kg 1.9 / 6.3 / 9.3 mg/L
Low: Germany, Brombach 2005; typical/high: Paris range 3.3-9.3 midpoint and top, Gasperi 2012 (via botturi); no UK value found
Total phosphorus 1.9 kg10 kg55 kg 1.2 / 2.6 / 5.4 mg/L
Low/high: Paris, Gasperi 2012; typical: Slovakia (via botturi). UK figure of 10 mg/L treated as an outlier
E. coli 160.5 billion organisms4.0 trillion organisms101.1 trillion organisms 10,000 / 100,000 / 1.0 million per 100 mL
Median range at CSO and retention-tank outlets, Stott et al. 2018 (via botturi); typical = log midpoint

Low combines the low spill rate with low concentrations, and high combines high with high, so the true figure is very likely inside the range. Long spills become more diluted as they go on, so the central figure tends to overstate the load of long events. The calculator does not estimate the effect on the receiving water, which depends on river flow or tide at the time of the spill.

Seaton Carew Sewage Treatment Works

Inlet overflow at sewage works · discharges to North Sea

Spills 2025
68 (235 hours) · down 20% on 2024
Spills 2024
85 (314 hours)
Long-term average
81.3 spills a year (monitored since 2019)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
Operational investigation ongoing
Improvement
No improvement action in reporting period
Bathing water
Seaton Carew North
WFD catchment
Tees Coastal (GB650301500005)
Outlet location
NZ5580032100&NZ5350030100 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL01170 · 254/1966

How the estimate works

  1. Dry-weather flow (DWF) = population × water use per person × (1 + infiltration). Water use is 136.5 L per person per day, England's per-capita consumption for 2024-25 [EA]. Infiltration of groundwater into sewers is taken as 0-40% of that flow [Escritt, via HBF]. The Environment Agency defines DWF as PG + I + E [EA].
  2. Population. The size of each works comes from the load entering it as reported under the Urban Waste Water Treatment Directive, in population equivalents (1 p.e. = 60 g of BOD a day) [UWWTD]. We treat population equivalent as population. That overstates flow where trade effluent adds load, and no official source links the two. Works serving fewer than 2,000 p.e. are not reported, so their size has to be entered by hand.
  3. Low spill rate = DWF. This is the method used by Giakoumis & Voulvoulis (2026), which they note likely underestimates storm loads [G&V].
  4. High spill rate = Formula A − flow to full treatment = (DWF + 1360P) − 3DWF. This is the largest flow the permit expects the storm tanks to handle before it passes on to treatment or overflows [EA]. The central rate is the geometric mean of the low and high rates.
  5. Volume = spill rate × hours spilling, with hours taken from the event duration monitor.
  6. Pollution = volume × published storm-sewage concentrations [Botturi et al.] [US EPA]. Organic load is also shown as person-days of untreated sewage at 60 g of BOD per person per day [UWWTD].

What this cannot tell you. It gives no real flow for any single spill, and no effect on the river or sea, which depends on the flow, tide and the other pressures on the water at the time. It gives no figure for spills from overflows on the sewer network, which serve catchments of unknown size. It is a way to put hours into rough physical terms, not a substitute for flow monitoring.

Sources

  1. EA: Water companies - environmental permits for storm overflows and emergency overflows
  2. EA: Water resources 2024 to 2025 - per capita consumption
  3. HBF: Foul sewer design - historic conventions (citing Escritt 1984 on infiltration)
  4. Giakoumis & Voulvoulis (2026), Environ. Sci.: Water Res. Technol., doi:10.1039/D5EW00860C
  5. Botturi et al. (2021), Crit. Rev. Environ. Sci. Technol. 51:1585 - CSO quality review, Table 2
  6. US EPA (2004) Report to Congress on CSOs and SSOs, chapter 4
  7. Urban Waste Water Treatment Directive, Article 2(6): 1 p.e. = 60 g BOD5/day
  8. Olympic-size swimming pool: 2,500 m³ at the nominal 2 m depth

← All Northumbrian Water works · Contains Environment Agency data licensed under the Open Government Licence v3.0. Spill start and stop times: © Environment Agency copyright and/or database right 2026. All rights reserved. They are water-company data and have not been verified by the Environment Agency. Works size: EEA Waterbase UWWTD. How to read the data.