Storm overflow register · Northumbrian Water

Carlton In Cleveland sewage works: storm overflow spills 2025

Carlton In Cleveland sewage treatment works, run by Northumbrian Water, has 1 monitored storm overflow discharging to Alum Beck. In 2025 it recorded 89 spills totalling 167 hours, against 93 spills and 324 hours in 2024. By hours spilling, it ranks 101 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.

JanFebMarAprMayJunJulAugSepOctNovDecCarlton in Cleveland…18 spills, 14.3 h, 1 Jan to 2 Jan24 spills, 28.6 h, 5 Jan to 6 Jan2 spills, 0 h, 20 Jan to 20 Jan7 spills, 2.2 h, 24 Jan to 24 Jan15 spills, 13.9 h, 26 Jan to 27 Jan3 spills, 1.4 h, 20 Feb to 20 Feb2 spills, 0.2 h, 21 Feb to 21 Feb23 Feb 2025 20:45 GMT, 1 min7 Mar 2025 02:06 GMT, 1 min11 Mar 2025 05:22 GMT, 1 min13 spills, 1.5 h, 12 Mar to 13 Mar3 spills, 0.1 h, 14 Mar to 14 Mar4 spills, 0.1 h, 22 Mar to 22 Mar6 spills, 0.2 h, 24 May to 24 May27 May 2025 14:54 GMT, 1 min2 spills, 0 h, 29 May to 29 May3 Jun 2025 06:10 GMT, 1 min6 spills, 1.7 h, 6 Jun to 6 Jun4 spills, 0.5 h, 7 Jun to 7 Jun8 Jun 2025 13:46 GMT, 29 min9 Jun 2025 20:56 GMT, 1 min3 spills, 0.8 h, 2 Jul to 2 Jul6 Jul 2025 05:39 GMT, 1 min14 Jul 2025 13:54 GMT, 18 min5 spills, 2.7 h, 15 Jul to 15 Jul10 spills, 7.6 h, 18 Jul to 19 Jul3 spills, 0.4 h, 20 Jul to 20 Jul22 Jul 2025 10:44 GMT, 1 min2 spills, 0 h, 23 Jul to 23 Jul2 spills, 0 h, 4 Aug to 4 Aug2 spills, 0.3 h, 27 Aug to 27 Aug2 spills, 0.4 h, 28 Aug to 28 Aug2 spills, 0 h, 30 Aug to 30 Aug31 Aug 2025 16:52 GMT, 22 min4 spills, 1.5 h, 1 Sep to 1 Sep2 spills, 1.1 h, 3 Sep to 3 Sep2 spills, 0.6 h, 4 Sep to 4 Sep5 spills, 0.1 h, 10 Sep to 11 Sep2 spills, 0.2 h, 13 Sep to 13 Sep6 spills, 0.3 h, 15 Sep to 15 Sep16 Sep 2025 05:39 GMT, 1 min19 spills, 23.7 h, 20 Sep to 21 Sep2 spills, 0 h, 28 Sep to 28 Sep14 spills, 2.3 h, 2 Oct to 3 Oct8 spills, 0.2 h, 19 Oct to 20 Oct4 spills, 0.9 h, 23 Oct to 23 Oct7 spills, 0.5 h, 24 Oct to 24 Oct28 Oct 2025 00:52 GMT, 1 min4 spills, 0.1 h, 4 Nov to 5 Nov10 Nov 2025 01:01 GMT, 1 min6 spills, 0.6 h, 11 Nov to 11 Nov30 spills, 6 h, 12 Nov to 15 Nov34 spills, 5 h, 18 Nov to 19 Nov20 Nov 2025 18:33 GMT, 1 min2 spills, 0.8 h, 23 Nov to 23 Nov20 spills, 3.5 h, 24 Nov to 24 Nov3 spills, 2.1 h, 25 Nov to 25 Nov26 Nov 2025 18:27 GMT, 1 min4 spills, 0.3 h, 28 Nov to 28 Nov14 spills, 12.1 h, 29 Nov to 30 Nov23 spills, 4.2 h, 1 Dec to 2 Dec3 spills, 0.1 h, 4 Dec to 4 Dec13 spills, 8.7 h, 5 Dec to 6 Dec7 Dec 2025 15:49 GMT, 1 min24 spills, 5.7 h, 9 Dec to 10 Dec36 spills, 8.2 h, 14 Dec to 15 Dec16 spills, 2.2 h, 17 Dec to 18 Dec3 spills, 0.1 h, 29 Dec to 29 Dec

Hours spilling by month, 2025

0204060Jan 2025: 59 hours spillingJanFeb 2025: 1.5 hours spillingFebMar 2025: 1.7 hours spillingMarApr 2025: 0.0 hours spillingAprMay 2025: 0.2 hours spillingMayJun 2025: 2.6 hours spillingJunJul 2025: 12 hours spillingJulAug 2025: 1.1 hours spillingAugSep 2025: 27 hours spillingSepOct 2025: 3.8 hours spillingOctNov 2025: 30 hours spillingNovDec 2025: 29 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
5 Jan 2025, 17:47Carlton in Cleveland STW20.9 h
20 Sep 2025, 09:46Carlton in Cleveland STW20.8 h
1 Jan 2025, 00:00Carlton in Cleveland STW13.7 h
29 Nov 2025, 16:03Carlton in Cleveland STW11.5 h
27 Jan 2025, 02:27Carlton in Cleveland STW8.5 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 estimate2,853 m³range 1,136 - 7,162 m³
In litres2.9 millionrange 1.1 million - 7.2 million L
Olympic swimming pools1.1at 2,500 m³ each
Organic load, as people's raw sewage4,279person-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) 45 kg257 kg1,432 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 119 kg1,212 kg5,164 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 2.2 kg18 kg67 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 1.4 kg7.4 kg39 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 113.6 billion organisms2.9 trillion organisms71.6 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.

Carlton in Cleveland STW

Inlet overflow at sewage works · discharges to Alum Beck

Spills 2025
89 (166 hours) · down 4% on 2024
Spills 2024
93 (324 hours)
Long-term average
79.0 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation ongoing
Improvement
Operational improvement ongoing
WFD catchment
Leven from Tame to River Tees (GB103025071880)
Outlet location
NZ5073004934 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL00248 · 25/04/1800

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.