Storm overflow register · Northumbrian Water

Moorsholm sewage works: storm overflow spills 2025

Moorsholm sewage treatment works, run by Northumbrian Water, has 1 monitored storm overflow discharging to Hagg Beck (Kilton Beck Trib). In 2025 it recorded 113 spills totalling 587 hours, against 127 spills and 719 hours in 2024. By hours spilling, it ranks 26 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.

JanFebMarAprMayJunJulAugSepOctNovDecMoorsholm Sewage…6 spills, 18.2 h, 1 Jan to 2 Jan5 spills, 40.1 h, 5 Jan to 7 Jan6 spills, 3 h, 24 Jan to 24 Jan41 spills, 30.5 h, 26 Jan to 29 Jan12 spills, 8.3 h, 10 Feb to 11 Feb2 spills, 0.6 h, 12 Feb to 12 Feb3 spills, 0.6 h, 20 Feb to 20 Feb21 Feb 2025 21:25 GMT, 25 min3 spills, 0.2 h, 23 Feb to 23 Feb5 spills, 1.7 h, 26 Feb to 27 Feb3 spills, 0.2 h, 11 Mar to 11 Mar8 spills, 2.6 h, 12 Mar to 13 Mar3 spills, 0.2 h, 14 Mar to 15 Mar16 Mar 2025 10:57 GMT, 30 min18 Mar 2025 11:20 GMT, 1 min5 spills, 2.9 h, 22 Mar to 22 Mar22 Apr 2025 19:41 GMT, 25 min4 spills, 0.2 h, 4 May to 4 May2 spills, 0.4 h, 22 May to 22 May3 spills, 1.6 h, 24 May to 24 May27 May 2025 14:56 GMT, 44 min3 spills, 0.6 h, 29 May to 29 May2 spills, 1.7 h, 1 Jun to 2 Jun2 spills, 1 h, 3 Jun to 3 Jun2 spills, 3.1 h, 5 Jun to 6 Jun7 spills, 2.4 h, 7 Jun to 8 Jun10 Jun 2025 07:47 GMT, 13 min2 spills, 0.9 h, 22 Jun to 22 Jun2 spills, 0.5 h, 24 Jun to 24 Jun2 Jul 2025 12:25 GMT, 3.1 h4 spills, 3.1 h, 15 Jul to 16 Jul4 spills, 3.9 h, 18 Jul to 19 Jul3 spills, 0.5 h, 20 Jul to 20 Jul22 Jul 2025 15:17 GMT, 2.1 h23 Jul 2025 12:33 GMT, 40 min5 spills, 2.1 h, 31 Jul to 1 Aug2 spills, 0.1 h, 3 Aug to 3 Aug2 spills, 1.6 h, 4 Aug to 4 Aug27 Aug 2025 17:59 GMT, 27 min28 Aug 2025 17:12 GMT, 14 min2 spills, 0.8 h, 30 Aug to 30 Aug3 spills, 0.6 h, 1 Sep to 1 Sep3 Sep 2025 05:44 GMT, 5 min4 Sep 2025 12:51 GMT, 6.3 h2 spills, 0.1 h, 11 Sep to 11 Sep3 spills, 0.6 h, 12 Sep to 12 Sep13 Sep 2025 22:45 GMT, 20 min3 spills, 1.7 h, 15 Sep to 16 Sep3 spills, 0.4 h, 17 Sep to 17 Sep3 spills, 31.9 h, 20 Sep to 21 Sep8 spills, 7.6 h, 2 Oct to 3 Oct4 spills, 1.2 h, 20 Oct to 20 Oct4 spills, 3.5 h, 23 Oct to 23 Oct6 spills, 7.2 h, 24 Oct to 25 Oct28 Oct 2025 00:50 GMT, 44 min2 spills, 0.7 h, 31 Oct to 31 Oct7 spills, 1.8 h, 4 Nov to 5 Nov6 spills, 2.3 h, 10 Nov to 11 Nov9 spills, 71 h, 12 Nov to 15 Nov8 spills, 2 h, 16 Nov to 17 Nov109 spills, 201.6 h, 18 Nov to 2 Dec46 spills, 73 h, 4 Dec to 10 Dec12 Dec 2025 09:07 GMT, 4 min16 spills, 19 h, 15 Dec to 16 Dec11 spills, 11.1 h, 17 Dec to 18 Dec4 spills, 0.2 h, 30 Dec to 30 Dec

Hours spilling by month, 2025

0100200300Jan 2025: 92 hours spillingJanFeb 2025: 12 hours spillingFebMar 2025: 6.3 hours spillingMarApr 2025: 0.4 hours spillingAprMay 2025: 3.5 hours spillingMayJun 2025: 9.8 hours spillingJunJul 2025: 14 hours spillingJulAug 2025: 4.6 hours spillingAugSep 2025: 42 hours spillingSepOct 2025: 21 hours spillingOctNov 2025: 269 hours spillingNovDec 2025: 113 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
22 Nov 2025, 03:06Moorsholm Sewage Treatment Works2.7 days
8 Dec 2025, 13:46Moorsholm Sewage Treatment Works1.8 days
5 Jan 2025, 14:16Moorsholm Sewage Treatment Works1.6 days
18 Nov 2025, 20:13Moorsholm Sewage Treatment Works1.4 days
29 Nov 2025, 13:21Moorsholm Sewage Treatment Works1.3 days

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 estimate10,054 m³range 4,005 - 25,242 m³
In litres10.1 millionrange 4.0 million - 25.2 million L
Olympic swimming pools4.0at 2,500 m³ each
Organic load, as people's raw sewage15,082person-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) 160 kg905 kg5,048 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 421 kg4,273 kg18,200 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 7.6 kg63 kg235 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 4.8 kg26 kg136 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 400.5 billion organisms10.1 trillion organisms252.4 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.

Moorsholm Sewage Treatment Works

Inlet overflow at sewage works · discharges to Hagg Beck (Kilton Beck Trib)

Spills 2025
113 (587 hours) · down 11% on 2024
Spills 2024
127 (719 hours)
Long-term average
94.2 spills a year (monitored since 2020)
Monitor uptime
99% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
Operational investigation ongoing
Improvement
Operational improvement ongoing
WFD catchment
Kilton Beck from Source to Middle Gill Beck (GB103025071920)
Outlet location
NZ6904015580 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL00903 · 25/06/1010

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.