Storm overflow register · Yorkshire Water

Danesmoor sewage works: storm overflow spills 2025

Danesmoor sewage treatment works, run by Yorkshire Water, has 2 monitored storm overflows discharging to River Rother. In 2025 they recorded 133 spills totalling 1,180 hours, against 114 spills and 999 hours in 2024. By hours spilling, it ranks 31 of 283 Yorkshire Water works, where 1 spilled longest.

Works size: 6,694 population equivalent (DANESMOOR WPC WORKS FINAL EFFLUENT, UWWTD 2018). Used for the spill volume estimate.

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.

JanFebMarAprMayJunJulAugSepOctNovDecDanesmoor WwTW9 spills, 48 h, 1 Jan to 3 Jan16 spills, 88.5 h, 5 Jan to 9 Jan15 spills, 19.3 h, 24 Jan to 25 Jan20 spills, 80.5 h, 26 Jan to 31 Jan3 spills, 6.3 h, 20 Feb to 20 Feb15 spills, 23.5 h, 23 Feb to 25 Feb2 spills, 4 h, 22 Mar to 22 Mar7 spills, 9.5 h, 27 May to 28 May4 spills, 3.5 h, 6 Jul to 7 Jul2 spills, 1.5 h, 20 Jul to 20 Jul3 Sep 2025 14:45 GMT, 45 min4 Sep 2025 12:15 GMT, 15 min6 spills, 8 h, 14 Sep to 15 Sep2 spills, 0.8 h, 15 Sep to 16 Sep13 spills, 16 h, 17 Sep to 18 Sep9 spills, 19.3 h, 20 Sep to 21 Sep12 spills, 19.3 h, 3 Oct to 4 Oct7 spills, 10 h, 19 Oct to 20 Oct9 spills, 12 h, 23 Oct to 23 Oct2 spills, 1 h, 31 Oct to 31 Oct5 spills, 4.3 h, 1 Nov to 2 Nov10 spills, 15.8 h, 4 Nov to 6 Nov47 spills, 147.3 h, 10 Nov to 17 Nov30 spills, 35 h, 18 Nov to 20 Nov23 spills, 36.3 h, 23 Nov to 25 Nov99 spills, 246.5 h, 29 Nov to 13 Dec47 spills, 146.8 h, 15 Dec to 23 DecDanesmoor WwTW2 spills, 4 h, 1 Jan to 1 Jan2 spills, 26 h, 5 Jan to 6 Jan8 Jan 2025 11:45 GMT, 15 min24 Jan 2025 04:30 GMT, 45 min5 spills, 6.8 h, 27 Jan to 28 Jan20 Feb 2025 15:45 GMT, 60 min4 spills, 8.8 h, 12 May to 12 May3 spills, 3.3 h, 15 May to 15 May28 May 2025 02:30 GMT, 45 min3 Sep 2025 14:00 GMT, 15 min14 Sep 2025 19:15 GMT, 45 min17 Sep 2025 05:30 GMT, 2.5 h2 spills, 6 h, 20 Sep to 21 Sep2 spills, 1.5 h, 3 Oct to 3 Oct2 spills, 1.5 h, 19 Oct to 19 Oct2 spills, 2.3 h, 23 Oct to 23 Oct8 spills, 12.3 h, 31 Oct to 1 Nov2 spills, 0.8 h, 3 Nov to 3 Nov4 Nov 2025 18:30 GMT, 2.5 h2 spills, 0.8 h, 7 Nov to 7 Nov7 spills, 8.3 h, 9 Nov to 12 Nov3 spills, 37.3 h, 14 Nov to 15 Nov2 spills, 2 h, 18 Nov to 19 Nov5 spills, 5 h, 23 Nov to 23 Nov7 spills, 6.3 h, 28 Nov to 29 Nov2 spills, 3.8 h, 1 Dec to 1 Dec2 spills, 3 h, 5 Dec to 5 Dec2 spills, 12.8 h, 9 Dec to 9 Dec12 Dec 2025 11:00 GMT, 45 min4 spills, 4.5 h, 15 Dec to 15 Dec2 spills, 8.8 h, 17 Dec to 18 Dec21 Dec 2025 21:30 GMT, 90 min

Estimated spill volume by month, 2025

Hours spilling each month × the estimated spill rate for a works of this size. The bars are central estimates and the whiskers show the low-high range. Method.

050k100k150kJan 2025: 274 h spilling ≈ 31,427 m³ (range 12,518-78,899 m³)JanFeb 2025: 31 h spilling ≈ 3,533 m³ (range 1,407-8,869 m³)FebMar 2025: 4.0 h spilling ≈ 459 m³ (range 183-1,152 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 22 h spilling ≈ 2,558 m³ (range 1,019-6,421 m³)MayJun 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)JunJul 2025: 5.0 h spilling ≈ 573 m³ (range 228-1,440 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 55 h spilling ≈ 6,251 m³ (range 2,490-15,693 m³)SepOct 2025: 52 h spilling ≈ 6,010 m³ (range 2,394-15,089 m³)OctNov 2025: 354 h spilling ≈ 40,546 m³ (range 16,150-101,792 m³)NovDec 2025: 383 h spilling ≈ 43,952 m³ (range 17,507-110,344 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
5 Jan 2025, 11:15Danesmoor WwTW3.5 days3,803 - 23,972 m³
14 Nov 2025, 01:30Danesmoor WwTW3.0 days3,267 - 20,589 m³
26 Jan 2025, 23:45Danesmoor WwTW2.2 days2,444 - 15,406 m³
17 Dec 2025, 20:45Danesmoor WwTW2.2 days2,364 - 14,902 m³
9 Dec 2025, 02:15Danesmoor WwTW1.9 days2,102 - 13,246 m³

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.

Volume, central estimate135,321 m³range 53,901 - 339,728 m³
In litres135.3 millionrange 53.9 million - 339.7 million L
Olympic swimming pools54at 2,500 m³ each
Organic load, as people's raw sewage202,981person-days of untreated BOD

Assumed spill rate while spilling: 12.7 - 80.0 L/s (central 31.9 L/s), from a dry-weather flow of 12.7 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 2,156 kg12,179 kg67,946 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 5,660 kg57,511 kg244,944 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 102 kg853 kg3,159 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 65 kg352 kg1,835 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 5.4 trillion organisms135.3 trillion organisms3.4 × 10¹⁵ 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.

Danesmoor WwTW

Storm tank at sewage works · discharges to River Rother

Spills 2025
85 (1,004 hours) · up 10% on 2024
Spills 2024
77 (910 hours)
Long-term average
92.0 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 completed, UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Rother from Source to Redleadmill Brook (GB104027052280)
Outlet location
SK4076063000 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00086 · 2138 · company name: DANESMOOR/STW

Danesmoor WwTW

Inlet overflow at sewage works · discharges to River Rother

Spills 2025
48 (176 hours) · up 30% on 2024
Spills 2024
37 (89 hours)
Long-term average
60.5 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 completed, UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Rother from Source to Redleadmill Brook (GB104027052280)
Outlet location
SK4076063000 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00087 · 2138 · company name: DANESMOOR/STW

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 Yorkshire 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.