Storm overflow register · Yorkshire Water

Flamborough sewage works: storm overflow spills 2025

Flamborough sewage treatment works, run by Yorkshire Water, has 1 monitored storm overflow discharging to North Sea/Hartendale Gutter. In 2025 it recorded 84 spills totalling 245 hours, against 11 spills and 61 hours in 2024. By hours spilling, it ranks 156 of 283 Yorkshire Water works, where 1 spilled longest.

Works size: 4,838 population equivalent (FLAMBOROUGH STW, 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.

JanFebMarAprMayJunJulAugSepOctNovDecFlamborough WwTW41 spills, 15.6 h, 1 Jan to 2 Jan7 spills, 19.5 h, 5 Jan to 5 Jan26 spills, 3 h, 6 Jan to 7 Jan6 spills, 1.9 h, 9 Jan to 10 Jan3 spills, 2.5 h, 24 Jan to 24 Jan29 spills, 9.5 h, 26 Jan to 28 Jan20 Feb 2025 16:36 GMT, 42 min4 spills, 0.6 h, 23 Feb to 23 Feb12 Mar 2025 01:28 GMT, 18 min3 spills, 0.7 h, 13 Mar to 14 Mar2 spills, 0.9 h, 22 Mar to 22 Mar15 Apr 2025 08:16 GMT, 4.6 h5 spills, 0.7 h, 21 Apr to 21 Apr7 spills, 1.8 h, 24 May to 24 May5 spills, 0.3 h, 3 Jun to 3 Jun2 spills, 0.2 h, 7 Jun to 7 Jun6 spills, 1.2 h, 8 Jun to 8 Jun10 Jun 2025 00:22 GMT, 18 min7 spills, 1.3 h, 2 Jul to 2 Jul2 spills, 0.4 h, 6 Jul to 6 Jul4 spills, 0.5 h, 7 Jul to 7 Jul5 spills, 1.1 h, 19 Jul to 19 Jul3 spills, 0.6 h, 20 Jul to 20 Jul3 spills, 0.1 h, 22 Jul to 22 Jul5 spills, 0.6 h, 24 Jul to 24 Jul3 spills, 1.3 h, 1 Aug to 1 Aug7 spills, 1.1 h, 4 Aug to 4 Aug29 Aug 2025 16:18 GMT, 60 min5 spills, 1.9 h, 4 Sep to 4 Sep2 spills, 2.1 h, 10 Sep to 10 Sep12 Sep 2025 14:16 GMT, 2 min14 Sep 2025 21:22 GMT, 42 min17 spills, 10.4 h, 20 Sep to 21 Sep2 spills, 0.1 h, 28 Sep to 28 Sep14 spills, 4.1 h, 3 Oct to 3 Oct7 spills, 0.6 h, 19 Oct to 19 Oct5 spills, 2.6 h, 23 Oct to 23 Oct25 spills, 1.3 h, 24 Oct to 25 Oct4 spills, 1.9 h, 27 Oct to 28 Oct2 spills, 0.2 h, 31 Oct to 31 Oct2 spills, 2.6 h, 4 Nov to 4 Nov30 spills, 11.3 h, 10 Nov to 10 Nov20 spills, 5.5 h, 12 Nov to 13 Nov9 spills, 10.7 h, 14 Nov to 15 Nov16 Nov 2025 20:58 GMT, 56 min80 spills, 21.6 h, 18 Nov to 21 Nov3 spills, 0.1 h, 22 Nov to 22 Nov16 spills, 5.7 h, 23 Nov to 25 Nov7 spills, 0.4 h, 26 Nov to 26 Nov120 spills, 33 h, 28 Nov to 2 Dec106 spills, 23.6 h, 4 Dec to 7 Dec23 spills, 17.1 h, 9 Dec to 10 Dec12 Dec 2025 14:16 GMT, 2 min13 spills, 1.4 h, 15 Dec to 15 Dec9 spills, 0.6 h, 16 Dec to 16 Dec27 spills, 12 h, 17 Dec to 19 Dec

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.

05,00010k15k20kJan 2025: 52 h spilling ≈ 4,319 m³ (range 1,720-10,843 m³)JanFeb 2025: 1.3 h spilling ≈ 108 m³ (range 43-271 m³)FebMar 2025: 1.9 h spilling ≈ 158 m³ (range 63-395 m³)MarApr 2025: 5.3 h spilling ≈ 439 m³ (range 175-1,103 m³)AprMay 2025: 1.8 h spilling ≈ 149 m³ (range 59-375 m³)MayJun 2025: 2.0 h spilling ≈ 166 m³ (range 66-416 m³)JunJul 2025: 4.7 h spilling ≈ 390 m³ (range 155-978 m³)JulAug 2025: 3.4 h spilling ≈ 282 m³ (range 112-708 m³)AugSep 2025: 15 h spilling ≈ 1,260 m³ (range 502-3,163 m³)SepOct 2025: 11 h spilling ≈ 887 m³ (range 353-2,227 m³)OctNov 2025: 84 h spilling ≈ 6,996 m³ (range 2,787-17,565 m³)NovDec 2025: 62 h spilling ≈ 5,148 m³ (range 2,051-12,924 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
29 Nov 2025, 10:02Flamborough WwTW19.4 h642 - 4,044 m³
5 Jan 2025, 05:24Flamborough WwTW16.3 h538 - 3,392 m³
9 Dec 2025, 04:38Flamborough WwTW16.0 h528 - 3,330 m³
14 Nov 2025, 18:26Flamborough WwTW10.3 h340 - 2,144 m³
5 Dec 2025, 19:52Flamborough WwTW9.0 h298 - 1,880 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 estimate20,301 m³range 8,086 - 50,967 m³
In litres20.3 millionrange 8.1 million - 51.0 million L
Olympic swimming pools8.1at 2,500 m³ each
Organic load, as people's raw sewage30,452person-days of untreated BOD

Assumed spill rate while spilling: 9.2 - 57.8 L/s (central 23.0 L/s), from a dry-weather flow of 9.2 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 323 kg1,827 kg10,193 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 849 kg8,628 kg36,747 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 15 kg128 kg474 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 9.7 kg53 kg275 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 808.6 billion organisms20.3 trillion organisms509.7 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.

Flamborough WwTW

Inlet overflow at sewage works · discharges to North Sea/Hartendale Gutter

Spills 2025
84 (245 hours) · up 664% on 2024
Spills 2024
11 (61 hours)
Long-term average
23.3 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
UWWTR investigation ongoing, Operational investigation completed
Improvement
No improvement action in reporting period
Bathing water
Danes Dyke, Flamborough; Flamborough South Landing
WFD catchment
Yorkshire South (GB640402491000)
Outlet location
TA2232068130 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS01125 · WA6514 · company name: FLAMBOROUGH VILLAGE/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.