Storm overflow register · Anglian Water

Ryhall sewage works: storm overflow spills 2025

Ryhall sewage treatment works, run by Anglian Water, has 1 monitored storm overflow discharging to River Gwash. In 2025 it recorded 62 spills totalling 706 hours, against 81 spills and 1,002 hours in 2024. By hours spilling, it ranks 22 of 419 Anglian Water works, where 1 spilled longest.

Works size: 2,257 population equivalent (RYHALL 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.

JanFebMarAprMayJunJulAugSepOctNovDecRyhall Water…523 spills, 48.4 h, 6 Jan to 10 Jan157 spills, 18.2 h, 25 Jan to 27 Jan28 Jan 2025 13:20 GMT, 6 min20 spills, 1.2 h, 29 Jan to 30 Jan3 spills, 1.8 h, 22 Mar to 22 Mar6 spills, 4.9 h, 11 Sep to 12 Sep21 spills, 1.9 h, 14 Sep to 14 Sep3 spills, 0.1 h, 23 Oct to 23 Oct6 spills, 0.7 h, 1 Nov to 1 Nov395 spills, 97.3 h, 14 Nov to 20 Nov419 spills, 42.1 h, 22 Nov to 25 Nov51 spills, 13.7 h, 29 Nov to 2 Dec1279 spills, 469.6 h, 4 Dec to 30 Dec27 spills, 6.2 h, 30 Dec to 31 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.

020k40k60kJan 2025: 68 h spilling ≈ 2,626 m³ (range 1,046-6,592 m³)JanFeb 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)FebMar 2025: 1.8 h spilling ≈ 70 m³ (range 28-175 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)MayJun 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)JunJul 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 6.7 h spilling ≈ 259 m³ (range 103-650 m³)SepOct 2025: 0.1 h spilling ≈ 3.9 m³ (range 1.5-9.7 m³)OctNov 2025: 147 h spilling ≈ 5,700 m³ (range 2,271-14,311 m³)NovDec 2025: 482 h spilling ≈ 18,648 m³ (range 7,428-46,816 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
9 Dec 2025, 00:00Ryhall Water Recycling Centre1.0 days370 - 2,330 m³
6 Dec 2025, 00:00Ryhall Water Recycling Centre1.0 days370 - 2,330 m³
19 Dec 2025, 04:38Ryhall Water Recycling Centre18.0 h277 - 1,744 m³
5 Dec 2025, 06:24Ryhall Water Recycling Centre17.6 h271 - 1,709 m³
7 Dec 2025, 07:44Ryhall Water Recycling Centre16.3 h251 - 1,579 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 estimate27,318 m³range 10,881 - 68,583 m³
In litres27.3 millionrange 10.9 million - 68.6 million L
Olympic swimming pools11at 2,500 m³ each
Organic load, as people's raw sewage40,977person-days of untreated BOD

Assumed spill rate while spilling: 4.3 - 27.0 L/s (central 10.7 L/s), from a dry-weather flow of 4.3 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 435 kg2,459 kg13,717 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 1,143 kg11,610 kg49,449 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 21 kg172 kg638 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 13 kg71 kg370 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 1.1 trillion organisms27.3 trillion organisms685.8 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.

Ryhall Water Recycling Centre

Storm tank at sewage works · discharges to River Gwash

Spills 2025
62 (706 hours) · down 23% on 2024
Spills 2024
81 (1,002 hours)
Long-term average
42.0 spills a year (monitored since 2022)
Monitor uptime
100% of the year
High-spill reason (company)
Performance - Asset configuration (e.g. PS/rising main/storm tanks)
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation ongoing
Improvement
Operational improvement ongoing
WFD catchment
Gwash (GB105031050610)
Outlet location
TF0404010700 (OS grid reference) · View on Apple Maps
EA ID / permit
AWS01084 · AW5NF5213 · company name: RYHALL 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 Anglian 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.