Thornham SSO - 115369
Storm overflow operated by Southern Water. The source names Chichester Hbr via Little Deep as the receiving water.
- 21
- Spills in 2025
- 236.9
- Recorded hours
- 100%
- Monitor operation
- 5
- Years listed
The reported spill count was 31 lower than in 2024. This compares event counts, not discharge volume.
Checking the latest monitor report…
How it compares in 2025
Thornham SSO - 115369 recorded 21 spills in 2025. That is more than 64% of the 14,239 overflows in England with a reported figure, and ranks 4,856th nationally. Among Southern Water overflows it ranks 260th of 975; the median Southern Water overflow recorded 7 spills. On the Great Deep waterbody it ranks 1st of 3.
| Group | Rank by spills | Median spills | Median hours |
|---|---|---|---|
| This outlet | – | 21 | 236.9 |
| England | 4,856th of 14,239 | 11 | 22.3 |
| Southern Water | 260th of 975 | 7 | 17 |
| Great Deep | 1st of 3 | 12 | 118.6 |
Rank 1 has the most spills. Equal counts share a rank. Only overflows with a reported count are ranked. Counts do not measure volume, so a higher rank does not mean more sewage.
Annual spill history
| Year | Spills | Duration | Monitor operation | Source |
|---|---|---|---|---|
| 2025 | 21 | 236.9 hours | 100% | Official data |
| 2024 | 52 | 602 hours | 100% | Official data |
| 2023 | 74 | 1,134.9 hours | 99.7% | Official data |
| 2022 | 22 | 272.6 hours | 100% | Official data |
| 2021 | 20 | 271.1 hours | 100% | Official data |
A missing figure means the source did not provide a usable value. A zero is shown as zero. Monitor operation below 90% can make comparison less reliable.
Outlet details
- Water company
- Southern Water
- Outlet type
- Storm tank at a wastewater treatment works
- Permit
- W00354
- Activity reference
- Settled Storm
- Grid reference
- SU7582004730
- Waterbody ID
- GB610070074000Official waterbody record ↗
- Location source
- Official annual grid reference
- Location precision
- About 1 metres
- Location note
- Unknown
About the name and type
The annual return lists this asset as “Storm tank at WwTW”: storm tank at a wastewater treatment works. The overflow comes from storm storage at a treatment works.
The source name includes SSO, which Southern Water defines as Settled Storm Overflow. The name and the listed type are separate source fields, so the name does not describe the layout of the site. Southern Water flow and spill reporting glossary ↗
The waterbody link opens the Environment Agency record for the exact ID in the return. It is a source lookup; we do not import its classification.
Where it is
The recorded position is about 1.7 km south-west of the Southbourne reference point in the ONS built-up areas data.
Area and water pages
Check the official record
Public access to this outlet is unknown. Do not enter restricted land or use this page as a route guide.
Open official source ↗Other outlet records nearby
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Questions about Thornham SSO - 115369
- Who operates Thornham SSO - 115369?
- Southern Water is the operator named in the annual record. The permit reference is W00354.
- Where does Thornham SSO - 115369 discharge?
- The source names Chichester Hbr via Little Deep as the receiving water. This does not show how far a discharge travelled.
- How many times did Thornham SSO - 115369 spill in 2025?
- The 2025 return records 21 counted spill events and 236.9 hours of recorded discharge. Spills are counted with the 12/24-hour method, so this is not a count of every start signal.
- Can I trust the 2025 figures for this outlet?
- The monitor worked for 100% of the reporting period, so the annual figures cover most of the year. They still do not measure discharge volume.
- Is Thornham SSO - 115369 discharging right now?
- This record is linked to a company live feed. The panel above shows the latest report we hold, with its date. That report can be old, and the monitor can be offline, so check the date before relying on it. A report that no discharge is taking place is not a water-quality result.
- How accurate is the map marker?
- The marker comes from the grid reference in the official annual return, which is accurate to about 1 metres. It shows the recorded outlet position, not the extent of any discharge.
- What kind of outlet is Thornham SSO - 115369?
- The annual return lists the asset type as “Storm tank at WwTW”, which means storm tank at a wastewater treatment works. The overflow comes from storm storage at a treatment works. The source name includes SSO, which Southern Water defines as Settled Storm Overflow. The name and the listed type are separate source fields.
- How does Thornham SSO - 115369 compare with other overflows?
- Thornham SSO - 115369 recorded 21 spills in 2025. That is more than 64% of the 14,239 overflows in England with a reported figure, and ranks 4,856th nationally. Among Southern Water overflows it ranks 260th of 975; the median Southern Water overflow recorded 7 spills. On the Great Deep waterbody it ranks 1st of 3. Ranks compare counted spill events only. They do not compare volume or harm.
- Does zero spills mean the water was safe?
- No. A zero means the annual return recorded zero counted spill events for this outlet and year. It is not a water-quality test, and pollution can come from other sources.