Research and analysis

Solent and South Downs water situation report: September 2025 summary

Updated 14 October 2025

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

1. Summary

Solent and South Downs (SSD) had above average rainfall in September, receiving 153% (100.9mm) of the long term average (LTA) of 66.15mm. Monthly mean river flows across SSD ranged from below normal to notably high. The end of month groundwater levels ranged from exceptionally low to above normal. Soils across SSD ended the month drier than the average for September. End of month reservoir stocks were below average at Ardingly Reservoir (Ouse) and at Arlington Reservoir (Cuckmere).

2. Rainfall

SSD had above average rainfall in September, receiving 153% (100.9mm) of LTA (66.15mm). The East Sussex Chalk areal unit received the highest rainfall during September with 179% (116.7mm) of LTA (65.29mm). The Arun areal unit received the lowest rainfall with 124% (81.5mm) of LTA (65.78mm). 

There were 2 periods in September with widespread rainfall. At the start of the month over 40% of the month’s rainfall fell in four days between 1 and 4 September. Then SSD received about 55% of the month’s rainfall in the middle of the month between 9 to 17 September. The rest of the month was mostly dry with scattered rain.

The wettest day was 12 September, when the highest daily total of 44.4mm was recorded at Folkington RG (Cuckmere). On the same day, 36.3mm was recorded at Isfield RG, 33.4mm at Popeswood TBR and 33.0mm at Barcombe RG, all in the Ouse Catchment.

The last 7 months has been the sixth driest March–September period on record for the Test Chalk areal unit.

For the 24-month period (starting October 2023) it was the seventh highest total for SSD.

All these statistics are based on records going back to 1871.

3. Soil moisture deficit and recharge

Soils across SSD ended the month much drier than the LTA for September.

4. River flows

Monthly mean river flows for September ranged from below normal to notably high across SSD.

Flows were below normal on the River Meon at Mislingford.

Flows were normal on the:

• River Test at Chilbolton
• River Test at Broadlands
• River Itchen at Allbrook and Highbridge
• River Lymington at Brockenhurst
• River Medina at Blackwater
• River Rother at Iping Mill
• River Ouse at Goldbridge
• River Cuckmere at Cowbeech

Flows were above normal on the:

• River Arun at Alfoldean
• River Wallington at North Fareham

Flows were notably high on the River Adur at Sakeham.

The notably high monthly mean flows for the River Adur at Sakeham were the eight highest on record for September since 1967.

5. Groundwater levels 

End of month groundwater levels for September ranged from exceptionally low to above normal across SSD.

Groundwater levels were exceptionally low at:

• Chilgrove (West Sussex Chalk)
• Beeding Hill (West Sussex Chalk)

Groundwater levels were below normal at:

• Carisbrooke Castle (Isle of Wight)
• Catherington (East Hampshire Chalk)
• Harting Common (Western Rother Greensand)

Groundwater levels were normal at:

• Clanville Gate (Test Chalk)
• Lopcombe Corner (Test Chalk)
• West Meon (East Hampshire Chalk)
• Houndean Bottom (East Sussex Chalk)
• Cornish Farm (East Sussex Chalk)

Groundwater levels were above normal at:

• Preston Candover (East Hampshire Chalk)
• Youngwoods Copse (Isle of Wight)

The groundwater level at Beeding Hill (West Sussex Chalk) was the third lowest September level (dating back to 1979). Chilgrove (West Sussex Chalk) was the fourth lowest September level since 1836.

6. Reservoir stocks

End of month reservoir stocks were below average for both Ardingly and Arlington Reservoirs. Ardingly Reservoir (Ouse) was at 30.1% (25 September) of total capacity (LTA 68%) and Arlington Reservoir (Cuckmere) was at 52.4% (27 September) of total capacity (LTA 57.7%).

7. Environmental impact 

Abstraction licence restriction

At the start of September there were 26 licence restrictions in force, which decreased to 4 licence restrictions by the middle of the month. By the end of the month 12 licence restrictions were in place. These included:

• 4 licences on the Arun
• one licence on the Pagham Rife
• 4 licences in the River Rother catchment
• 2 licences on the River Meon
• 8 licences on the Isle of Wight
• one licence on the Lymington River
• 3 licences on Walkford Brook
• 2 licences on the River Blackwater (in Hampshire)
• one licence on the River Test (Hampshire Tertiaries)

Flood Warnings in Force

There was one flood alert issued in September 2025. The fluvial flood alert was issued on 3 September in the Ouse catchment. 

Author: HydrologySSD@environment-agency.gov.uk  

Contact Details: 03708 506 506

All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained in this report.