Groundwater flood risk in Staines and surroundings

Dr Jonathan Paul (jonathan.paul@rhul.ac.uk)�Senior Lecturer in Earth Science

Department of Earth Sciences, RHUL

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Project context: Summer 2023 – now

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How did it come about?

EA colleague suggested flooding in Staines getting worse and attributable to groundwater -> MSc project at RHUL, June – September 2023

Who is funding it?

£10,000 from Research England – independent UK-wide funder, part of block funding allocated to every UK university (“QR funding”). Towards equipment and staff time

Where are the results published?

Open-access, peer-reviewed scientific journal article: J. Flood Risk Management, April 2025

What next?

The “Egham Experiment” and water quality issues. Additional funding applications

Below our feet in Spelthorne

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River Terrace Gravels

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On average 5 m thick

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Lithologically highly variable (e.g. Langley Silt Member, Shepperton Gravel Member)

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Highly permeable and porous (50%) superficial aquifer

Scientific context

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Problem

Worst local flooding since 2014; this will get worse e.g. climate changes

Hypothesis

Water flowing through gravel substrate is a major, yet hidden, contributor

Work plan

• Geophysical and hydrogeological surveys: how close is the groundwater to the surface; where is it going; how does it respond to rainfall
• Engage local community to co-produce maps of local flood risk
• Explore fluvial / pluvial / groundwater flood risk governance
• Laboratory tests for water quality and provenance

Automatic tipping-bucket rain gauge

Early GPR system

Seismic reflection

Fluorescein tracer testing

Flood water provenance – water quality lab tests

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Thames

Aquifer

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Flood water provenance – water quality lab tests

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Thames

Aquifer

Floodwater

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Also – Guildford St floodwater, March 2024:

• Groundwater affinity
• 840 E. Coli / 100 mL (>100 = “high risk”)
• Listeria spp. present
• Mixing with foul sewage line

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Tracer transit time from injection (star) given in hours (orange contours)

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Yellow hatching = qualitative “high” flood risk region based on intersection of:

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• 95% of reported groundwater flooding

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• Fast groundwater flow pathways

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• Steep gradients in water table (i.e. head)

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A local integrated water monitoring network

Black bars = rainfall

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Thick red, green, blue lines = level of R Thames upstream, downstream, & Sweeps Ditch

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Thin red line = groundwater level under Staines

Key results

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• Groundwater level is more spatially variable than expected: influence of old backfilled gravel pits, basements, surface drainage?
• Observed flooding is groundwater (vertical seepages); long lag time of groundwater after rainfall sustains flooding
• Thin, variable gravel aquifer is enormously sensitive to obstructions
• Fast, intense groundwater flow pathways suggest aquifer integrity breaks down (analogous to karst in limestones) -> enhanced pollution
• Not much water connection between groundwater and Thames – this is unexpected – so dredging could heighten flood risk
• High flood risk areas = low elevation + “lee” side of sub-surface obstructions + rapid groundwater movement + recharge (e.g. soakaways)

Planning – central Staines

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Red outline = Draft Allocations 2023–37

Blue = Proposed for removal

Green = Under construction/extant planning permission

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1: ST4/004: 96–104 Church St

2: ST4/023: Two Rivers Retail Park Terrace

3: ST3/012: Staines Telephone Exchange

4: ST3/014: Birch House/London Rd

5: ST4/009: Elmsleigh

Centre & Adjoining

6: ST1/037: Thameside House, South St

7: ST3/004: Oast House, Kingston Rd

8: ST1/028: Leacroft Centre

9: ST2/006: Builders Yard, Gresham Rd

10: ST1/031: Thameside Arts Centre

11: ST4/019: Former Debenhams site

12: ST4/024: Frankie & Benny’s/Travelodge

13: ST4/026: Communications House

14: ST4/028: William Hill/ Vodafone, 91 High St

15: 22/00765/RVC: Eden Grove, 17–51 London Rd

16: 20/01199/FUL: The Old Telephone Exchange

17: 22/00591/FUL: Renshaw Industrial Estate, Mill Mead

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A

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Red outline = Draft Allocations 2023–37

Blue = Proposed for removal

Green = Under construction/extant planning permission

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Blue stripes = Flood Zone 3b (>5% annual flood likelihood)

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1: ST4/004: 96–104 Church St

2: ST4/023: Two Rivers Retail Park Terrace

3: ST3/012: Staines Telephone Exchange

4: ST3/014: Birch House/London Rd

5: ST4/009: Elmsleigh

Centre & Adjoining

6: ST1/037: Thameside House, South St

7: ST3/004: Oast House, Kingston Rd

8: ST1/028: Leacroft Centre

9: ST2/006: Builders Yard, Gresham Rd

10: ST1/031: Thameside Arts Centre

11: ST4/019: Former Debenhams site

12: ST4/024: Frankie & Benny’s/Travelodge

13: ST4/026: Communications House

14: ST4/028: William Hill/ Vodafone, 91 High St

15: 22/00765/RVC: Eden Grove, 17–51 London Rd

16: 20/01199/FUL: The Old Telephone Exchange

17: 22/00591/FUL: Renshaw Industrial Estate, Mill Mead

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3

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A

B

C

D

E

15

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Red outline = Draft Allocations 2023–37

Blue = Proposed for removal

Green = Under construction/extant planning permission

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Blue stripes = Flood Zone 3b (>5% annual flood likelihood)

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Light blue stripes = Flood Zone 3a (>1% annual flood likelihood)

1: ST4/004: 96–104 Church St

2: ST4/023: Two Rivers Retail Park Terrace

3: ST3/012: Staines Telephone Exchange

4: ST3/014: Birch House/London Rd

5: ST4/009: Elmsleigh

Centre & Adjoining

6: ST1/037: Thameside House, South St

7: ST3/004: Oast House, Kingston Rd

8: ST1/028: Leacroft Centre

9: ST2/006: Builders Yard, Gresham Rd

10: ST1/031: Thameside Arts Centre

11: ST4/019: Former Debenhams site

12: ST4/024: Frankie & Benny’s/Travelodge

13: ST4/026: Communications House

14: ST4/028: William Hill/ Vodafone, 91 High St

15: 22/00765/RVC: Eden Grove, 17–51 London Rd

16: 20/01199/FUL: The Old Telephone Exchange

17: 22/00591/FUL: Renshaw Industrial Estate, Mill Mead

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1

2

3

4

5

6

7

8

9

10

11

12

13

14

A

B

C

D

E

15

16

17

Red outline = Draft Allocations 2023–37

Blue = Proposed for removal

Green = Under construction/extant planning permission

​

Blue stripes = Flood Zone 3b (>5% annual flood likelihood)

​

Light blue stripes = Flood Zone 3a (>1% annual flood likelihood)

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Black squares = High groundwater flood risk zone

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1: ST4/004: 96–104 Church St

2: ST4/023: Two Rivers Retail Park Terrace

3: ST3/012: Staines Telephone Exchange

4: ST3/014: Birch House/London Rd

5: ST4/009: Elmsleigh

Centre & Adjoining

6: ST1/037: Thameside House, South St

7: ST3/004: Oast House, Kingston Rd

8: ST1/028: Leacroft Centre

9: ST2/006: Builders Yard, Gresham Rd

10: ST1/031: Thameside Arts Centre

11: ST4/019: Former Debenhams site

12: ST4/024: Frankie & Benny’s/Travelodge

13: ST4/026: Communications House

14: ST4/028: William Hill/ Vodafone, 91 High St

15: 22/00765/RVC: Eden Grove, 17–51 London Rd

16: 20/01199/FUL: The Old Telephone Exchange

17: 22/00591/FUL: Renshaw Industrial Estate, Mill Mead

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3

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5

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A

B

C

D

E

15

16

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Red outline = Draft Allocations 2023–37

Blue = Proposed for removal

Green = Under construction/extant planning permission

​

Blue stripes = Flood Zone 3b (>5% annual flood likelihood)

​

Light blue stripes = Flood Zone 3a (>1% annual flood likelihood)

​

Black squares = High groundwater flood risk zone

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Units: <100; 100 – 400; >400

1: ST4/004: 96–104 Church St

2: ST4/023: Two Rivers Retail Park Terrace

3: ST3/012: Staines Telephone Exchange

4: ST3/014: Birch House/London Rd

5: ST4/009: Elmsleigh

Centre & Adjoining

6: ST1/037: Thameside House, South St

7: ST3/004: Oast House, Kingston Rd

8: ST1/028: Leacroft Centre

9: ST2/006: Builders Yard, Gresham Rd

10: ST1/031: Thameside Arts Centre

11: ST4/019: Former Debenhams site

12: ST4/024: Frankie & Benny’s/Travelodge

13: ST4/026: Communications House

14: ST4/028: William Hill/ Vodafone, 91 High St

15: 22/00765/RVC: Eden Grove, 17–51 London Rd

16: 20/01199/FUL: The Old Telephone Exchange

17: 22/00591/FUL: Renshaw Industrial Estate, Mill Mead

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Deliverables and next steps

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Publications

Paul J.D., et al. (2025). Groundwater flooding of superficial gravels in an urbanized catchment. Journal of Flood Risk Management, 18(2), e70050

Staines-on-Thames: A case study of groundwater flooding exacerbated by rapid urbanisation. New Civil Engineer (March 2025).

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Flood risk governance

Identified need for (a) unified regulatory body for pluvial, fluvial, groundwater flooding; (b) higher-resolution hydrogeological site investigation. Regulate new building on floodplain.

Meetings with Spelthorne BC and EA/Surrey CC upcoming – May/June 2025

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Current research

Water quality testing of surface drainage and lakes. Mapping old landfill sites.

Contact: Jonathan Paul (jonathan.paul@rhul.ac.uk)

Department of Earth Sciences, Royal Holloway, University of London