Aviation·Environment Agency·—·Environment Agency

Environment Agency Clays Lake Flood Storage Reservoir (Gatwick)

400,000m³ capacity · 280+ homes and Gatwick Airport protected · 1-in-10,000-year dam design

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Key insight

Gatwick's £4m contribution to the scheme (protecting a fraction of what a single disrupted Christmas Eve cost in 2013) demonstrates the cost-effectiveness of catchment-scale flood storage over site-specific flood barriers.

Transferability to UK: HighFlood storage reservoir approach at catchment scale is directly applicable to UK airports and transport hubs in flood-prone river catchments.

The Clays Lake Scheme — one of four flood storage reservoirs in the Upper Mole Flood Alleviation Scheme — increased a lake's capacity from 10,000m³ to nearly 400,000m³, providing 1-in-50-year fluvial flood protection to Gatwick Airport, over 280 homes, and key road infrastructure. The 2013–14 storms, which caused 145 Gatwick flight cancellations and disrupted 13,000 passengers, directly drove this investment.

Climate drivers

Flooding – fluvialFlooding – surface waterStorms and high winds

Impacts

→Water damage→Airport operational disruption→Service cancellations

Adaptation measures

  • Flood storage reservoir (dam)
  • Catchment flood risk management
  • Leaky dams and nature-based upstream interventions

Assets affected

Mechanical and electrical equipmentBuildings and stationsAirport servicesAirfield

Investment

£4m Gatwick contribution; £17m total Upper Mole scheme (4 reservoirs)

Band: £10m–£100m

Delivery period

—

  • Gatwick Airport Limited (GAL) is built across the low relief, impermeable clay flood plain within the River Mole Catchment in the Thames River Basin District.
  • The impermeable geology gives the Mole a naturally rapid (“flashy”) flooding response to rainfall events; precipitation flows as surface run-off into streams and channels.
  • The area has suffered significant flooding in 1947, 1960, 1968, 1974, 1990, 2000 and the winter of 2013 to 2014 .
  • In 2000, the A23 under GAL’s South Terminal was closed for three days due to flooding and 109 homes were affected in Crawley .
  • The 2013-14 storms and flood events severely impacted GAL’s airfield operations: o Three electrical sub-stations serving the airfield were affected by flooding, and 35 inbound flights were diverted away from Gatwick due to high winds . o Due to the high winds, unsecured aircraft baggage containers blew onto the airfield, resulting in the damage of the runway instrument landing system . o Flooding of GAL’s North Terminal electrical systems ultimately led to the cancellation of 145 flights, 77% of planned departures, and further delays; impacting over 13,000 passengers on Christmas Eve .
  • The Airport shares responsibility for managing the river with other land users and the Environment Agency.
  • Wetter winters and more intense rainfall events leading to flash floods are projected to increase across the UK under climate change, increasing in intensity through the century.

Ref: ID_15 · Environment Agency · Curated & verified by HIVE

Transferability to UK: High

Flood storage reservoir approach at catchment scale is directly applicable to UK airports and transport hubs in flood-prone river catchments. Nature-based upstream interventions (leaky dams, peatland restoration) provide complementary benefits.

UK contexts

UK airports in flood-risk catchmentsTransport hubs adjacent to riversLondon and South East transport infrastructure

London & South East

Transfer to other sectors (AI)