Flooding in Boscastle, England (2004)

One of the most devastating floods and peacetime rescue operations took place in the small Cornish village of Boscastle.

The village flooded in August 2004, washing cars and buildings into the sea and putting peoples' lives in danger.

Physical factors

Climate

Over 60 mm of rainfall (typically a month's rainfall) fell in two hours. This led to a flash-flood event.

The ground was already saturated due to the previous two weeks of above average rainfall.

How flash floods occur: 1. Heavy rain falls onto waterlogged ground; 2. Rainfall cannot soak in so runs down into river; 3. River rises dramatically and bursts its banks, flooding valley floor.How flash floods occur

Geology: impermeable slate

Photograph of Emergency services on the scene of the flooded village of Boscastle
Emergency services on the scene of the flooded village of Boscastle

The drainage basin has many steep slopes, and has areas of impermeable slate causing rapid surface run-off.

Boscastle is at the confluence of three rivers - Valency, Jordan, and Paradise.

A large quantity of water arrived within a short space of time causing the rivers to overflow.

Annual regime

The flooding coincided with a high tide, making the impact much worse.

Human factors

Many tourists were in Boscastle during the day, as it was the middle of the summer holidays. This meant that a higher than normal number of people needed to be evacuated.

The old road bridges became a major obstacle to debris transported by the river.

Physical causes of the Boscastle floodHuman causes of the Boscastle flood
Rain for 12 out of 14 days in August.Many trees had been cut down for farming. This limited interception and water went straight into the river channel.
A depression brought a thunderstorm on 16 August with over 200mm of rain in 24 hours.Increase in buildings within the drainage basin meant that there were more impermeable surfaces which directed water back to the river faster.
Steep valley sides - water flowed into the river channel very quickly.A few old arch bridges got blocked up with the flood debris. The bridge acted like a dam and eventually smashed through causing a surge of water up to 5m high.
The rock in the local area is slate which does not allow percolation.
The soils were quite thin and made up of impermeable peat soils. These became saturated so water became surface run-off very quickly.
There were very few trees to absorb water and slow the amount of water going into the river.

Effects

  • Homes, businesses and cars were swept away, affecting more than 1,000 people.
  • Income from tourism was lost. This had an impact on livelihoods and the local economy.
  • There were vast numbers of subsequent insurance claims.
  • No lives were lost, partly due to the rapid response of the emergency services.

Once the water had receded, the extent of the damage became clear. More than 70 vehicles were washed downstream by the flash-flood in Boscastle.