Flooding Case Study: Boscastle
Geography: KS3, topic 8.2.4
What Caused The 2004 Boscastle Flash Flood?
On the 16th of August 2004, there was a flash flood in Boscastle (in Cornwall).
Removal of vegetation
- The removal of trees and vegetation upstream of Boscastle increased surface runoff.
Steep relief
- Boscastle is in a very steep valley, which means surface runoff is high and fast.
- The steep valley acted like a funnel, channeling all of the rain into Boscastle.
The low bridge in Boscastle
- A bridge over the River Valency in Boscastle was not very tall and had a low arch.
- When the flash flood came, cars and debris became stuck under the arch creating a dam. This led to even worse flooding.
Intense rainfall
- 200mm of rainfall fell in 24 hours (the monthly average was 75mm).
- Between 50mm and 100mm fell in the space of a few hours.
- July and August 2004 had been rainy, so there was already a lot of surface runoff.
Lack of flood defences
- Boscastle had no flood defences. This meant that it was vulnerable to any especially heavy rainfall.
Test yourself on Flooding Case Study: Boscastle
When was Boscastle, England last devastated by severe flash floods?
How much rainfall did Boscastle get in a period of two hours just before the 2004 flash flood?