The Boscastle flood of 2004 occurred on Monday, 16 August 2004 in the two villages of Boscastle and Crackington Haven in Cornwall, England, United Kingdom. The villages suffered extensive damage after flash floods caused by an exceptional amount of rain that fell over eight hours that afternoon. The flood in Boscastle was filmed and extensively reported but the floods in Crackington Haven and Rocky Valley were not mentioned beyond the local news.

The floods were the worst in local memory.A study commissioned by the Environment Agency from hydraulics consulting firm HR Wallingford concluded that it was among the most extreme ever experienced in Britain. The peak flow was about 140 m? /s, between 5:00pm and 6:00pm BST. The annual chance of this (or a greater) flood in any one year is about 1 in 400.

The probability each year of the heaviest three-hour rainfall is about 1 in 1300 (although rainfall probability is not the same as flood probability).At midday on the 16th August 2004, heavy thundery showers had developed across the South West due to a weak disturbance to the northeast of the United Kingdom. [1] The last time Boscastle had suffered notable flooding was in 1996 as a result of Hurricane Lili, but floods are recorded in 1847, 1957, 3 June 1958 (one man drowned) and 1963. On 16 August 1952 the small town of Lynmouth, 50 miles (80 km) north-east along the north coast in Devon near Exmoor, suffered extensive damage in a catastrophic flood, in which 34 people lost their lives. Coincidentally, this was 52 years to the day before Boscastle's 2004 flood.