Boscastle Floods

What caused the floods?

A map of England and Wales. The location of Boscastle is highlighted by the red marker (image courtesy of Google Maps).
In order to understand what caused the floods, we must first take a look at the geography of Boscastle and the surrounding area.
Boscastle is located in Cornwall, an area in the far south-west of England. The village is located in a natural inlet, forming a natural harbour which was expanded in 1584 by esteemed explorer Richard Grenville, who built two stone harbour walls which stand to this day.
The surrounding area is rather hilly and is famous among walkers for its panoramic views and coastal scenery.
There are two important factors about Boscastle's surroundings that are of interest to us. The first is that the village (and Cornwall as a whole) is exposed to mild, semi-tropical winds blowing West from the Atlantic ocean.
The second is that near the village is a hill known locally as "Brown Willy". At 420 metres high, it is the highest point in Cornwall.

A combination of these two factors produces an irregularity known as the "Brown Willy Effect".

The Brown Willy Effect

Brown Willy in all its glory.
The Brown Willy effect is when warm, moist air from the Atlantic ocean blows over the hills surrounding Boscastle (Brown Willy being one of them) they are slowed by friction. Because Cornwall is very narrow, winds from the North and South coast actually meet near the middle, where they converge and follow whatever direction the wind is prevailing in. If the winds blow over any of Cornwall's moors (and there are a lot of them), they are lifted into the air because of the moor's high altitude. This causes the moisture in the winds to condense, bringing much more rain to Cornwall than other parts of England. Thus, the Brown Willy effect.

The consequences of the Brown Willy effect.

The river Valency, July 16th 2004.
On the day of the floods, an unusually warm wind blew over the Atlantic towards Cornwall, picking up a large amount of moisture as it went. When this wind blew over Cornwall, the Brown Willy effect caused an abnormal amount of rain to fall around Boscastle. At one point it was recorded that 9cm of rain fell in one hour, an amount that soon caused the river Valency (which flows through the village) to burst its banks after water levels rose by over seven feet.

Of course, the consequences of the river overflowing were disastrous.