Introduction: Exe in Flood
The West Country was hit by a series of floods during the autumn of 1960
when over two-thirds of the average annual rainfall fell in 10 weeks from
27th September to 5th December.
The Tributaries of the
Exe absorb the rainfall and pass the volume of water downstream creating
a massive surge of rising water down the valley towards Exeter. Exeter has
long suffered from flooding but 'Black Thursday' 27th October 1960 was to
lead to the development of the Exeter Flood Alleviation Scheme.
Measuring the volume of flood water
The discharge of a river is measured in units known as cumecs (cubic metres
per second). It is calculated by measuring the cross-section of the river
channel and multiplying it by the speed of the flow of the water e.g. a 15
metre wide river with a depth of 5 metres with water flowing at 4 metres a
second would produce 15x5x4 cumecs (300 cumecs)
Before 1960 the Exe river channel was able to cope with between 280 - 450
cumecs. That fateful autumn saw flows of 700 cumecs and severe flooding!
This sort of flood level may be said to occur once in every 50 years whilst
a 500 cumecs discharge may be every 30 years. A once in 100 year flood would
be in the order of 900 cumecs. This is only a likelihood gauge and does not
The Exe Flood Alleviation Scheme 1965-1979 was designed to cope with a 700