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 necessarily happen.

The Exe Flood Alleviation Scheme 1965-1979 was designed to cope with a 700 cumecs discharge.