Sir – The announced cost of £123m for the Western Conveyance Flood Relief Channel seems excessive (Report, April 24). It is to run, you say, from Botley Road to Sandford Lock, about four miles, and to be as wide as the River Thames.

The construction costs for the Oxford Canal, about 230 years ago, were £3,374 per mile (Charles Hadfield, The Canal Age), or £13,400 for four miles. We want something much wider than the canal, so multiply by say five, giving about £70,000.

There has been some inflation since 1780 of course. Oxford Canal was built by navvies with shovels and wheelbarrows, so if we were going to do the same, the inflation factor would be that for labourers’ wages, perhaps 500 or so, making a cost of £35m.

But one would suppose that the use of modern earth-moving equipment should reduce this substantially. £10m-£15m perhaps? Can anyone tell us how the figure of £123m was arrived at?

David Witt, Old Marston