BARRY VAUGHAN, of Victoria Road, Dartmouth, writes:

I would like to clarify a very common confusion about river flow and tidal heights which crept in twice in Mr Hutch-eson's letter about tides . No quantity of river flow will raise the incoming ambient tidal height.

Tides flood in at that height as set by normal moon connected limits plus whatever wind is driving that tidal flow towards and estuary or river mouth.

River water can only flow down under the effect of gravity, it cannot flow upwards to form its own pond higher than the mass steady level of the sea.

Almost certainly, this common confusion comes from the usual actions of a storm, where wind blows, as well as carrying heavy rain.

It seems then as though the flooding river is helping to raise the final tide level – but it is the wind out in the sea all the times – the river can only flow to sea level.