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It’s only the depth which alters

You often hear people saying that they think the harbour is silting up, but is there any way of checking this?

Well, yes, there is: I did it without leaving my armchair and so can you. My grandfather was a Master Mariner, a First World War naval captain, Commodore of his local yacht club, a lifeboat crew member and a keen yachtsman. He used to sail the Fastnet race in his 2½ ton Hilliard (yes, 2½ ton: it would not be allowed now). As a result I have a 1933 Salcombe chart in pristine condition. Presumably Grandpa had it in case he needed to put in and did not do so.

The soundings are in feet, but it is not difficult to compare them with a modern chart, which has soundings in metres. In the 70 years between 1933 and 2002 (the date of my current chart) most parts of the harbour have become about half a metre shallower, although the Bag and Snapes Point are now very significantly deeper.

It’s not difficult to see why. The harbour (as I am sure all schoolchildren know) is not an estuary of a running river, but a ria – a flooded valley or a fjord. There is no great river flushing out the silt, only the tide flowing in and out. It is true that the tidal flow is such that about half the water is changed at every tide; but tides alone will not clear a ria of mud.

The Victorians knew this. They used to dredge creeks and drag chains behind the paddle steamers going up to Kingsbridge, leaving the tide to do the rest. But dredging today is expensive not least because of the cost of disposing of the spoil, and run-off from fields has increased because 4-wheel drive tractors can now plough steep fields that previously had to be left to pasture.

However we have found a solution and tried it out in Batson Creek. A Dutch company (www.vanoord.com) has developed a method of dredging by injecting water into the mud to create a slick about a metre thick which then slips out on the tide. This is cleaner, as the mud never breaks the surface; and it is cheaper as you don’t have to pay for carrying-away the spoil. Environmental tests have shown that the mud clears the Bar about 40 minutes after leaving Batson and deposits itself somewhere near Bolt Head – as it happens, where we would otherwise dump dredged spoil. The fact that this method works, seems environmentally friendly, and is more affordable, means that the harbour can now resume dredging without breaking the bank.

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