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The view from the top of Exceat Hill is one of the best views of the Cuckmere meanders. Unless contained within artificially maintained banks, rivers are rarely straight. More often they follow a curved course and when this is repeated in a distinctive pattern, they are called meanders after the River Menderes in Turkey. Although the cause of meandering is not fully understood, it is known that rivers assume this shape because less energy is then used in the discharge of the water than would be necessary if their courses were shorter and straighter. The mechanics of river flow are complex and in part controversial, but the effects of a curved channel on water moving downstream exaggerates the curve of the river. The water corkscrews round the bend eroding the outer curve of the bank and depositing the silt on the inner curve. The resulting features on the Cuckmere can still be found, even though the processes ceased when the meanders were severed by the straight channel which was cut in 1846 to facilitate drainage. The whole of the valley, up until 500 years ago, was a salt marsh as a result of a minor rise of sea-level in historic times which initially turned it into a shallow tidal estuary. The brownish material in the banks of the meanders, a brackish-water silt or alluvium, are those marsh deposits. The shallow depressions which wind their way across the valley floor towards the meanders, are traces of former creeks which were once like the modern ones seen on the saltmarsh. As suggested by the valley sides which appear to plunge below the flat valley floor, there must be a considerable thickness of other deposits below the silt. Borings have been made in the similar Ouse valley 7 miles to the west and by analogy, we would expect to find up to 8 metres (25 feet) of alluvial silts and clays. Below this, there is probably up to 10 metres (33 feet) of peat formed from the decay of largely alder swamp vegetation between about 4000 and 1200 B.C. Finally, resting, on the chalk, there are sands and gravels which started the valley fill process when sea-level rose in response to the melting of the world's glaciers at the end of the last Ice Age. The still earlier history of the Cuckmere River is even less certain and the evolution of the South Downs and the Sussex rivers which has been generally accepted over the past 40 years, is now being questioned. The last few million years have yet to reveal their secrets. |
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