Meanders

Aerial view of meanders 2
Aerial view of meanders

Unless contained within artificially maintained banks, rivers are rarely straight. Meanders are formed as a river flows sinuously across any flat area. 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. These curves in the river are increased over time and may eventually join up to form an ox-bow lake. The word 'meander' comes for the name of the river Menderes in Turkey.

Meanders Sunset
Sunset over the Meanders

The meander pattern that can be seen on the valley floor at the Seven Sisters Country Park is a landscape remnant from a time when the river Cuckmere followed a different course. In 1847 a straight cut was put in the river which effectively diverted any flow from the meanders and instead sent it straight up the river to beyond the causeway (which the A259 now passes over). This means that, apart from two sluices which are used to manage the water levels in the meanders, there is no flow of water passing through the meanders. This has led to their gradual silting up, which has resulted in some areas being only a few centimetres deep.

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.

Meanders
Meanders

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-levels rose in response to the melting of the world's glaciers at the end of the last Ice Age.

Seven Sisters Country Park
meanders