9th December 2013 The changing landscape of the estuary
The Cuckmere estuary is generally thought of as an ‘unspoiled landscape’, but it has actually been subject to human intervention for hundreds of years.
The land around the estuary has been farmed for centuries. Records dating back to the early 1700s show areas of arable planting on the rich clay running along the top of the downs, with grazing on the lower slopes.
But the shape of the land was very different then. The floodplain was very wide, formed at the end of the last ice age when huge amounts of meltwater washed over the Downs to the sea. This floodplain would have been intertidal (partially covered at high tide), with mudflats and saltmarsh. The river was naturally functioning, meandering across the floodplain. Flints deposited in the last ice age formed a wide barrier beach running across the mouth of the estuary, which was moving in an eastward direction through the process of longshore drift. This movement formed a spit across the mouth of the estuary, with the river mouth on the east side.
Shortly after this period the meanders started to silt up, possibly as a result of artificial building up of the river sides. This would have restricted the river’s natural movement within the flood plain. Partly as a result of this silting up, flows through the river were slow and therefore the mouth periodically blocked.
The course of the river was radically change in 1846 by the creation of the cut, which effectively isolated the meanders from the river, and fixed them in place.
The reasons for digging the cut are unclear, but it may have been to aid navigation, or to reduce flooding upstream – or a combination of both.
The banks of the river continued to be built up, holding the new course in place and allowing reclaimation of the flood plain for farmland.
By the end of the century, the spit still existed but had shrunk because of the restriction in the sediment being deposited. The mouth of the river therefore migrated across the estuary, depending on the river flow, from the west side (then called ‘The Marshes’) to the east (‘The Salts’).
The beach on the west side was much narrower because of the reduction in sediment supply from the west, possibly due to sea defences built further up the cost, which interrupted the process of longshore drift.
At first glance the estuary looks the same, but by the early 20th century man had continued to impose himself on the system in an attempt to halt natural processes.
The spit had disappeared, and the river was now in the middle of the estuary. The banks of the river continued to be built up, and fixed training walls had been put in place to hold the river mouth in one position. Because of continued erosion to the west beach, groynes had been put in place to hold the beach in place, at an unnatural angle. Shingle was extracted from the beach in this period.
Throughout the last century the floodbanks were defended from erosion from both river and tidal flows, and the training banks holding the mouth in place have been upgraded. Despite the groynes on the west beach, longshore drift continued, meaning that twice a year shingle had to be dug out from the river mouth and deposited back on the west beach.
The estuary today
Today, the estuary faces a number of threats. Sea levels on the south coast of Britain are predicted to rise by over a metre during the next century, and the frequency and intensity of storms caused by climate change is expected to increase.
As well as the threat of sea level rise, other factors mean that any attempt to continue to hold back nature may be unsustainable.
- The meanders are silting up, because there is no flow through them.
- The shingle is not naturally being replenished, leading to the erosion of the beach.
- The river walls and flood banks are coming to the end of their useful life, and water levels already reach the top of the banks at high tide.
In December 2008, the Environment Agency published its decision, under its Flood Risk Management Strategy, to with draw maintenance of the river banks.
Now, the Cuckmere Estuary Partnership wants to work with local residents and businesses to agree how best to manage the inevitable changes that will take place as the Cuckmere gradually reverts to a naturally functioning estuary.