Estuarine, Coastal and Shelf Science

Transcription

The Blackwater estuary on the coast of Essex. A place where land meets sea and human and natural processes interact. The estuary forms an environment of diverse habitats and species and is an area used in a variety of ways. It's a flatland of marshes, creeks and mudflats, used for fishing, farming and recreation. But it's the relationship between the sea and the land that is fundamental. A relationship that may at first seem predictable, until nature unleashes a freaky bent which can upset the whole balance. By looking more closely at this relationship, we can begin to understand the themes of change, contest and response that enable us to explore the environment. The first of these, the theme of change, emphasises the dynamic relationship between land and sea over time. Well, talking about change, if we just look the last 100 years, the last two generations of people, they would have seen, first of all, a salt marsh out here and not sea. Then the salt marsh washed away and it became a mudflat. Then the mudflat went and it became a beach. These changes are talking place all the time. Change is the order of the day. Change is what coasts are about. When people look at a coastline like this, they think that it's always been the same, that this is static. In actual fact, only 10,000 years ago, a microsecond of geological time, this was part of a fresh-water system with the Thames, the Thames sweeps up here. If we go forward in time from then, from those big changes at the end of the last Ice age, if we went out there now and we went out a mile on that mud, when the tide goes down, you can go a mile out, you'll come across 4,000-year-old oak forests when it was dry land. 400 year ago, this bit of sea, which is right by the beach, had sheep grazing on it. Then we come to the 14th century, the mini Ice age came. The sea level has stopped rising, all the static. That's when all the sea walls went in. It's during that period that man realised the importance of using its coast, particularly for agricultural gain. At the mouth of the Blackwater is a 7th-century Saxon chapel of St Peter, itself on the site of a Roman fort. Here, Kevin Bruce describes the impact of humans on the local landscape. The most significant factor in this has been human changes. It's been the desire of man to reclaim natural salt marsh for agricultural purposes. So the landscape that we have here is very much a man-made landscape. The farmers found it beneficial to reclaim the land here because previous than building any sea walls at all, twice a day the saltings would have been flooded by the tides. They found these saltings extremely good for pasturing sheep and Doomsday Book records that hundreds of sheep were kept on the Essex's marshes, all round the Essex coast. And from the Middle Ages, right up to the 19th century, more and more land was being recovered from the sea. It's been a constant process. What these farmers discovered on building a new sea wall, then they changed the tidal patterns. The sea was beginning to slow down and enable deposition to take place further out on the saltings. It's actually recorded in many of the documents. The farmers reckon that within five or ten years of building a sea wall, there will be new, fresh saltings for them to enclose. So, bit by bit, they must have pushed out the level of the saltings and when they found it convenient, they would enclose them to produce new land. You can actually see from the maps how far the saltings extended. But once the sea level began to rise, the situation changed again. As time went on and the mini Ice age ended, in about 1860, this coastline here, which would have been salt marshes by now, because the sea's come up a bit... There was no beach here then. In fact, this beach, in the 1930s, was a little tiny, narrow strip. As the mud is washed away, the coarse material gets washed ashore and forms these beaches. Then behind us we get these rebeds forming. You have to bear in mind, in between the rebed there, and the trees behind it and the houses on the top, that cliff was a sea cliff in Saxon times. The sea level is always going up and down since the end of the last Ice age but with a steady and consistent trend upwards and you can't stop that.