Presentation on theme: "The Holderness Coastline – The Management of Coastal Erosion Holderness is a lowland region of England that lies between the chalk hills of the Wolds and."— Presentation transcript:
The Holderness Coastline – The Management of Coastal Erosion Holderness is a lowland region of England that lies between the chalk hills of the Wolds and the North Sea. It is part of the East Riding of Yorkshire. The Holderness Coast is one of Europe's fastest eroding coastlines. The average annual rate of erosion is around 2 metres per year. The main reason for this is because the bedrock is made up of till. This material was deposited by glaciers around 12,000 years ago. Information source: The University of Hull
How might the geology of the area affect the shape of the coastline? What processes are acting upon this coastline? Geology Map of Holderness Altitude Map of Holderness
What processes are acting upon this coastline? The Holderness Coastline is made up of soft boulder clays (tills) left after the retreat of the Devensian ice sheets about 12 000 years ago. They can be seen on the coast, being rapidly eroded by the sea. To look at, they are a mass of brown clay containing pieces of rock (erratics) brought here by the glaciers from Scandinavia, Scotland, the Lake District and Northeast England. These soft, recent deposits sit on a platform of chalk which slopes away gently to the east. Erratics in till at Mappleton
What processes are acting upon this coastline? Erosion of the Holderness cliffs is a cyclic, four stage process: 1.The soft Boulder Clay cliffs become saturated with rain water and lose their strength. 2.The cliff is too steep and fails either as a block of material or as a slurry slide 3.Cliff failure reduces the angle and prevents further erosion but … 4.Large waves from the North East remove the debris in longshore drift to the South and the cliff oversteepens, rain falls and the cycle begins again.
The order of this presentation… 1.Flamborough Head. 2.Mappleton 3.Aldbrough 4.Withernsea 5.Kilnsea 6.Spurn Head
1. Flamborough Head The chalk of Flamborough is a resistant rock that provides examples of erosion, features such as caves, arches and stacks. The chalk has formed a headland.
2. Mappleton Situated approximately 3km south of Hornsea lies the village of Mappleton. Supporting approximately 50 properties, the village has been subject to intense erosion at a rate of 2.0m per year, resulting in the access road being only 50m from the cliff edge at its closest point. Mappleton lies upon unconsolidated till (boulder clay). This material was deposited by glaciers during the last ice age 12,000 years ago.
Mappleton Mappleton is an excellent case study of an attempt at coastal management. In 1991 two rock groynes and a rock revetment made from huge blocks of Scandinavian rock were built. As a consequence a substantial beach accumulated between the groynes halting erosion (picture 1 below). However, further south the rate of erosion has increased significantly (picture 2 below). This is because material which is being carried south is not being replaced (it is trapped within the groynes). Therefore there is no beach to protect the cliffs. Even during a neap tide ( a tide which is 30% less than the average tidal range) the sea reaches the base of the soft cliffs and erosion occurs. 1 Cliffs to the north. Sea defences mean that the beach has grown and the cliffs are stable (look at the grass growing!) 2 Cliffs to the south. The sea defences don’t protect this area and the land is retreating rapidly.
Mappleton Northern section Defences = Beach build up Southern section No defences = Beach erosion
3. Aldbrough Aldbrough is a small settlement to the south of Mappleton. Where Mappleton had substantial sea defences built, Aldbrough has none. The cliffs here are rapidly eroding. Some residents think that the sea defences at Mappleton has made things worse. Why would they think this?
5. Kilnsea The old settlement of Kilnsea has now been completely lost. Sea defences were built here in the early 1900s to protect the Godwin Battery - a defensive gun emplacement and the rail-head for a light railway to further military installations on Spurn point. The sea defences are now crumbling and erosion is progressing rapidly.
Kilnsea Old map of KilnseaCurrent aerial photo of Kilnsea
6. Spurn Head The area known as Spurn forms the southern extremity of the Holderness coast and includes the unique feature of Spurn Head, a sand and shingle spit 5.5km long, reaching across the mouth of the Humber. Spurn is made up of the material which has been transported along the Holderness Coast. This includes sand, sediment and shingle. Spurn Point provides evidence of longshore drift on the Holderness Coast. It is an excellent example of a spit. How would sea defences along the coastline affect Spurn?
Spurn Head 1.The material eroded from the Holderness cliffs is swept southwards. 2.North easterly waves move the coarser sands and gravel down towards the mouth of the Humber 3.The finer sands and clays are swept offshore and continue southwards towards the Wash. 4.Spurn Head ‘hangs like a rudder’ for six kilometres off the end of Holderness, built by the sands and gravels eroded from the cliffs and transported south by longshore drift 5.In the past Spurn Head seems to have grown and been washed away in a regular cycle, slowly moving towards the east to keep pace with the erosion of the Holderness cliffs. 6.For over 100 years the position of Spurn has been fixed by artificial sea defences. These defences are now falling into disrepair and the sea is starting to erode parts of the peninsula once again.
Spurn Head Spurn Head changes position. Most of the spit has flexible road surfaces, which are like mats that can be picked up and moved following major storms. There is plenty of evidence of this movement. Former railway tracks that were built to move building materials along Spurn (for the building of Bull Fort in the Humber Estuary) now appear to lead into the sea.
Spurn Head Is Spurn eroding? The end of Spurn is fairly stable. This is due to it’s size and the presence of deep rooted plants. The rest of Spurn erodes and moves constantly. There are some groynes to protect it, but these are very old now.
Spurn Head Is it important to protect access to Spurn Point? Full time lifeboat men live here with their families. The Humber estuary is very busy with large ships. It is one of the most dangerous estuaries in Europe, so pilots guide boats in and out. Their base is on Spurn for quick access to sea. The pilots do not live on Spurn. Spurn is also important for birds and wildlife.
The future? Oil terminal Wind turbines Lifeboat Station Humber Pilots Many key industries, farms and homes lie within 50 meters of the coastline. 1.Should they be saved? 2.What effects would saving these have on other areas of the coastline? 3.Who should pay?
How can the coastline be protected? Hard engineering techniques aim to stop coastal processes from occurring. Soft engineering methods try to work with nature to protect the coast.
What has been done to protect Swanage? What is the purpose of each scheme at Swanage? Match the correct scheme to its purpose!