[size=0.9em]Feb 23, 2014 [size=0.9em]2389 Words [size=0.9em]10 Pages
[size=0.9em]The Holderness coastline is very low lying and runs along the North East coast of the UK from the chalk cliffs of Flamborough Head in the north to the sand spit of Spurn Point in the south, a distance of 61 km.
The Holderness Coast is famous due to its history of being one of Europe's fastest eroding coastlines. Essentially erosion is the process by which coastline rocks are broken up by the action of the sea and transported out to sea or along the coast by waves and the wind. Coastal erosion can occur in numerous forms:
Seawater can compress air into cracks in rocks. When the air escapes it does so under pressure and shatters the rock (hydraulic action)
Large waves throw beach material against the cliffs - a process known as corrasion.
In a process known as attrition waves cause rocks and pebbles to crash into each other, causing them to break up.
Certain types of coastal material, such as chalk are slowly corroded by acids dissolved in the sea water.
Coastal erosion processes create a number of significant landforms. There are a number of factors which affect the rate of this erosion:
Rock Type – A more resistant rock, such as granite, will be eroded slowly, whilst a less resistant rock, such as clay or mud, can be eroded very quickly.
Jointing / Faulting – The more faults and joints a rock has the more susceptible it is to erosion, both from coastal and sub-aerial processes.
One more point to consider before I look specifically at the Holderness Coast is the two different types of waves:
Constructive waves - have a strong swash (movement up the beach) and a weak backwash (movement back down the beach).
Destructive waves have a weak swash (movement up the beach) and a strong backwash (movement back down the beach).
The Holderness Coast is one of Europe's fastest eroding coastlines. The average annual rate of erosion is around 2 metres per year. This is around 2 million tonnes of material every year and since Roman times 4 km of land has been lost. Holderness was not always a low lying coastal area. Before the ice age (during the tertiary period) it was a large, wide bay backed with chalk cliffs running from Flamborough head to hessle, west to the city of Hull. Following the ice age the coastline was weakened the main reason for this is because the bedrock is made up of till. This material was deposited by glaciers over 18,000 years ago.
One of the driving factors of the rapid erosion is linked to the fetch. Holderness is exposed to the wind and waves from the north-east which have a small fetch of around 500-800 km. This is not far but the coast at Holderness is attacked by other factors affecting the ferocity of the waves:
Currents – or swell – which circulate around the UK from the Atlantic and into the North sea. The Atlantic fetch is 5000 km or more and its currents add energy to waves in the North sea. Therefore, there are often powerful destructive waves along this coastline
Low pressure weather systems passing over the North sea are often intense, and locally produce very strong winds and waves
The sea floor is deep along the Holderness coast. Therefore, the waves reach the cliffs without first being weakened by the friction with shallow beaches
Flamborough Head
The most striking aspect of Flamborough Head are the white chalk cliffs that surround it. The chalk lies in distinct horizontal layers, formed from the remains of tiny sea creatures millions of years ago. Above the chalk at the top of the cliffs is a layer of till (glacial deposits) left behind by glaciers 18,000 years ago, during the last Ice Age. As the cliffs below are worn away by the action of the waves, the clay soil often falls into the sea in huge landslips. Landslips; also known as rotational slumps, are occasional rapid movements of mass of earth or rock dropping down a concave plane. Water percolating through sandstone gets into the clay beneath, saturating it. With the weight of the rock above forcing down on it the clay moves seawards as a mud flow. With the clay moving sideways the sandstone above slumps down. Undercutting of a steep slope by the sea weakens the rock above, making a slump more likely.
The sea attacks the coast around the headland in two ways. Waves beat against the vertical cliffs and, at the high water line, weak points in the chalk are worn away into caves. The weakest points are where vertical cracks or fault lines have appeared in the horizontal beds of chalk. At places on the cliffs where the chalk juts out, these caves are worn away into rock arches. If the top of an arch collapses, the result is a pillar of chalk cut off from the rest of the headland - this is called a stack. Flamborough Head has many caves and arches, as well as a few stacks. The process of erosion that has created them can take hundreds of years to do its work.
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.
The strategic position of the sand spit, guarding the entrance to a major waterway lead to its use as a position for shipping beacons and lighthouses. Historical accounts of settlements and lighthouses, particularly accounts of their destruction and the break up of the spit have enabled us to discover that over the last 1000 years there have been five 'Spurn points'. Each spit has grown until it has become unstable, been destroyed and then rebuilt slightly to the west of the former one, the cycles lasting approximately 250 years. The current spit is nearing the end of the cycle, and despite considerable coastal defences the neck is in continual danger of being breached.
Process of Creation:
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.
Why protect Spurn point?
Spurn Point protects many wildlife habitats and ecosystems which have developed behind the spit. Spurn Point itself has essential services such as the Lifeguard station. Many wooden groynes and other coastal defences have been built to protect and preserve the spit. However if sediment is prevented from reaching Spurn Point the consequences could be immense.
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 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.
Before we look specifically at the Holderness I’m going to explore in general why coastlines should be protected.
The aim of coastal management is to protect people and the environment from the impacts of erosion and flooding. Coastlines need protecting because:
1) Increasing development of coastal areas including urban areas (towns) means there are more people at risk from coastal flooding such as local residents living near the coast.
2) This risk is likely to increase in the future as climate change brings about rising sea levels and an increase in the number of coastal storms.
3) Increased amenity value (use as leisure and recreation such as surfing) of coastline. Increased wealth and leisure time has led to increased demand for water sports such as Calshot Spit activity centre.
4) Increased economic/transportation/industrial value (use as making money such as industries like Exon oil refinery on The Solent, largest oil refinery in the UK handling 2000 oil tanker movements a year and Easington gas station on the Holderness coast). Southampton is the UK’s busiest cruise port handling 250 cruise ships per year with ¾ million passengers.
5) Increased environmental/nature conservation value (use as key and fragile habitats for rare wildlife such as seahorses in Studland Bay and Keyhaven Marina (SSSI), 2000 acres of saltmarsh and mudflats behind Hurst Castle spit).
Planning Approaches
There are five generic approaches that can be opted for during the planning stages of coastal defence strategies
1) Abandonment (do nothing) - An option considered when the land is of low value and there are no significant risks to the human population. Inexpensive at first but as the land erodes compensation may be needed to be paid if people begin to loose their property.
2) Managed Alignment (managed retreat) - This is applied to specifically designated areas, mostly places of low value that are adjacent to the cost and are allowed to erode or flood to allow natural dynamic processes to occur/re-occur. The benefit of this is that it is low cost and help creates natural defences such as beaches.
3) Hold the line - Mainly hard engineering solutions are adopted for instance sea walls or rip rap. Defences are built and maintained because they protect towns, infrastructure or places of economic significance.
4) Move seawards - This involves constructing new defences in front of or as well as previously existing defences
5) Limited intervention (accommodation) - Adjustments are made to be able to cope with inundation and erosion. In Morecambe the sea walls and land behind have been designed to accommodate flooding i.e new development is set back from the sea wall and the land close to the wall has low cost development such as play parks, cycle paths and car parks.
Holderness coast erosion impacts:
Impacts on people:
Homes near cliffs are at risk of collapsing into the sea which means insurance is literally impossible to get.
Property prices have fallen
The gas terminal in Easington is at risk as its only 25m from the cliff and it counts for 25% of Britain's gas supply.
Accessibility to settlements has been affected along the coast as roads have collapsed into the sea.
Impacts on the environment:
Some sites of special scientific interest (SSSI’S) have been threatened e.g. Lagoons near Easington. The lagoons are separated from the sea by a narrow bar however if the bar is eroded the lagoons will be destroyed.
Management strategy problems:
Groynes protect local area but cause narrow beaches to form further down the Holderness coast which increase erosion further down the coast e.g. Cowden Farm is now at risk of falling into the sea.
The material produced from the erosion of Holderness is normally transported south into the Humber estuary and down the Lincolnshire coast. Reducing the amount of material that’s eroded and transported south increases risk of flooding in the Humber estuary as there is less material to slow the flood water down. Also the rate of coastal retreat along the Lincolnshire coast has increased because less new material is being added.
Spurn head is at risk of being eroded away because less material is being added.
Bays are forming between the protected areas and the protected areas and becoming headlands which are being eroded more heavily, which means maintaining the defences in the protected areas is becoming more expensive
Below is a news paper article (Taken from the Observer, 1st December, 1998) about the town of Mappleton along the Holderness coast. The article describes the situation in the town; in particular the extent at which the rapid erosion is affecting the village people and land.
The Future for Holderness
The erosion along the Holderness coast has been a serious problem for people since the Roman era when settlement first grew there in about 400 A.D. Historical evidence shows that around 23 towns/villages have been lost over that last 1600 years. An estimated 3 miles of land have been lost to the sea over this period and research suggests that the current rate of erosion (2 meters per year) is not going to stop or slow down. Although unclear some research even suggests that the rate erosion is going to increase. This is due to factors such as sea level rise, along the Holderness cost the sea is thought to be rising by about 6mm per year and this is not been helped by land subsidence, another problematic issue facing stretches of the coastline
Our knowledge of defending our costs has evolved over a century or so and has shown us that it is not as straight forward as building hard engineering defences such as sea walls, an approach opted for in the in the Victorian period. Many modern engineering solutions now favour soft defence option or accommodation approaches. New projects planned for Holderness includes plans to create Britain's first large-scale underwater artificial barrier reefs made from concrete moulds are among some of the new solutions.
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