Unit 3 Increasing Risks

•Describe and explain the causes of rapid erosion on the Holderness coast.•Evaluate the impact of rapid erosion on the residents of the Holderness coast.

With ever increasing numbers of people choosing to live near the coast the risks presented by coastal erosion and rising

sea levels have also increased

Coastlines are worn away (eroded) by wind action, tidal currents, wave currents, or

drainage.

For centuries there has been an erosion problem along the Holderness coast, which stretches between Flamborough Head in the North and Spurn head in the South.

On average 2m of coastline are lost each year – the fastest in Europe.

Since Roman times it has eroded by 4km and 29 villages have been lost.

Other villages are disappearing now. In 1967 a storm caused the loss of 10m in

one night and 12 bungalows near Bridlington were so near the sea that they had to be destroyed.

The shape of the coastline Width of beach Length and direction of the fetch Where the wave breaks Height or steepness of wave Wave energy Rock resistance Structure Human activity

The three main reasons for the rapid erosion at Holderness are:

Geology Fetch Longshore drift and beach material

The two main types of rock on the Holderness coast are Boulder clay and chalk

The boulder clay has very little resistance to erosion, especially when wet, making it very susceptible to erosion

Most of the coastline is boulder clay, which is also known as glacial till.

It is a mixture of fine clays, fine sands and boulders deposited by glaciers after the last ice age.

It has very little resistance to erosion, especially when wet.

It produces shallow sloping cliffs, between 5 and 20m high.

These cliffs are rapidly eroding, on average 2m a year.

Waves are caused by the transfer of energy from wind to the sea water – it is the form of the wave that moves forward, not the water

Height and power of wave depends on the strength of the wind, the amount if time it has been blowing and the fetch.

As waves reach shore – water depth decreases – wave energy concentrated in a narrowing zone – changing the form of the wave until it collapses and water is thrown on the beach – releasing the wave energy.

With waves the greater the wind the greater the frictional drag and therefore the size of wave

Those that travel short distances and are the result of local waves are seen as sea waves

Those that are formed from distant storms and travel large distances are known as swell.

Holderness is exposed to winds and waves from the north-east, which have a fetch of about 500-800km. 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 5000km 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.

Small, almost enclosed seas, like the North sea, often generate huge waves during storms. Waves move within the sea but cannot disperse their energy – rather like water slopping up against the side of a washbasin

The sea floor is deep along the Holderness coast. Therefore, the waves reach the cliffs without first being weakened by friction with shallow beaches.

SO WAVES CAN BE HUGE ON THE NORTH SEA COAST!!

CREST TROUGH WAVE PERIOD LENGTH VELOCITY STEEPNESS ENERGY SWELL

CREST – Highest point of the wave TROUGH WAVE PERIOD LENGTH VELOCITY STEEPNESS

CREST – Highest point of the wave TROUGH – lowest point of the wave WAVE PERIOD LENGTH VELOCITY STEEPNESS

CREST – Highest point of the wave TROUGH – lowest point of the wave WAVE PERIOD – Time taken for wave to

travel one wave length LENGTH - VELOCITY STEEPNESS

CREST – Highest point of the wave TROUGH – lowest point of the wave WAVE PERIOD – (T) Time taken for wave

to travel one wave length LENGTH – (L) Distance between two

successive waves VELOCITY - STEEPNESS

CREST – Highest point of the wave TROUGH – lowest point of the wave WAVE PERIOD – (T) Time taken for wave

to travel one wave length LENGTH – (L) Distance between two

successive waves VELOCITY – (C) speed of movement of a

crest in a given period of time STEEPNESS –

CREST – Highest point of the wave TROUGH – lowest point of the wave WAVE PERIOD – (T) Time taken for wave to

travel one wave length LENGTH – (L) Distance between two successive

waves VELOCITY – (C) speed of movement of a crest in

a given period of time STEEPNESS – (H/L) ratio of wave height divided

by length it can not exceed 1:7 (0.14) as it will break

CREST – Highest point of the wave TROUGH – lowest point of the wave WAVE PERIOD – (T) Time taken for wave to

travel one wave length LENGTH – (L) Distance between two successive

waves VELOCITY – (C) speed of movement of a crest in

a given period of time STEEPNESS – (H/L) ratio of wave height divided

by length it can not exceed 1:7 (0.14) as it will break

Cliff foot through a number of processes:Hydraulic action

Corrasion/AbrasionSolution/Corrosion

Cliff face processes:Weathering

PhysicalBiologicalChemical

Mass movement

Due to the fact that coastlines are usually not found as straight lines, it is unusual to find an area where waves hit the coastline at right angles.As a result waves will often hit the coast obliquely leading to a process called long

shore drift which is due to reflection of the waves.

This process results in the movement of sediment along the coast

Longshore Drift and removal of material may also

occur as a result of Tidal movement.Tides move in Flows and Ebbs.This movement may be at right angles to

the coastor along the coast (especially if the

direction offlow is through a narrow channel).

The beaches at Holderness are its main problem. Boulder clay erodes to produce mainly clay particles, which are easily transported out to sea, rather than accumulating close to the cliffs as beach sand. Although there are beaches, there is never enough sand to stop the waves reaching the cliff base at high tide.

What little sand is produced is taken southwards by longshore drift, leaving the Holderness cliffs poorly protected against wave attack. Eventually, a small amount of beach material reaches a spit at Spurn Head, where it accumulates.

Case Study: Rapid erosion of the Holderness Coast You are required to research three areas of the Holderness

coast: Withernsea, Mappleton, Flamborough Identify the coastal processes that are changing the shape of the

coast at each of the locations Identify evidence in the form of specific landforms and/or

damage to property at each of the three locations. Suggest likely impacts to residents of the processes at work in

each location. Suggest likely impacts on the natural environment of such rapid

erosion. E.g. will there be damage to coastal wetlands? You should then work to annotate a map of the coastline with

details of the erosion and impact at each location with the aim of creating a wall display of the information. You may wish to supplement your information with images of each area that show landforms and impacts.

Websites to use: http://maps.google.co.uk/maps?hl=en&tab=wl http://www.geography.learnontheinternet.co.uk/topics/

holdernesscoast.html http://www.sln.org.uk/geography/schools/blythebridge/

WLA2Coasts.htm Other resources to use: Ordnance survey maps of the Holderness coast. AS Geography for Edexcel, Oxford Publications photocopy

Location Processes Evidence/ landforms Impacts on residents Impacts on environment

Flamborough

Mappleton

Withernsea

Hard Engineering Techniques:Wooden groynes at Hornsea

These have been built to trap sediment carried by longshore drift, keeping the beach in place at Hornsea, which in turn protects both the cliffs and the town.

However, south of Hornsea the village of Mappleton was being starved of sediment being trapped due to the groynes. Waves eroded the cliffs so much in the early 1990’s that nearly 4 metres was being lost every year and the village was in danger of disappearing.

Rock Groynes at Mappleton

After a campaign by residents to protect Mappleton, Humberside council built two rock groynes to protect the village. These are boulders of granite, laid out like groynes, and cost almost £2million. The cliff face was also rebuilt to make it less steep and therefore more stable.

After this, at Cowden (3km south of Mappleton) sediment starvation was also causing these cliffs to be eroded, with the rate of erosion increasing from 2.5 metres per year in 1991 to 3.8 metres per year in 2007. This process is called terminal groyne syndrome and happens frequently when groynes are stopped.

Revetments at EasingtonA rock revetment has been built to

protect Easington’s gas terminal. Like stone groynes, a revetment consists of large granite boulders. The boulders are placed like a wall in a line of defence along the shoreline/ It works by absorbing – not reflecting – wave energy using large air spaces between the boulders and a broad surface area. Revetments are very expensive but lone lasting.

Sea walls at Withernsea

Withernsea replaced its old straight sea wall with a recurved wall at a cost of 6.3 million pounds. The cost benefit analysis showed that it was worth investing in the wall to protect the local properties and save tourism employment.

Negatives are the noise of the waves crashing against the wall and views from the hotels are restricted. Some tourists argue that the rip rap at the base of the sea wall are unattractive.

Soft Engineering TechniquesBeach nourishment at Hornsea

This had added sediment to the beach at Hornsea, by dredging and pumping from offshore straight onto the beach.

This was to:- create a wider beach to protect the

cliff line- to add sediment into the coastal

system so that areas downdrift benefit.

The downside is that its sediment can be taken away in a single storm, and so it has to be replenished every one or two years.

Coastal ZoningThis is also known as red-lining, and

is a device used by planners to divide stretches of coast into land use zones. Red-lining identifies those zones at risk to erosion where the costs of protection exceed the possible benefits. Decisions are then made as to which areas need protecting, and zones that are decided to not, are denied planning permission for anything along the coast that may protect the coast.