Yr12 Coasts: Coastal erosion – Physical & Human Causes & Physical, Socio-Economic Consequences
(Case Study)
Definition: Coastlines are dynamic (constantly changing) environments. Along high energy coastlines such as the south-west of England,
strong south-westerly prevailing winds fed by low pressure systems and a 6000km long fetch (distance the wave has travelled) across
the Atlantic Ocean provides considerable energy to create destructive waves that can erode the coastline by wave pounding (sheer
weight of the wave); abrasion (sand hurled at the cliff); attrition (pebbles knocking into each other and becoming smaller and rounded);
and corrosion, where alkaline rocks such as limestone react with slightly acidic seawater and dissolves. However, the rate of erosion is
dependent on a number of factors:
Generic Physical Causes:
Wave steepness and breaking point e.g. waves breaking at the cliff-foot (due to narrow beach or storm conditions) will exert far more
energy
Fetch – the distance the wave has travelled
Sea depth – a steeply-shelving sea bed will create higher, steeper waves
Coastal configuration (shape of the coast) – Headlands attract energy through wave refraction
Width and shape of beach e.g. shingle beaches with a steep profile are good at dissipating high energy waves by percolation through
the pebbles.
Isostatic / Eustatic change: In areas such as south-east England, this change is causing an increase in sea levels and potential erosion.
Geology: Less resistant rocks such as glacial till which has a low angle cliff profile is more susceptible to cliff-foot erosion and
rotational slumping as the fine silts are transported in suspension and not deposited on the beach, making it narrow and prone to
increased rates of erosion.
Differential erosion will take place for instance along discordant coastlines with headlands (resistant) and bays (less resistant) rocks
Lithology: the characteristics of the rock e.g. granite is very resistant, clay is weak; whilst limestone is resistant, it has joints which
forms lines of weaknesses for chemical weathering and corrosion.
Generic Human Causes:
Sea walls and coastal defences: hard engineering works against the coastal system and strategies such as groynes restrict the
movement of sediment by longshore drift and increase the rate of erosion down-drift.
Land reclamation: Reclaimed land such as the fens in East Anglia from the 15th century is only protected from erosion by sea walls.
Development: New coastal housing developments increase surface run-off and instability in the soil e.g. Bungalows built in Charmouth
(Dorset) required extensive drainage which saturated the clay geology and led to cliff retreat of 5m per year.
1
Yr12 Coasts: Coastal erosion – Physical & Human Causes & Physical, Socio-Economic Consequences
(Case Study)
Case study: Holderness Coastline, North-East England, UK
Where: Holderness coastal sediment cell, stretches 50kms from Flamborough Head in the north to
Spurn Head at the Humber estuary.
When: Constantly eroding, 29 villages have fallen into the sea since Roman times.
Why:
Specific Physical Causes:
Weather: deep low-pressure systems in the North Sea, particularly in the winter months drive northeasterly dominant winds, higher sea levels (surges) and heavier precipitation which increases subaerial processes and mass movement (slumping).
Waves – destructive north-east dominant waves with a relatively long fetch of up to 800kms provide a
strong backwash, eroding and transporting silts out to sea.
Rip currents - excavate ‘ords’ or deep hollows generates steep high energy waves, which intensifies
coastal erosion e.g. Great Cowden and Easington with recorded rates of 10 metres per year.
Geology – Weak boulder clay cliffs left by the last ice age (12000 years ago), retreating at 1.8 metres
per year. Precipitation saturates the clay, creating a slip plane and rotational slumping. Long-shore
drift carries an estimated half a million tonnes of sediment by suspension southwards per year, with
little deposition leaving narrow, low angle beach profiles susceptible to cliff-foot erosion
Specific Human Causes:
Development: Increasing population density and urban development such as leisure and holiday
facilities at Bridlington and Hornsea increase surface run-off, which need drains; increasing the saturation of the clay geology and
increasing rotational slumping by up to 5 metres per year.
Interfering with natural coastal processes – Groynes at Hornsea, Mappleton and Withernsea have meant that settlements down drift
such as Great Cowden have seen rapid rates of erosion of up to 10 metres per year which may be attributed to sediment starvation
caused by this hard management strategy.
Eustatic changes in sea level – human processes contributing to climate change may increase the incidence of storms in the North Sea
and rates of coastal erosion.
2
Yr12 Coasts: Coastal erosion – Physical & Human Causes & Physical, Socio-Economic Consequences
(Case Study)
What are the consequences of coastal erosion on the Holderness coast?
Specific Physical Consequences:
Loss of land at rates of between the average of 1.8 to the extreme of 10 metres per year (Great Cowden)
Geology of glacial till left by the last ice age 12000 years ago means that it is very susceptible to sub-aerial processes, the saturation
of clay strata and mass movement by rotational slumping.
The undercutting of cliffs by cliff-foot erosion processes and transportation of ½ million tonnes of silt southwards per year has left
a narrow, low angle beach profile which means erosion is a relatively continuous process leading to cliff retreat.
Specific Socio-Economic Consequences:
Loss of agricultural land e.g. Grange Farm at Cowden has experienced the loss of 10 metres per year; however, the economic loss of
this land is of less significance compared to other land use such as housing and tourist facilities found at Hornsea and Withernsea.
Consequences of a ‘managed realignment’ coastal protection policy against coastal erosion e.g. Aldbrough is located approximately
10 km south-east of Hornsea. The cliffs here are rapidly eroding so that Seaside Road now terminates at the cliff edge. Several
buildings have been lost to the sea since 1885 including businesses such as the Spa Inn, the Talbot Hotel and the Royal Hotel. Despite
these significant and potentially economically valuable land-uses; cost-benefit analysis suggests that it is too expensive to protect the
remaining buildings from rotational slumping meaning property values for the residents have fallen dramatically and are unable to insure
their properties from the effects of cliff retreat; fragmenting a small tight-knit community.
Assessment:
The physical causes of coastal retreat along the Holderness coast are the most important; significantly the weak geology of the area
composed mainly of unconsolidated glacial till which provides little resistance along this high energy coastline that regularly
experiences low pressure systems; resultant destructive waves; undercutting and cliff retreat at 2 metres per year. The human causes
serve mainly to increase the rate of cliff retreat; particularly through ‘hold the line’ hard management strategies such as groynes,
which fail to understand how the coast works as a system by increasing cliff retreat between 3-8 metres per year due to the
starvation of sediment from unprotected sections of the Holderness coastline such as at Aldbrough and Great Cowden.
It could be argued that the physical consequences of coastal erosion are more significant along the Holderness coast, with cliff
retreat the fastest in Europe at 1.8 metres per year and resultant loss of land and re-shaping of our dynamic coastline. Even when
roads and businesses are lost such as at Aldbrough, the socio-economic consequences are not considered significant enough to afford
protection. Only when there is a significantly higher land value or population density such as at Hornsea (pop. 8300) or Withernsea (pop.
3
Yr12 Coasts: Coastal erosion – Physical & Human Causes & Physical, Socio-Economic Consequences
(Case Study)
6000), are the potential socio-economic consequences taken seriously with £5.2 million and £6.3 million respectively invested to
protect tourist economic activity and halt the fall in property prices.
4