Coasts

COASTS: WAVE ENERGY & FETCH Waves are ‘energy movements‛ through the water caused by the wind They play a very important role in shaping the coastline and they the main way in which the sea erodes, transports, and deposits material The energy of a wave is determined by the HEIGHT (distance between its trough and crest) and LENGTH (distance between two crests)

Four Major Factors affect Wave Size and Energy *FETCH

the distance over open sea over which the wind has blown (further it has travelled, the larger it is)

The main FETCH affecting the UK (Fetch is the distance of open sea over which the wind has blown)

THIS IS THE MOST IMPORTANT FACTOR CONTROLLING WAVE ENERGY *STRENGTH OF WIND the stronger the wind, the larger the wave *DURATION OF WIND the longer the wind blows, the larger the wave *OFFSHORE GRADIENT waves ‘break‛ early in shallow water – the steeper the offshore gradient, the larger the wave

Near the Coast, Waves slow down in the shallow water, causing them to ‘break,‛ becoming unstable Seawater moving up the beach is SWASH and moving back to the sea is BACKWASH

COASTS: WAVE TYPE CONSTRUCTIVE / DESTRUCTIVE All waves ‘Break‛ in the same way BREAKING WAVES

1. Wave approaches shallow water 2. Lower part slowed down by friction from sea bed 3. Upper part continues moving forward 4. Top of wave is unsupported and unstable 5. Wave topples forward and breaks 6. Crashes into cliffs or surges up a beach

Swash is a wave surging up a beach Backwash is a wave washing back down a beach Waves can be CONSTRUCTIVE or DESTRUCTIVE CONSTRUCTIVE WAVES Calm conditions – light winds Long in relation to height Swash is stronger than backwash Gentle waves – 6 to 9 per minute Deposition and Transport occurs

DESTRUCTIVE WAVES Storm conditions – high winds (not always) High in proportion to length Backwash is stronger than swash Frequent waves – 11 to 15 per minute Erosion rates are high

COASTS: EROSION The Sea ERODES the Coast in four main ways: HYDRAULIC ACTION

lots of sea water crashes against the land, and air and water are trapped and compressed in rock surface cracks. When the sea moves away the air expands explosively weakening the rocks, enlarging the cracks and breaking pieces off WAVE POUNDING (linked to Hydraulic Action) the ‘battering-ram‛ action of the weight of the pounding waves

CORRASION

is very effective and is caused by broken rock fragments battering the land, cliffs etc and breaking off other pieces of rock

ATTRITION

occurs when rock fragments grind each other down into smaller and smoother pebbles, shingle, and finally sand which is later deposited as beaches

CORROSION

involves chemical action of sea on rock. If the rock is limestone, it dissolves in the sea-water – some sea salts can also react with certain rocks and cause them to rot

(Also SUB-AERIAL processes – people walking along the tops of cliffs will wear pieces away)

COASTS: TRANSPORTATION Beach material is TRANSPORTED up, down and along the coast in four ways 1. 2. 3. 4.

TRACTION SALTATION SUSPENSION SOLUTION

boulders and cobbles are rolled along by powerful waves pebbles are bounced along by waves sand and silt are carried in suspension calcium carbonate and salts are dissolved in the sea water

Ø LONGSHORE DRIFT Ø This is the transportation of beach material along the coast by waves It occurs when waves break at an angle to the shore due to the Prevailing Wind This means that each wave pushes material along the beach a bit more Many Coastal features can be formed by this process (e.g. Spits)

COASTS: DEPOSITION Beach material is deposited by CONSTRUCTIVE waves to form coastal landforms Offshore deposition forms sandbars and gravel banks Onshore deposition forms BEACHES and SPITS Beach material is described by its size – boulders, cobbles, pebbles, sand and silt Beach material may come from eroded cliffs, offshore sediment banks or river bedload

COASTAL LANDFORMS: SPITS SPITS are long curved beaches of sand and pebbles that extend out into the Sea. They are formed by LONGSHORE DRIFT and DEPOSITION Spits tend to be formed at: across River mouths where the Coast suddenly changes direction where tides meet calmer waters of a bay or inlet At the end of the Spit there are usually some hooks or recurves formed by occasional strong winds from another direction Waves can‛t reach the Sea areas behind the spit, so they‛re often Mud Flats and Salt Marshes Hooked end will develop if the wind sometimes blows from the other direction

Beach material is transported along the coast by Longshore Drift

Silt is deposited in the sheltered area behind the Spit to form a Salt Marsh

Coastline

Ø Over many years the Spit grows longer following the direction of the PREVAILING WIND Ø

SPURN HEAD SPIT, HOLDERNESS

This is how a SPIT appears on an OS Map

COASTAL LANDFORMS: TOMBOLOS TOMBOLOS are found where an island is joined to the mainland by a ridge of deposited material e.g. CHESIL BEACH, SOUTH COAST 18km long joining the Isle of Portland to the mainland

COASTAL LANDFORMS: BARRIER BEACHES BARRIER BEACHES are found where a Spit extends right across a shallow bay e.g. SLAPTON SANDS, SOUTH DEVON the water behind it is left as a lagoon which may slowly become a marsh

COASTAL LANDFORMS: HEADLANDS & BAYS HEADLANDS and BAYS are formed in areas with different rock types If there are alternate bands of Hard and Soft rocks in the coastline, the harder rocks take longer to erode than the softer rocks – because the sea has less effect The HARD ROCK is left jutting out forming one or more HEADLANDS The SOFT ROCK is eroded more quickly to form BAYS (often beaches will form)

e.g. Chalk

e.g. Clay

e.g. Limestone

Ø SMALL BAYS may also form along FAULT LINES in the rock – areas of WEAKNESS are eroded MORE QUICKLY Ø

COASTAL LANDFORMS: CAVES, ARCHES & STACKS CAVES, ARCHES, STACKS and STUMPS are formed by the erosion of a narrow HEADLAND Faults and Joints are natural areas of weakness found in rocks

Cracks are formed as faults and joints are eroded by waves – wave energy is usually strong where the Headland juts out Caves are formed as the cracks are enlarged and the cliff undercut Arches form as further erosion enlarges the Cave and it breaks through the Headland The roof of the Arch is often unstable and eventually collapses under its own weight – this forms a Stack or series of Stacks Stumps are the remains of Stacks which have collapsed Ø COASTLINES WITH A LIMESTONE OR CHALK GEOLOGY ARE PRONE TO THIS KIND OF EROSION Ø

OLD HARRY, THE FORELAND, DORSET

This is how STACKS appears on an OS Map

COASTAL LANDFORMS: BEACHES Beaches are a build-up of sand, pebbles and cobbles on a wave-cut platform (SEE BELOW) They are formed by the transportation and deposition of beach material

This is how a BEACH appears on an OS Map

CLIFFS AND WAVE-CUT PLATFORMS Sea cliffs and wave-cut platforms are the most widespread coastal landforms They are formed by coastal erosion

1. 2. 3. 4. 5.

Waves erode rocks along the shoreline by hydraulic action, corrosion, corrosion and pounding A notch is slowly formed at the high water mark which may develop into a cave Rock above the notch becomes unstable with nothing to support it and it collapses The coastline can retreat over many years as this process continues to form a wave-cut platform The actual size and angle of the cliff will depend on the rock type etc This is how CLIFFS & WAVE-CUT PLATFORMS appear on an OS Map

This is a ‘real-life‛ WAVE-CUT PLATFORM

COASTAL PROTECTION: HARD STRATEGIES Many Coastal areas are heavily populated and have a high economic value When areas are at risk from Coastal erosion or Coastal flooding a number of strategies may be used to reduce the risk There are FIVE main HARD ENGINEERING Defences GROYNES These are wooden structures placed at right angles to the coast where Longshore Drift occurs They reduce movement of material along the coast and hold the beach in place – protecting the cliff from further erosion The beach will then protect low areas from flooding and absorbs the impact of the waves

SEA WALLS These reduce erosion – but they deflect (NOT absorb) the waves so these cab wash away the protective beach The waves also erode the wall itself which can eventually collapse Sea walls protect against floods in lowland coasts

REVETMENTS These are slatted barriers built where a sea wall is too expensive, e.g. out of towns etc They break the wave force trapping beach material behind them and protecting the cliff base They are more effective than sea walls but look ugly and don‛t give full protection

GABIONS These are steel mesh cages containing boulders, built into the cliff face above a sea wall The rocks absorb some of the energy and cut down erosion – they‛re cheap but ugly

ARMOUR BLOCKS These are large boulders piled high on beaches where erosion is likely They are cheap but ugly and can be undermined or moved by waves

CLIFF STABILISATION Coastal cliffs often collapse when they become saturated rainwater Installing drains at the top of cliffs strengthens them by removing water quickly Cliffs may also be graded (Terraced) to make them more stable

ADVANTAGES

these strategies are effective in preventing erosion and flooding Beach and Cliff stabilisation benefits the economy e.g. Tourism

DISADVANTAGES

these strategies are not sustainable in the Long Term They are extremely expensive, ugly, need constant maintenance as they have a limited life Preventing Coastal Erosion in one area often causes problems further down the Coast

COASTAL PROTECTION ONLY GOES AHEAD IF THE VALUE OF THE LAND AT RISK EXCEEDS (IS MORE THAN) THE COST OF THE COASTAL DEFENCES

COASTAL PROTECTION: SOFT STRATEGIES Many Coastal areas are heavily populated and have a high economic value When areas are at risk from Coastal erosion or Coastal flooding a number of strategies may be used to reduce the risk

The easiest soft engineering approach is to leave the sea to do what it wants The main problem is that without control the sea would destroy lots of land by erosion and flooding Soft engineering approaches try to fit in with natural coastal processes and protect habitats

BEACH NOURISHMENT This involves adding more mud and sand to a beach This is an excellent natural flood defence by replacing all lost sediment that‛s eroded The problem is getting sediment but avoiding environmental damage somewhere else It can expensive as process needs to be continually repeated

SHORELINE VEGETATION The planting of marshbeds on the shoreline binds the beach sediment together, slowing erosion DUNE STABILISATION Dunes are excellent defences against storm floods Sediment is added and erosion is reduced by footpath control and marram grass planting

MANAGED RETREAT This is about slowing coastal erosion but not trying to stop it (instead of pumping money into a losing battle) It occurs in areas of low economic value where the sea is allowed to erode and flood the land Gradually mud flats, salt marshes and beaches develop, forming natural coastal defences Eventually buildings will have to be moved but this can often cheaper than investing in constant coastal control SET BACKS This means building houses set back from the coast‛s edge

ADVANTAGES

Low-cost and Long-term form of management New habitats for Coastal Wildlife

DISADVANTAGES

Loss of homes, roads and farmland Ú VERY ANGRY PEOPLE

COASTAL PROTECTION: SCARBOROUGH, YORKSHIRE ATTRACTIONS ü Located close to North York Moors National Park ü Two sandy beaches ü landscaped gardens and parklands ü visitor attractions e.g. Atlantis Waterpark and Sea Life Centre

BENEFITS OF TOURISM ü provides 17% of employment ü generates income of £250-£300million per year ü locals have access to tourist facilities PROBLEMS WITH TOURISM ? decline in visitor numbers due to overseas competition ? seasonal nature of tourism results in unemployment in winter ? beaches polluted with sewage MANAGING TOURISM * new markets such as business conferences developed * tourist seas extended with festivals and cheap breaks * new sewage outfall to remove sewage

COASTAL PROTECTION: HOLDERNESS COAST The Holderness Coastline has one of the fastest rates of Coastal Erosion in the World

PROBLEMS ? cliffs formed from soft clay called Till (When waves crash against the bottom of the cliffs the rock crumbles, the cliffs collapse and the pieces are washed away) ? rapid Coastal erosion – up to 2m per year ? 29 small villages have been lost to the Sea in the last 1000years ? village of Mappleton and important Coastal road at risk

SOLUTIONS ü £2million spent on Coastal defences – rather than re-route the road ü rock groynes built out to sea to trap sand ü beach built up to provide natural defence – this now absorbs wave energy and erosion has stopped ü rock armour has been built up to provide natural defence

Coastal defences at Mappleton IMPACTS ! coastal erosion at Mappleton has stopped ! groynes have reduced Longshore Drift – area to the south is now deprived of beach material ! erosion has increased to 10m per year ! farmers have lost land and even their homes