Coastal Environments

• Wind velocity - wind speed
• Duration - period of time during which the wind blew
• Fetch - distance over which the wind blew

The orbital movement that waves produce is affected by how shallow the water is as the wave approaches the coast, casuing wave height increase and legnth decrease.

Factors affecting size and formation: wind speed, fetch, gradient of beach, duration.

Constructive Waves - swash greater than backwash (due to gravity), this results in sediment being added to the beach which backwash cannot remove producing gentle build up of beach material creating berms. 6-8 waves per minute.

Destructive Waves - shorter and steeper wave legnth with more frequent waves. Waves plunge at near vertical so produce stong backwash capable of moving sediment impeding incoming waves. 10-14 waves per minute.

Wave Refraction - Where coastline is irregualr some parts of the wave will be slowed down by frictional contact (shallower water) and some remain largely impended and may move faster (deeper water).

Tides are caused by the effects of the gravitational pull of the moon and sun on the oceans. The moon has the greatest influence as it is close to earth than the sun and so has more gravitational pull.

The moon orbits the Earth every 29 days : tide cycle is 12 hours and 25 minutes so there are approximately 2 high tides and 2 low tides per day.

Spring Tide - the Moon is between the Earth and the Sun creating the biggest bulge of water due to gravitational pull. High tide is at its highest and low tide at its lowest (range is greatest).

Neap Tide - Earth, Moon and Sun are at right angles so their gravitational pull interfere with one another. Lowest high tide and highest low tide (smallest tidal range).

INPUTS

• Marine - waves, tides
• Atmospheric - weather/climate, climate change, solar energy
• Land - rock type and structure, tectonics
• People - human activity, recreation, sea defences

PROCESSES

• Weathering and mass movement
• Erosion
• Transportation
• Deposition

OUTPUTS

• Erosional landforms - headlands, cliffs, arches, stacks
• Depositional landforms - beaches, spits, sand dunes

CLIFF FACE/SUB-AERIAL:

• Solution eg. of salt
• Salt crystallisation
• Freeze-thaw weathering
• Chemical weathering
• Mass movement eg. rock falls slumping

CLIFF FOOT/MARINE PROCESSES:

• Corrasion
• Hydraulic Action

Attrition - banging together of material causing them to become smaller and more rounded.

Hydraulic Action - the sheer pressure and force of the water pushes air into cracks or faults in the rock. The air becomes compressed and so expands the cracks causing them to become weak and break off.

Abrasion - rubbing of rocks on cliff face scouring the surface.

Corrasion - throwing of rocks by waves

Corrosion - carbon dioxide dissolves to form a weak acid, dissolving rocks by chemical processes; mainly limestone and chalk.

Mechanical or physical weathering is weathering by which physical forces break down or reduce a rock to smaller and smaller fragments, no chemical change:

Freeze Thaw- in areas that experience diurnal temperature. The water freezes and expands, widening cracks in which it is held, and capture more water during thaw period. This is repeated and stresses and fracures the rock.

Pressure Release - removal of overlying rock which releases pressure on underlying strata (rock layers) causing them to expand and crack.

Biological Weathering - lichens and mosses grow on essentially bare rock surfaces. The attachments of the seedlings sprouting on a crevice and plant roots exert physical pressure and provide a pathway for water. Also burrowing animals and insects disturb the soil layer and increasing water filtration.

Chemical weathering is the breakdown of rock by chemical mechanisms. Chemical weathering changes the composition of the rock material. Water is especially an active agent by ay of fractures and causing rocks to crumble. There are several types of chemical weathering:

Carbonisation - slow dissolving of calcium carbonate from rocks like limestone and chalk. Water forms a weak carbonic acid when these rocks absorb carbon dioxide from the air. This acid reacts with the calcium carbonate to form calcium bicarbonate, making it easily dissolved.

Salt Weathering - salt water is readily available in tidal zones. When it evaporates it leaves behind salt crystals which grow larger and exert stress on the rock. Salt is also capable of corroding the rock.

Oxidation - a type of chemical weathering occuring when metal ions in a rock react with oxygen in air or water eg. iron.

Acid Rain - dissolving of rock due to a high acidity in the rain.

Hyrolosis - leads to decomposition.

Soil Creep - Slow movement on gentle slopes. When soil is wet it expands (soil particles increase in size and weight) and at right-angles, however when it dries it contracts vertically. As a result the soil slowly moves downslope creating almost wrinkles in the soil surface.

Mudflow - Saturated soil flows over impermiable sub soil, with little vegetation, on a steep slope between 5-15 degrees. Causes rapid movement between 5-15km a year after long period of heavy reain causing great devestation.

Solifluction - Occurs in tundra areas where soils are frozen for 9 months of the year with sparse vegetation. Top soils thaw in breif summer so have additional water leading to a flowing active layer. Appears to look like the upper layer of soil has melted.

Rockfall - Bare well-jointed rock and gravity causes the rapid free-fall of rock on a steep cliff face (greater than 40 degrees). Caused by freeze-thaw weathering and created a scree slope at the bottom of the cliff. 

Rotational Slip/Slumping - Permiable rock (sand and gravel) lies on impermiable rock (clay) water soaks through permiable rock and collects on impermiable rock. The layer collapes down the front of cliff face in a rotational manner.

Headlands and bays are formed at two types of coastline:

Discordant Coastline - alternating layers of hard and soft rock perpendicular to the coast. Sfot rock gets eroded faster than the hard rock causing headlands and bays.

Concordant Coastline - alternating layers of hard and soft rock running parallel to the coast. Hard rock acts as a protective barrier to the sodt rock preventing erosion. However if the hard rock is breached, the soft rock will be exposed and a cove can form eg. Lulworth Cove.

The cliff is eroded where the waves hit the rock face, which is at the bottom of the cliff. It is eroded due to corrasion, abrasion and hydraulic action. The notch created at the bottom of the cliff gets deeper and the rock above collapses due to gravity. This is a continual process and so the cliff face progressively gets furthur back and creates a 5 degree platform of hard rock.

Firstly there are lines of weakness in a cliff called geos these are eroded very quickly due to hydraulic action. These geos crack and become larger which causes a cave to form via hydraulic action and corrosion. This cave can form into a blowhole when the roof of the cave is weakened along a major joint by hydraulic pressure, the roof then collapses.

A cave can from on the opposite side of a headland and create a stack. The caves are being swilled around it can turn into an arch. This has no support so is very susceptible to weathering such as exfiliation, salt crystallisation and biological which causes a stack to form. This stack is then exposed to the full force of the waves and so via corrasion the stack is reduced into a stump.

Beaches have 3 main components starting from offshore which has no influence on the sea bed and activity is limited to deposition and sediment:

• Nearshore - zone in which waves affect the seabed. It begins at the breaking point of waves at low tide.
• Foreshore - this is the intertidal zone at the lower back often where ridges and runnels are found.
• Backshore - usually above the influence of waves - this is teh upper beach usually 10-20 degrees where berms and cusps are found.

There are 2 types of beach:

• Swash-aligned - this is inbetween a headland with the movement of material up and down.
• Drift-aligned - this is at a bay, the swash occurs at an angle and backwash at perpendicular to the coast causing long-shore drift.

Long shore drift occurs when the swash carries sediment up the beach parallel to the prevailing wind, so at an angle. Backwash carries sediment back down the beach at right angles to the shoreline. This often causes movement of material down the beach.

These landforms begin at the back of the beach nearing the waves:

Storm beach - strong swash at spring high-tide will create a storm beach. It is a ridge composed of the biggest boulders thrown by the largest waves.

Berms - as a result of constructive waves sand and shingle is slowly moved up the beach. This gradually increases the gradient of the beach and creates a series of ridges (berms) marking the successively lower high tides as the cycles goes from spring to neap and will move accordingly.

Cusps - they are semi-circular shaped depressions which when waves break onto the beach both swash and backwash are strong and equal. The sides of the cusps channel incoming swash which deepens them and drags material to the outside of the cusp. They usually occur at the junction of shingle and sand and the waves are neither constructive or destructive.

Ridges and Runnels - formed at the interaction of tides, currents, sediments and beach topography and only form on shallow gradient beaches. They mirror berms and mark the point where the backwash will deposit material and form as a simple drainage route for tides. They will move up and down the beach depending where the tides are in cycle of spring or neap tide.

Spit - Material is moves by long-shore drift, changing the shape and direstion of the coastline. Material is deposited in shallow, calm water and the spit is curved with the change of wind directions and the way the prevailing winds blow. It is a thin stretch of land that leaves the coast - about 10-30 km wide with its widest point at the end. It has a legnth of 500m sticking out from the coast and is made of sediment; one the insdie sand and salt marsh behind it. They form on drift-alighned beaches where longshore drift moves large amounts of sediment.

Bar - If a bay between two headlands is blocked off by a spit then this spit is known as a bar, it can occur due to a seasonal river. The body of water behind it is known as a lagoon.

Tombolo - They are formed when there is an island offshore. Wave refraction attacks the headland and causes deposotion of the bay. Longshore drift moves sediment around both sides of the island accumulating it from the mainland which changes the shape of the headland creating a spit. The spit grows towards thr island and joins the mainland.

Pioneer Species - They are a hardy species and are first to colonize damaged or distrupted ecosystems. They begin a chain of ecological succession leading to a more biodiverse steady-state ecosystem.

Seral Stage - an intermediate stage advancing towards its climax community.

Climatic Climax Vegetation - if natural conditions are not interrupted this is the final stage. It is the natural vegetation found in an area. E.g. in the UK it would be deciduous woodland like oak or ash.

Psammosere describes the sand dune system.

• The development of a sand dune system requires a peice of drift wood or plant reducing movement of sand increasing nutrients in this area (stability and shelter).
• The seashore has little wave action abd there is a source of mud like from an estury.

7ph (alkalai)  / 0.1OM - poor water retention

Plants include sea rocket, saltwort, sandwort, sea coach:

• waxy leaves that retain moisture and withstand winds
• prostrate (low) to avoid strong winds
• deep tap roots - obtain available moisture
• high salt tolerance

6.5ph / 0.23OM - reduced wind speeds, some humus forming, stable ground due to roots.

Plants include marram grass:

• salt tolerant
• inrolled leaves to reduce moisture loss
• thrives in buries sand
• long tap roots

Marram grass grows on top of saltwort, seacoach etc. as it outcompetes.

5-6ph / 1.0OM - little mobile sand, higher hummus content, sheltered by higher dunes.

Plants include heather, cotton grass and sea spurge:

• high species diversity
• marram grass is sparse
• surface lichens give a grey appearance
• mainly perennials

4ph (most acidic) / 12.1OM (most organic matter) - acidic soil, high organic matter, little maritime influnence, sheltered from winds.

Plants include heather and sea buckthorn:

• human interference means that the true mixed woodland climax vegetation is rarely seen on dune systems in the UK.
• most dune systems develop into a community of heathland, woody perennials and scattered trees.

• Isostatic - change in height of the land level out of the sea, it occurs whe a large weight is removed from land such as melting ice caps - local sea level change. During an ice age, isostatic change is caused by the build up of ice on the land. As water is stored on the land in glaciers, the weight of the land increases and the land sinks slightly, causing the sea level to rise slightly (compression). When the ice melts at the end of an ice age, the land begins to rise up again and the sea level falls. This is referred to decompression or isostatic rebound. Isostatic rebound takes place incredibly slowly and to this day, isostatic rebounding is still taking place from the last ice age.

• Eustatic - chnage in height of sea level due to a change in the volume of water - global sea level change. During and after an ice age, eustatic change takes place. At the beginning of an ice age, the temperature falls and water is frozen and stored in glaciers inland. This results in water being taken out of the sea but not being put back in leading to an overall fall in sea level. Conversely, as an ice age ends, the temperature begins to rise and so the water stored in the glaciers will reenter the hydrological cycle and the sea will be replenished, increasing the sea levels.

This is a river valley that’s been flooded by the eustatic rise in sea level. They’re almost exactly like a typical river valley but they have even more water in them. The cross section of a ria is really similar to the one you’d find for a river in the lower course. The floodplain of the river also gets flooded, altering the cross profile of a ria ever so slightly so that it includes the floodplain. 'Drowned estury'.

A valley can form when a glacier moved through the river and melted. Origionally it was a V-shape, but the base was filled with sea water creating the image of a lake. River valleys at the upper and middle course are flooded, and the deepest part is the end as rivers flow to base level.

These are steeper and deeper than riases that are relatively narrow for their size. They have a u-shaped cross profile and are often found in particularly icy sections of the world such as Norway. They’re flooded glacial valleys. In general, fjords are really deep however they have a shallow mouth (known as a threshold) as this is where the glacier deposited its load.

The glacier removed interlocking spurs giving their characteristic inlets and creating a straight and deep profile. They are marked by a reduction at the end where ice was thinner and eroded the rock basin less, and isostatic recovery.

Former wave-cut platformsare now rasied above sea level. Still display recognisable features of marine erosion such as wave cut notches and caves. Subarial weathering and marine weathering mwans debris collects at cliff foor producing gentler slopes. Their actual height above sea level varies laterally. Often many rasied beaches can be seen.

Causes:

• Global warming
• Thermal expansion
• Hurricanes
• Storms

Effects:

• Increased cliff and beach erosion
• Coastal flooding through inundation and storm surges
• Salinisation of farmland
• Salinisation of water supply
• Destruction of coastal ecosystems and habitats

Soft Engineering - natural systems for coastal defense such as beaches and dunes which can absorb and adjust to wave and tide energy. It involves manipulating and maintaining these systems without changing their fundamental structures, these are much cheaper than hard.

Hard Engineering - artificial structures ti control the forces of nature. They are man made engineering structures such as sea walls and groynes which are very expensive.

The idea that the land will eventually be lost and so land-use management can minimise this impact. For example putting caravan parks on cliff tops as they can easily be removed and re-sited.

Advantages:

• very sustainable and appropriate behavioural approach.

Disadvantages:

• people may aregue with land restriction.
• difficult to implement retrospectively.

Marram grass can be planted to restabilise sand, areas can be fenced off to stop people destroying newly planted dunes.

£200-2000 for 100m

Advantages:

• maintains natural coastal environment
• wildlife habitats
• cheap and sustainable

Disadvantages:

• time consuming
• people don't respond well to fenced off areas.

A from of managed retreat, allowing low-lying areas to be flooded so the land becomes a salt marsh.

Cost varies depending on size.

Advantages:

• cheap and reverts land to before agriculture
• buffer to waves
• wildlife habitat

Disadvantages:

• agricultural land lost
• landowners/farmers need to be compensated

Addition of sand or pebbles to make the beach higher or wider.

£300,000 for 100m

Advantages:

• cheap and easy to maintain
• looks natural and blends in with existing beach
• bigger beach - increase in tourism

Disadvantages:

• needs constant maintenence - natural processes of erosion and lonshore drift deplete the beach.

Timber or rock structures built at right-angles to the coast, trapping sediment from long-shore drift; buildingup the beach.

£5000-£10000 each

Advantages:

•  a built-up beach increases tourism
• land protection
• not too expensive
• works with natural procesess to build up beach

Disadvantages:

• starve the beach of sediment
• unnatural and unnatractive
• increase erosion elsewhere

Rock barrier that break up waves before they reach the coast.

Similar to rock armour in price (£100,000-£300,000 per 100m)

Advantages:

• effective permiable barrier

Disadvantages:

• visually unappealing
• potential navigation hazard

Large, tough rocks dumped at foot of cliff or top of beach. Allows some water through.

£100,000-£300,000 per 100m

Advantages:

• cheap and easy to construct and maintain
• fishing and sunbathing for tourists
• permiable

Disadvanges:

• doesn't fit in with local geology
• obtrusive
• dangerous for climbers

Cpnstruction of partly submerged wall in a bay (eg. Cardiff Bay) or estury. Regulate water in and out and can generate tidal power.

£20 million (Cardiff Bay)

Advantages:

• muilti-purpose use such as electricity generation, harbour, tourism, marina.

Disadvantages:

• expensive and damaging as shoreline and environments are disturbed.

Wire cages filled with small rocks, can be built up to create walls.

£5,000 - £50,000 for 100m

Advantages:

• inexpensive and flexible
• upper beach stability
• eventually blnd in with landscape as they become overgrown by vegetation

Disadvantages:

• look bad in the beggining
• cage can rust and become dangerous
• smell overtime

Woodne ot rock barriers at foot of cliff or top of beach and they brake up wave energy.

£4,500 a metre

Advantages:

• relatively inexpensive

Disadvantages:

• intrusive and unnatural looking

A concrete ot rock wall at thefoot of cliffs and beach, usually with curved face to reflect waves back into sea.

£6,000 a metre

Advantages:

• effective at stopping sea
• usually includes promenade- tourism

Disadvantages:

• obtrusive and unnatural
• expensive to build and upkeep