UK Physical Landscapes – Coasts & Rivers Unit 1

Coastal Processes

Waves are formed by wind blowing over the sea. The size of wave is determined by the strength of the wind, the duration of the wind and the

distance the wind blows over (fetch).

Constructive waves are low with long wavelengths. The swash is stronger than the backwash. They build beaches Destructive waves are higher with shorter wavelengths. The backwash is stronger than the swash eroding the coast.

Weathering

Weathering is the decomposition or disintegration of rock in its original place (erosion involves moving rock)

Chemical – Dissolves rocks Mechanical – breaks rocks apart

• Carbonation. Carbon dioxide dissolved in rainwater forms a weak acid. Reacts with limestone and chalk to form a solution (dissolving them)

• Oxidation – oxygen in rain reacts with iron

• Freeze thaw.

• Salt weathering – salt in sea water expands to form cracks.

Landforms of erosion

Wave cut platforms

Wave erosion Caves, arches and stacks

Mass Movement

Mass movement is the movement of material downslope under the influence of gravity. It is the falling, sliding or flowing of rock, sediment or soil most often along a slip plane (line of weakness). Different types of mass movement can include rockfall, landslides and rotational slumping.

Rockfall Landslide Slumping

Individual fragments of rock fall off cliff usually due to freeze thaw weathering.

Rocks slide down the cliff in a linear fashion along bedding plains.

Occurs on a curved surface saturated (full) of water

Coastal Erosion

Erosion is the wearing away of rocks by waves – abrasion, attrition, hydraulic action & corrosion. (see rivers sheet).

Landforms of deposition

Development of Sand dunes

Spits and Salt Marshes

Coastal Deposition

Deposition: Sediment dropped by the waves. Creates beach. The beach is made of material transported by long shore drift.

The shape of the coast is determined by geology. Hard rocks (chalk, granite) erode slowly & form headlands Softer rocks (clay) erode faster & form bays. E.g. Lulworth Cove on the Jurassic Coast. Where the hard rock is limestone & the soft rock is clay.

•Embryo dunes form around deposited obstacles such as pieces of wood. •These develop and become stabilised by marram grass to form fore dunes & tall yellow dunes. •In time rotting vegetation adds organic matter to make sand more fertile. •Winds can form depressions in the sand called dune slacks where ponds may form.

Bars

A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end. Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift (see next page) which transports the material along the beach. Salt marshes may be formed behind a spit. The zone behind a spit becomes a sheltered area. Water movement slows down and so more material is deposited. Deposition of material may form a salt marsh.

Longshore drift carries material along a beach in a zigzag fashion through swash & backwash in the direction of the prevailing wind. When the sediment reaches a bay it cuts it off leaving a bar or barrier beach.

Wave Refraction

As waves approach a coast they are refracted so that their energy is concentrated around headlands but reduced around bays. Waves energy decreases as water depth decreases. So headlands shelter bays from the erosive power of waves.

Coastal Management example – Minehead What is the problem?

• Prevailing winds mean material is moved from West to East through LSD • Major flooding of the area was a regular occurrence up until the new sea

defences were completed in 2001 • Butlins is the major contributor to the economy of the area and so

Minehead was protected with a ‘hold the line’ policy – whereas other areas along the coast e.g. Porlock Village have been left to ‘no active intervention’.

Management strategies Problems

• Rock armour groynes, curved sea wall and beach replenishment at a cost of 12.3 million (half the cost was paid for by Butlins itself).

• 4 new rock armour groynes trap sand and create a beach to protect the town and Butlins.

• The sea wall is designed to reflect the power of the waves if they ever reach the back of the beach.

• Minehead is protected but groynes prevent sediment moving East leading to increased erosion East of Minehead.

• Farms and a pub have been lost East of Minehead.

• The sand is piling up at the East side of Minehead and so will need to be moved back down to protect the Western end of the beach.

• Groynes make walking down the beach difficult and they can be dangerous.

Coastal Management Strategies

Hard Engineering

Strategy Benefits Costs

Sea wall – concrete structure at top of beach acts as a barrier to sea

• Very effective at reflecting energy of waves back to sea through curved top.

• Stops coastal flooding.

• Very expensive. • Ugly & cut off access to the

beach. • Creates a strong backwash

which erodes under the wall.

Rock Armour – large boulders at foot of cliff to reduce force of waves

• Absorb wave energy so reduce erosion & flooding.

• Cheap compared to sea walls.

• Ugly • Can be dangerous to public • Cut off access to beach • Can be moved around by strong

waves so need to be replaced.

Gabions – wire cages filled with rocks. Permeable so allow water through from both sides e.g. Cliff drainage

• Flexible & less likely to be moved by strong waves.

• Cheaper & quick to construct.

• Absorb wave energy

• Not attractive • Cages can break e.g. Through

corrosion of metal. • Need replacing every 10 years

Groynes – wooden or stone fences built at right angles to coast to stop longshore drift

• Create wider beaches which slow wave energy & erosion.

• Wide beach prevents flooding

• Fairly cheap to build

• Starve beaches further down the coast of sand making them narrower and so more likely to erode.

• Need some maintenance

Soft Engineering

Beach nourishment Adding sand to a beach or changing its shape eg high ridges.

• Looks natural & attractive.

• Creates amenity for tourism

• Wide beaches are best defence against erosion

• Needs constant maintenance • Less effective than hard

engineering • If sand is dredged from sea bed

then ecosystems can be damaged e.g. Coral.

Dune Regeneration Planting marram grass so that the roots hold the sand in place.

• Natural • Dunes are an excellent

defence against wave erosion

• Increase biodiversity

• Time consuming to plant and maintain

• Easily damaged by storms • Protection limited to a small

area

Managed Retreat

Managed Retreat Allow the sea / nature to act on the coast. E.g. At Porlock.

• Salt marshes provide a natural barrier

• New ecosystem created • Biodiversity improves, eg

habitats • More attractive

• Low value land is lost to sea

• Local people have to move & be compensated

Coastal Transportation

Transportation: Sediment is carried along the coast in the direction of the prevailing wind by the process of LSD.

Rivers and river valleys

Fluvial Processes

River Erosion

Term Definition

Hydraulic action Flowing water erodes the bed and banks. Found at waterfalls and meanders

Abrasion Scraping of rivers bed by particles of rock – like sandpaper

Attrition Rounding and smoothing of rock as they rub against each other

Solution Dissolving of soluble chemicals esp. limestone

Vertical erosion Downwards erosion – common in upper course

Lateral erosion Sideways erosion – common in middle and lower course

River Transportation

Traction Rolling of large rocks

Saltation Bouncing of small rocks

Suspension Particles suspended in water

Solution Chemicals dissolved in river

River Landforms

Upper course (erosion)

Interlocking spurs - a typical steep sloped v-shaped valley with interlocking spurs. Streams in upper course are not strong enough to erode the hills so flow around them.

V-shaped valleys – 1. rivers erode vertically through abrasion. 2 – The steep sides are attacked by weathering e.g. Freeze thaw. 3 – gravity transports the lose material down slope & rivers transports it away. 4 – leaving a V-shaped valley.

Waterfalls –Found where there are layers of hard & soft rock. Water flows over hard rock & erosion undercuts the soft rock below leaving an overhang of hard rock – which is eventually weathered & collapses into the plunge pool .

Gorges – as a waterfall retreats the overhang (cap rock) collapses and the process starts again forming a steep sided gorge.

Middle Course (erosion and deposition)

Meanders – bends in the river. Erosion happens on the outside bend where flow is fastest due to centrifugal force. Deposition happens on the inside bend as the flow is slowest leaving a slip off slope.

Oxbow Lakes –outside bends of rivers erode laterally due to fast flow e.g. Hydraulic action – two outside bends erode towards each other leaving narrow land between (swan’s neck). The river cuts across the neck & takes a straighter course – leaving behind an ox bow lake.

UK Physical Landscapes - Rivers

Lower course (deposition)

Levees – Raised banks formed after a river floods. The largest sediment is transported less far at times of flood as it is heavier. Large rocks rolled out (traction) of the river when it bursts it’s banks build up at the sides forming natural embankments (levees).

Floodplains – wide areas of flat land. Rivers erode laterally as they meander across a valley in the middle to lower course – flattening the valley floor. At times of flood smaller materials are transported across the valley floor & deposited in layers to form a flat flood plain.

Estuaries – A tidal area of a river – where it meets the salt water of the sea. The river flow is slow & slowed further by the tide coming from the opposite direction which leads to deposition and the formation of salt marshes. (see coasts).

Factors affecting discharge & lag time ( flooding).

Physical Human

• Precipitation – heavy rain increases surface run off to rivers. (SRO)

• Geology – impervious rocks increase SRO.

• Relief – steep slopes increase SRO & risk of flooding.

• Urbanisation – impermeable surfaces e.g. Concrete increase SRO whilst permeable surfaces decrease it.

• Deforestation – trees intercept rain & reduce SRO so cutting them down increases SRO & risk of flood.

Lateral erosion Lateral erosion

1 2

3 4

River bend Swan’s neck

Ox Bow Lake

Y axis measures Discharge: Volume of water that flows through a river measured in CUMECS & rainfall measured in mm. X axis: measures time in hours Peak: highest amount recorded. Lag time: peak discharge in hours minus peak rainfall in hours Rising a falling limbs: If these are steep & lag time is short then flood risk increases. Lag time can be increased by e.g. Planting trees to increase interception & reduce surface run off.

River Management Strategies

Hard Engineering

Strategy Benefits Costs

Dams & Reservoirs– Concrete dams (huge walls) usually in the upper course - control river flow by creating artificial reservoir behind them to store water.

• Can be used for Hydro Electric Power generation HEP (renewable energy)

• Lake can be used for tourist activities e.g. Sailing.

• Creates new wetland habitats • Creates source of drinking water • V effective at reducing flooding

further down river.

• V expensive (Clywedog Dam cost £100s millions)

• Social costs of displacing residents whose homes are flooded.

• Reservoirs silt up & need dredging.

• Can lead to conflict over water rights between countries e.g Nile

Channel Straightening – water flows out of area faster

• Insurance premiums may fall • Effective • Navigation by boat improved

• Can lead to flooding downstream as velocity increases.

• High maintenance

Embankments – artificially raised using concrete to deepen channel

• Increased capacity for carrying water in the channel

• Creates walkways (e.g London) • New river bank habitats

• Expensive • Looks artificial • More serious flooding if

embankment fails (New Orleans)

Flood Relief Channels – new channels to by pass towns

• Opportunities for recreation (fishing and walking)

• New aquatic habitats created • Insurance premiums reduced

• V expensive – Jubilee River cost £110 million)

• Regular maintenance needed • Habitats disturbed

Soft Engineering

Flood Warnings. - monitoring rivers to allow floods to be predicted

• Sustainable • Low cost • Focus on helping people

• People may not respond • Need for monitoring equipment

Floodplain Zoning – not building in flood areas

• Low cost • Conserves water meadows for

recreation and wildlife

• Restricts economic development • Housing shortage • Hard to implement

retrospectively

Planting trees – Trees increase interception and slow flooding

• Crates habitats • Natural • Low cost

• Loss of farmland • Loss of economic use of land • Not totally effective

UK River example - Severn

• The River Severn flows through Wales and England

• It is 350 miles long • Its source is in the Cambrian Mountains

(610 metres above sea level) • It flows to the Bristol Channel • It has a tidal estuary.

Key Features

Source – Plynlimon in Cambrian Mountains. Interlocking spurs – Ashes Hollow Waterfalls - Severn Breaks it’s neck & Blaenhafren. Gorge – in Hafren Forest Meanders – with swan’s neck at Welshpool & Shrewsbury Flood Plain – At Tewkesbury which often floods Estuary – Tidal range of 15 metres on Severn Estuary near Bristol is the 3rd largest in the world.

River Severn’s Long Profile

River Severn on OS maps

Look out for: -Orange contour lines show height of land. -The closer together the lines are the steeper the slope . (The numbers show height above sea level) -Rivers are marked as thin blue lines in the upper course & get wider as the river moves downstream.

Upper Course evidence on maps

-High land (Over 180 metres) on R.Severn -The river is a thin blue line. Which crosses lots of orange contour lines in a short distance (steep) -The V-shape of the valleys made by the contours & the river is pointing uphill to the source. -The symbol for cliffs – black blocky lines & close contour lines with a river is evidence of waterfalls.

Lower Course evidence on maps

-Lowland (Less than 15 metres) -The river is wide (a thick blue line). -The river doesn’t cross any orange contour lines very gently sloping. -The river meanders across a wide flat area (flood plain). -Large meanders with deposition (sand colour) as river is slow here.