(1.2.1-1.2.2)- River + Coastal processes/landforms + factors affecting change

What is erosion in rivers?

The wearing down of the bank and bed along with the particles being carried.

What is transportation in rivers?

The movement of material with the flow of the river

What is deposition in rivers?

The dropping of material carried due to the loss of energy of the river.

Name the fluvial processes of erosion in rivers?

Attrition

Abrasion

Hydraulic Action

Solution

What is attrition in rivers?

The shrinking and rounding of sediment as they collide and break as they are moved in the flow of the water.

What is abrasion in rivers?

The grinding and wearing away of a river’s load against the banks.

What is hydraulic action in rivers?

The sheer force of the water forces itself into cracks in the bed and banks, pushing water into cracks and compressing the air. Pressure increases and erosion occurs.

What is solution/corrosion in rivers?

The acids in the water slowly dissolve the soluble materials in the bed and bank.

Name the types of transportation in rivers.

Suspension

Traction

Saltation

Solution

What is suspension in rivers?

Fine, light material is carried along by the river

What is traction in rivers?

Large boulders and rocks are rolled along the riverbed.

What is solution in rivers?

Minerals are dissolved in the water.

What is saltation in rivers?

Small pebbles and stones are bounced along the riverbed.

Name the factors that lead to deposition in rivers.

Reduction in gradient

Reduced discharge (dry weather)

Shallow water (inside of meander)

Increase in load size (not enough energy to carry it)

River floods its banks (reduced velocity on the floodplain)

What are the features of a river in the upper course?

high velocity due to rapid downhill flow → high energy → high vertical erosion power

What are the features of a river in the middle course?

low height of land, wide valley floor, lots of meandering with few tributaries.

What are the features of a river in the lower course?

Very flat land with low height, meandering

What changes does a river undergo as it moves downstream to the lower course?

More water in the river (tributaries) → wider and deeper → faster flow due to shape and direction → more power to erode and carry load (increased competence + capacity) → meandering flow

Use becomes more human focused.

How does geology affect river landform change?

the relative resistance and structure of the rock type in the area:

concordant vs discordant coastlines

harder rock type - slower rate of change due to slower erosion

softer rock type- faster rate of change due to faster erosion

How does climate affect the rate of river landform change?

Seasonal Variation- lower discharge in the summer- more deposition due to less energy

Extreme weather- heavy rainfall = high discharge- more eroding power

How does human activity affect landform change in rivers? + unintended consequences?

Line channel with concrete for faster flow and less chance of build up causing floods.

Building dams- reducing the energy to erode and flood

unintended:

Straightening river to get flood water away from vulnerable area just moves the problem downstream.

Downstream of a dam, the river carries less sediment and therefore has more energy to erode.

Factors affecting the River Parrett: Geology

Geology:

• source- in Dorset and flows NW through Somerset

• flows through the Somerset Levels- an area of easily eroded ground made of deposited sediment

• low-lying + flat so is susceptible to flooding

Factors affecting the River Parrett: Climate

• The drainage system cannot cope during extreme weather events.

• early 2014- 2x as much rainfall than normal, led to floods so it cannot cope with extreme rainfall

Factors affecting the River Parrett: Human Activity

• Embankments and floodwalls in Bridgewater

• Before 1990, it was regularly dredged (removal of debris led to increased capacity and less likely flooding. Also meant river is faster and increased erosion)

• unintended consequences: reduced flooding in one area leads to increased flooding further downstream as the water flows faster and with less obstruction.

Factors affecting the River Tees: Geology

• source- Cross Fell in the Pennines

• both hard and soft rocks through its courses

• High Force waterfall in the upper course due to soft and hard rock

• steep slopes + impermeable bedrock leads to high surface runoff, high discharge- prone to flash floods

Factors affecting the River Tees: Climate

• 2000mm of annual rainfall is quickly transported (saturated peat and run off) leading to high discharge

• high discharge means high energy leading to faster erosion and susceptibility to floods.

Factors affecting the River Tees: Human Activity

• Implementation of levees, embankments and flood barriers

• Construction of reservoir- issues downstream due to less sediment and energy = high erosion

What happens when a river meets the sea?

It slows down so large amounts of sediment is deposited as energy is lost.

How is a V-shaped valley formed?

1. Low discharge of river → vertical erosion, steepening sides

2. Valley’s sides are weathered, broken down and transported towards the river channel, steepening sides.

3. Leaves steep-sided, narrow valley

How are waterfalls formed?

1. Softer rock under a harder rock is eroded quicker causing undercuts of hard rock.

2. An overhang is created, and collapses under its own weight.

3. The rocks from this drop further erodes the base under the force of the water, turning it into a deep plunge pool.

4. Undercut and collapse repeats over time, causing the waterfall to retreat, forming a gorge.

What is a floodplain and how is it formed?

A wide flat area of land either side of a river, covered during floods. Formed due to the deposition of sediment on the areas on either side of a river during floods.

How are meanders formed?

As the river flows, lateral erosion

occurs more aggressively on the outside of bends

due to higher velocity.

The bends largen through erosion

and may create an oxbow lake

by cutting across a curve during high flow events.

What are levees and how are they formed?

Raised banks formed on the sides of a river in the lower course.

During floods, the largest, coarse material will be dumped close to the bank due to the loss of velocity as the water rises, forming levees.

What are river cliffs and how are they formed?

Steep banks formed by the erosion of the river on the outside bend of meanders, typically in the middle course.

Fast moving water erodes the bank, undercuts it and can create a vertical drop.

What is weathering?

The process of breaking up or dissolving rocks in situ. Can be chemical, mechanical and biological. On cliff faces, this results in mass movement.

What is freeze-thaw weathering?

Water enters cracks

it freezes + expands → increasing pressure on the rock

cycle repeats, causing the rock to crack.

What is mass movement? (cliff face)

The downhill movement of material under the influence of gravity, leading to cliff retreat.

Name the types of mass movement.

Rockfalls

Landslides

Mudflow

Rotational Slip

What causes a rockfall?

Fragments of rock breaking away from the cliff face, often due to freeze thaw weathering.

What causes a landslide?

The movement of a mass of rock, debris or earth down a slope.

What causes a mudflow?

The fast moving flow of saturated debris and dirt down a slope.

What causes a rotational slump?

The slump of saturated soil and weak rock along a curved surface within the slope.

Name the types of coastal erosion.

Abrasion

Attrition

Hydraulic action

Solution/Corrosion

Describe attrition at coasts.

Waves smash rocks and pebbles on the shore into each other, making them smoother and rounder

Describe abrasion at coasts.

Fragments of rock and sand in waves grind down cliff surfaces

Describe hydraulic action at coasts.

Air may become trapped in cracks on a cliff face. The air is compressed when a wave breaks, weakening the cliff and causing erosion.

Describe solution/corrosion at coasts.

Acids contained in sea water will dissolve some types of rock eg. chalk and limestone.

Transport at coasts is the same as in rivers. However there is an additional process that occurs at coasts. Name and describe it.

Longshore drift is the process where:

• the direction of the prevailing wind dictates the angle at which the waves approach the coast

• the swash will carry the material towards the beach at an angle

• the backwash carries sediment down the beach with gravity- at right angles to the beach

• repeats in zig-zag motion

Describe deposition in coasts.

No longer enough energy to sustain the load so it is reduced through deposition. Occurs where accumulation is greater than removal. Often in bays, where energy is lower.

Describe the links between sediment supply/erosion, transport and deposition to create landforms.

Erosion creates loose sediment which is then transported from one location and deposited elsewhere, creating landforms.

Factors affecting landform change in coasts: Geology

The structure and resistance of rocks eg. concordant/discordant coastline

concordant- similar rock type, parallel to the coast, uniform coastline

discordant- alternating hard and soft rock, perpendicular to the coast, irregular and dramatic with bays + headlands

Factors affecting landform change in coasts: Climate

• Prevailing wind and wind speed influences the movement of sediment through longshore drift

• Destructive waves in storms make the beach smaller

• Summer- generally more constructive waves building up beaches

Factors affecting landform change in coasts: Human Activity

• Groynes can block longshore drift, building up beach and reducing wave energy through the deposition

Consequences:

• Down the shore, beaches are starved of the sediment that has been blocked higher up. This makes them thinner, increasing erosion.

Factors affecting the Dorset Coast: Geology

• Discordant coastline (soft- clay and sands, hard- chalk and limestone) → formation of headlands and bays due to differing rates of erosion

• Hard rock has formed Old Harry rocks - chalk headlands

Factors affecting the Dorset Coast: Climate

• Temperate climate- below freezing to above 30C

• Waves driven by Atlantic storms are powerful

Factors affecting the Dorset Coast: Human Activity

• Groynes implemented help prevent longshore drift erosion

• Studland Beach was replenished with sand.

Factors affecting the Holderness Coast: Geology

• Protective beach can’t form due to storm waves

• Chalk headland, clay coast that is prone to slumping, eroding and being moved

Factors affecting the Holderness Coast: Climate

• Powerful, NE, high energy storm waves

• Spit formed due to longshore drift

Factors affecting the Holderness Coast: Human Activity

• Residential areas along coastline

• Rock groynes at Mappleton- preventing longshore drift

• Withernsea- heavy management: rock wall, promenade, rock armour

• Hornsea- groynes, curved wall

• Bridlington- Heavy management

• Skipsea- no management

What is a headland and how is it formed?

A headland is a piece of land that projects from a coastline into the sea.

Formation:

On a discordant coastline, soft and hard rock erode at different rates.

Hard rock, such as chalk and limestone, erode slower so, when soft rock is eroded inwards, it is left sticking out into the sea, forming a headland.

They now experience the more powerful waves as they are not shielded.

What is a bay and how is it formed?

A bay is an inlet of the sea where the land curves inwards and a beach will deposit.

Formation:

On a discordant coastline, rocks erode at different rates.

Softer rocks such as clay and sand, erode faster. Through deposition, a beach will sometimes form.

What are joints and bedding planes in cliffs?

Bedding planes: layers in cliffs formed by sedimentary rock

Joints: Vertical cracks in the cliff

What are wave-cut platforms and how are they formed?

• The sea erodes the base of a cliff through hydraulic action and corrosion.

• A wave cut notch will form and, through erosion, deepen and enlarge, creating an overhang in the cliff’s profile.

• The cliff will eventually collapse under its own weight.

• The cliff line has retreated.

• The material that fell is used to further erode the cliff, forming a new wave cut notch. The cliff retreats further.

• There is a limit to a platform as eventually, the waves will use up their hydraulic power travelling over it.

Describe the formation of caves.

• Caves occur when waves containing sand and other materials force their way into cracks in the cliff face, grinding away at the rock until the crack becomes a cave.

• The primary process is hydraulic action.

Describe the formation of arches, stacks and stumps.

• If a cave is formed in a headland, it may eventually break through the other side through erosional processes, forming an arch.

• The arch gradually widens until the sides can no longer support the top. When it collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.

• The stack will be attacked at the base the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.

How is a beach formed?

• Eroded material that has been transported from elsewhere and deposited by the sea.

• Waves must have limited energy to deposit material so this often occurs in sheltered areas like bays.

  • Constructive waves build beaches (strong swash, weak backwash)

What is the difference between the 2 types of beaches?

Swash aligned- the wave crests are parallel to the beach alignment.

Drift aligned- waves break at an angle to the coast. (longshore drift waves)

How are spits formed?

• A spit is a depositional landform formed by longshore drift.

• Prevailing wind pushes constructive waves up the beach. (swash)

• The backwash travels back down at 90 degrees to the beach.

• Sediment is pushed and dragged according to this. This continues down the entire beach, leading to mass transportation of sediment until mainland ends.

• Sediment is deposited and builds up, caused an extension of the mainland out into the sea.

How are rock pools formed?

Repetitive hydraulic action and abrasion causes weaker areas in the inter-tidal zone to deepen and widen.