Topic 2 - River Landscapes

Question 1

What does the cross profile of the river look like?

Answer 1

Cross profile - cross-section of the valley and channel of a river.

Upper course - increase invertical erosion. The channel is shallow and narrow because there is not a lot of water in the channel.
Middle course– some vertical erosion but morelateral erosion. The channel is wider and deeper as a result.
Lower course- a lot less erosion, with only some lateral erosion. The channel is at its widest and deepest.

Question 2

What does the long profile of the river look like?

Answer 2

Long profile - a section of the course of a river drawn from source to mouth.

Upper course- in the upper course, where the river starts, there is often an upland area. The river’sloadis large in the upper course, as it hasn’t been broken down byerosionyet.
Lower course- in the lower course, the land is a lot flatter. The river’s load is fine sediment, as erosion has broken down the rocks.

Question 3

What is a drainage basin and its characteristics?

Answer 3

A drainage basin is the area of land around the river that is drained by the river and itstributaries.

Watershed- the area of high land forming the edge of a river basin
Source- where a river begins
Mouth- where a river meets the sea
Confluence- the point at which two rivers meet
Tributary- a small river or stream that joins a larger river
Channel- this is where the river flows

Question 4

What is deposition?
What are the factors leading to it?

Answer 4

When the river loses energy, it drops any of the material it has been carrying. This is known asdeposition.

Factors leading to deposition:
shallow water
at the end of the river’s journey, at the river’smouth
when the volume of the water decreases

Question 5

What are the transportational processes?

Answer 5

Traction- large, heavy pebbles are rolled along the river bed (most common near the source of a river, as here theloadis larger).
Saltation- pebbles are bounced along the river bed (most commonly near thesource).
Suspension- lighter sediment is suspended (carried) within the water (most commonly near themouthof the river).
Solution- the transport of dissolved chemicals (varies along the river depending on the presence of soluble rocks).

Question 6

What are the 6 different types of erosion?

Answer 6

Vertical erosion - land eroded/worn away in a downwards direction, eg a river that is high up will erode vertically because gravity pulls the water downwards.

Lateral erosion - wearing away of the landscape when a river erodes sideways.

Hydraulic action- power of the water eroding the river banks and beds.
Abrasion- rocks carried along the river wear down the river bed and banks.
Attrition- rocks that the river is carrying knock against each other and break into smaller and more rounded particles.
Solution- when the water dissolves certain types of rocks, eg limestone.

Question 7

How is the depositional landform of estuaries formed?

Answer 7

Anestuaryis where the river meets the sea.
The river here is tidal and when the sea retreats the volume of the water in the estuary is reduced.
When there is less water, the river deposits silt to formmudflats (sheltered coastal areas where mud is deposited by tides or rivers)which are an important habitat for wildlife.

Question 8

How is the depositional landform of levees formed?

Answer 8

Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.
Sediment that has been eroded further upstream is transported downstream.
When the river floods, the sediment spreads out across the floodplain.
When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away.
After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water (a greater discharge) and flooding is less likely to occur in the future.

Question 9

How is the depositional landform of floodplains formed?

Answer 9

A floodplain is an area of low-lying land next to a river which is prone to flooding.

Floodplains form due to botherosionanddeposition.
Erosion removes anyinterlocking spurs, creating a wide, flat area on either side of the river.
During a flood, material being carried by the river is deposited (as the river loses its speed and energy to transport material).
Over time, the height of the floodplain increases as material is deposited on either side of the river.
Floodplains are often agricultural land, as the area is very fertile because it’s made up ofalluvium(deposited silt from a river flood). The floodplain is often a wide, flat area caused bymeandersshifting along the valley.

Question 10

How is the erosional and depositional landform of oxbow lakes formed?

Answer 10

Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time.
Erosion narrows the neck of the land within the meander and as the process continues, the meanders move closer together.
When there is a very highdischarge(usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route.
Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.

Question 11

How is the erosional and depositional landform of meanders formed?

Answer 11

As the river makes its way to themiddle course, it gains more water and therefore more energy.Lateral erosionstarts to widen the river. When the river flows over flatter land they develop large bends calledmeanders.

As a river goes around a bend, most of the water is pushed towards theoutside (thalweg - line of fastest flow). This causes increased speed and therefore increased erosion (throughhydraulic actionandabrasion).
The lateral erosion on the outside bend (pool) causes undercutting of the bank to form ariver cliff.
Water on the inner bend is slower (riffle), causing the water to slow down and deposit the eroded material, creating a gentle slope of sand and shingle.
The build-up of deposited sediment is known as aslip-off slope(or sometimes river beach).

Question 12

How is the erosional landform of interlocking spurs formed?

Answer 12

In the upper course there is morevertical erosion (define!). The river cuts down into the valley.
If there are areas of hard rock which are harder to erode, the river will bend around it.
This createsinterlocking spursof land which link together like the teeth of a zip.

Question 13

How are the erosional landforms of waterfalls and gorges formed?

Answer 13

Awaterfallis a sudden drop along the river course. It forms when there are horizontal bands of resistant rock (hard rock) positioned over exposed, less resistant rock (soft rock).

The soft rock is eroded quicker than the hard rock and this creates a step.
As erosion continues, the hard rock is undercut forming an overhang.
Abrasionandhydraulic action (define!)erode to create aplunge pool.
Over time this gets bigger, increasing the size of the overhang until the hard rock is no longer supported and it collapses.
This process continues and the waterfall retreats upstream.
A steep-sided valley is left where the waterfall once was. This is called agorge.

Question 14

Where are erosional landforms primarily found and give examples?
Erosional and depositional?
Depositional?

Answer 14

Upper course - interlocking spurs, waterfalls and gorges
Middle course - meanders and ox-bow lakes
Lower course - levees, floodplains and estuaries

Question 15

What was Morpeth’s flood alleviation scheme? Hard and soft engineering strategies?

Answer 15

Hard engineering:
New flood walls were built.
Tree poles were put in the river to collect debris (unmonitored = debris build up).
A 1.5m flood wall was built behind residents’ gardens and landscaped to look like the surroundings.
Flood storage scheme upstream of Morpeth. The reservoir can store more than 1.4 million m cubed of water when river levels are high.
Existing embankment was raised by 25cm.
The existing flood defence embankment was refurbished.
A new flood wall was built - approx 30cm higher than the existing one.

Soft engineering
9000 trees were planted near Morpeth (afforestation).
An embankment made of earth and soil was built (cheaper but not as effective as concrete).

Question 16

What were the responses to the 2008 Morpeth Floods?

Answer 16

effective, ineffective
Sun 7 Sep - Morpeth Lions Club + Red Cross launched Morpeth Flood Disaster Fund and 10/9 had raised over £20,000 to help those affected the most.
More than 400 residents were evacuated and shelter was provided in the Town Hall, King Edward VI High School and County Hall.
Error made by Environment Agency meant 198 properties did not receive a flood warning - couldn’t prepare.
Firefighters, ambulance crews, RAF, RNLI and the British Red Cross were among the emergency services involved in rescue and recovery operations.

Question 17

What were the impacts of the 2008 Morpeth Floods?

Answer 17

social, environmental, economic
The library suffered severe structural damage due to the heavy debris transported by the river - so damaged structural engineers were required to test its safety.
At the peak of the flood, Morpeth High Street was under 60cm of water.
Lots of flooding in town centre but also areas surrounding Morpeth are predominantly farmland - losses estimated at over £1 mill.
Local residents’ houses full of mud and sewage - 95 Morpeth properties directly affected by flood water.
1000/1062 properties sited on floodplain faced some sort of damage - Journal Newspaper claimed £40 mill worth of damages
Many residents had to be forced from their homes and lived in caravans/with relatives as rebuilding took place.

Question 18

What were the causes of the 2008 Morpeth Floods?

Answer 18

human, physical
Increased urbanisation since the 1960s in Morpeth = most water would have drained directly to the river channel.
Urbanisation = impermeable surfaces like pavements and roads covering the flood plain.
Already saturated soil as a result of the wet summer - ensured rainfall quickly flowed into the river channel (runoff).
Figures suggest that in Morpeth alone there 86mm of rain in 1 day compared to an average of 74mm for a month!
Prolonged rainfall - 150mm of precipitation fell into the Wansbeck drainage basin between 5-6 September 2008.

Question 19

Where is Morpeth?

Answer 19

Morpeth is located in the north east of England, north of the city of Newcastle.
The river Wansbeck runs through the city, a confluence of the river situated in Morpeth - splits into river Front and Wansbeck.
Morpeth is relatively flat - more susceptible to infiltration but also has permeable forests.
Urban areas = impermeable surfaces = no infiltration + drains arrive at river quickly

Question 20

What is the soft engineering strategy of river restoration?
What are its advantages and disadvantages?

Answer 20

River restoration:
Involves restoring the river channel back to its natural state - can involve lowering floodplains to create natural water storage areas.

Question 21

What is the soft engineering strategy of afforestation?
What are its advantages and disadvantages?

Answer 21

Afforestation
Planting trees reduces the risk of flooding by leaves, interception and root uptake - less water reaches the ground and the water that does reach the ground is absorbed by the roots of trees and plants.

Advantages
reduces flooding risk as there are plants on both sides of the river absorbing the water

Disadvantages
plants can become saturated
takes time to grow plants, expensive to buy fully grown

Question 22

What is the soft engineering strategy of floodplain zoning?
What are its advantages and disadvantages?

Answer 22

Floodplain zoning:
Allowing only certain land uses on the floodplain reduces the risk of flooding to houses and important buildings.

Advantages
More expensive buildings and land uses are further away from the river, so have a reduced flood risk.
Less damage is caused, leading to fewer insurance claims.

Disadvantages
Not always possible to change existing land uses.
Planners have to decide what type of flood to plan for.

Question 23

What is the soft engineering strategy of flood warnings?
What are its advantages and disadvantages?

Answer 23

Flood warnings and preapration:
The environmental agency monitors rivers and issues warnings via newspapers, TV, radio and the internet when they are likely to flood so people can prepare.

Advantages
People have time to protect their properties, eg with sandbags.
Many possessions can be saved, resulting in fewer insurance claims.

Disadvantages
Some people may not be able to access the warnings.
Flash floods may happen too quickly for a warning to be effective.
They do not stop land from flooding - they just warn people that a flood is likely.

Question 24

What is the hard engineering strategy of flood relief channels?
What are its advantages and disadvantages?

Answer 24

Flood relief channels:
The floodwater flows into the relief channel and is taken either to an area where it can be absorbed, or re-enters the river further down its course.

Advantages
Removes excess water from the river channel to reduce flooding.

Disadvantages
Expensive to build.
If water levels continue to rise, the relief channel may also flood.

Question 25

What is the hard engineering strategy of embankments?
What are its advantages and disadvantages?

Answer 25

Embankments:
Raising the banks of a river means that it can hold more water.

Advantages
Cheap with a one-off cost
Allows for flood water to be contained within the river.

Disadvantages
Looks unnatural.
Water speeds up and can increase flood risk downstream.

Question 26

What is the hard engineering strategy of river straightening and dredging?
What are its advantages and disadvantages?

Answer 26

River straightening and dredging:
Straightening the river speeds up the water so high volumes of water can pass through an area quickly. Dredging makes the river deeper so it can hold more water.

Advantages
More water can be held in the channel.
It can be used to reduce flood risk in built-up areas.

Disadvantages
Dredging needs to be done frequently.
Speeding up the river increases flood risk downstream.

Question 27

What is the hard engineering strategy of dams and reservoirs?
What are its advantages and disadvantages?

Answer 27

Dams and Reservoirs:
The dam traps water, which builds up behind it, forming a reservoir. Water can be released in a controlled way.

Advantages
Can be used to produce electricity by passing the water through a turbine within the dam.
Reservoirs can attract tourists.

Disadvantages
Very expensive.
Dams trap sediment which means the reservoir can hold less water.
Habitats are flooded often leading to rotting vegetation. This releases methane which is agreenhouse gas.
Settlements are lost leading to the displacement of people. In developing countries locals are not always consulted and have little say in where they are relocated.

Question 28

What are hydrographs?
What are the different features of hydrographs?
What are factors influencing lag time?

Answer 28

Hydrograph - graph to show how a river responds to a period of rainfall.

Peak discharge- maximum amount of water held in the channel.
Peak rainfall– maximum amount of rainfall (millimetres).
Lag time- the time taken between peak rainfall and peak discharge.
Rising limb- shows the increase in discharge on a hydrograph.
Falling limb- shows the return of discharge to normal/base flow on a hydrograph.
Base flow- the normal discharge of the river.

Factors influencing lag time include:
Size of drainage basin
Vegetation
Valley side steepness
Soil type

Question 29

What are the causes of flooding?

Answer 29

Prolonged rainfall- if rains for a long time, land around a river -> saturated. More rainfall cannot be soaked up, = surface run-off.

Heavy rainfall- heavy rain = less chance of infiltration so it runs off into the river. The faster the water reaches the river, the more likely it will flood.

Relief- steep valley = more likely to flood than a flatter valley because rainfall will run off into the river more quickly.

Geology-permeable rocksallow water to pass through pores + cracks, impermeable rocksdo not. If valley = impermeable rocks, higher chance of flooding as increase in surface run-off.

Vegetation- trees + plants intercept water. Lots of will reduce flood risk. Deforestation will increase the flood risk, as the water not = intercepted + flow into the river.

Urban land use- area surrounding a river is built on = increase in amount of tarmac + concrete = impermeable surfaces. Drains + sewers take water directly to river - increases flood risk.

Question 30

What is flooding and when does it occur?

Answer 30

Flooding occurs when a river bursts its banks and overflows onto the surrounding land. There are many factors which can cause a flood - often the natural landscape can influence flooding and also human interactions can increase the risk.