Water On the Land

Question 1

Erosion: hydraulic action

Answer 1

The sheet force of the water hitting the bed and the banks. This is most effective when the water is moving fast and there is a lot of it. The force of water can dislodge materials. Air bubbles forced into cracks can suddenly collapse and vibrations caused can weaken the rock.

Question 2

Abrasion

Answer 2

The load the river is carrying repeatedly hits the river bed and the banks, causing some of the material to break off.

Question 3

Attrition

Answer 3

When the stones and boulders carried by the river knock against each other and over time are weekend, causing bits to fall off and reduce in size

Question 4

Solution erosion

Answer 4

The river flows on rocks, such as chalk and limestone that are soluble in rain water and become part of the water as the are dissolved by it

Question 5

traction

Answer 5

Method for moving the largest material. This is too heavy to loose contact with the bed, so materials such as boulders is rolled along

Question 6

Saltation

Answer 6

Moves the small stones and grains of sand by bouncing them along the bed. This lighter load leaves the river bed in a hopping motion.

Question 7

Suspension

Answer 7

Is a means of carrying very fine material within the water so that it floats in the river and is moved as it flows.

Question 8

Solution transportation

Answer 8

Solution is where the load is dissolved in the river and it only occurs with certain types of rocks that are soluble in rainwater. This is true of chalk and limestone and the load is not visible.

Question 9

What is deposition

Answer 9

Where the river dumps or leaves behind material first as it is the heaviest to carry. The smaller the load, the further downstream than the larger load. The river drops its load when there is a fall in the speed of the water or the amount of water is less. This often occurs when the gradient changes at the foot of a mountain or hen a river enters a lake or sea.

Question 10

What is a long profile

Answer 10

A line representing the course of the river from its source to its mouth and the changes in height along its course

Question 11

What is a cross profile

Answer 11

A line that represents what it would be like to walk from one side of a valley, across the channel and up the other side

Question 12

Typical long profile

Answer 12

The steep reduction in height near the source gives way to a more gradual reduction in height further downstream, giving a typical concave profile. The river has much potential energy near the source due to the steep drop. This is then replaced by energy from a large volume of water. A perfect long profile is rare due to land being uplifted, sea levels changing and bands of hard and soft rock crossing the path of the river.

Question 13

Typical Cross profiles

Answer 13

As the river flows downstream the valley becomes wider and flatter, with lower valley sides.

Question 14

Upper course of the tiver

Answer 14

Shallow, narrow channel 
Vertical erosion
Hydraulic action, abrasion and attrition
Some traction and saltation at high flow
Deposition of large material
Large load

Question 15

Middle course

Answer 15

Wider, deeper channel
Some vertical erosion; lateral erosion more important
Hydraulic action less important
Suspension main transportation; saltation and traction still present
Deposition more obvious
Load size reduced

Question 16

Lower course

Answer 16

Widest, deepest channel
Less erosion; only a little lateral
All erosion much less important
Suspension dominant
Deposition of fine material
Large amount of load, size now very small

Question 17

Which direction does a river erode the most

Answer 17

Close to the source- vertical erosion

Further down the course- lateral erosion

Question 18

What landforms are in the upper course

Answer 18

Vertical erosion dominant- waterfalls and gorges

Question 19

What landforms are dominant in the middle course

Answer 19

Lateral erosion and deposition- meanders and ox-bow lakes

Question 20

Which landforms are dominant Lower course

Answer 20

Deposion- floodplains and levees

Question 21

Waterfall formation

Answer 21

The river flows over soft rock which is less resistant. Therefore it erodes more quickly by abrasion and hydraulic action. This process causes undercutting. As the less resistant rock is eroded, the tougher rock is left unsupported which is called overhang. Processes of erosion also erode downward and create a plunge-pool. Eventually, the more resistant rock collapses onto the river bed. This process is repeated and over time the waterfall retreats upstream leaving a steep-sided gorge

Question 22

Oxbow lakes

Answer 22

River meanders erode to form a meander neck. This is where two sides of the meander loop together. The river breaks through the barrier and water flows straight along the channel and no longer through the meander loop. Erosion occurs on the outside and Deposition on the inside separating the channel to the meander forming an ox-bow lake which sometimes dries out forming a meander scar.

Question 23

How does a floodplain form

Answer 23

• formed by both erosion and deposition
• lateral erosion is caused by meanders and the slow migration downstream to widen the floodplain.
• the river carried large quantities of suspended load
• the deposition on the slip off slopes provided sediment to build up on the valley floor
• as the water floods onto the floodplain and looses energy, there is greater friction, the water is shallow and the rivers velocity falls so deposition of its suspended load occurs. Regular flooding results in the building up of layers of nutrient rich alluvium which forms a flat and fertile floodplain
• over thousands of years the deposits build up to form a great thickness of alluvium which is why floodplains have fertile soil for farming

Question 24

Levee formation

Answer 24

Before the flood the river is contained within banks under normal flow. threre is wider, flatter valley caused by meanders shifting along valleys.
When the river is in flood the banks overfill and the larger material is deposited next to the channel and the smaller material is carried further out. This causes a raised bank next to the channel. Successive floods cause layers of material to form and the levees to increase in height. The valley forms a fertile floodplain

Question 25

Floodplain

Answer 25

The flat area next to the river channel, especially in the lower part of the course. This is a natural area for water to spill onto when the river reaches the top of its banks

Question 26

Precipitation

Answer 26

Any source of moisture reaching the ground, rain snow frost ect

Question 27

Interception

Answer 27

Water being prevented from reaching the ground surface by trees or grass

Question 28

Surface storage

Answer 28

Water held on the ground surface e.g. Puddles

Question 29

Inflitration

Answer 29

Water sinking into soil/rock from the ground surface

Question 30

Soil moisture

Answer 30

Water held in a soil layer

Question 31

Percolation

Answer 31

Water seeping deeper below the surface

Question 32

Groundwater

Answer 32

Water stored in the rock

Question 33

Transpiration

Answer 33

Water lost through pores in vegitation

Question 34

Evaporation

Answer 34

Water lost from ground/vegetation surface

Question 35

Surface run-off/overland flow

Answer 35

Water flowing on top of the ground

Question 36

Throughflow

Answer 36

Water flowing through the soil later parallel to the surface

Question 37

Groundwater flow

Answer 37

Water flowing through the rock layer parallel to the surface

Question 38

Water table

Answer 38

Current upper level of saturated rock/soil where no more water can be absorbed

Question 39

Storm hydrograph

Answer 39

Shows how the river responds to a period of rainfall. Rivers that respond rapidly to rainfall have a high peak and short lag time and are referred to as flashy. A lower peak and a long lag time shows a delayed hydrograph

Question 40

Physical factors affecting river discharge

Answer 40

A lot of rain falling causes high river levels, while less rainfall results in lower river levels. This is because high amounts of rain saturate the soil and underlying rock increasing surface runoff. In drizzle there is time for water to infiltrate the soul and underlying rock, freeing up the space for more rain.
Temperature affects the loss of water from the drainage basin and therefore the level of discharge. When temperatures get higher, there is greater water loss via evaporation and transpiration, so river levels go down.
If it has previously dry it will take longer for the water to reach the river and the amount of water will be less because the soil and rock will not be saturated and can hold a lot of the water.
Steep slopes encourage fast runoff as the water flows rapidly due to gravity. The rock type is also decides how much water infiltrates. Impermeable rocks have more surface run off increasing discharge and compacted soil reduces the chance for infiltration increasing surface run off.
A lack of vegetation means there is less interception increasing runoff.

Question 41

Human factors affecting river discharge

Answer 41

Deforestation means there is less interception increasing run off and the amount of water that makes its way to the river. Urbanisation creates an impermeable surface meaning surface run off is increased.
Poor maintenance of sewage systems or insufficient drainage networks can cause blockages and increase surface run off.
Climate change increases the severity of storms and hurricanes
Flood defences failing such and levees and dams cause high river discharge and flooding

Question 42

How was the frequency and location of flood events changd

Answer 42

Flooding appears to be becoming an increasingly frequent event. In 1607 a great flood affected devon, Somerset and South Wales. Major floods however were infrequent in the UK. In martvh 1946 major floods did occur, affecting many areas of southern, central and northeastern england. Including york, tewkesbury, sheewsbury, sheffield nottingham and london following the rapid melting of snow. The combined effects of storm surge and high tides contributed to the floods of January 1953 that hit the east cost, including suffolk, essex and kent, when huge waves washed away sea defences and 307 people died. In 1968 another great flood affected countries in south-east england.
There is little reference to major floods until recently. In 1998 headlines about floods have been an almost annual occurrence.

Question 43

Hard engineering approaches to flood control

dams advantages

Answer 43

•Building artificial structures aimed at controlling natural processes
•dams- an artificial structure designed to hold hack water to recreate a reservoir. It has a large capacity as it kept partly full so when it rains heavily or their is snow melt a large amount of of water can be captured in the reservoir and released slowly downstream to prevent flooding. If the dam was not there a huge amount of water will rush down the river
Advantages- •recreational facilities, boating, camping, picnic areas and boat launch facilities,
•collect large amounts of water preventing uncontrolled flooding, helps prevent the loss of life and property. •Flood control impound flood waters and release them under control to the river below the dam store or divert the water for other uses such as hydroelectric power. It reduces fossil fuel consumption as it is renewable, and the production of greenhouse gas and particulates.
•The water can be used for irrigation, agriculture and industry.
•Dams are designed to last many decades.
•Only 7 years payback time.
•Building and maintaining the dam will provide employment.

Question 44

Dams disadvantages

Answer 44

• Expensive to build and maintain.
• Water table has been lowered by Aswan Dam in Egypt leading to damage to ancient monuments as minerals are deposited into the stone work
• hover dam in the US triggered earthquakes and depressed the earths surface
• dams built on rivers going through multiple countries can cause conflict as the water supply is controlled by the country with the dam
• can cause geological damage
• the flooding of large areas of land means that the natural environment is destroyed. People living in villages and towns that are in the valley that has been located, must move out. This means they loose their farms and businesses. In some countries people are forcibly removed so that hydro-power schemes can go ahead.
• dams have been known to be breeched(give way under the weight of water) leading to deaths and flooding
• eroded material is deposited in the reservoir and not along the river causing farmland downstream to be less fertile

Question 45

Hard engineering Straightening the river advantages

Answer 45

• digging a straighter shorter channel in areas where rivers meander so that water can travel faster along the course and diverting floodwaters away from settlements
• there will be less flooding in certain areas with busy settlements as the water is able to travel through the course after as there is less undulation in the rivers course
• river will have to be directed through farm land increasing irrigation, therefore decreasing crop yield and local economy
• likely to be permanent and to decease and stop flooding
• small amount of maintenance after initial construction

Question 46

straightening the river disadvantages

Answer 46

• more expensive than soft engineering
• if a major collapse happened there would be maintenance work however less likely to be damaging as it flows through a field
• not a completely secure way of preventing floods
• rivers such as the Mississippi USA start naturally meandering again due to erosion
• straightening may increase the erosive power of the river downstream

Question 47

Soft engineering

Flood plain zoning advantages

Answer 47

•geographic areas where the flood risk across different parts of the floodplain is accessed and resulting land use takes this into account. It takes into account the frequency wnd the serverity of flooding
Advantages:
•impermeable surfaces arent created such as buildings and roads •there arent any houses or roads to be damaged near to the river, so the cost of flood damages is reduced

Question 48

Disadvantages to floodplain zoning

Answer 48

• any development alters the floodplain and the dynamics of flooding
• building and infrastructure may still be damaged by periodic flooding
• the expansion of urban area is limited if there aren’t any suitable development sites
• if the floodplain has already been developed on, there isn’t anything thay can be done to reverse this without forcing people off the floodplain

Question 49

Soft engineering flood warnings and preparing the community advantages

Answer 49

• community is told as soon as possible that there will be a flood coming so everyone has enough time to evacuate safely
• enough time to to gather important belongings. They can also move their expensive items upstairs to try and save it from the water
• sand bags handed out and rescue teams will be going around to make sure nobody is injured or needs help
• it doesnt cost a lot of money
• no drastic changes to the community
• people can get text alerts and check on the internet for flood updated which is fast and efficient
• people have enough time to take their belongings and turn off electricity, gas and water

Question 50

Disadvantages of flood warnings and prepare the community

Answer 50

• community will get flooded for sure
• some of the peoples belongings may be damaged or houses will be flooded
• loss in land value

(Environment agency website is an UK government agency)

Question 51

Afforestion soft engineering advantages

Answer 51

• planting trees in drainage basin to increase interception and storage while reducing surface run off reducing rivers discharge so making it less likely to flood
• helps prevent soil erosion which reduces the amount of soil entering the river and keeps the capacity
• creates new habitats for animals
• improves water quality by filtering pollutants out of rainwater
• low cost option
• trees are self sustainable so do not require a lot of attention and do not need to be looked after installation

Question 52

Disadvantages of afforestation

Answer 52

• requires a lot of space to be effective
• could be unpopular among farmers on the floodplain as they won’t be too happy with trees sapping nutrients from the soil
• takes a long period for the trees to grow into adults, causing a long wait for the trees to be used to maximum potential
• it requires a lot of labour in planting all the seeds and ensuring the growth of them