Paper 1 Section C River erosion, depostion and features

Question 1

Whatis a drainage basin and what are the key features of it?

Answer 1

A drainage basin is the area that is drained by a river. (Think of it as a sink and all the drops of water that fall in it and around it end up down the plughole - the river!)

Question 2

Vocab check: What is the source? Tributary? Confluence?

Answer 2

Source - the start of the river (as a stream) in highland areas
Tributary - a small stream joining the main river
Confluence - the point where the tributary and river meet

Question 3

How does the river’s profile change along its course?

Answer 3

LONG profile - think of the river’s journey sideways on.
Start in the hills: the initial course (the upper course) is steep
The middle course is more gently sloping and the lower course is mainly very gentle (almost flat) to the mouth of the river at the sea.
The CROSS profile: shows cross sections at various points along the river
Inthe upper course the vally sides will be very steep (a V-shaped valley) where the river is shallw, flows fast and erodes downwards. The valley sides are shaped by mass movement - see the coastal unit of work.
In the middle course the valley widens out. the valley floor is wider and a floodplain is created. the river is wider and deeper causing lateral (at the sides) erosion
At the mouth of the river the valley is very wide, levees may be seen where the river has flooded. The river is wide and deep and carries a lot of light sediment
YOU HAVE STUDIES THE RIVER TEES inthe nE of Eng

Question 4

How does a river erode? (recap coastal erosion)

Answer 4

Hydraulic action - water gets into the cracks in the river sides and bed, creates pressure which, when released takes particles of rock with it making the cracks wider
Abrasion - material in the water scrapes along the sides and bottomof the river, dislodging more particles of rock (sandpaper effect)
Attrition - the sediment bashes against each other becoming smaller and more rounded
Solution - the water dissolves some of the chemicals inthe rock eg limestone

Question 5

How does river transport its material/load? (Recap coastal erosion)

Answer 5

Traction
Saltation
Suspension
Solution

Question 6

When does deposition happen?

Answer 6

Velocity is the river’s speed. When this decreases the river may not be able to move its load and so it is deposited.
Most erosion occurs in the steeper, upper and middle courses as the river uses gravity as well as its power (espcially when there has been a lot of rainfall). However, the biggest material is not moved far.
Lighter material that is suspended (floating) in the water will be carried much further and depasited where the river flows slowly due to the flatter land ie at the mouth (deltas, mudflats etc)

Question 7

How are interlocking spurs formed?

Answer 7

In the upper course vertical erosion occurs creating a V-shaped valley. The river winds round more resistant rock at the base of the hills creating interlocking spurs - DIAGRAM!

Question 8

How are waterfalls and gorges formed?

Answer 8

Waterfalls occus in the upper course of rivers.
A band of hard rock overlies softer rock
The hard rock is more resistant to erosion and creates steps in the landscape.
As the water falls over the resistant rock and splashes back it erodes the softer rock bu hydraulic action and abrasion.
The force of the river falling over the hard rock also creates a plunge pool in the river.
The hard rock layer is undercut, meaning it is not supported and it will collapse into the plunge pool.
The waterfall ‘retreats’ (ie the edge of the waterfall moves back, like cliffs at the coast) creating a narrow, steep-sided valley called a gorge
SEE DIAGRAM! Eg High Force on the R Tees

Question 9

How are meanders and ox-bow lakes formed?

Answer 9

meanders are wide, sweeping bends in the river found in the middle course. They are features of erosion AND deposition and constantly change/exaggerate their shape.
SEE DIAGRAM
The fastest current in the water moves to the outside bend of the river, causing erosion.
As most water has moved to the outside bend there is little on the inside of the bend so deposition occurs (the river beach or slip-off slope)
As the meander widens the neck of the meander narrows and eventually in storm conditions the river will break through the neck and flow in a straight line.
This leaves the curve of the meander isolated - an oxbow lake.
This will eventually drain, water will evaporate and vegetation will grow in it.

Question 10

How do floodplains form?

Answer 10

Floodplains are a feature of deposition
They are wide, flat areas on either side of the river in the middle and lower courses. They are created as the meanders migrate (move their shape) and river floods depositing silt (the small, light pieces of material fromtheriver’s load). This forms alluvium over time - a rich, fertile soil.

Question 11

How do levees form?

Answer 11

Levees are the naturally formed steeper sides of the river which form a barrier against flooding.
In the lower course of the river, material is deposited and the river doesn’t have as much capacity for the water it carries.
When the river floods the material it carries is depositedon the banks and ‘sorted’ with the larger material being deposited (needs more energy to move it) nearer the river and the lighter material (needing less energy to move it) carried further away
Levees can be reinforced or created with concrete to help manage flooding in high risk areas

Question 12

How do estuaries form?

Answer 12

Estuaries form at the mouth of the river, where it meets the sea.
Tides and waves affect the deposition of the river. If the tide is coming in - up the river - the river can’t flow into itso material is deposited by the river. This causes mudflats to form which may eventaully form saltmarshes.
eg at the mouth of the R Tees at DARLINGTON.

Question 13

Knowledge of one river?

Features of the RIVER TEES

Answer 13

Flows fromits source in the Pennine Hills in the North of England.
It flows mainly eastwards to the North Sea at Middlesborough
High Force is the waterfall we have studied. It is in the Upper course and the waterfall drops 20m. The hard rock here is IGNEOUS rock
p74 in your revision guide shows an OS Map. Practice picking out key features eg meanders, levees and floodplain areas. How will you recognise these features?
Also use the scale and grid references to pint out features and tourist attractions in the area.

Question 14

Explain 6 causes of river flooding? (3 physical and 3 human)

Answer 14

Physical:
1. Long periods of rain or torrential storms
2. Geology - the rock type - some are permeable (let water through); some are impermeable (don’t let water through)
3. Relief: the height and shape of the land. If the land is steep water will flow quickly to the river causing it to flood.
Human causes:
1. Urbanisation - increasing numbers of people living in towns and cities means more homes, roads etc need to be built. Roads are impermeable causing water to flow quickly to rivers.
2. Deforestation - trees absorb water through their roots and by interception. The fewer trees there are the more quickly water flows to the river
3. Agriculture (Farming): bare soil causes water to flow to rivers more quickly.

Question 15

What is a storm hydrograph?

Answer 15

SEE DIAGRAM
This is a graph that shows the flow of a river compared with the point of highest rainfall.
Key fetures:
Peak rainfall
Peak dischage (point of most water in the river)
Lag time (the time taken from peak rainfall to peak discharge. The shorter the lag time the greater the risk of flooding)
Rising limb (the steepness with which the river level rises)
Falling limb (the time it takes the river to get back to its normal flow)

Question 16

What factors afftect the shape of a hydrograph?

Answer 16

River basin size
Drainage density
Rock type
LAnd use in the area
Relief
Soil moisture (water table levels)
Rainfall intensity
Previous rainfall (in recent days/weeks)

Question 17

How can river flooding be managed and what are the costs and benefits? (To what extent are river management strategies effective?)

Answer 17

Hard engineering:
1. Dams and reservoirs - used to regulate the flow of rivers esp in dry areas eg the R Nile (Aswan Dam), the Lesotho Highland Water project or Keiderwater in the NE Eng.
Also used to create Hydro-electric power (HEP)
Water is stored in reservoirs which often flood large areas of land (people displaced)
2. Channel strainghtening - cutting through meanders speeds up the flow of water but can cause flooding further downstream
Straightened channels are often lined with concrete (visual pollution) which can affect wildlife habitats.
3. Embankments - like levees raise the height of the river bank to allow maore ater to flow in the river. If they are breached flooding is more catastrophic. River dredging is cheaper, more sustainable and more effective
4. Flood relief channels: these hold additional water in the river until it can be pumped back into the river. Expensive. Often needed inurban areas. Visual pollution. eg the 11km Jubilee River at Maidenhead takes excess water from the R Thames in the SE. Effective and has created a wildlife wetland environment.

Question 18

Explain how 4 methods of soft engineering can be used to protect from river flooding?

Answer 18

1. Afforestation - plantingtrees
2. Wetlands and flood storage areas - wetlands deliberately allowed to flood
3. Floodplain zoning - only certain types of land use allowed on floodplains eg farmland for grazing animals, playing fields, parks.
4. River restoration - restore the river’s original course to slow down flow and build up key features eg meanders, floodplains.

Question 19

How can areas prepare for floods?

Answer 19

The Environment Agency issues flood warnings. These are often given out with weater forecasts.
3 levels of warning Flood watch (be prepared), flood warning (threat to homes and businesses - move upstairs) and severe flood warning extreme danger to property and life. Evacuate or move upstairs).
Flood maps are also used to show areas most at risk. Sandbags should be used. Floodgates closed if any in area.
Local authorities and emergency services have plans in place and use flood maps to plantheir specific response.

Question 20

Using an area you have studied analyse the costs and benefits of the flood management strategy

Answer 20

BANBURY, north of Oxford in the Cotswold Hills.
Population 45,000
Much of the town is buit on the floodplain of the R Cherwell (a tributary of the R Thames)
Has a history of flooding eg 1998 railway and roads closed - cost £12.5million in damages. 2007 flooded again.
2012: flood defence scheme opened
Roads raised (A361 stayed open in floods); footpaths and green spaces created.
Cost £18.5million paid for by Env Agency and Cherwell District Council
400 houses and 70 businesses protected (Valued at £100m)
Flood control structures can control the rate of river flow towards Banbury. Excess water builds up in the storage area.
Local materials used eg earth banking created small reservoir locally. Embankment created a flood storgae areal.
New wildlife habitats created with ponds, trees, hedges.