Topic 4: River Proccesses

Question 1

Formation of a waterfall?

Answer 1

• Occurs when more resistant rock lies of less resistant rock
• The less resistant rock below erodes faster than the more resistant rock through abrasion and hydraulic action creating an overhang
• The eroded sediment swirls at the base of the waterfall creating a plunge pool
• The overhang eventually collapses
• The collapsed material adds the erosion of the less resistant rock
• Another overhang is created and the process is repeated again

Question 2

What is the river shape in the upper course?

Answer 2

V shaped, narrow but deep

Question 3

What is the river shape in the middle course ?

Answer 3

Gentle sloping valley, wider and not as deep as in the upper course

Question 4

What is the river shape in the lower course?

Answer 4

Flat and wide floodplain, the river is bigger than it was in the upper course and so despite the fact it is wider than it is deeper, it is still deeper than the upper course river

Question 5

When is velocity of a river at its peak?

Answer 5

In the lower course

Question 6

What is discharge?

Answer 6

The volume of water flowing in a river measured in m^3 per second

Question 7

How does the gradient change from the river source in the upper course to the river mouth in the lower course?

Answer 7

The gradient DECREASES the closer it gets to the river mouth in the lower course (it is steeper in the upper course)

Question 8

How does the discharge change from the source to mouth?

Answer 8

It INCREASES as it reaches the river mouth as more tributaries join the river increasing its volume

Question 9

How does the channel width change from the source to mouth?

Answer 9

The channels width INCREASES the closer it gets to the mouth as the river gains discharge and has more erosive power to make more space by eroding the river sides.

Question 10

How does the channel depth change from the source to mouth?

Answer 10

It INCREASES as the river gains discharge and has more erosive power

Question 11

How does the velocity change from the source to mouth?

Answer 11

It INCREASES as there are fewer obstructions to reduce and obstruct the river flow in the lower course. This is partly due to the rivers increased erosive power in the lower course and so rocks blocking the river are eroded

Question 12

How does the sediment load volume change from the river source to mouth?

Answer 12

It INCREASES as it moves downstream it picks up more sediment

Question 13

How does the sediment particle size change from the source to mouth?

Answer 13

It DECREASES as attrition breaks down the rocks more as it gains erosive power, meaning attrition occurs more in the lower course making the rocks downstream smaller

Question 14

How does the channel bed roughness change from the source to mouth?

Answer 14

It DECREASES as the increased erosive power of the river allows for more erosion of the river bed and therefore a smoother river bed

Question 15

How does a V shaped valley form?

Answer 15

• The river has a low discharge and so only vertical erosion takes place
• The valley sides are broken down by weathering
• The weathered sides begin to fall away
• This created steep slopes on each side of the river … creating a V shaped valley

Question 16

What are interlocking spurs ?

Answer 16

• They form in areas of less and more resistant bands of rock
• The river flows around the sections of more resistant rock creating swerves in the river and various hills of either sides of the river

Question 17

Formation of a meander?
And point bar?
And flood plain?
And oxbow lake?

Answer 17

• Helicoidal flow sends the river energy to the sides of the river
• The current is forced to the outer bend where it undercuts the bank, producing a steep edge or river cliff
• This eventually collapses
• Helicoidal flow transports the sediment from the collapsed bank to the opposite bank and begins to form a point bar
• As the river channel moves the point bar increases … it eventually forms a flood plain
• Continued erosion creates a narrow neck between the two meanders created and eventually during a storm the neck breaks to create an oxbow lake

Question 18

What is lag time ?

Answer 18

• The time between peak rainfall and peak discharge, e.g. between when most rainfall occurred and when the river had the most water in it
• It is the time taken for most of the rain to reach the river

Question 19

What is the rising and falling limb?

Answer 19

• Rising limb : the increase in river discharge as rainwater flows into the river
• Falling limb : the decrease in river discharge as the river returns to its normal level

Question 20

What effects storm hydrographs?

Answer 20

• Geology : areas with impermeable rocks = increased surface runoff
• Soil type : impermeable soils cannot absorb much water e.g. clay
• Slope gradient : steeper slopes = less infiltration = increased surface runoff
• Urbanisation : more concrete and roads = more surface runoff
• Deforestation : less trees = less interception = increased surface runoff

Question 21

What is the named example for a river flood?

Answer 21

Sheffield

Question 22

What are the human factors causing the flood ? (Sheffield)

Answer 22

• Lack of river defences : the water easily outward of the river
• It was highly urbanised : the concrete increased surface leading to higher river discharge and meant that when the flood hit the water remained for longer

Question 23

What were the physical factors effecting the flood? (Sheffield)

Answer 23

• Heavy rainfall : previous to the flood there had been lots of heavy rainfall therefore the soil was already saturated and the river already had a higher river discharge than normal (the antecedent conditions were wet)
• Bottom of hills : the town was bellow a series of hills, water was directed into the town. The steep slopes also led to increased surface run off

Question 24

Ways the council could have prevented the flood?

Answer 24

• River defences
• Planning permission for projects and driveways, less concrete
• Improved drainage systems

Question 25

What are the impacts of flooding?

Answer 25

• Destroys local businesses
• Power cuts
• Homes destroyed
• Money spent on emergency services
• Money spend on clean up and damage dealt
• Travel routes blocked
• Crops destroyed