Geography Rivers Sept 2017

Question 0

Describe the features that are in the drainage basin

Answer 0

The source of the river is where the river starts in the mountains. As it winds it’s way towards the sea, smaller rivers called tributaries join. Sometimes a bigger river or confluence will join it. Where it reaches the sea is called the mouth. Around the drainage basin is an imaginary line called the watershed

Question 1

What is relief?

Answer 1

Relief is a term used by geographers to describe height, shape and steepness of a landscape

Question 2

Describe a river channel in the upper section of a river

Answer 2

The valley is steep-sided and ‘v’ shaped. The river is narrow, shallow and turbulent

Question 3

Describe the river channel in the middle section of a river

Answer 3

The valley is wide and has a flat floor. The river is wide and deep

Question 4

Describe the river channel in the lower section of a river

Answer 4

The valley is very wide and flat and has a flood plain and levees. The river is wide, deep and has a large sediment load

Question 5

What are the four types of erosion?

Answer 5

Abrasion, attrition, hydraulic action and solution

Question 6

What are the four types of transportation?

Answer 6

Traction, saltation, suspension and solution

Question 7

How is a waterfall formed?

Answer 7

The soft rock is eroded by hydraulic action and leaves an overhang or hard rock. The hard rock collapses and due to abrasion and attrition creates a plunge pool.

Question 8

How is a gorge formed?

Answer 8

A gorge is formed after a waterfall has retreated. It is the river channel with steep sides left behind. (In an exam, explain how the waterfall is formed first)

Question 9

How are meanders formed?

Answer 9

Meanders are formed in the middle course of the river. They form when there is an obstruction in the path of the river, for example a large boulder that is unable to be moved. The river winds around it eroding the sides of the river. Deposition leaves behind a slip off slope on the inside bend and abrasion, attrition and hydraulic action make the outside bend bigger. This creates being winding meanders in the river.

Question 10

How is an ox-bow lake formed?

Answer 10

An ox-bow lake is formed next to meanders. They form when two meanders become too close together and the land in between is eroded. After time deposition occurs in the old meander blocking off the water. The water left behind forms the ox-bow lake

Question 11

How does the long profile of a river change downstream?

Answer 11

Nearer the source in the upper course of the river there is a steep gradient. Moving further downstream into the middle course the gradient is gentle and then becomes very gentle as the river enters the lower course.

Question 12

When does deposition take place?

Answer 12

Deposition takes lace when the velocity of the river slows down. Larger rocks are usually deposited in the upper course of the river. Finer sediment is deposited further downstream where the velocity is slowed by friction. The majority of deposition occurs at the mouth due to the force of the waves and the very gentle gradient greatly decreasing the velocity of the river.

Question 13

What river landforms are in each course of the river?

Answer 13

Upper course - Interlocking spurs, waterfalls & gorges.
Middle course - Meanders & ox-bow lakes.
Lower course - Floodplains, levees and estuaries.

Question 14

What is an estuary?

Answer 14

Estuaries are transitional zones between river and coastal environments and are affected by wave action as well as river processes.

Question 15

What is a floodplain? How is it formed?

Answer 15

Definition - A floodplain is a wide flat area of fertile land
on either side of a river.
Formed by - Meanders migrating across due to lateral
erosion or when a river floods it deposits
silt which after many years builds up to
create flat fertile land.

Question 16

What is a levee? How is it formed?

Answer 16

Definition - A levee is a raised river bed or ridge of
sediment.
Formed by - When a river floods the deposited
sediment flows out over the river bank.
They are then deposited again on the river
bank with larger rocks being nearest the
river decreasing to finer sediment further
away from the river.

Question 17

What is lag time?

Answer 17

The time between the peak rainfall and peak discharge.

Question 18

What is a hydrograph?

Answer 18

A graph that plots the river discharge after a storm.

Question 19

What are the physical factors that cause flooding?

Answer 19

Precipitation - Torrential rainstorms can lead to sudden
flash floods as the river channels cannot
contain the large amount of water.
Several days of rain can also lead to
flooding of ow land river channels.
Geology - Impermeable rocks do not allow water to
flow through them so water flows over them
into river channels which speeds up water
flow increasing flood risk.
Steep slopes - Steeper slopes cause higher water
speeds which increases the transfer of
water to river channels increasing flood
risk.

Question 20

What are the human factors that cause flooding?

Answer 20

Urbanisation - Building on floodplains creates many
impermeable surfaces causing water to
flow into river channels causing them to
overflow and flood.
Deforestation - Most water that falls on trees is
temporarily stored in the leaves or
evaporated quickly. When trees are
removed there is suddenly a larger
amount of water trying to flow into the
ground causing the soil to clog
increasing surface run-off.
Agriculture - In arable farming soil is left unused and
exposed to the elements for large periods
of time. This can lead to more surface run-
off . When soil is ploughed flood risk is
also increased as water can flow more
easily in the furrows.

Question 21

What are the 2 methods used to manage flooding?

Answer 21

Hard engineering and soft engineering.

Question 22

What are examples of soft engineering? How do they work?

Answer 22

Flood storage areas - Areas of land nearby river
channels can be deliberately
flooded to reduce the water
capacity in the river.
Floodplain zoning - This restricts certain land use in
locations near river channels. Areas
closest to the river with higher flood
risks are kept clear of high value
land use such as housing and
industries and instead is used for
pastures, playing fields or parkland.
River restoration - This restores a river to its original
course. Where a river has been
changed (where hard engineering
has occurred) the river is then
returned to its original course.

Question 23

What are examples of hard engineering? How do they work?

Answer 23

Channel straightening - Areas of land between
meanders are dug up to create
straight river channels. This
speeds up the flow of water
removing the flood risk from the
area, however the flood risk is
then increased further
downstream.
Embankments - An embankment is a raised river bed.
This allows river channels to hold more
water before flooding occurs.
Flood relief channels - A flood relief channel is a man-
made river channel that by-
passes urban areas. During
periods of high rainfall, gates can
be opened to allow water to flow
down the water relief channels.