Rivers

Question 1

How does a river’s long profile change?

Answer 1

The river starts upland. The load is large as it hasn’t been broken down by erosion.
The lower course is a lot flatter. River’s load is fine sediment as erosion has broken down the rocks.

Question 2

How does a river’s cross profile change?

Answer 2

Upper course - vertical erosion, shallow and narrow with steep sides in a v-shaped valley.

Middle course - less vertical erosion more lateral erosion so wider. It has a deeper channel and gently sloping sides

Lower course - Little erosion no vertical at all. Very wide and an almost flat valley with the channel at its deepest

Question 3

What are the 4 main processes of erosion?

Answer 3

Hydraulic Action
Abrasion
Attrition
Solution

Question 4

What is Hydraulic Action?

Answer 4

A form of erosion

The force of the river water colliding with rocks breaks particles away from the river channel

Question 5

What is Abrasion?

Answer 5

A form of erosion

Eroded rocks are picked up by the river and they scrape and rub against the bottom of the channel. Wearing it away

Question 6

What is Attrition?

Answer 6

A form of erosion

Eroded rocks are picked up by the river and crash into each other and break them into smaller pieces. This decreases their size and the rocks become more round as the river progresses from source to mouth.

Question 7

What is solution?

Answer 7

River water dissolves some type of rock like chalk.

Question 8

What is transportation?

Answer 8

Transportation is the movement of eroded material.

Question 9

What are the 4 methods of transportation?

Answer 9

Traction
Saltation
Suspension
Solution

Question 10

What is traction?

Answer 10

Large particles like boulders are rolled along the river bed by the force of the water.

Question 11

What is Saltation?

Answer 11

Pebble-sized particles are bounced along the river bed by the force of the water.

Question 12

What is Suspension?

Answer 12

Small particles like silt and clay are carried along by the water.

Question 13

What is Solution?

Answer 13

Soluble materials dissolve in the water and are carried along

Question 14

How are waterfalls and gorges formed?

Answer 14

Waterfalls form when a river flows over an area of hard rock followed by an area of soft rock.

The soft rock erodes (hydraulic action and abrasion) faster than the hard rock creating a step. As water flows over the step it erodes into a steep drop called a waterfall.

The hard rock is undercut by erosion and eventually collapses. This hard rock swirls around at the bottom where it erodes the softer rock by abrasion and creates a plunge pool.

Over time more undercutting causes more collapses and this leaves behind a STEEP SIDED GORGE.

Question 15

How are interlocking spurs formed

Answer 15

Vertical erosion in the upper course of the river creates steep-sided V-shaped valleys.

The river lacks power so there is no lateral erosion so they wind around hillsides that stick out on either side.

They interlock with each other as the river winds around them. These are called interlocking spurs.

Question 16

Why do rivers deposit sediment?

Answer 16

When a river loses velocity and energy.

Volume of water falls
Amount of eroded material increases
Water is shallower
River reaches its mouth

Question 17

How are meanders formed?

Answer 17

As the current is faster on the outside of the bend it erodes faster due to the water being deeper so there is less friction these forms river cliffs.

On the inside of the bend, the water is slower so the eroded sediment is deposited here forming slip-off slopes

Question 18

How are Ox-bow lakes formed?

Answer 18

Ox-bow lakes are formed from meanders as they get larger over time.

Erosion causes the outside of the bend to get closer until there is only a small bit of land left called the neck.

The river eventually breaks through this and the water takes the faster route. Deposition eventually cuts off the meander forming an ox-bow lake.

Question 19

What is a flood plain?

Answer 19

Flood plains are wide valley floors on either side of the river that occasionally flood.

When they do flood the water traveling on the floodplain loses its energy and deposits its energy. This builds up the floodplains

Meanders widen when they move across flood plains. The deposition that happens on slip-off slopes builds up these flood plains.

Question 20

What are Levees?

Answer 20

They are natural embankments next to the river and floodplains. As when the river floods the heaviest material is deposited right next to the river. This builds up the levees along the edges.

Question 21

What are Estuaries?

Answer 21

An estuary is 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 form mudflats which are an important habitat for wildlife.

Question 22

What is Hard engineering?

Answer 22

Man made structures built to control the flow of rivers and reduce flooding

Question 23

What is Soft engineering?

Answer 23

Schemes set up using knowledge of a river and its processes to reduce the effects of flooding.

Question 24

Name 4 examples of hard engineering.

Answer 24

Dams and reservoirs

Channel straightening

Embankments

Flood relief channels

Question 25

What are Dams and Reservoirs Pros and cons.

Answer 25

Dams are barriers built across rivers usually in the upper course. A reservoir is formed behind it. Pros: Stores water and can be used to create hydroelectric power Cons: Very expensive to build. Reservoirs can flood existing settlements.

Question 26

What is Channel Straightening?

Answer 26

Meanders are removed by building straighter artificial channels. PROS: Water leaves the area fast and reduces the risk of flooding CONS: Flooding may happen downstream instead. Faster water causes erosion

Question 27

What is Channel Straightening?

Answer 27

Meanders are removed by building straighter artificial channels. PROS: Water leaves the area fast and reduces the risk of flooding CONS: Flooding may happen downstream instead. Faster water causes erosion

Question 28

What are Embankments?

Answer 28

Raised river walls are built. PROS: River can hold more water so less frequent flooding CONS: Expensive to build. Risk of severe flooding if water rises over the top or if embankments break.

Question 29

What are Flood Releif Channels

Answer 29

Channels are built t divert water around settlements and split excess water. PROS: Gates on channels can control the release of water, reducing flood risk. CONS: Increased discharge where the channels rejoin causing flooding in other areas.

Question 30

What are the 4 examples of Soft Engineering? (Rivers)

Answer 30

Flood warnings and prep Flood plain zoning Planting trees River restoration

Question 31

What are Flood warnings and prep? Pros and cons..

Answer 31

Local councils and environment agency issues warnings. Buildings are modified to reduce damage PROS: Gives residents time to prepare or evacuate so it reduces the impact of flooding CONS: Don't prevent flooding and gives people a false sense of security

Question 32

What is Flood plain zoning?

Answer 32

Restrictions prevent people building on flood plains. PROS: Flood risk is reduced. Impact is reduced as no damaged buildings. CONS: Expansion of urban area is limited. Doesn't help areas with existing buildings.

Question 33

How does Planting Trees affect floods?

Answer 33

Planting trees in the river valley increases the interception of rainwater. Increases lag time.

Question 34

What is River restoration?

Answer 34

Making the river more natural by removing hard engineering such as levees so the flood plain can flood naturally. PROS: Little maintenance and less risk of flooding downstream. CONS: Local flood risk can increase

Question 35

What does a Hydrograph show?

Answer 35

It whos the discharge at a certain point in the river over time in relation to rainfall.

Question 36

What is Peak Discharge?

Answer 36

The highest discharge in the period of time you are looking at.

Question 37

What is Lag Time?

Answer 37

The delay between peak rainfall and peak discharge.

Question 38

What is Rising Limb?

Answer 38

The increase in the rivers discharge as water flows into the river.

Question 39

What is Falling limb?

Answer 39

The decrease in the rivers discharge as the river returns to its normal level.

Question 40

What is the discharge in a river?

Answer 40

The volume of water flowing per second, measured in cumecs

Question 41

Why does lag time occur?

Answer 41

As rainfall does not all occur directly into the river: Some lands on impermeable land and flows into the river while other rain soaks into the land and then slowly filters into the channel underwater.

Question 42

What and how do physical factors affect flood risk?

Answer 42

Heavy rainfall - Rain arrives too quickly to infiltrate the surface leading to lots of surface run off and less lag time - increasing discharge Geology - Some rocks are more permeable than others, so runoff is increased Prolonged rainfall - Can saturate the soil, increasing runoff into river channels Relief (Change in land gradient) - Steep-sided valleys, means water reaches river channels faster - rapidly increasing discharge