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GEOGRAPHY > Rivers > Flashcards

Rivers Flashcards

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1
Q

How does a river’s long profile change?

A

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.

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2
Q

How does a river’s cross profile change?

A

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

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3
Q

What are the 4 main processes of erosion?

A

Hydraulic Action
Abrasion
Attrition
Solution

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4
Q

What is Hydraulic Action?

A

A form of erosion

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

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5
Q

What is Abrasion?

A

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

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6
Q

What is Attrition?

A

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.

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7
Q

What is solution?

A

River water dissolves some type of rock like chalk.

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8
Q

What is transportation?

A

Transportation is the movement of eroded material.

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9
Q

What are the 4 methods of transportation?

A

Traction
Saltation
Suspension
Solution

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10
Q

What is traction?

A

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

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11
Q

What is Saltation?

A

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

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12
Q

What is Suspension?

A

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

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13
Q

What is Solution?

A

Soluble materials dissolve in the water and are carried along

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14
Q

How are waterfalls and gorges formed?

A

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.

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15
Q

How are interlocking spurs formed

A

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.

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16
Q

Why do rivers deposit sediment?

A

When a river loses velocity and energy.

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

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17
Q

How are meanders formed?

A

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

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18
Q

How are Ox-bow lakes formed?

A

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.

19
Q

What is a flood plain?

A

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.

20
Q

What are Levees?

A

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.

21
Q

What are Estuaries?

A

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.

22
Q

What is Hard engineering?

A

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

23
Q

What is Soft engineering?

A

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

24
Q

Name 4 examples of hard engineering.

A

Dams and reservoirs

Channel straightening

Embankments

Flood relief channels

25
Q

What are Dams and Reservoirs

Pros and cons.

A

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.

26
Q

What is Channel Straightening?

A

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

27
Q

What is Channel Straightening?

A

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

28
Q

What are Embankments?

A

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.

29
Q

What are Flood Releif Channels

A

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.

30
Q

What are the 4 examples of Soft Engineering?

(Rivers)

A

Flood warnings and prep

Flood plain zoning

Planting trees

River restoration

31
Q

What are Flood warnings and prep?

Pros and cons..

A

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

32
Q

What is Flood plain zoning?

A

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.

33
Q

How does Planting Trees affect floods?

A

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

34
Q

What is River restoration?

A

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

35
Q

What does a Hydrograph show?

A

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

36
Q

What is Peak Discharge?

A

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

37
Q

What is Lag Time?

A

The delay between peak rainfall and peak discharge.

38
Q

What is Rising Limb?

A

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

39
Q

What is Falling limb?

A

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

40
Q

What is the discharge in a river?

A

The volume of water flowing per second, measured in cumecs

41
Q

Why does lag time occur?

A

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.

42
Q

What and how do physical factors affect flood risk?

A

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

43
Q
A

GEOGRAPHY (16 decks)

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