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Flashcards in Rivers Deck (34):
1

What are the main processes

erosion
Transportation
Deposition

2

Vertical erosion

Deepens The Valley

Makes it into a V shape

Dominant in the UPPER course

Rough angular particles scape along the river bed

3

Lateral Erosion

Widens the river valley

During formation of meanders

Dominant in the middle and lower course

4

Four processes of erosion

Hydraulic action
Abrasion
Attrition
Solution

5

Hydraulic action

The force of water breaks rock particles away from the river channel

6

Abrasion

When the rocks scrape the riverbed, wearing it away

7

Attrition

When rocks smash into each other and break into smaller fragments

Causes particles size to decrease between the long profile

Their edges become smooth by rubbing them together

8

Solution

River water dissolves some type of rock

Eg limestone or chalk

9

Types of transportation

Traction
Suspension
Solution
Saltation

10

Traction

Large particles pushed along the riverbed

11

Suspension

Small particles are carried along by the water

12

Saltation

Pebble sized particles bouncing along the riverbed by the force of the water

13

What is deposition

Explain

When the river drops eroded material

When the river losses it’s velocity
It loses its velocity because:
Decrease in the volume of water
The river reaches its mouth
The water is shallower

14

Water falls (upper)

1) river flows over HARD and SOFT ROCK
2) a STEP is created because the softer rock ERODES (hydraulic action and abrasion) more than the hard rock
3)erosion CONTINUES to create a steep drop -waterfall
4) HARD rock is then UNDERCUT by erosion. It becomes UNSUPPORTED and COLLAPSES
5) the collapse rock erodes the bottom of the waterfall (abrasion) where there is softer rock
6) CONTINUATION leads to a RETREAT

15

Interlocking Spurs (upper)

1) Vertical Erosion - V shape valleys
Discharge and volume is low
2) freeze thaw wearing widens The Valley
3) the stream twists and turns around resistant rocks
The river takes the easiest routes
4) faster flow on the outside bend
It undercuts the outside and deposits on the inside

16

Meanders (middle)

1) FASTEST FLOW on the OUSIDE BEND because the river is deeper (less friction to slow it down)- more erosion takes and forms a RIVER CLIFF

2) SLOWEST FLOW on the INSIDE BEND because it’s shallower
It deposits it’s load of mud and shingle.
Steep side slopes are formed from the deposits.
Velocity is low because there is more friction to lower the velocity

17

Ox Bow lakes (middle)

The river erodes the outside bend by lateral erosion, hydraulic action and abrasion (DEFINE THEM) cause it to widen

Decrease in velocity means deposition happens on the inside bend

Meander necks starts to thinner over a long period of time

During a flood, the river cuts the neck because of the increase in velocity and discharge

After the flood, the river takes the shortest routes and deposits sediment on the inside

18

Flood plain (lower)

It occasionally gets flooded

When it does the water slows down and deposits the eroded material that it’s transporting.
Makes the floodplain higher

Meanders migrate across the flood plain making it wider
Meanders migrate downstream flattening The Valley floor

Deposition happens on the slip off slopes of meanders also builds up the flood plain

19

Levees (lower)

Natural Embankments along the edges of the river
Eroded material is deposited during a flood over the flood plain
Heaviest material-deposit closest to river channel (it’s dropped 1st when the river slows down)
Overtime deposited material builds up

20

Estuaries (lower)

Found at the mouth of a river
River valley it’s at its widest
Water is tidal- river level rises and falls each day
Deposition of sediment when the water is moving very slow at high tide
When fresh water meets salty water, friction occurs -velocity is then lost -deposition -builds up layers of mud flats
Mud flats are visible at low tide

21

What is river discharge

The VOLUME of WATER flowing in a river

22

Hydro graphs shows how the discharge at a certain point in a river changes over time

1) PEAK DISCHARGE: highest charge in the period of time
2) LAG TIME: the delay between peak rainfall and peak discharge
3) RISING LIMB: the increase in river discharge as rainwater flows into the river
4) FALLING LIMB: the decrease in river discharge as the river returns to its normal level

23

Why does floods occur?

1) PROLONGED RAINFALL- the soil become saturated so no more water can infiltrate. It increases surface run off - more discharge
2) GEOLOGY- some rocks are impermeable so runoff increases - increase discharge
3) HEAVY RAINFALL- no infiltration so runoff increases- increase in discharge
4) RELIEF- faster on steep sided valley - discharge increases
5) BUILDINGS- impermeable surfaces (concrete) increase runoff- increase in discharge

24

Types River Hard engineering

Dams and Reservoirs
Channel straightening
Embankments
Flood relief channels

25

Types of River Soft engineering

Flood warnings
Preparations
Planting trees
Flood plain zones
River restoration

26

Dams and Reservoirs

Huge walls built across the river and a Reservoir is an artificial lake behind the dam

+ stores water - reducing the risk of flooding
+ water can be used to generate hydroelectric power
+ water is drinkable for locals

- very expensive
- less fertile farm land down stream as deposition in the the reservoir

27

Channel straightening

Artificial straight channels that straightens rivers course

+ water moves out of the area as quickly because it doesn’t travel as far

- flooding downstream as water is carried there faster
- more erosion downstream- water is flowing faster

28

Embankments

Raised walls along the riverbanks

+ the river can hold more water
+ protecting building on the floodplain

- quite expensive
- a risk of severe flooding if river levels exceed the embankments or if they break

29

Flood relief channels

They divert water around important areas

+ river discharge is reduced
+ release of water are controlled by the gates

- flood if water levels gets too high for the relief channels
-increase discharge when the channel rejoins a river

30

Flood warnings (soft)

Through TV, radio, newspapers

+ gives people time to move possessions upstairs or to evacuate

- they don’t stop the floods
- some people may not have access to the warnings

31

Planting trees (soft)

It increase the interception of rainwater and increase lag time

+ vegetation reduces soil erosion in the valley
+provides habitats and wildlife

- less land available - used for farming

32

Flood plain zoning (soft)

Prevents the building on high risk areas

+ impermeable surfaces aren’t created
+ reduces impact - no buildings to be damaged

- doesn’t help already built buildings on floodplain
- limited expansion in urban area

33

River restoration (soft)

Makes the river look more natural so it can flood naturally

+ little maintenance is needed
+ better habitats for wildlife
+ less risk of flooding downstream because discharge is reduced

- local flood risk can increase

34

Preparations (soft)

Modified buildings to reduce the amount of damage.
People make plans for what to do in a flood ( emergency kit)

+ less damaged buildings
+people know what to do so there’s less worry about the threat

-doesn’t guarantee safety
- can give people a false sense of security
- expensive to modify buildings