RIVERS - all non case study knowledge

Question 1

what is surface run off?

Answer 1

when water runs off the surface of the ground

Question 2

what is groundwater flow?

Answer 2

when water flows through the rocks and soil underground

Question 3

where does the water cycles start?

Answer 3

the sea

Question 4

what happens to the sea water in the second stage of water cycle?

Answer 4

evaporates into water vapour into the air, when the sun heats the water

Question 5

what happens to the water vapour?

Answer 5

cool and condenses to form clouds

Question 6

what happens the the clouds in the water cycle?

Answer 6

falls as rain, snow etc

Question 7

what is the final stage in the water cycle?

Answer 7

precipitation going back into the sea either by groundwater flow or surface run off

Question 8

what is a drainage basin?

Answer 8

area of land that is drained of all its precipitation by a river and its tributaries

Question 9

how is a drainage basin formed?

Answer 9

created by a natural dividing of the highest land forms.

Question 10

what is a watershed?

Answer 10

the edge of a river basin

Question 11

what is the source of a river?

Answer 11

the start of the river

Question 12

what is a confluence?

Answer 12

where tributaries joins a larger river

Question 13

what is the mouth of a river?

Answer 13

the end of a river, where it usually joins the sea

Question 14

what is a tributary?

Answer 14

a small stream that joins a larger river

Question 15

where do you find erosional features in a long river profile?

Answer 15

upper and mid sections, things like waterfalls, rapids and v-shaped valleys are formed

Question 16

where do depositional features occur?

Answer 16

mid and lower sections of a river, meanders and deltas

Question 17

how does a river erode near the source and why?

Answer 17

• at the source of the river the discharge is low so it only has enough energy to erode downward (vertical erosion)

Question 18

how does a v-shaped called occur?

Answer 18

1. river erodes vertically into the river bed
2. exposed sides are attacked by freeze-thaw weather
3. slumping on the sides occur because of animals and loosened river materials move into the river channel
4. river transports its new load through traction and saltation

Question 19

how are interlocking spurs formed?

Answer 19

1. bands of hard rock occur and the river wants to take the path of least resistance so it flows around them and outcrops known as spurs are formed
   - they usually form an interlocking pattern

Question 20

how is a waterfall formed?

Answer 20

○ Waterfalls are an upper course and lower course feature.

	1. The soft rock is eroded quicker than the hard rock and this creates a step
	2. Abrasion and hydraulic action erode to create a plunge pool  
	3. As erosion continues, the hard rock is undercut forming an overhang 
	4. Over time this gets bigger, increasing the size of the over hang until the hard rock is no longer supported and it collapse
	5. This process continues and the waterfall keeps retreating upstream.

Question 21

how do potholes occur?

Answer 21

1. River water is swirled around in irregularities in the river bed creating vertical eddies
   2. Rocks get swept into the small depression and abrade the hollow. These rocks are called grinders.
   3. The process continues deepening and enlarging the pothole.

Question 22

how are meanders formed?

Answer 22

lateral erosion

1. Lateral erosion dominates as the river swings in large bends known as meanders.

	2. Water is pushed to the outer bend. This reduces friction with the bed and banks. 
	3. Water in meander does not travel at the same speed. The fastest and most powerful water travels around the outside of the bend. 
	4. On the outer bend the river has more energy for transporting material which can erode the outside bank via abrasion. 
	5. On the inside of the bend, the water is shallower and as a result it has less energy. This leads to deposition as the river no longer has enough energy to carry its load.

Question 23

how is an oxbow lake formed?

Answer 23

• if a meander gets too big the river wants the path will least energy so
• continual erosion occurs on the meander neck and weakens it
• it then cuts through the neck
• deposition occurs along the banks of the river and eventually cuts of the meander to leave an oxbow lake
• it will slowly dry up, unless high rainfall prevents it from doing so

Question 24

what are levees?

Answer 24

naturally raised river banks, or ridges of sediment formed by lots of flooding
- made up from gravel, stones and alluvium

Question 25

what is a flood plain?

Answer 25

A flood plain is wide, flat area on marshy land on either side of a river, and found in the middle and lower courses.

Question 26

how is a flood plain created?

Answer 26

○ When the river floods it deposits silt, creating a very flat flood plain. Layer upon layer builds up over many years to form a thick deposit of fertile alluvium.

Question 27

what are deltas?

Answer 27

○ Deltas are river sediments deposited when a river enters a standing body of water such as a lake, a lagoon, a sea or an ocean. They are fundamentally features of river deposition, not marine deposition.

Question 28

what are the certain conditions needed for a delta to form?

Answer 28

• A river with high sediment load (such as the Nile, Mississippi or the Ganges)
  - Usually a large river. This condition is necessary for marine deltas otherwise the action of the sea might disperse the sediment.
  - Reasonably shallow water offshore. (very deep water inhibits delta building)
  - A coast on which the wave energy is low.