Rivers key terms

Question 1

Evaporation

Answer 1

The process which liquid water is transformed into water vapour

Question 2

Transpiration

Answer 2

The process by which water is lost from a plant through stomata in its leaves

Question 3

Evapotranspiration

Answer 3

The total amount of moisture removed by evaporation and transpiration from a vegetated land surface

Question 4

Groundwater flow

Answer 4

The slowest transfer of water within the drainage basin. Provides the main input of water during drought or dry seasons. Flows through bands of sedimentary rock.

Question 5

Infiltration

Answer 5

The passage of water into the soil. Takes place quickly at the beginning of a storm, but as the soil becomes more saturated, infiltration rates drop. sandy soils infiltrate more than clay.

Question 6

Interception

Answer 6

The process by which raindrops are prevented from directly reaching the soil surface. Leaves and stems intercept water.

Question 7

Percolation

Answer 7

The downward movement of water within the rock under the soil surface. The rate of percolation depends on the nature of the rock.

Question 8

Precipitation

Answer 8

Water in any form that falls from the atmosphere to the surface of the earth. Includes rain, snow, sleet and hail.

Question 9

Runoff

Answer 9

All the water that enters a river and eventually flows out of the drainage basin.

Question 10

Stemflow

Answer 10

The water that runs down the stems and branches of plants and trees during and after rain to reach the ground

Question 11

Throughfall

Answer 11

The water that drips off leaves during a rainstorm. It occurs when more water falls onto the interception layer of the tree canopy than can remain on the leaves.

Question 12

Throughflow

Answer 12

The water that moves down-slope through subsoil, pulled by gravity

Question 13

Soil moisture surplus

Answer 13

Soil water store is full which gives a surplus of soil moisture for plant use and runoff into streams

Question 14

Soil moisture use

Answer 14

Plants must rely on stored water which is gradually used up

Question 15

Soil moisture deficiency

Answer 15

Plants must have adaptations to survive for long periods or land must be irrigated

Question 16

Soil moisture recharge

Answer 16

The soil water store starts to be recharged

Question 17

Return period

Answer 17

An estimate of the likelihood of an event

Question 18

Abrasion

Answer 18

Rocks hitting the river bed and bank

Question 19

Hydraulic action

Answer 19

The power of moving water erodes the river

Question 20

Solution (erosion)

Answer 20

Rocks dissolved by acids and erode the river

Question 21

Attrition

Answer 21

Rocks hitting each other which make them smaller and rounder

Question 22

Suspension

Answer 22

Fine, light material carried along in the river

Question 23

Solution (transportation)

Answer 23

Dissolved rock carried along in the river

Question 24

Saltation

Answer 24

Small pebbles and stones bouncing along river bed

Question 25

Traction

Answer 25

Large rocks rolling along river bed

Question 26

Example of a waterfall and gorge

Answer 26

High force on River Tees, Northern England

Question 27

Example of a meander and oxbow lake

Answer 27

River cuckmere

Question 28

MEDC flood case study

Answer 28

Cumbria Floods - Cockermouth, Cumbria

Question 29

LEDC flood case study

Answer 29

Pakistan - Indus River

Question 30

Hard engineering case studies

Answer 30

• Mississippi River, USA

- Three Gorges Dam, China - Yangtze River

Question 31

Soft engineering case studies

Answer 31

• Yellow River, China - Afforestation
• Rhine River, Germany - floodplain zoning
• Met Office/ The EA - forecasting floods and warning

Question 32

Causes of high velocity?

Answer 32

• High discharge
• High hydraulic radius
• Increase of gradient
• Low wetted perimeter

Question 33

What is velocity determined by?

Answer 33

• Channel shape in cross section
• Roughness of channel beds and banks
• Channel gradient

Question 34

What is hydraulic radius?

Answer 34

Shows channel efficiency

Question 35

Hydraulic Radius calculation

Answer 35

Cross sectional area - channel width X depth
____________________________________
Wetted perimeter

Question 36

What is the Hjultsrom curve?

Answer 36

Shows the relationship between river velocity and size of particles that can be eroded, transported and deposited.

Question 37

What are the key points on the Hjultsrom curve?

Answer 37

1) silt/sand are picked up at lowest velocities
2) clays are difficult to erode as pebbles, although small, they are cohesive and clay bed is smooth.
3) large boulders are dropped easily
4) clay particles can be transported in suspension at low velocities

Question 38

What is the Bradshaw model?

Answer 38

Illustrates the main changes expected down the long profile of a river
Can make hypotheses on expected changes in the channel characteristics down the long profile

Question 39

Formation of deltas

Answer 39

Deltas form only when the rate of deposition exceeds the rate of sediment removal.

Question 40

Formation of braided streams

Answer 40

Braiding occurs when the river is forced to split into several channels separated by islands.

Question 41

Formation of potholes

Answer 41

Potholes are formed where there are depressions, fine particles and large boulders may become trapped and swirled around by the current

Question 42

Why does river rejuvenation occur?

Answer 42

Occurs when there is a rise of fall in sea level. The river adjusts to this change and creates landforms

Question 43

What are river rejuvenation land forms?

Answer 43

• Knick points
• River Terraces
• Incised Meanders

Question 44

Formation of a Knick Point

Answer 44

Formed due to sudden increase in gradient. Rejuvenation always starts closest to the sea and migrates upstream. A knick point marks each period of rejuvenation which resulted in an incised valley floor.

Question 45

Formation of a River Terrace

Answer 45

They are the remains of a former floodplain which has been left at a higher level after rejuvenation. The down cutting of a renewed river leaves old flood plain above the level of the present river at a suspended level.

Question 46

Formation of a Incised Meander

Answer 46

Renewed energy from rejuvenation results in an increase of vertical erosion and incised meanders. Ingrown meanders are also found in this process which incision is less rapid and lateral erosion is dominant.