Rivers Key Terms Flashcards Preview

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Flashcards in Rivers Key Terms Deck (76):
1

Attrition

The impacting of particles upon one another, causing their gradual reduction in size.

2

Base level

The theoretical level down to which (but not below) the river can erode its valley. The ultimate base level is sea level.

3

Base flow/groundwater flow

Process by which water moves downslope below the water table under the influence of gravity

4

Bed load

The coarser material carried along the bed of a river by the force of streamflow

5

Capacity

The total load actually transported by the river

6

Catchment area

The area of land which water drains into a river

7

Cavitation

A form of hydraulic action where bubbled of air collapse and resulting shockwaves hit and slowly weaken poorly consolidated banks. Slowest and least effective erosion process.

8

Channel efficiency

The ability of a river channel to transport its water and its load

9

Competence

The diameter of the largest particle that a river can carry at a given velocity

10

Discharge

The volume of water passing a fixed position in a given time. Cross sectional area x average velocity. Measured in cumecs.

11

Drainage basin

The area of land drained by a river and its tributaries

12

Entrainment

The process by which sediment/rocks are drawn into a moving body of water

13

Ephemeral channel

A channel which only contains water after intermittent downpours of rain, separated by longer periods when channel is dry.

14

Evaporation

The process by which water is transferred from the earth's surface to the atmosphere. It represents an output from the drainage basin.

15

Evapotranspiration

Process accounting for the total output of water vapour from the drainage basin system to the atmosphere through a combination of evaporation and transpiration

16

Floodplain

The area on either side of a river channel consisting of alluvium across which the river spills when it's over bank full

17

Graded profile

The concave long profile of a stream where erosion, transportation and deposition are in a state of equilibrium. Discharge and available energy are in balance with the available load.

18

Groundwater

The water filling all the pore spaces in the zone of saturation

19

Groundwater store

Th water held below water table in aquifers

20

Headward erosion

Erosion occurring at the source of a stream, resulting in the lowering of the land surface, allowing stream to rise further back or further uphill. Possible for streams to erode through watershed allowing them to capture streams in other valleys.

21

Helicoidal flow

A type of corkscrew flow superimposed on the primary downstream flow of a river. Flow moves across river from inside bank of meander to outside. The flow eroded meanders on outside bend and deposits on inside.

22

Hjulstrom's curve

A logarithmic graph showing the relationship between stream velocity and particle size (competence)

23

Hydraulic Action / Scour

A process of fluvial erosion whereby water washes beds and banks. As water flows towards other banks of the meander, water and air is compressed into cracks and blasts out material as pressure is released.

24

Hydraulic radius

Measure of channel efficiency. Divide cross sectional area by wetted perimeter. The higher the ratio = the more efficient. Efficiency increases downstream - depth and width increase so less discharge is in contact with the bed and banks = less friction slows it down

25

Hydrograph

Storm hydrograph records the surge in discharge due to a single rainfall event. Plots discharge against time. Stormflow shows surface and subsurface discharge due to the storm, and base flow shows continuous release of groundwater into river.

26

Flashy hydrograph

Rapid response to storm with short lag time and steep rising limb

27

Hydrological cycle

Movement of water between the land, air and sea

28

Incised meanders

A river meander which cuts down deeply into the bedrock due to rejuvenation

29

Infiltration

Process by which water moves downwards from the surface to soil pores.

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Infiltration capacity

The maximum rate which water can be absorbed by a soil or rock in a given condition

31

Infiltration rate

The rate of water absorption expressed in millimetres per minute

32

Interception

Process by which incoming precipitation is trapped by vegetation and buildings. Water is then transferred to the earth's surface or evaporated.

33

Interlocking Spurs

Protrusions of higher land characteristic of the upper sections of a river valley resulting from the river's winding course and more resistant rocks.

34

Isovel

A lining joining pointed of equal velocity in a river channel.

35

Knick point

A break of slope in the long profile of river due to rejuvenation. Because of the renewed down cutting a new long profile is created and where this intersects the former long profile a Knick point is created.

36

Lag time

The time between peak precipitation and peak discharge

37

Laminar flow

Horizontal movement of water

38

Levee

A bank of sediment along the edge of a river channel, deposited naturally with floodwaters. Often raised and strengthened artificially to contain floodwaters.

39

Load

Pebbles, particles and dissolved matter carried by a river

40

Long profile

A river course from its source in an upland area along its channel to its mouth.

41

Meander

A bend in a river with a sinuosity ratio of more than 1:5

42

Natural levee

An embankment on the sides of a river formed by the deposition of silt during flooding

43

Overland flow / surface run off

Process by which water moves downslope over the earth's surface in unconfined channels under the influence of gravity. Saturated overland flow occurs when excess water flows across the ground surface due to subsurface being saturated.

44

Percolation

Process by which water moves vertically downwards through soil and rock

45

Permeability

Ability of rocks, soil or sediment to permit water to flow through it. Permeable rocks allow water to pass through them via bedding planes and joints e.g. Limestone. Impermeable rocks like granite produce more run off and streams.

46

Point bar

Sediment deposited under water on the inside bed of a meander

47

Pools and riffles

The alternating pattern of deep pools and is reaches where a river flows across gravel bars. Distribution if regularly spaced with the distance between pools being 5-7 times greater than the channel width.

48

Porous rocks

Allow water to pass through them via pores e.g. Sandstone and chalk

49

Recessional limb

Part of the hydrograph showing the speed at which the discharge declines after a peak back to its pre storm level

50

Precipitation

Process by which water is transferred from the atmosphere to surface in the form of snow, sleet, hail, rain, fog. Input into drainage system.

51

Recharge

Water added to groundwater or soil to replace that lost by evaporation or transpiration

52

River regime

Variation in discharge from January to December

53

Rejuvenation

The state of a river when it's energy has been revitalised leading to an increase in erosional capability. Results from a fall in base level, due to fall in sea level or uplift of land.

54

Rising limb

The part of a flood hydrograph which shows how quickly floodwaters rise due to storm event

55

River cliff / Bluff

Erosional landform on the outside bend of a meander

56

Saltation

Bed load is transported by bounding motion of lighter particles

57

Sinuosity

The curving nature of the meander. The actual channel length divided by the straight line distance.

58

Soil moisture budget

The balance between moisture inputs and outputs in a soil over time.

59

Soil moisture deficit

A shortage of soil moisture. Evapotranspiration > precipitation- in summer

60

Soil moisture recharge

A period after summer or drought when lost moisture has to be replaced

61

Soil moisture surplus

Occurs after a period of recharge when precipitation > evapotranspiration (winter). Soils saturated = surface run off dominates.

62

Dissolved load / Solute

Part of load that's in solution

63

Solution

Process by which minerals in rocks making up the bed and bank are dissolved by carbonic or humic acids in water. Occurs continuously and unaffected by discharge or velocity.

64

Suspension

Lighter material held in water flow by turbulent eddies.

65

Stem flow

Intercepted precipitation which runs down stems of plants to ground

66

Storm hydrograph

Graph showing discharge against time following single precipitation event

67

Suspended load

Solid particles carried within the current but not touching bed

68

Thalweg

The longitudinal profile of a streambed along its line of max velocity

69

Through fall

Incoming precipitation which falls through vegetation and is NOT intercepted

70

Through flow

Process by which water moves through the soil under the influence of gravity

71

Traction

Bed load is transported by rolling of heavy particles

72

Transpiration

Process by which water is transferred from vegetation to atmosphere via stomata on leaves - output from drainage system

73

Water table

The upper boundary of the saturated rock beneath which cracks and pores are full of water. Upper surface of ground water layer. Rises in winter and falls in summer in response to variations in precipitation

74

Watershed

The boundary between one drainage basin and another marked by a ridge of high land beyond which precipitation will fall into adjacent basins

75

Wetted perimeter

Total length of water in a cross section of a river in contact with the bed and banks

76

Abrasion

Process of fluvial erosion whereby beds and banks are eroded by water borne sediments