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Flashcards in Rivers Key Terms Deck (76)
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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.

30

Infiltration capacity

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