The water cycle

Question 1

Define atmospheric water

Answer 1

Water found in the atmosphere; mainly water vapour with some liquid water (cloud and rain droplets) and ice crystals.

Question 2

Define cryospheric water

Answer 2

The water locked up on the Earth’s surface as ice.

Question 3

Hydrosphere

Answer 3

A discontinuous layer of water at or near the Earth’s surface. It includes all liquid and frozen surface waters, groundwater held in soil and rock and atmospheric water vapour.

Question 4

Oceanic water

Answer 4

The water contained in the Earth’s oceans and seas but not including such inland seas as the Caspian Sea.

Question 5

Terrestrial water

Answer 5

This consists of groundwater, soil moisture, lakes, wetlands and rivers.

Question 6

Define condensation

Answer 6

The process by which water vapour changes to liquid.

Question 7

Define cryospheric processes

Answer 7

Those processes that affect the total mass of ice at any scale from local patches for frozen ground to global ice amounts. They include accumulation (the build up of ice mass) and ablation (the loss of ice mass).

Question 8

Define drainage basin

Answer 8

This is an area of land drained by a river and its tributaries. It includes water found on the surface, in the soil and in near-surface geology.

Question 9

Define evaporation

Answer 9

The process by which liquid water changes to a gas. This requires energy, which is provided by the sun and aided by wind.

Question 10

Define evapotranspiration

Answer 10

The total output of water from the drainage basin directly back into the atmosphere.

Question 11

Define ground water flow

Answer 11

The slow movement of water through underlying rocks.

Question 12

Define infiltration

Answer 12

The downward movement of water from surface into soil.

Question 13

Define interception storage

Answer 13

The precipitation that falls on the vegetation surfaces (canopy) or human-made cover and temporarily stored on these surfaces. Intercepted water either can be evaporated directly to the atmosphere, absorbed by the canopy surfaces or ultimately transmitted to the ground surface.

Question 14

Define overland flow

Answer 14

The tendency of water to flow horizontally across land surfaces when rainfall has exceeded the infiltration capacity of the soil and all surface stores are full to overflowing.

Question 15

Define percolation

Answer 15

The downward movement of water within rock under the soil surfaces. Rates vary depending on the nature of the rock.

Question 16

Define run-off

Answer 16

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

Question 17

Define saturated

Answer 17

This applies to any water store that has reached its maximum capacity.

Question 18

Define stem flow

Answer 18

The portion of precipitation intercepted by the canopy that reaches the ground by flowing down stems, stalks or tree bole.

Question 19

Define storm and rainfall event

Answer 19

An individual storm is defined as a rainfall period separated by dry intervals of at least 25 hours and an individual rainfall event is defined as a rainfall period separated by dry intervals of at least 4 hours.

Question 20

Define through fall

Answer 20

The portion of precipitation that reaches the ground directly through the gaps in the vegetation canopy and drips from leaves, twigs and stems. This occurs when the canopy-surface rainwater storage exceeds its storage capacity.

Question 21

Define through flow

Answer 21

The movement of water down-slope through the subsoil under the influence of gravity. It is particularly effective when underlying permeable rock prevents further downward movement

Question 22

Define transpiration

Answer 22

The loss of water from vegetation through pores (stomata) on their surfaces.

Question 23

Define water balance

Answer 23

The balance between inputs (precipitation) and outputs (run-off, evapotranspiration, soil and groundwater storage) in a drainage basin.

Question 24

Define bankfull

Answer 24

The maximum discharge that a river channel is capable of carrying without flooding.

Question 25

Define baseflow

Answer 25

This represents the normal day-to-day discharge of the river and is the consequence of slow moving through flow and groundwater seeping into the river channel.

Question 26

Define discharge

Answer 26

The amount of water in a river flowing past a particular expressed as m3s-1 (cumecs)

Question 27

Define lag time

Answer 27

The time between the peak rainfall and peak discharge.

Question 28

Define peak discharge

Answer 28

The point on a flood hydrograph when river discharge is at its greatest.

Question 29

Define storm flow

Answer 29

Discharge resulting from storm precipitation involving both overland flow, through flow and groundwater flow.

Question 30

Define storm hydrograph

Answer 30

A graph of discharge of a river over the time period when the normal flow of the river is affected by a storm event.