Drainage Basin Terms And Definitions

Question 0

Evaporation

Answer 0

The transformation of water droplets into water vapour in the atmosphere by heating.

Question 1

Precipitation

Answer 1

All forms of moisture that is transferred from the atmosphere to the earth’s surface, subsequent to evaporation and condensation e.g. Rain, hail, sleet or snow.

Question 2

Potential evaporation

Answer 2

The amount of water loss that would take place from a surface given unlimited supply of water.

Question 3

Transpiration

Answer 3

Transformation of moisture from within a plant’s leaves to become water vapour in the air, via the minute pores i.e. stomata.

Question 4

Evapotranspiration

Answer 4

Collective name for evaporation and transpiration.

Question 5

Condensation

Answer 5

The process which water vapour is converted to water droplets (usually visible as cloud). It usually accompanies a fall in temperature and requires condensation nuclei.

Question 6

Sublimation

Answer 6

Transfer of water from its solid form (ice) directly into its gas form (water vapour).

Question 7

Interception

Answer 7

The interruption of precipitation falling to the earth’s surface. Water or snow can be stored temporarily on leaves of plants, trees, buildings etc.

Question 8

Leaf drip/throughfall

Answer 8

Intercepted water falling from leaves to the ground surface.

Question 9

Stem flow

Answer 9

Intercepted water trickling down stems and branches to the ground.

Question 10

Surface storage

Answer 10

Water which lies on the surface of the ground e.g. lakes, ponds, puddles, and reservoirs.

Question 11

Surface runoff/overland flow

Answer 11

The movement of water over the surface of the land, usually when the ground is saturated or frozen or when precipitation is too intense for all to infiltrate.

Question 12

Channel flow

Answer 12

The movement of water within the river channel.

Question 13

Infiltration

Answer 13

The downward movement of water into the ground surface. N.b. water seeps vertically into the soil/rock through pores (air spaces).

Question 14

Infiltration capacity/rate

Answer 14

The maximum rate at which water can pass through the soil (mm/hr).

Question 15

Field capacity

Answer 15

When soil is saturated i.e. all available pore spaces between soil particles are filled.

Question 16

Throughflow

Answer 16

The movement of water laterally/downslope through the soil ( above water table).

Question 17

Percolation

Answer 17

The downward movement of water in the soil or rock layers, due to gravity.

Question 18

Groundwater storage

Answer 18

Water stored beneath ground surface in permeable ground strata (usually above an impermeable rock layer) creating a zone of saturation.

Question 19

Water table

Answer 19

The upper level of the zone of saturation.

Question 20

Groundwater flow

Answer 20

The lateral movement of water below the water table or in underlying rock strata.

Question 21

Stream/channel flow

Answer 21

Water moving over the surface in a contained channel.

Question 22

Recharge

Answer 22

When groundwater stores depleted by a dry spell are refilled by water percolating through soil and rock layer.

Question 23

Channel catch

Answer 23

Precipitation falling directly into a stream or river - a small % of precipitation as most falls into the drainage basin.

Question 24

Base flow

Answer 24

Normal flow in a hydrograph.

Question 25

Floodplain

Answer 25

Area around a river which is very flat and that should be allowed to flood

Question 26

Lag time

Answer 26

Time between peak rainfall and peak discharge (velocity of river X volume of water).