A.1.1: Drainage Basin as an open system

Question 1

Drainage Basin

Answer 1

The area of land drained by a river and its tributaries

Question 2

Watershed

Answer 2

The imaginary line separating different drainage basins

Question 3

The hydrological cycle

Answer 3

Water moving between the atmosphere, lithosphere and biosphere; this operates at a local scale within drainage basins

Question 4

Why is the drainage basin a open system

Answer 4

It allows the movement of energy and matter across its boundaries

Question 5

Throughfall (flows)

Answer 5

Water that falls through gaps in vegetation or drops from leaves and twigs

Question 6

Stemflow (flows)

Answer 6

Water that trickles along twigs and branches and finally down the trunk of the tree

Question 7

Overland Flow (flows) (surface runoff)

Answer 7

Water that flows over the land’s surface

This occurs when precipitation exceeds infiltration or when the land is impermeable or saturated

Question 8

Infiltration (flows)

Answer 8

When water soaks into the soil

The infiltration capacity is the maximum rate at which rain can be absorbed by a soil

Infiltrations is most effective on porous soils like sand

Infiltration is also more effective under vegetation, because interception slows water reaching the ground

Antecedent moisture is the pre-existing levels of moisture. If this is high then infiltration rates are low.

Question 9

Percolation (flows)

Answer 9

When water moves slowly down from the soil into the bedrock

This occurs more quickly in permeable rock such as limestone and chalk

Question 10

Throughflow (flows)

Answer 10

Water flowing through the soil

It flows in percolines (lines of concentrated water flow between soil horizons)

This occurs most quickly in porous soils such as sand.

Question 11

Groundwater (flows)

Answer 11

Subsurface water

Question 12

Interception (stores)

Answer 12

The water that is caught and stored by vegetation

Question 13

Soil moisture recharge (stores)

Answer 13

Occurs when dried up pores are refilled with water

Question 14

Soil moisture surplus (stores)

Answer 14

The period when soil is saturated and so additional water flows over the surface

Question 15

Soil water utilisation (stores)

Answer 15

The process by which soil moisture is drawn to the surface by capillary action

Question 16

Surface water (stores)

Answer 16

Includes temporary stores such as puddles, and permanent stores such as lakes

Question 17

Groundwater (stores)

Answer 17

Water stored in the phreatic zone (the permanently saturated zone within solid rocks)

The upper layer of this is called the water table

Question 18

Channel storage (stores)

Answer 18

Refers to all water stored in rivers and streams

Not all rivers are permanent; some may be seasonal or disappear underground

Question 19

Evaporation (outputs)

Answer 19

The process by which a liquid is changed into a gas (water vapour)

This occurs most effectively under warm, dry and windy conditions.

Question 20

Sublimation (outputs)

Answer 20

Misses out the liquid phase and a solid changes into a gas

For example when intense sun shines on a snow field the frozen water can change directly into water vapour

Question 21

Transpiration (outputs)

Answer 21

The process by which water vapour escapes from living plants into the atmosphere

Question 22

Evapotranspiration (outputs)

Answer 22

The combined effects of evaporation and transpiration. This accounts for the majority of water loss in areas with vegetation

Question 23

Potential evapotranspiration (outputs)

Answer 23

The water loss that would occur if there was an unlimited supply of water in the soil for the vegetation.

For example in Egypt actual EVT is 250mm, but due to high temperatures if there was high rainfall then there would be much EVT. Therefore the P.EVT is 2000mm

Question 24

River discharge (outputs)

Answer 24

The movement of water in a channel, and water may leave the drainage basin by flowing out into the sea

Question 25

Aquifers (groundwater)

Answer 25

Rocks containing significant quantities of water, and are permeable rocks such as sandstone and limestone

Water here moves very slowly and acts as a natural regulator of water

Water may reach the surface as a spring

Question 26

Groundwater Losses occur due to:

Answer 26

• Evapotranspiration where water table is close to surface
• Seepage into rivers
• Leaked into other aquifers
• Artificial abstraction for irrigation and human use

Question 27

Groundwater Recharge occurs due to:

Answer 27

• Infiltration and percolation from above
• Seepage from surface water such as lakes
• Artificial recharge from reservoirs, irrigation etc

Question 28

Channel Flow (flows)

Answer 28

The movement of water in channels such as streams and rivers

Question 29

Base Flow (flows)

Answer 29

Part of a river’s discharge that is provided by groundwater seeping into the bed of the river

Question 30

Interception loss (stores)

Answer 30

Water retained by plant surfaces and later evaporated away or absorbed by the plant.

This is most effective on dense vegetation, especially deciduous woodland in summer as the trees have broad leaves.

Question 31

Soil water (stores)

Answer 31

The subsurface water held in soil above the water table.

Water may be held in pores, and lots can be held n porous soils such as sands

Question 32

Field capacity (stores)

Answer 32

The amount of water held in the soil after excess water is drained away

Question 33

Wilting point (stores)

Answer 33

The range of moisture content in which permanent wilting of plants occur

Question 34

Soil moisture deficit (stores)

Answer 34

How far below field capacity soil moisture falls.

After long periods without precipitation the deficit is large

Question 35

Baseflow

Answer 35

The part of a river’s discharge that is provided by groundwater seeping into the bed of the river