Operation of the Drainage Basin as an Open System

Question 1

Catchment

Answer 1

The area of land drained by a river and it’s tributaries

Question 2

Watershed

Answer 2

The highland which divides and separates waters to flowing rivers

Question 3

Condensation

Answer 3

The change from a gas to a liquid, such as when water vapour changes into water droplets

Question 4

Dew point

Answer 4

The temperature at which dew forms; it is a measure of atmospheric moisture

Question 5

Convectional Rainfall

Answer 5

Often associated with intense thunderstorms, which occur widely in areas with ground heating such as the Tropics and continental interiors

Question 6

Cyclonic Rainfall

Answer 6

A period of sustained, moderately intensive rain; it is associated with the passage of depressions

Question 7

Orographic Rainfall

Answer 7

Concentrated on the windward slopes and summits of mountains

Question 8

Interception loss

Answer 8

This is water retained by plant surfaces and later evaporated or absorbed by the vegetation and transpired

Question 9

Throughfall

Answer 9

This is when the rainfall persists or is relatively intense, and the water drops from the leaves, twigs, needles etc

Question 10

Stem Flow

Answer 10

This is when the water trickles along twigs and branches and then down the trunk

Question 11

Infiltration

Answer 11

The movement of water from the ground surface into soil

Question 12

Infiltration Capacity

Answer 12

The maximum rate at which rain can be absorbed by soil

Question 13

Surface run-off

Answer 13

The movement of water that is unconfined by a channel across the surface of the ground. Also known as overland flow

Question 14

Percolation

Answer 14

The transfer of water from the surface or from the soil into the bedrock beneath

Question 15

Saturated Overland Flow

Answer 15

The upward movement of the water table into the evaporation zone

Question 16

Evapotranspiration

Answer 16

The combined effects of evaporation and transpiration

Question 17

Channel flow

Answer 17

The flow of water in streams or rivers

Question 18

Channel Storage

Answer 18

The storage of water in streams or rivers

Question 19

Potential Evapotranspiration

Answer 19

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

Question 20

Deforestation

Answer 20

The cutting down and removal of all or most of the trees in a forested area

Question 21

Afforestation

Answer 21

The planting of trees in an area that has not been forested in recent times

Question 22

Drainage basin

Answer 22

The area of land drained by a river and its tributaries

Question 23

Drainage Basin

Answer 23

The area of land drained by a river and it’s tributaries

Question 24

Inputs of drainage basin

Answer 24

Precipitation

Question 25

Impacts of inputs on drainage basin depend on:

Answer 25

``` The amount of precipitation The type of precipitation Seasonality Intensity of precipitation Variability ```

Question 26

Secular variability

Answer 26

Long term variability, result of climate change trends

Question 27

Periodic variability

Answer 27

Happens in annual, seasonal, monthly, diurnal context

Question 28

Stochastic Variability

Answer 28

Results from random factors, such as the localisation of a thunderstorm within a basin

Question 29

Interception

Answer 29

Process by which water is stored in the vegetation, 3 main components - interception loss, through fall and stem flow.

Question 30

Factors affecting interception loss

Answer 30

- point of storm, more interception loss at start and following dry period - type of tree: coniferous tree greater, as dense needles. - seasonality in deciduous forests: summer/winter - wind speeds: decrease, intercepted water dislodged, and increases evaporation - intensity & duration of rainfall - amount of rainfall increases, less water intercepted as tree canopies become saturated - agricultural crops- more interception with more dense crop

Question 31

Factors affecting infiltration

Answer 31

- decreases with time during a period of rainfall as a constant low level is reached - Antecedent soil moisture, wet soils, less infiltration as already saturated - Soil texture, level of porosity - Type, amount and seasonal changes in vegetation. More vegetation = more infiltration - Nature of soil surface, compact promotes overland flow - Slope angle, steep = more runoff, flat = infiltration

Question 32

Throughflow

Answer 32

The lateral transfer of water down slope through soil via natural pipes and percolines.

Question 33

Percolines

Answer 33

Lines of concentrated water flow between soil horizons to the river channel

Question 34

Fluxes in drainage basin

Answer 34

Interception, Infiltration

Question 35

Flows and transfers in drainage basin

Answer 35

- Overland flow/surface runoff - Throughflow - Percolation - Saturated overland flow - Channel flow

Question 36

Outputs of drainage basin

Answer 36

Evaporation, transpiration

Question 37

Factors affecting Evaporation rate

Answer 37

- Climatic factors; temperature, hours of sunshine, humidity and windspeed. Temperature most important. - size of water body - depth of water - water quality - type of vegetation cover - colour of water surface

Question 38

Factors affecting transpiration rate

Answer 38

- Time of year - type and amount of vegetation cover - degree and availability of moisture in the atmosphere - length of growing season

Question 39

Physical factors affecting the drainage basin system

Answer 39

- Climate - Soils - Geology - Relief - Vegetation

Question 40

Human factors affecting the drainage basin

Answer 40

- River management: Building dams/reservoirs, reduces flows. Abstracting water for domestic and industrial use, reduces flow. Abstracting groundwater for irrigation, reduces the water table. - Deforestation: reduces evapotranspiration, increases infiltration and surface runoff - Changing land use - AGRICULTURE: soils compacted by livestock, increased surface runoff. soils aerated by ploughing, increased infiltration as soils loosened - Changing land use - URBANISATION: changing to urban land surfaces, increased surface runoff and less infiltration and percolation. Drains move rainfall to rivers and streams faster, increased chance of flooding.

Question 41

Components of drainage basin mostly affected by humans

Answer 41

- evaporation & evapotranspiration - interception - infiltration - groundwater - surface runoff