Block 2 (Catchment Hydrology - The Drainage Basin As A System)

Question 1

Define a drainage basin?

Answer 1

Catchment area of land which is drained by a particular river/body of water

Question 2

Define watershed?

Answer 2

Dividing line between adjacent drainage basins (often marked by high relief features, e.g. mountains)

Question 3

What type of system is a drainage basin?

Answer 3

Open system

- Inputs + outputs of energy + matter

Question 4

What is the one input into a drainage basin?

Answer 4

Precipitation

Question 5

How can precipitation vary?

Answer 5

• Different types
• Different amount
• Different intensity
• Different duration

Question 6

How can precipitation type vary (what are the three types?)

Answer 6

• Orographic/relief
• Convectional
• Frontal

Question 7

How can precipitation amount vary?

Answer 7

Different volumes of precipitation can fall

Question 8

How can precipitation intensity vary?

Answer 8

Amount of rain that falls in a certain period can vary

Question 9

How can precipitation duration vary?

Answer 9

Length of time precipitation falls for can vary

Question 10

What are the eight drainage basin flows?

Answer 10

• Throughfall
• Stemflow
• Infiltration
• Throughflow
• Percolation
• Groundwater flow
• Surface runoff/overland flow
• Channel flow

Question 11

Define throughfall?

Answer 11

Water dripping from leaves of veg -> ground

A drainage basin flow

Question 12

Define stemflow

Answer 12

Water dripping off veg down stem/trunk -> ground

A drainage basin flow

Question 13

Define infiltration

Answer 13

Water movement from ground surface -> soil

A drainage basin flow

Question 14

Define throughflow

Answer 14

Water movement laterally through the soil

A drainage basin flow

Question 15

Define percolation

Answer 15

Water movement from soil -> underlying bedrock

A drainage basin flow

Question 16

Define groundwater flow

Answer 16

Water movement vertically + laterally through underlying bedrock

(A drainage basin flow)

Question 17

Define surface runoff/overland flow

Answer 17

Water movement over the land surface

A drainage basin flow

Question 18

Define channel flow

Answer 18

Water movement through the river channel

A drainage basin flow

Question 19

What is the water level?

Answer 19

Level at which the ground is saturated up to

Question 20

What two factors affect the amount of groundwater flow (through underlying bedrock)?

Answer 20

• Porosity (amount of water that can be held in rock)

- Permeability (ease of flow through rock)

Question 21

What are the two reasons why surface runoff/overland flow can occur?

Answer 21

SATURATION-EXCESS OVERLAND FLOW

• High duration of rainfall
• Soil becomes saturated, so no more water can infiltrate

INFILTRATION-EXCESS OVERLAND FLOW

• High intensity of rainfall
• Ground may not be saturated, but intensity is so great that not all rain can infiltrate

Question 22

Which area of the drainage basin becomes saturated first during rainfall?

Answer 22

Areas close to bottom of slopes - form SATURATED WEDGE

Question 23

What does it mean to be a drainage basin flow?

Answer 23

A way in which inputs are transferred through the drainage basin

Question 24

What are the six drainage basin stores?

Answer 24

• Interception store
• Vegetation store
• Surface store
• Soil moisture store
• Channel store
• Groundwater store

Question 25

Define interception store

Answer 25

Temporary store of water on plant surfaces

Question 26

Define vegetation store

Answer 26

‘Green water’ held within vegetation biomass

Question 27

Define surface store

Answer 27

Water collected on ground surface (as snow or rain in hollows)

Question 28

Define soil moisture store

Answer 28

Water held in soil

Question 29

Define channel store

Answer 29

Water held in river channel

Question 30

Define groundwater store

Answer 30

Water held in bedrock underneath soil

Question 31

What are the three ways water can be held in the soil moisture store

Answer 31

1) Hydroscopic water - thin films of water molecularly attracted to surface of soil particles 2) Capillary water - thicker films of water held into small soil pores by surface tension 3) Gravitational water - water occupying large spaces in soil after rainfall

Question 32

Define field capacity?

Answer 32

Total water in soil moisture store when all gravitational water is drained away (the amount of water constantly available in soil - without any precipitation event)

Question 33

Define wilting point

Answer 33

When water stores become too low to compensate for plant loss via transpiration

Question 34

What are the four drainage basin outputs?

Answer 34

- Channel discharge - Evaporation - Transpiration - Evapotranspiration

Question 35

Define channel discharge

Answer 35

Volume of water leaving a drainage basin via main stream/river (A drainage basin output)

Question 36

Define evaporation

Answer 36

Water changes from liquid to gas when heated, transferring it from surface stores in basin -> atmosphere (A drainage basin output)

Question 37

Define transpiration

Answer 37

Water changes from liquid to gas, diffusing out of plant stomata in basin -> atmosphere (A drainage basin output)

Question 38

Define evapotranspiration

Answer 38

Combination of evaporation + transpiration removing water from the soil and the plants growing within it (A drainage basin output)

Question 39

What are three factors that may increase the rate of evaporation or transpiration

Answer 39

- High heat - High wind speed (increase water conc gradient) - Low humidity (increase water conc gradient)

Question 40

What does it mean to be an input to a drainage basin?

Answer 40

A way that water enters the drainage basin system

Question 41

What does it mean to be an output to a drainage basin?

Answer 41

A way that water leaves the drainage basin