Lesson 3 - Water budgets and river regimes

Question 1

Define the term ‘water budget’?

Answer 1

Within the drainage basin, the balance between inputs (precipitation) and outputs (evapotranspiration) is known as the water balance or budget.

Question 2

When is the drainage basin said to be in dynamic equilibrium?

Answer 2

When inputs and outputs of the drainage basin system are balanced, it is said to be in dynamic equilibrium.

Question 3

What does it mean if a drainage basin has a positive water budget?

Answer 3

If a drainage basin has a positive water budget, inputs are greater than outputs.

Question 4

What does it mean if a drainage basin has a negative water budget?

Answer 4

If a drainage basin has a negative water budget, outputs are greater than inputs.

Question 5

Define the term water surplus?

Answer 5

If precipitation exceeds evapotranspiration and the excess is not being used by plants then the soil has a water surplus.

Question 6

Define the term water deficiency?

Answer 6

Evapotranspiration exceeds precipitation, soil moisture stores have been used up, plants may need adaptations to survive.

Question 7

Define the term recharge?

Answer 7

Replacement of water lost from soil during drier periods.

Question 8

Define the term soil moisture utilisation?

Answer 8

Soil water is used by people and plants, reducing the amount remaining in the soil and river channels.

Question 9

Define the term field capacity?

Answer 9

The maximum amount of water that soil can hold.

Question 10

What is a river regime?

Answer 10

A river regime is the annual variation in discharge or flow of a river at a particular point or gauging station, usually measured in cumecs.

Question 11

Give some factors which influence the characteristics of a river regime?

Answer 11

• The size of the river and where measurements are taken in the basin
• The amount, pattern and intensity of the precipitation: regimes often reflect rainfall seasonal maxima or when the snow fields or glaciers melt
• The temperatures experienced: evaporation will be marked in the summer as the temperatures are warmer
• The geology and overlying soils, especially their permeability and porosity
• The amount and type of vegetation cover: wetlands can hold water and release it very slowly into the system
• Human activities, e.g. dam construction

Question 12

What is the most important factor which determines stream flow?

Answer 12

Climate