Lecture 13: soil water

Question 1

What is the difference between soil water and groundwater?

Answer 1

soil water = water in the unsaturated zone. (soil particles + water + air, located above groundwater table)

groundwater = water in the saturated zone

Question 2

What is the capilary fringe?

Answer 2

The capillary fringe is a zone of soil located just above the water table in the ground. In this zone, water is drawn upward from the water table by capillary action. Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or against, external forces like gravity.

Question 3

Movement in unsaturated zone is caused by?

Answer 3

• Precipitation
• Evaporation
• Transpiration (plants)
• Infiltration
• Surface run-off
• Throughflow
• Percolation
• Capillary rise

Question 4

Why is the unsaturated zone important?

Answer 4

Oxygen is taken up by roots to supply energy for growth. Roots search for optimal combination of water, oxygen and minerals.

Question 5

Why is soil water important?

Answer 5

Storage of precipitation surplus
Supply in dry period
Plant roots need water and oxygen

Question 6

What is the difference between cohesion and adhesion?

Answer 6

Cohesion is the attraction of water molecules to other water molecules. Adhesion is attraction by soil particles.

Question 7

What is matric suction?

Answer 7

combined effect of soil texture and soil water content.

Question 8

Soil water is necessary in periods when …. is higher than ….

Answer 8

evaporation is higher than precipitation

Question 9

What is the wilting point?

Answer 9

The minimum water content of the soil at which plants can extract water.

Question 10

What are reasons why water cannot infiltrate?

Answer 10

• the groundwater reached the level of the surface
• surface sealing: a crust is formed as a result of impact of raindrops