Soil Water

10 important questions on Soil Water

Five things you need to know about the unsaturated zone:

1. Medium for plants to grow.
2. Intermediate transport zone to groundwater recharge.
3. Passage and/or transformation of pollutants.
4. Source of transported sediment (erosion) (sloping terrain).
5. Influences water and energy fluxes in the atmosphere.

What are the three forces contributing to the retention of water in the soil?

1. Van der Waals attraction.
2. Electrostatic dipole / Osmotic force.
3. Capillarity

Is capillary rise higher in a sand or a clay soil?

In clay because small pores exert a larger suction than larger pores.
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When does a convex meniscus occur?


When the molecules have a stronger attraction to each other (cohesion) than to the material of the container (adhesion).

When does concave meniscus occur?


when the molecules of the container attract those of the liquid, causing the surface of the liquid to cave downwards.

What type of meniscus is water in a glass?

A concave meniscus.

Capillary action is the result of? (2 things)


1. Adhesion of the water (= liquid phase) onto the capillary wall (=
solid phase) causes a hollow meniscus.
2. Internal cohesion of the water molecules at the air-water
interface.

How can water move in the unsaturated zone?


Water is under tension or suction and a force is required to move it.

How can water move in the saturated zone?


Water is under pressure and free to move.

What are the two main potentials in the unsaturated zone?

1.  Gravimetric potential.
2. Matrix potential (capillarity).

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