Chapter 4 Multiple choice questions

. The energy of water can be described…
…per unit mass as φ
…per unit volume as p
…per unit weight as h.
If ρ = density of water and g = acceleration due to gravity, then

. A dry homogeneous sediment is wetted; there are no macropores and there is no preferential flow. Which one of the following alternatives is correct?

First large pores will fill with water; because the soil is initially dry the water rapidly percolates to the water table.

First large pores will fill with water; because the soil is initially dry the water slowly percolates to the water table.

First small pores will fill with water; because the soil is initially dry the water rapidly percolates to the water table.

First small pores will fill with water; because the soil is initially dry the water slowly percolates to the water table.

.

The above figure gives the soil moisture characteristic (soil moisture retention curve; pF curve) for four different soils; the water table is located at an intermediate position at 2.5 m below the land surface. Which soil has the largest amount of soil water available for plants?

soil 1

soil 2

soil 3

soil 4

. A soil contains 5% moisture from 0 to -20 cm and 15% moisture from -20 to -40 cm. The soil moisture characteristic curve shows that the soil contains 20% moisture at pF = 2 (from 0 to -40 cm). How much water in cm should minimally be added to the soil to establish field capacity (pF = 2) for both soil layers?

2

3

4

5

.

The above left-hand figure shows the soil moisture characteristic (soil moisture retention curve; pF curve) for a sand and clay soil; the above right-hand figure shows the relation between hydraulic conductivity and matric potential for a sand and clay soil.
Which one of the following alternatives is correct?
Curve a in the left-hand figure is for:

clay; curve a in the right-hand figure is for sand.

clay; curve a in the right-hand figure is for clay.

sand; curve a in the right-hand figure is for sand.

sand; curve a in the right-hand figure is for clay.

. In a non-saline soil only the gravitational potential and matric potential determine the total potential of the water: water may flow from
option 1: a high, wet to a low, almost dry position;
option 2: a high, almost dry to a low, wet position;
option 3: a low, wet to a high, almost dry position;
option 4: a low, almost dry to a high, wet position.

Only option 1 is physically possible.

Only options 1 and 2 are physically possible.

Only options 1, 2, and 3 are physically possible.

All above options are physically possible.

.

The above figures 1 to 4 show the energy components of subsurface water (cm) with depth (cm); depth is along the vertical axis
ψ = matric potential (cm); Figure ch04q07a.jpg

= pressure head (cm); z = elevation head (cm) = gravitational potential (cm).
Which one of the above figures is correct?

Figure 1

Figure 2

Figure 3

Figure 4

. The Green and Ampt equation can be written as follows:
Figure ch04q08.jpg

This equation is

derived from Darcy's law and describes ponded infiltration.

not derived from Darcy's law and describes ponded infiltration.

derived from Darcy's law and describes non-ponding infiltration.

not derived from Darcy's law and describes non-ponding infiltration.

. A dry soil surface receives rainfall. After some time ponds and puddles occur at the surface. After this, the infiltration capacity

increases and the unsaturated hydraulic conductivity increases.

increases and the unsaturated hydraulic conductivity decreases.

decreases and the unsaturated hydraulic conductivity increases.

decreases and the unsaturated hydraulic conductivity decreases.

.

The above figure gives the water pressure in cm along the horizontal axis. The soil depth in cm is given along the vertical axis; the soil surface is taken as reference level or zero level.
With regards to the vertical volume flux density, which of the following statements is correct?

There are no depths with a zero volume flux density.

The volume flux density between 0 and -10 cm equals zero.

Only between -40 and -50 cm does the volume flux density equal zero; there are no zero flux planes.

The volume flux density at -10, -20, and between -40 and -50 cm equals zero.

. The matric potential ψ is measured by two tensiometers. The matric potential at 30 cm below the land surface equals -30 cm; the matric potential at 20 cm below the land surface equals -70 cm. The unsaturated hydraulic conductivity K(ψ) in cm day^-1 and the matric suction -ψ in cm are related by the following equation as:
Figure ch04q11.jpg

Assuming a linear relation of the matric suction -ψ with depth, which of the following alternatives is correct?
The vertical volume flux density in cm day^-1 between the two depths equals

0.1

0.2

0.3

0.4

.

A layer with a low hydraulic conductivity is located above a layer with a high hydraulic conductivity as shown in the above Figures a and b. At the start of rainfall both layers contain little water; rainfall is heavy and of long duration.
Which one of the below alternatives is correct?
The upper layer will:

gradually (first slowly; then more rapidly) deliver water to the lower layer; when, after a long time both layers are saturated, the flow will occur as drawn in Figure b.

gradually (first slowly; then more rapidly) deliver water to the lower layer; when, after a long time both layers are saturated, the flow will occur as drawn in Figure a.

deliver water to the lower layer only after the matric suction in the upper layer (near the interface of the upper and lower layer) falls below a critical threshold value; when, after a long time both layers are saturated, the flow will occur as drawn in Figure b.

deliver water to the lower layer only after the matric suction in the upper layer (near the interface of the upper and lower layer) falls below a critical threshold value; when, after a long time both layers are saturated, the flow will occur as drawn in Figure a.

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