Groundwater - The Changing Earth: Exploring Geology and Evolution - page 331

Zone of
aeration

Capillary
fringe

⎧
⎪
⎪
⎪
⎪
⎪
⎨
⎪
⎪
⎪
⎪
⎪
⎩

Suspended
water

Water
table

Zone of
aeration

Zone of
saturation

Water
table

Capillary fringe

⎧
⎪
⎪
⎪
⎨
⎪
⎪
⎪
⎩

Zone of
saturation

Groundwater

◗

Figure 13.2 Water Table The zone of aeration contains both air and water within its pore spaces, whereas all pore spaces in the zone
of saturation are fi lled with groundwater. The water table is the surface separating the zones of aeration and saturation. Within the capillary
fringe, water rises by surface tension from the zone of saturation into the zone of aeration.

and has its lowest elevations beneath valleys. Several factors
contribute to the surface confi guration of a region's water table,
including regional differences in amount of rainfall, perme-
ability, and rate of groundwater
movement. During periods of
high rainfall, groundwater tends
to rise beneath hills because it
cannot flow fast enough into
adjacent valleys to maintain a
level surface. During droughts,
the water table falls and tends to
fl atten out because it is not being
replenished. In arid and semiarid
regions, the water table is usually
quite fl at regardless of the overly-
ing land surface.

the ground moves through the zone of aeration to the zone
of saturation (

Figure 13.3). When water reaches the water
table, it continues to move through the zone of saturation

◗

Localized
aquiclude

Perched
water table

Main
water
table

Springs

Zone of
aeration

High pressure

High pressure

GROUNDWATER
MOVEMENT
Gravity provides the energy for
the downward movement of
groundwater. Water entering

Zone of saturation

Low pressure

◗

Figure 13.3 Groundwater Movement Groundwater moves down through the zone of aeration to
the zone of saturation. Then some of it moves along the slope of the water table, and the rest moves
through the zone of saturation from areas of high pressure toward areas of low pressure. Some water
might collect over a local aquiclude, such as a shale layer, thus forming a perched water table.