Submitted by: Submitted by Franco
Views: 10
Words: 4616
Pages: 19
Category: Other Topics
Date Submitted: 12/02/2015 06:43 PM
Chapter 1
Ground water
If a hole is dug, only the water that flows freely into the hole is groundwater. Since
the air in the hole is at atmospheric pressure, the pressure in the groundwater must
be higher if it is to flow freely into the hole. This is what distinguishes groundwater
from the rest of the underground water.
Definition 1.1. Water, below the surface, at a pressure greater than atmospheric
pressure, which thus flows freely into a hole through interconnected void spaces,
is groundwater.
Groundwater and soil water together make up approximately 0.5% of all water
in the hydrosphere. Figure 1.1 illustrates the various zones of water found beneath
the surface. Water beneath the surface can essentially be divided into three zones:
1) the soil water zone, or vadose zone, 2) an intermediate zone, or capillary fringe,
and 3) the ground water, or saturated zone. The top two zones, the vadose zone and
capillary fringe, can be grouped into the zone of aeration, where during the year
air occupies the pore spaces between earth materials. Sometimes, especially during
times of high rainfall, those pore spaces are filled with water.
Vadose zone
Pw < P a
Capillary fringe
Water table Pw = Pa
Fig. 1.1 Soil moisture and
distribution of fluid pressure
Pw relative to atmospheric Pa
in the ground.
Saturated zone
Pw > P a
Beneath the zone of aeration lies the zone of saturation, or the groundwater zone.
Here water constantly occupies all pore spaces. The water table divides the zone of
1
2
1 Ground water
aeration from the zone of saturation. The elevation of the water table is determined
to be where the pore water pressure, Pw , is equal to atmospheric pressure, Pa . The
height of the water table will fluctuate with precipitation, increasing in elevation
during wet periods and decreasing during dry. In general, the water table has an
undulating surface which generally follows the surface topography, but with smaller
relief.
1.1 Porosity
Ground water and soil moisture occur...