Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2002-07-17
2004-11-23
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C073S073000
Reexamination Certificate
active
06823264
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods of determining the depth to saturated soils and more particularly to using that information to determine whether a particular site is a wetland.
BACKGROUND OF THE INVENTION
Wetlands may include marshes, bogs, and swamps. Wetland delineations tend to be controversial because such a determination often pits the interest of environmental protectionists against the interests of landowners. Therefore, standards or guidelines have been created to standardize wetland delineations. These guidelines also attempt to balance the interests of the public and private landowner. According to typical guidelines, whether a particular parcel of land qualifies as a wetland generally depends upon the percentage of the growing season that the surface of the soil is continuously saturated with water.
One example of wetland delineation guidelines includes the Corps of Engineers' Wetlands Delineation Manual of January 1987 (“'87 Manual”). The '87 Manual provides guidelines that may be used to determine whether a particular parcel of land is a wetland. Generally, land qualifies as a wetland if it is continuously saturated to the surface between 5% and 12.5% of the growing season. However, the '87 Manual indicates that many sites are not wetlands despite being continuously saturated to the surface between 5% to 12.5% of the growing season. A delineation in these cases is left to the judgment of the delineator. According to the '87 Manual, sites not continuously saturated at least 5% of the growing season are not wet enough to be considered wetlands.
The '87 Manual provides that, delineators (persons who determine whether a site is a wetland) may consider three parameters, soil characteristics, vegetation, and hydrology, when evaluating whether a site is a wetland. Soil characteristics may be used to determine whether the soils at the site are hydric soils. Hydric soils form under conditions of saturation including flooding that persists long enough to develop anaerobic conditions in the soil. These anaerobic conditions, characteristic of hydric soils, may be observed as color changes in the soils.
The hydrology determination, i.e., the depth to saturation in the soil, is the most controversial determination because a delineator cannot directly observe the hydrologic condition of the ground. Therefore, the delineator must rely on other indicators such as vegetation and soil characteristics to make the hydrology determination. Accurately evaluating the site in this manner requires numerous visits to the site. However, it is not uncommon for a delineator to make a delineation based on only a single visit. After the hydrology determination is made, it may be compared with standard hydrological criteria, such as those found in the '87 Manual.
Digging a pit in the ground and measuring the depth at which water appears in the pit will yield the depth of the water table (the upper boundary of a free groundwater body at atmospheric pressure). However, the depth of the upper boundary of saturated soil (referred to hereafter as the depth to the saturated soil) is not necessarily equal to the depth of the water table. Capillary action, described in more detail below, may draw water up through the grains of soil to a level above the water table causing saturated soil to occur above the water table. The volume of water located between the depth to the saturated soil and the water table is known as the capillary fringe. Both the depth to the saturated soil and the water table may rise during rainfall and shrink when depletion mechanisms such as drainage, evaporation, and transpiration deplete water from the soil.
Referring
FIGS. 1A-1E
, the capillary fringe will be explained in greater detail.
FIG. 1A
depicts a barrel
10
of soil grains
14
and water
12
. In
FIG. 1A
, the water
12
extends above the top surface of the soil grains
14
. Because the water table
16
extends above the surface of the soil, there is no capillary tension.
FIG. 1B
depicts barrel
10
after water
12
has been depleted from the barrel
10
to the point that the depth to the saturated soil and the water table
16
are at the top of the surface of the soil grains
14
. Therefore, there is no capillary fringe.
FIG. 1C
depicts barrel
10
after one additional drop of water has been depleted from the barrel depicted in FIG.
1
B. Menisci
20
form between soil grains
14
at the surface of the soil. As can be seen in
FIG. 1C
, the water table
16
has dropped to well below the surface of the soil while the depth to the saturated soil remains at the surface of the soil. Each menisci
20
has water
12
on one side and air on the other. Because the water
12
is attracted to the soil grains
14
, the water
12
relentlessly seeks to encompass more soil grains
14
. Capillary forces draw the water
12
upward to the surface of the soil forming a zone of negative pressure, known as a capillary fringe
22
, between the depth to the saturated soil and the water table
16
. The surface of the capillary fringe
22
is formed by menisci
20
. The surface of the capillary fringe
22
may also be referred to as the capillary front. The capillary fringe
22
is depicted as a gray area between the water table and the surface of the soil. The capillary fringe
22
will move upward until negative pressure behind it reaches the maximum the menisci
20
can support. In this manner, the capillary forces create a pressure differential across the menisci
20
between the saturated soil and the air above the menisci
20
. Above the menisci
20
, the pressure is atmospheric. Below the menisci
20
, the pressure may be as low as minus 12 inches of water. The negative pressure along the surface of the soil makes a visual observation of the depth to the saturated soil difficult because the surface of the soil may appear dry despite the fact that the soil grains directly underneath the surface grains are fully saturated with water.
FIG. 1D
depicts barrel
10
after an additional drop of water has been depleted. In this figure, the water table
16
has fallen to the maximum distance the menisci
20
will support. This is evidenced by the fact that air entry
26
has occurred at the surface of the soil. Because the negative pressure between the menisci
20
and the water table is at its maximum, as the water table drops, it will pull the depth to the saturated soil downward with it. Under the conditions depicted in
FIG. 10
, the capillary fringe
22
is at its maximum length, which may be as large as approximately 12 inches of water. Again, the negative pressure along the surface of the soil will make the soil appear dry despite the fact that ground remains saturated to the surface of the soil.
Further water depletion from the barrel, as depicted in
FIG. 1E
will produce a non-saturated condition at the surface of the soil. Under these conditions, the depth to the saturated soil (i.e., depth to the surface of the capillary fringe
22
), and the water table
16
will change depths at the same time separated by the full extent of the capillary fringe
22
(up to 12 inches).
Specific yield is the fraction of the saturated soil consisting of water that will drain by gravity when the water table drops. The magnitude of the drop in the depth to the saturated soil from
FIG. 1D
to
FIG. 1E
is a function of the specific yield of the soil contained in barrel
10
.
In
FIGS. 1A through 1E
, as water was depleted from the barrel
10
, no additional water was added. Of course, this is generally not the case in the field. When water is added, such as by precipitation, the surface of the capillary fringe becomes disturbed when new water fills in the menisci and relaxes the tension between the surface of the capillary fringe and the water table. When the tension is relaxed, the pressure in the area of negative pressure increases to atmospheric and the water table moves upward to the depth to the saturated soil. Under these circumstances, the water table and saturated soils may occur
Barlow John
Christensen O'Connor Johnson Kindness pllc
Le Toan M.
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