Environmental Engineering Reference
In-Depth Information
120
1978
1979
Precipitation
Lysimeter drainage
100
80
60
40
20
0
Figure 5.16 Monthly rainfall and lysimeter drainage
at Fleam Dyke (reprinted from Journal of Hydrology , v. 58,
Kitching and Shearer ( 1982 ), Figure 2, copyright (1982) with
permission from Elsevier).
and snow gauges, a neutron probe to monitor
soil-water content, and equilibrium tension
lysimeters (ETLs) to measure water drain-
age below the root zone. The lysimeters have
a porous stainless steel surface that allows
collection and measurement of drainage.
Tensiometers and a vacuum system allowed
the pressure head at the surface of an ETL to
be set slightly less than that recorded in the
bulk soil surrounding the lysimeter. The flow
into an ETL should be similar to natural drain-
age. The top surface of each ETL, which was
0.75 m long and 0.25 m wide, was set at a depth
of 1.4 m beneath undisturbed soil through the
wall of a 2 m deep trench.
Precipitation rates were similar at all sites
( Fig ure 5.17 ). Evapotranspiration rates for the
prairie site were slightly greater than those for
the no-tillage site, which were slightly greater
than those from the chisel-plow site. Drainage
occurred from late January to mid-June at all
sites. There were substantial differences among
sites in terms of total drainage for the study
period: 199 mm for the prairie, 563 mm for
the no-tillage, and 793 for the chisel-plow site.
Drainage increased with increasing disturbance
of the land surface. The ETLs are difficult to
install and maintain, but they provided excel-
lent temporal and spatial resolution of drainage
rates for this study.
where water flow is primarily in fractures.
The lysimeter surface area is large enough to
minimize edge effects. Drainage rates can be
measured at a high frequency. The lysimeter
has some drawbacks, however. Installation and
maintenance of such a facility are expensive. It
is unlikely that many studies could afford such
an undertaking. Installation also could disrupt
natural flow patterns within the unsaturated
zone, although Kitching and Shearer ( 1982 )
examined this issue and found minimal dis-
ruption. An additional consideration was the
condensation of water in the underground tun-
nels. Precautions were taken to ensure that con-
densed water did not pass through the piling
walls into the lysimeter.
Example: Columbia County, Wisconsin
Brye et al . ( 2000 ) determined water budgets
for a 132-week period between 1995 and 1998
at three sites in Columbia County, southern
Wisconsin: a restored natural prairie, maize
under no tillage, and maize with chisel-
plow tillage. Instrumentation included rain
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