Environmental Engineering Reference
In-Depth Information
Fig. 3.27 Diurnal
temperature response at the
wetland bed and at a well
screen installed 1 m beneath
the wetland for upward and
downward groundwater flow
beneath the wetland
(Modified from Stonestrom
and Constantz (
2003
).
Published with kind
permission of the
U.S. Geological Survey.
Figure is public domain in
the USA. All Rights
Reserved)
GAINING WETLAND
time
LOSING WETLAND
time
The vertical hydraulic gradient can be obtained with the installation of a shallow
piezometer in the wetland bed. This installation also allows convenient deployment
of a temperature sensor to provide data at depth to compare with temperature at the
bed of the wetland. Although
K
v
can be determined in-situ,
K
v
often is heteroge-
neous and is scale dependent. Therefore,
K
v
usually serves as the model calibration
factor that is adjusted until the simulated time-series temperature data generated by
the model match the measured time-series temperature data. Once
K
v
is calibrated
so the modeled and measured temperatures are in good agreement, the model
produces
q
, the specific groundwater flux across the sediment-water interface.
Temperature sensors are among the most accurate, robust, and inexpensive
devices commonly used in the earth sciences, making this method particularly
attractive. Thermal conductivity (
K
T
), the heat-flow equivalent of hydraulic con-
ductivity (
K
), is a property that varies over a much narrower range than hydraulic
conductivity. It can be reasonably estimated based on the type of sediment present
