Environmental Engineering Reference
In-Depth Information
Fig. 3.26 Streambed
temperature profiles for
downward water flow and
upward water flow (Modified
from Constantz (
2008
).
Published with kind
permission of the
U.S. Geological Survey.
Figure is public domain in
the USA. All Rights
Reserved)
either
G
i
or
G
o
. A good discussion of errors associated with use of the water budget
to determine groundwater exchange terms can be found in LaBaugh and Winter
(
1984
), Krabbenhoft et al. (
1990
), or Choi and Harvey (
2000
).
3.8.4 Measurement of Temperature to Quantify
Groundwater-Surface-Water Exchange
Diurnal and seasonal temperature changes in wetland water are attenuated with
depth beneath the sediment-water interface. Attenuation is controlled by the capac-
ity of the sediments to conduct heat. Direction and rate of groundwater flow
modifies the conduction-driven attenuation. Net upward flow reduces, and net
downward flow increases, the amplitude of diurnal or seasonal temperature
responses with depth beneath the sediment-water interface (Figs.
3.26
and
3.27
).
Robert Stallman (Stallman
1965
) developed a method that could determine
vertical flow of water through sediment based on measurement of temperature.
The method required measurement of diurnal (or seasonal) fluctuation of tempera-
ture at two depths, the volumetric heat capacity of the water, and estimates of
thermal conductivity and volumetric heat capacity of the bulk sediment. If the time
series of the diurnal or seasonal temperature data are sinusoidal, this method
provides a reasonable indication of the groundwater flow to or from a surface-
water body. However, when applied to the typical wetland setting where wetland
stage (and, therefore,
i
) is often highly variable over time, a method is needed that
can solve for flow that may be substantially non-uniform.
Fortunately, several numerical models exist that simultaneously solve for heat
and fluid flow in porous media. In addition to the parameters listed above, reason-
able assumptions regarding boundary conditions, and values for
i
v
and
K
v
, are all
that is needed to determine the flow of water across the sediment-water interface.
