Environmental Engineering Reference
In-Depth Information
Fig. 3.20 Components required to determine exchange between groundwater and surface water
using the Darcy method (Modified from Rosenberry et al. (
2008
). Published with kind permission
of the U.S. Geological Survey. Figure is public domain in the USA. All Rights Reserved)
well to the shoreline of the wetland (Fig.
3.20
). The minus sign is included to
indicate that the flow (
Q
) occurs in response to a decrease in hydraulic head along a
groundwater flowpath. The ratio
h/l
is also called the hydraulic gradient and is
commonly indicated with lower-case
i
, leading to the shorthand version of the
Darcy equation:
Δ
Q
¼
KiA
(3.35)
Note the absence of the negative sign that appears in Eq.
3.34
. In Eq.
3.35
,
i
is
formulated so that the difference between heads is positive. The hydraulic gradient
is usually the easiest term to quantify, requiring only measurements of the water
level in a nearby monitoring well, wetland stage, and the horizontal distance
between the well and the shoreline. The elevation of the top of the monitoring
well relative to the water surface of the wetland also is needed to relate the water
level in the monitoring well to wetland stage.
