Environmental Engineering Reference
In-Depth Information
Wetland
Wetland
Land surface
Land surface
Stream
Direction of groundwater flow
Direction of groundwater flow
(a)
(b)
FIGURE 3.42
(a) Wetland receiving water. (b) Wetland discharging water.
(1) lakes have larger surface areas and (2) there is less shading from the vegetation around
a lake than from the dense riparian vegetation often present along a stream or riverbank
(Winter et al. 1998).
3.6.3 Wetland Interaction with Groundwater
Wetlands prevent rapid drainage of water from the land surface, and similar to lakes and
streams, wetlands can receive groundwater inflow, recharge groundwater, or do both.
The wetlands situated in topographic depressions of the land surface exhibit interac-
tions similar to lakes and streams. Figure 3.42a depicts a wetland receiving groundwa-
ter inflow, and Figure 3.42b shows a wetland discharging water to groundwater (Winter
et al. 1998).
The United States has just over 40,468,564 ha (100 million ac) of wetlands remaining
(Dahl and Allord 1994). The remaining wetland areas in the United States are concen-
trated along the southeast coast, the Mississippi River Valley, and the formerly glaciated
regions of the upper Midwest. Figure 3.43 shows where the country's wetlands remain
(Winter et al. 1998).
3.6.4 Ocean Water, Groundwater, and Surface Water Interaction
Coastal regions may exhibit more complex hydrogeology than other regions, because sur-
face water and groundwater interact with saline water at the ocean surface and in the
subsurface. In addition, other forces such as ocean currents, storms, and tidal fluctuations
may significantly influence these interactions. Therefore, understanding the geology of
coastal regions is the first step toward understanding this complex system (Barlow 2003).
Figure 3.44 shows a generalized view of surface water, groundwater, and ocean water
interaction (Heath 1983).
Under normal conditions, the seaward movement of freshwater prevents saline water
from encroaching coastal aquifers as depicted in Figure 3.45. The zone of dispersion or
transition zone shown in Figure 3.45 is a diffuse boundary where freshwater and saline
water mix (Barlow 2003).
One method used to estimate the depth to the zone of dispersion is called the Ghyben-
Herzberg relation named after the two scientists who developed it independently in
the late 1800s (Barlow 2003). The thicknesses of freshwater and seawater is related by
Equation 3.8:
Search WWH ::




Custom Search