Environmental Engineering Reference
In-Depth Information
General hydrogeologic cross section of the region
South
North
Surficial
aquifer
Sea
level
Intermediate aquifer system
Confining
Bed
Top of intergranular
evaporites
Floridan aquifer system
Top of highly
permeable zone
1000
See blow-up
0
0
10
20
30
30
Miles
10
20
Kilometers
Surficial
aquifer
Intermediate
aquifer
system
Verticle scale greatly exaggerated
2000
Top of highly
permeable zone
Floridian aquifer system
Top of intergranular evaporites
Figure 2-3
Florida hydrology is affected by a slight lowering of the water table, so recharge
is critical.
table, especially in very wet environments such as Florida (Figure 2-3). The
lowering of the shallow water table is the result of both upland impervious
surfaces and substantial groundwater withdrawals for potable supply or irrigation.
First-Order Streams
The emergence of groundwater from seeps and springs represents the continued
flow of infiltrated rainfall across the land surface, producing what we refer to
as
first-order streams
(Figure 2-4). This term defines a single perennial (year-
round) stream that flows downgradient to combine with ever larger elements
of a watershed or drainage network. The concept of surface stream ordering
[9] is one that has received great study in the analysis of fluvial processes in
surface streams, but defines much more of stream hierarchy from an ecological
perspective.
To consider a first-order stream as the beginning of life in a watershed is not
an exaggeration. The groundwater emerging from the ground is rich in dissolved
minerals but does not contain any living organisms, except bacteria from the soil
mantle. The exposure of the flowing water to sunlight, oxygen, and the detritus
of decaying surface vegetation begins a food chain that quickly evolves from
simple decomposing microbes to higher life forms, ultimately resulting in the
finfish and shellfish that we have long harvested as a protein source.
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