Environmental Engineering Reference
In-Depth Information
Groundwater
outflow
Groundwater
inflow
0
″
0
″
15
″
15
″
Groundwater
reservoir
0
″
Soil
moisture
Net
36
″
37
″
Infiltration
22
″
Evapo-
transpiration
22
″
1
″
Precipitation
45
″
1
″
1
″
2
Depression
storage
″
Evaporation
1
″
1
″
15
″
(Base flow)
8
″
8
″
Surface
runoff
21
″
21
″
Stream
flow
Ocean
Figure 1-3
The hydrologic cycle or water balance model for a watershed in southeastern
Pennsylvania: the Brandywine model project, 1984.
As each raindrop is added to this groundwater, it begins to move in the
direction of available energy, created by the inexorable pull of gravity. Since
the easiest pathway for displacement is through the soil (and fractures in the
rock) following the surface of the land, this water eventually travels down-
hill, emerging as a seep or spring, flowing over the surface to a swale or
steam channel. Actually, as each raindrop enters the groundwater, it displaces
water from the low end of the saturated zone. A single raindrop may actu-
ally take weeks or months to complete the journey from where it falls on
the land surface to the point of discharge downgradient, as it returns to the
surface.
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