Page 295 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

9.2
GROUNDWATER INTERACTION WITH STREAMFLOW
Runoff and groundwater together supply the water to keep streams flowing. Groundwater can maintain streamflow when runoff does not occur. The diagrams show the relationship of the water table and streamflow in humid and dry climates.
Water table
Water table
Stream
Effluent conditions
Humid climate– effluent conditions
The water table is higher than the stream channel, so water flows out from the surrounding ground into the stream.
Stream
Influent conditions
Dry climate– influent conditions
The water table is lower than the stream channel, so the stream’s water flows into groundwater.
[Bobbé Christopherson.]
(9) Confined aquifer
A confined aquifer is bounded above and below by impermeable layers (aquicludes)
(10) Potentiometric surface
The potentiometric surface is the level to which groundwater under pressure can rise on its own, and can be above ground level.
(11) Artesian wells
Artesian water is groundwater in a sloping, confined aquifer where groundwater is under pressure. If the top of a well is lower than the potentiometric surface, artesian water may rise in the well and flow at the surface without pumping.
Polluting industry
Toxic seepage
Zone of saturation
Spills and leaks
Disposal pond improperly placed on aquifer recharge area
Artesian well requiring pumping
Well near coastline (pumped)
(13) Seawater intrusion
In coastal areas, overuse of groundwater can cause salty seawater to move inland, contaminating a freshwater aquifer. A rise in sea level can force seawater intrusion, forcing the local water table upwards to the surface, with resulting flooding.
Seawater Ocean 13 intrusion
Buried
wastes 9
12
surface
10
artesian well
rm
(well polluted)
Potentiometric Flowing
11
Confined aquifer saturation
Impermeable rock
(12) Pollution of aquifer
In industrial areas, spills, leaks, and improper disposal of wastes can pollute groundwater.Notice the improper placement of a disposal pond in the aquifer recharge area.
Zone of
Explain: Suggest steps to prevent such groundwater pollution.
Springs occur where the water table meets the ground surface (see number 8 in GIA 9.1). [holbox/Shutterstock.]
GEOquiz
1. Apply Concepts: Where in Figure 9.1 could you drill a well 2. Predict: What would happen to a stream with influent that was free of pollutants and saltwater contamination? conditions if runoff were greatly reduced?
Explain.
259
Dry river channel, influent conditions
geosystems in action 9GROUNDWATER
No
w
a
l
e
a
t
r
t
a
b
l
Water table
e Aquiclude
Aquiclude