Fresh Water of the Continents
•Ground Water
•Limestone Solution by Ground Water
•Problems of Ground Water Management
•Surface Water
•Stream Flow
•Lakes
•Surface Water as a Natural Resource
Fresh Water of the Continents
the hydrologic cycle of water from the oceans and the continents to the
atmosphere through evapotranspiration; back to the ocean and continent
surfaces through precipitation and eventually returning to the oceans
through surface runoff (rivers) after storage (lakes, ground water, ice
sheets)
water
Figure 15.1, p. 513
Ground Water
when precipitation reaches the ground, it either runs off or infiltrates into the
soil - as runoff, it flows into streams - as infiltration, it either returns to the air
through evapotranspiration or seeps downward to become ground water
Figure 15.2, p. 514
Ground Water
zones of subsurface water - water in the soil water belt is available
to plants, water in the unsaturated zone percolates downward to the
saturated zone of ground water, where all pores and spaces are
filled with water
Figure 15.3, p. 514
Ground Water
the water table marks the top of the saturated zone of ground water
- highest under hilltops and divides, and it slopes to intersect the
surface at lakes, marshes, and streams.
Figure 15.4, p. 515
Ground Water
an aquifer is a layer
of rock or sediment
that contains
abundant, freely
flowing ground
water
aquicludes are beds
of clay and shale
which are relatively
impermeable and
hold little free water
a perched water
table is an
accumulation of
water suspended or
perched above the
main water table by
an impermeable
lens of rock (usually
shale)
Figure 15.5, p. 515
Limestone Solution by Ground Water
cavern development limestone dissolves at the top of the ground
water zone
when rapid erosion of streams lowers the water table, caverns
result in the unsaturated zone
water flow through the caverns results in travertine deposition
Figure 15.7, p. 516
Travertine
A form of calcium carbonate
(CaCO3)
This specimen has fluorescent hydro-
carbons within the limestone. It's
color-banded crystalline help us to
see how sedimentary rocks are
formed in layers. The texture or
patterns are beautiful. Travertine
becomes colored by the minerals in
the water and by biological action.
Travertine from this region is
quarried for use as decorative stone.
Limestone Solution by Ground Water
carbonic acid action
dissolves limestone,
producing caverns
cavern collapse creates
sinkholes and a karst
landscape
Figure 15.10, p. 518
IG4e_15_08
Cave Formations
Sinkholes
IG4e_15_09
Karst Mountains –
Guilin, China
IG4e_15_11
Problems of Ground Water Management
wells drawdown the
water table at a point,
creating a cone of
depression
as many wells exploit
an aquifer, their cones
of depression merge to
create a general
lowering of the water
table
Figure 15.12, p. 519
Problems of Ground Water Management
sanitary landfills can release pollutants and toxic compounds
that infiltrate to the water table, causing ground water contamination
that renders adjacent well waters unfit for consumption
Figure 15.13, p. 520
Overland Flow – Holbrook Arizona
IG4e_15_14
Surface Water
a stream is a long, narrow body of flowing
water occupying a trench-like depression,
or channel, and moving to lower levels
under the force of gravity
the channel of a stream is a narrow trough
shaped by the forces of flowing water to
most effectively move the quantities of
water and sediment supplied to the stream
as a stream flows under the influence of
gravity, the water encounters resistance
(friction) with the channel bed and walls
as a result, water close to the bed and
banks moves slowly, while water in the
central part of the flow moves faster
changes in stream gradient (slope) affect
the cross-sectional area and velocity of
the stream
Figure 15.15, p. 521
Surface Water
stream discharge (volume rate of flow) at a location on a stream is
determined by noting the height, or stage, of the surface of the stream with
respect to a fixed level nearby, such as a marker on a bridge abutment
stage is measured by a stream gage, which uses a float inside a stilling well
to record the height of the water surface
stage is then converted to discharge by consulting a table made from flow
measurements acquired at that location at various stages in the past
Figure 15.16, p. 524
IG4e_15_16b
Surface Water
the relative magnitude of discharge of major rivers in the United States
Figure 15.17, p. 524
Surface Water
a drainage basin consists of a branched network of stream channels and
adjacent slopes that feed the channels - bounded by a drainage divide
Figure 15.18, p. 525
Surface Water
a hydrograph plots stream flow with time
peaks in the hydrograph occur after rainfall events
between rains, stream flow falls to base flow, which is fed by
ground water seepage into the stream’s channels
Figure 15.19, p. 526
Surface Water
a flood occurs when a
river rises to leave its
bed and cover adjacent
lands
flood forecasts rely on
precipitation patterns,
past history, and present
river levels to predict
when and how high a
flood will crest
flood expectancy graphs
Figure 15.23, p. 529
IG4e_15_22c
Surface Water as a Natural Resource
human society is
heavily dependent
on fresh surface
water for irrigation,
potable water
supplies, and
industrial
consumption
artificial dams can
increase freshwater
supplies and
generate power, but
may have
environmental costs
Figure 15.28, p. 538
Lakes
a lake is a body of standing water found within continental
margins that is enclosed on all sides by land
ponds (which are small, usually shallow water bodies), marshes, and
swamps with standing water can all be included under the definition of a
lake
lakes receive water input from streams, overland flow, and ground water,
and so are included as parts of drainage systems
Figure 15.25, p. 533
Lakes
salinization and waterlogging are undesirable side effects of
long continued irrigation (arid regions watered by exotic rivers
are most affected)
water pollutants include various types of common ions and
salts, as well as heavy metals, organic compounds, and acids
excessive plant nutrients in runoff feeding lakes can lead to
eutrophication - the artificial “aging” of a lake
Great Salt Lake, Utah
Aral Sea
Shrinkage
due to purposely
cutting off most
of the inflow for
irrigation
purposes
IG4e_15_p523
Venice –
Sinking
The Great Lakes
IG4e_15_p534
IG4e_15_p534b
Polychlorinated Biphenyls
Or PCB’s
IG4e_15_p535
Flooding that
causes
chemicals into
the river
IG4e_15_22b
Strip-mine
Acidification
IG4e_15_27
Salt encrustations on the
Bonneville Salt Flats
IG4e_15_26