2. Global OverviewGlobal Overview
While 67% of Earth’s surface is covered by
water, only less than 2.7% of global water
is freshwater. Most of the freshwater
(2.05%) are locked in ice caps and glaciers.
Only less than 0.7% is available for human
use.
3. Over two thirds of the
earth's surface is covered
with water, 97.2% of which
is contained in the five
oceans. The Antarctic ice
sheet, containing 90% of all
fresh water on the planet, is
visible at the bottom.
Atmospheric water vapour
can be seen as clouds,
contributing to the earth's
albedo.
5. Volume of water stored inVolume of water stored in
the water cycle's reservoirsthe water cycle's reservoirs
Reservoir Volume of water
(106
km³)
Percent
of total
Ocean 1370 97.25
Ice caps & glaciers 29 2.05
Groundwater 9.5 0.68
Lakes 0.125 0.01
Soil Moisture 0.065 0.005
Atmosphere 0.013 0.001
Streams & rivers 0.0017 0.0001
Biosphere 0.0006 0.00004
10. Using Dams and Reservoirs to SupplyUsing Dams and Reservoirs to Supply
More Water: The Trade-offsMore Water: The Trade-offs
Large losses
of water through
evaporation
Flooded land destroys
forests or cropland and
displaces people
Downstream flooding
is reduced
Downstream cropland and
estuaries are deprived of
nutrient-rich silt
Reservoir is useful for
recreation and fishing
Can produce cheap electricity (hydropower)
Migration and spawning of some fish are disrupted
Provides water
for year-round
irrigation of
cropland
11.
12. Instream flows
Result – the more we know about stream ecology, the more we
realize that all the water has instream value, meaning there is no
surplus
Compromises and minimizing impact – thresholds for rate of
impact
Other ways to achieve ecosystem goals – wider view, not just
flows – watershed land management
13. Legal/political aspects of instream flowLegal/political aspects of instream flow
provide a flow of water sufficient to adequately support
food fish and game fish populations in the stream
(RCW 77.55.050)
provide protection and preservation and where possible
enhancement, of wildlife, fish, … and other
environmental values … (RCW 90.54)
protect fish, game, birds, and other wildlife,
recreational and aesthetic values and water quality (RCW
90.22)
antidegradation requirements of Washington’s water
quality standards (Ch. 173-201 A WAC, following Federal
Clean Water Act)
14. Instream flowsInstream flows
• Other ways to achieve ecosystem goals – wider view,
not just flows – watershed land management
• Avoid headwater disturbance
• Vegetation
• Geology and topography
• Maintain longitudinal and lateral connectivity
• Avoid mainstem in-channel storage
• Allow floodplain to function as floodplain
21. Threats to fresh water resourcesThreats to fresh water resources
Climate change causes change in
frequencies of droughts and floods.
Depletion of aquifers caused by over-
consumption as a result of population
growth.
Pollution and contamination by sewage,
agricultural and industrial runoff.
