Global Water Distribution & Sources of Water.ppt

Class notes

1. WRM 209: Water Quality
Assessment and Monitoring
DR. AMOS KYALO MUTUA
Ph.D; Marine Biology (UoN-Kenya),
M.Sc Ecological Marine Management
(VUB-Belgium);
B.Sc Zoology and Botany (UoN-Kenya).

2. Global Water Distribution
•Globally, water sources are distributed as shown
below.

3. Sources of Water; Surface water:
•Surface water is precipitation that does
not infiltrate into the ground or return to
the atmosphereby transpirationor
evaporation.
•It may be loosely defined as water that
stands or flows on the surface of the Earth
and is commonly referred to as runoff.

4. Surface water
•Since the spread of urbanization associated with
the change from an agrarianto industrial societies,
human beings have drained landscapes using
essentially the same approach.
•Standing water is perceived as a hazard and
therefore we have tried to move the runoff, or
storm water, quickly, safely and economically into
sewers, and then with the same emphasis into the
nearest watercourse.
•However, urbanization changes the local natural
hydrological cycleas the impermeable surfaces
associated with development reduce infiltration
and transpiration, and instead divert the
precipitation into the drainage system.

5. Surface water: Cycle
•The Figure below shows how the volume of surface
runoffchanges between natural and urbanized
environments.
•

6. Sources of Water
•Surfacewater:
•Examples
–Rivers, lakes or fresh water wetlands. Surface
water is naturally replenished by precipitation
and naturally lost through discharge to the
oceans, evaporation, evapotranspirationand
sub-surface seepage.
–Total quantity of water in surface systems
depends on storage capacity, the permeability of
the soilbeneath these storage bodies, the runoff
characteristics of the land in the watershed, the
timing of the precipitation and local evaporation
rates.

7. Surface Water Cont’d
•Natural surface water can be augmented
(increased) by importing surface water from
other watersheds through canals or pipelines.
•Human beings can also cause surface water to be
"lost" (i.e. become unusable) through pollution.

8. Sources of water
•UnderRiverflow
–Water flowing through sub-surface rocks and
gravels that underlie the river and its floodplain.
–This region is called the hyporheic zone.
–For many rivers in large valleys, this unseen
component of flow may greatly exceed the visible
flow.
–The hyporheic zone often forms a dynamic
interface between surface water and true
ground-water receiving water from the ground
water when aquifers are fully charged and
contributing water to ground-water when ground
waters are depleted.

9. Sources of Water
•Groundwater
–ThisisSub-surfacewaterwhichisfreshwater
locatedintheporespaceofsoilandrocks.
–Itisalsowaterthatisflowingorheldwithin
aquifersbelowthewatertable.
–Twotypes
•sub-surfacewaterthatiscloselyassociatedwith
surfacewaterand
•deepsub-surfacewaterinanaquifer(sometimes
called"fossilwater").

10. Ground Water Cont’d
•The natural input to sub-surface water is seepage
from surface water. The natural outputs from sub-
surface water are springsand seepage to the
oceans.
•If the surface water source is subject to substantial
evaporation, sub-surface water source may become
saline.
•In coastal areas, human use of a sub-surface water
may cause the direction of seepage to ocean to
reverse which can also cause soil salinization.
•Humans can also cause sub-surface water to be
"lost" (i.e. become unusable) through pollution.
•Humans can increase the input to a sub-surface
water source by building reservoirs or detention
ponds.

11. Sources of Water
•Desalination
–Desalination is an artificial process by which
saline water(generally sea water) is converted
to fresh water. The most common desalination
processes are distillationand reverse osmosis.
Desalination is currently expensive compared
to most alternative sources of water, and only
a very small fraction of total human use is
satisfied by desalination. It is only
economically practical for high-valued uses
(such as household and industrial uses) in arid
areas. The most extensive use is in the Persian
Gulfe.g. Israel and Libya, and other
Mediterranean and Middle East Countries.

12. Desalination Cont’d
•Distillation: Boiling to vapour state to remove
salts. Resulting water vapour is cooled to give
fresh water.
•Reverse osmosis(RO) is a filtrationmethod that
removes large moleculesand ionsfrom solutions
by applying pressure to a solution through a
selective membrane.
•In the normal osmosisprocess the solvent
naturally moves from an area of low solute
concentration, through a membrane, to an area
of high solute concentration. Applying an
external pressure to reverse the natural flow of
pure solvent, thus, is reverse osmosis.

13. Sources of Water
•Frozenwater
–Use of Icebergs in the polar regions and high altitudes
as water sources
–Glacier Run off is however considered as surface run
off.
–The Himalayas, contain some of the most extensive
area of glaciers and permafrost outside of the poles.
Ten of Asia’s largest rivers flow from there, and more
than a billion people’s livelihoods depend on them.
–NOTE:Global temperatures are rising more rapidly
around Himalayas than the global average. In Nepal
the temperature has risen with 0.6 degree over the
last decade, whereas the global warming has been
around 0.7 over the last hundred years.

14. Rain Water
•Collected from roof tops and rock catchments.
•Rainwater is naturally soft (unlike well water),
contains almost no dissolved minerals or salts, is
free of chemical treatment, and is a relatively
reliable source of water for households.
Rainwater collected and used on site can
supplement or replace other sources of
household water.
•Rainwater harvesting systems is their flexibility.
A system can be as simple as a whiskey barrel
placed under a rain gutter down spout for
watering a garden or a complex multi-tank,
pumped and pressurized construction to supply
residential and irrigation needs.

15. (2): Uses of Water
•Categories of water use
–Commercial water use includes fresh
water for motels, hotels, restaurants,
office buildings, other commercial
facilities.
–Domesticuse includes water that is used
in the home every day, including water for
normal household purposes, such as
drinking, food preparation, bathing,
washing clothes and dishes, flushing
toilets, and watering lawns and gardens.

16. Uses of Water
•Industrial:For such purposes as processing,
cleaning, transportation, dilution, and cooling
in manufacturing facilities. Major water-using
industries include steel, chemical, paper, and
petroleum refining.
•Irrigation:water is artificially applied to
farms for crop production; chemical
application, for the leaching of salts from the
crop root zone (Rhizosphere). Nonagricultural
activities include self-supplied water to
irrigate public and private golf courses,
parks,

17. Uses of Water
•Livestock:water for stock animals, feed lots,
dairies, fish farms, etc. Water is needed for the
production of red meat, poultry, eggs, milk, and
wool, and for horses, rabbits, and pets. Livestock
water use only includes fresh water.
•Mining:for the extraction of naturally occurring
minerals; solids, such as coal and ores; liquids,
such as crude petroleum; and gases, such as
natural gas. The category includes quarrying,
milling (such as crushing, screening, washing, and
flotation), and other operations as part of mining
activity.

18. Uses of Water
•Public Supply:water withdrawn by public and
private water suppliers, such as county and
municipal water works, and delivered to users
for domestic, commercial, and industrial
purposes.
•Thermoelectric Power Production:Production
of electric power generated with heat. The
source of the heat may be from fossil fuels,
nuclear fission, or geothermal. They generate
electricity by turning a turbine using steam
power.
•Hydroelectric Power Production:Force of water
to turn turbines