Transcript - Catalyst

TESC 211
The Science of Environmental Sustainability
Autumn Quarter 2011 UWT
How can we ensure adequate water supplies?
• Pumping ground water
• Building Dams to capture water
• Desalination
• Water transfer systems
All these systems have costs and benefits
Aquifers are renewable resources provided:
• They don’t become contaminated
• They are replenished faster than they are utilized
Aquifers provide water for ~50% of the World’s people.
In the US aquifers supply:
• Nearly all drinking water in rural areas
• 20% of drinking water in urban areas
• 37% of irrigation water
Over pumping of aquifers is occurring in many parts of the
World.
e.g. Mexico City
Irrigation of grain crops is responsible for much of this over use.
The three largest grain producers China, India and the US all
have issues with aquifer over use.
e.g. On average in the US groundwater is being withdrawn four
times faster than it is being replenished
The Ogallala aquifer is the World’s largest known aquifer . It is
also relatively shallow (<300 feet).
The Ogallala aquifer:
• Underlies ~27% of irrigated land in the US
• Provides ~30% of groundwater used for irrigation
• Provides ~80% of all drinking water for people living inside its
boundary.
The Ogallala aquifer is
being seriously over
exploited.
Over exploitation of ground water resources has
consequences:
• Aquifer depletion (loss of resource)
• Subsidence
• Salt water intrusion of coastal aquifers
• Exacerbated by rising sea levels
A variety of strategies have been proposed to limit or prevent
groundwater depletion:
• Prevention
• Waste less water
• Subsidize water conservation
• Limit number of wells
• Do not grow water-intensive crops in dry areas
•Control
• Raise price of groundwater
• Tax water
• Enforce minimum stream flow levels
•Divert run-off to recharge aquifers
Some scientists have proposed exploiting “deep aquifers”:
• Contain very large amounts of water (could support Human
use for hundreds of years)
• Typically, non-renewable
• Geological and ecological impacts of exploiting these
aquifers unknown
• Likely very expensive to access
• Not clear who has ownership (potential for conflict)
Dams and reservoirs are devices that capture and store run-off.
This water may then be released in order to :
• Drive turbines to produce electricity
• Control flooding
• Supply water for irrigation
• Supply drinking water
• Supply water for industry
Grand Coulee dam in Washington
State performs most of these
functions
There are more than 45, 000 large dams in the World.
Approximately half of these are in China.
Net result is reliable run-off available for human use has
increased by ~1/3rd .
• Reservoirs hold 3-6 times the amount of water flowing in
a the World’s rivers.
• Hydroelectric dams produce ~20% of the World’s
electricity
These dams have:
• Displaced 40-80 million people
• Flooded an area of 164, 000 miles2 (equivalent in size to
the state of California)
• Significantly impaired the function of rivers
• It is estimated:
• 1 out of 5 of the World’s freshwater fish and plant
species is extinct or endangered as a result of
dams and water withdrawals
• Only 21 out of the 117 of the planets longest rivers
flow freely from their sources to the sea.
Tunnels, aqueducts and pipes are all examples of devices known
as “water transfer systems”
They are typically, used to move water from reservoirs and dams
in water rich areas to water poor areas.
One of the World’s largest examples of this is combination of the
“Californian Water Project” and the “Central Arizona Project” .
• These projects serve to transfer water form northern
California to southern California and Arizona.
The Californian Water
Project directs water South
from the Sacramento River
The Colorado River
provides water for the
Central Arizona Project
Since the inception of the “Californian Water Project” northern
and southern regions of the state have been feuding over
allocations:
• 75% of all withdrawals are for agriculture, much of which
waters “thirsty” crops grown in the relatively arid San
Joaquin Valley.
•Cities such as Los Angeles and San Diego lack sufficient
local sources of water to support themselves.
• Decreased flows in the Sacramento River
Perhaps one of the most well known examples of a water
transfer project is that of the Aral Sea in the former Soviet Union.
August 1985
August 1989
The disappearance of the Aral
Sea is a result of diversion of
water from the Volga and Ural
Rivers.
August 2009
The Aral Sea is now estimated to be ~10% of its original size.
The fishing industry has been effectively destroyed bringing
much economic hardship to the region.
What remains is heavily polluted and highly saline.
85% of the areas wetlands have been eliminated.
50% of bird and mammal species have disappeared.
80% of native fish species are presumed extinct.
Massive salty dust storms are know common as a result of the
barren area exposed where the sea once was.
September 1, 2006
Much of the water that is diverted from the Aral Sea is used to
irrigate cotton and rice crops.
The disappearance of the Aral Sea has had substantial effect on
the climate of surrounding areas.
In general weather has become more extreme:
• Colder, wetter winters
• Hotter, drier summers
These effects have contributed to a 20-50% decrease in crop
yields in many areas.
• Increased and inappropriate use of pesticides and
fertilizers to counter lost productivity
One alternative to utilizing freshwater resources for human needs
is to desalinate sea water or saline aquifers.
A variety of methods exist the most popular being:
• Distillation
• Reverse osmosis
However, these methods have not found wide spread use,
primarily because of:
• Cost
• High energy demands
• Destruction of marine environment
Reducing water use by cutting waste is by far the most effective
means to reduce demand on our natural water resources.
It is estimated:
• ~70% of water is unnecessarily wasted through evaporation,
leaks and other losses.
• In the US ~50% of water is wasted
• It is economically feasible to reduce water waste to 15%
Why are so wasteful with water?
Because we believe we can afford to be.
Significant reduction in water waste can be achieved by
improving irrigation techniques
• ~60% of irrigation water applied throughout the World does not
reach the intended crops.
• Unlined ditches, prone to evaporation and seepage loses
However, well designed sprinkler systems can reduce loses to
10-5%.
• Central pivot sprinkler systems
• Drip irrigation
Different places perform better with the implementation of these
techniques than others:
• Globally ~1% of crops irrigated with drip systems
• 4% in the US
• 13% in California
• 66% in Israel
• 90% in Cyprus
What does this tell us?
Technologically widespread use of drip irrigation is possible.
Irrigation water waste can be reduced in several other ways:
• Line canals and irrigation ditches
• Monitor soil moisture and add water only when necessary
• Irrigate at night to prevent evaporation
• Encourage organic farming
• Avoid growing water thirsty crops in dry areas
• Irrigate with treated waste water
• Import water intensive crops
Industrial and domestic water waste can be reduced:
• Redesign manufacturing processes
• Recycle water in industry (especially cooling water)
• Landscape and irrigate yards appropriately
• Fix water leaks
• Price water appropriately
• Use waterless toilets
• Use frontloading washers, water saving shower heads and
toilets
• Reuse household water for irrigation and toilet flushing