Download Water resources chapter 13

WATER RESOURCES
CHAPTER 13
Peyton Adams
Will we have enough usable water?
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We are using available freshwater unsustainably by wasting it, and charging too little for this irreplaceable
natural resource.
One of every six people does not have sufficient access to clean water, and this situation is likely to get
worse.
Saltwater covers 71% of the earths surface
Water is irreplaceable, we can only survive a few days without water.
It takes large amounts of water to supply us with food, energy, and most other things that we use to meet
our daily needs and wants.
Despite its importance, water is one of our most poorly managed resources. We waste and pollute water.
3,900 children younger than the age of 5 die from waterborne infectious diseases because they do not
have access to safe drinking water.
Water is an economic issue because it is vital for reducing poverty and producing food and energy.
Almost half of the worlds people do not have access to water in their homes, so they have to get some from
nearby wells.
Water is an environmental issue because excessive withdraw of water from rivers and aquifers results in
falling water tables, decreasing river flows, shrinking lakes, and disappearing wetlands.
Most of the earths freshwater is not
available to us.
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About 0.024% of the planets enormous water
supply is available to us in groundwater
deposits and in lakes, rivers, and streams. The
rest is in salty oceans, frozen polar ice caps/
glaciers, and deep underground, in inaccessible
locations.
The worlds water supply is continually
collected, purified, recycled and distributed in
the earths hydrologic cycle (the movement of
water in the seas, air, and on land, which is
driven by solar energy and gravity).
This irreplaceable water recycling and
purification system works well, unless we
overload it with pollutants or withdraw water
from under ground and surface water supplies
faster than it can be replenished.
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We can also alter precipitation rates
and distribution patterns of water
through our influence on projected
climate change. In some parts of the
world, we are doing all these things,
mostly because we have thought of
the earths water as essentially a free
and infinite resource.
On a global basis, we have plenty
of freshwater, but it is not distributed
evenly.
Canada has 20% of the worlds
liquid freshwater, China has 7% of
the worlds supply, and Asia has 30%
of the water supply.
Water shortages will grow
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The main factors that cause water scarcity in any particular
area are a dry climate, drought, too many people using a
water supply more quickly than it can be replenished, and
wasteful use of water.
More than 30 countries now face stress from water scarcity.
30% of the earths land area experiences drought.
By 2059, as much as 45% of the earths land surface could
experience extreme drought.
Two or more countries share the available water supplies in
each of 263 of the worlds water basins, which together
cover nearly half of the earths surface and are home to
about 40% of the worlds people.
There are several ways to increase
freshwater supplies
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We can provide more water
by reducing unnecessary
waste of water.
Other solutions involve
increasing water supplies by
withdrawing groundwater,
building dams and reservoirs
to store runoff in rivers for
release as needed,
transporting surface water
from one area to another, and
converting saltwater to
freshwater.
Is extracting groundwater the answer?
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Groundwater used to supply cities and grow food is being pumped
from aquifers in some areas faster than it is renewed by
precipitation.
Aquifers provide drinking water for nearly half of the worlds
people.
In the US, aquifers supply almost all of the drinking water in rural
areas, one fifth of that in urban areas, and 37% of the country's
irrigation water.
More than 400 million people, including 175 million in India and
130 million in China, are being fed by grain produced through this
unsustainable use of groundwater, according to the world bank. This
number is expected to grow until the water runs out or until
governments put caps on aquifer withdrawal rates and stop
providing subsidies that encourage over pumping and water waste.
Advantages and disadvantages of
withdrawing groundwater
Advantages
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Useful for drinking and
irrigation.
Exists almost
everywhere.
Renewable if not over
pumped or
contaminated.
Cheaper to extract than
most surface waters.
Disadvantages
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Aquifer depletion from
over pumping.
Sinking of land from
over pumping.
Pollution of aquifers
lasts decades of
centuries
Deeper wells are
nonrenewable.
Aquifer depletion in the United States
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In the US, groundwater is being withdrawn from
aquifers, on average, four times faster than it is
replenished.
One of the most serious overdrafts of groundwater in in
the lower half of the Ogallala, the worlds largest
known aquifer, which lies under eight Midwestern states
from southern South Dakota to Texas.
The problem with the Ogallala is that it is essentially a
one time deposit of liquid natural capital with a very
slow rate of recharge.
The Ogallala helps to support biodiversity.
Groundwater Depletion
Prevention
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Waste less water
Subsidize water
conservation
Limit number of wells
Do not grow water
intensive crops in dry
areas.
Control
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Raise price of water to
discourage waste
Tax water pumped from
wells near surface waters
Set and enforce minimum
stream flow levels
Divert surface water in
wet years to recharge
aquifers.
Is building more dams the answer?
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A dam is a structure built across a river to control
the rivers flow.
Usually, dammed water creates an artificial lake
(reservoir), behind the dam.
The main goals of a dam and reservoir are to
capture and store runoff, and release it as needed
to control floods, generate electricity, and supply
water for irrigation and for towns and cities.
Reservoirs also provide recreational activities such
as swimming, fishing, and boating.
Advantages and disadvantages of
building dams
Advantages
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Provides irrigation water
above and below dam.
Provides water for drinking
Reservoir useful for recreation
and fishing
Can produce cheap electricity
Reduces downstream flooding
of cities and farms.
Disadvantages
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Flooded land destroys forests or
cropland and displaces people
Large losses of water through
evaporation
Deprives downstream cropland
and estuaries of nutrient rich silt
Risk of failure and devastating
downstream flooding
Disrupts migration and spawning
of some fish.
Is transferring water from one place to
another the answer?
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Transferring water from one place to another has greatly
increased water supplies in some areas but has also
distributed ecosystems.
Using a lot of water to produce a particular type of food or
other product is not necessarily bad if it is done n an area
where water is plentiful and water waste is controlled.
Water waste is part of the reason why many products
include large amounts of virtual water.
One factor contributing to inefficient water use- for
example, growing thirsty lettuce in desert like areas- is that
governments subsidize the costs of water transfers and
irrigation in some dry regions. Without such subsidies,
farmers could not make a living in these areas.
Case study
California transfers massive amounts of water
from water rich areas to water poor areas
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One of the worlds largest
transfer projects is the California
Water Project. It uses a maze of
giant dams, pumps, and lined
canals to transport water from
water rich northern California, to
water poor southern California's
heavily populated cities and
agricultural regions. This project
supplies massive amounts of
water to areas that, without such
water transfers, would be mostly
desert.
The Aral sea disaster: a striking example
of unintended consequences.
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The shrinking of the Aral sea,
once a large inland body of
saline water, is the result of a
large scale water transfer project
in an area of the former soviet
union with the driest climate in
central Asia. Since 1960,
enormous amounts of irrigation
water have been diverted from
the two rivers that supply water
to the Aral Sea. The goal was to
create one of the worlds largest
irrigated areas, mostly for
raising cotton and rice.
Is converting salty seawater to
freshwater the answer?
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We can convert ocean water into freshwater, but the cost is high, and the
resulting salty brine must be disposed of without harming aquatic or
terrestrial ecosystems.
Desalination involves removing dissolved salts from ocean water or from
brackish water in aquifers or lakes.
The two most widely used methods for desalinating water are distillation
(heating saltwater until it evaporates) and reverse osmosis (uses high
pressure to force saltwater through a membrane filter with pores small
enough to remove the salt).
There are three major problems with the widespread use of desalination. 1)
there is a high cost, 2) pumping large volumes of sea water through pipes
and using chemicals to sterilize the water kills marine organisms and
requires large amounts of energy, and 3) this produces huge quantities of
salty wastewater that must go somewhere.
Reducing water waste has many
benefits
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Some benefits of reducing wastewater are about two thirds of the
water throughout the world is unnecessarily wasted through
evaporation, leaks, and other losses.
In the US, about half of the water drawn from surface and
groundwater supplies is unnecessarily wasted. It is economically and
technically feasible to reduce water waste to 15%, thereby meeting
most of the worlds water needs for the foreseeable future.
A basic rule of economics is that you get more of what you reward.
Withdrawing environmentally harmful subsidies that encourage
water waste and providing environmentally beneficial subsidies for
more efficient water use would sharply reduce water waste and help
to reduce water shortages.
Solutions to…
Reducing irrigation water waste
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Line canals bringing water to irrigation
ditches.
Irrigate at night to reduce evaporation
Monitor soil moisture to add water only
when necessary
Grow several crops on each plot of land
Encourage organic farming
Avoid growing water thirsty crops in dry
areas
Irrigate with treated waste water
Import water intensive crops and meat
Reducing water waste
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Redesign manufacturing processes to use less water
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Recycle water in industry
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Landscape yards with plants that require little water
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Use drip irrigation
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Fix water leaks
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Use water meters
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Raise water prices
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Use waterless composing toilets
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Require water conservation in water short cities
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Use water saving toilets, showerheads, and front
loading clothes washers.
Collect and reuse household water to irrigate laws and
nonedible plants
Purify and reuse water for houses, apartments, and
office buildings.
Some areas get too much water from
flooding
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Some areas have too little water, but others sometimes have too
much because of natural flooding by streams, caused mostly by
heavy rain r rapidly melting snow.
A flood happens when water in a stream overflows its normal
channel and spills into an adjacent area, called a floodplain.
These areas, which usually include highly productive wetlands, help
to provide natural flood and erosion control, maintain high water
quality, and recharge groundwater.
Floods kill thousands of people each year and cost tens of billions of
thousands of dollars in property damage.
Floods are usually considered natural disasters, but since the 1960s,
human activities have contributed to a sharp rise in flood deaths and
damages, meaning that such disasters are partly human made.
Solutions to reducing flood damage
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Preserve forests on
watersheds
Preserve and restore
wetlands in floodplains
Tax development on
floodplains
Use floodplains
primarily for recharging
aquifers, sustainable
agriculture and forestry.
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Straighten and deepen
streams
Build levees or
floodwalls along streams
Build dams.
Big ideas of the chapter
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One of the worlds major environmental problems is the
growing shortage of freshwater in many parts of the
world.
We can increase water supplies in water short areas in
a number of ways, but the most important way is to
reduce overall water use and waste by using water
more sustainably.
We can use water more sustainably by cutting water
waste, raising water prices, slowing population growth,
and protecting aquifers, forests, and other ecosystems
that store and release water.