Chapter 13 Lecture Outline:
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It takes a huge amount of water to supply you with food, shelter and meet every day needs
Water plays key role in sculpting Earth’s surface, moderating climate and removing waste and
pollutants
Hydrologic (Water Cycle): World’s freshwater supply continuously collected, purified, recycled
and distributed
 Driven by solar energy and gravity
 We interfere by polluting, destroying wetlands, deforestation, and altering rate and
distribution pattern
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One of most poorly managed resources – waste and pollute it
Access to water is global health issue
o WHO estimates 1.6 million people (90% under age 5) die from largely preventable
water born diseases
Water is economic issue – vital for producing food and energy
Water is women and children’s issue – developing countries women and children get water
National global security issue – increasing tensions between nations over water resources
Environmental issue – excessive withdrawal from rivers and aquifers/ pollution
o Low water tables
o Lower river flow
o Shrinking lakes
o Fish populations
o Loss of wetlands
On a global basis we have plenty of freshwater, but differences in annual precipitation and
economic resources divide the world’s continents, countries, and people into water haves and
water have-nots
o Canada has only 0.5% population but 20% of world’s liquid freshwater
o China has 20% world population but only 7% of water supply
o Asia has 60% of world population but only 30% water supply
Groundwater: When precipitation infiltrates the ground downward until it a impermeable layer
of rock stops it – water in these spaces
o ONE OF MOST IMPORTANT SOURCES OF FRESHWATER
Zone of Saturation: Below a certain depth where the spaces in the soil and rock are completely
full of water
o Spaces near surface hold little moisture
Water Table: The top of the groundwater zone
o Falls lower during dry weather, or when we remove it faster than it replenishes
o Rises during wet weather
Aquifers: Deeper down, geologic layers, underground caverns, porous layers of sand/gravel/or
bedrock through which groundwater flows
o Groundwater normally moves from higher/high pressure to lower elevations/lower pressure
o Like large elongated sponges through which groundwater seeps – only about 1 meter per year and
at most 0.3 meters per day
o Impermeable layers of rock or clay below aquifers keep the water from escaping deeper into Earth
Natural Recharge: precipitation percolates downward
Lateral Recharge: from the side by nearby rivers/streams
o Recharge tends to be VERY SLOW
o Urban/paved areas
Nonrenewable Aquifers: get very little/no recharge. Found deep underground and formed tens of
thousands of years ago
o This is like mining non-renewable resource
o Unsustainable use of this resource
Surface Water: freshwater from precipitation and snowmelt that flows across Earth’s land surface
and into rivers, streams, lakes, wetlands, and ultimately to the ocean
Surface runoff: Precipitation that does not infiltrate the ground or return to the atmosphere by
evaporation
o Surface water replenished by runoff is classified as a renewable but finite resource
Watershed/Drainage Basin: The land from which surface water drains into a particular river, lake,
wetland, etc.
Reliable Surface Runoff: The remaining 1/3 of runoff not lost for human use by seasonal floods (2/3)
o Amount of surface runoff that we count as source of freshwater
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During the last century human population tripled – global water withdrawal increased sevenfold, per
capita withdrawal quadrupled
We now withdraw 34% of World’s reliable surface runoff
o Estimated: by 2025 global withdrawal to 70%
o Even 90% if per capita withdrawal continues increasing at same rate
o Arid American Southwest – 70% of reliable runoff is withdrawn for humans
o Unsustainable as ecological footprint
70% of water we withdraw is to irrigate cropland
20% Industry
10% cities and residences
Affluence vs. poverty
Case Study: US:
Drought: prolonged period in which precipitation is at least 70% lower and evaporation is higher than
normal in an area that is normally not dry
 Arid/semi-arid regions – irrigation accounts for 85% of water use
 A good portion is unnecessarily wasted
 Almost ½ water used comes from groundwater
o The rest rivers, lakes, reservoirs
 Water tables lowering
 Excessive drainage from aquifer near a river/stream can decrease or deplete surface water
o When water table drops below the level of the stream, its water drains into aquifer
 36 US states likely to face water shortages by 2013
Water Shortages will grow:
 UN estimates by 2025 at least 3 billion of the projected 7.9 billion people will lake access to safe
water
 Hydrological poverty in arid/semi-arid areas
o Flood of refugees can cause intense conflict –Middle East
Ogallala aquifer: largest known aquifer
 Supplies 1/3 of all groundwater used in US
 Great Plains agriculture
 Very slow recharge
 Southern States aquifer is thinner and water being depleted rapidly
o Texas-Oklahoma
 Loss of wetlands – loss of biodiversity
 Groundwater withdrawal near coastal areas can lead to salt water intrusion
Reservoir: Artificial body of water created by damming river
Look at positives and negatives for building dams/reservoirs
Case Study: The Colorado River Basin— an Over tapped Resource
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Water mostly from snowmelt from the Rocky Mountains
Desert area with rain shadow
14 major dams and reservoirs and canals that support water to farmers, ranchers and cities
Water and electricity for more than 25 million people in 7 states
Area produces about 15% nations crops
Major cities – Las Vegas Nevada, California, Arizona
Recreation – white water rafting, boating, fishing, hiking, camping (multibillion dollar industry)
Lake Mead – 90% for Las Vegas
By 2021 Lake Mead could run dry – decreased flow and greater demand for water
Amount of water flowing to the mouth of the river has dropped
Decreased sedimentation (fertile) loss of coastal wetlands
California Water Project: Water Transfer: uses maze of giant dams, pumps, and aqueducts to transport
water from water rich Northern California to water poop Southern California
 To areas that would otherwise be mostly desert
 Southern CA wants more water for crops
 Northern CA says sending more water will degrade Sacramento River and fisheries
 Making irrigation more effective to prevent water loss?
 Low water prices from government subsidies deter farmers from investing in better technologies
Desalination: removing dissolved salts from ocean water/brackish water in aquifers or lakes for domestic
use
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Distillation – heating saltwater until it evaporates then condenses again
Reverse Osmosis (microfiltration) – uses high pressure to force salt water through membrane filter
15,000 plants in 125 countries – mostly in Middle East
Saudi Arabia has world’s largest number of desalination plants
By 2008 Israel has been getting ½ of its water from desalination
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Distillation requires 10x as much energy as reverse osmosis
Use of chemicals to sterilize water
Wastewater with a lot of salt and other minerals – dumping increases salinity of ocean
Problems – only works for water-short wealthy counties
Using desalination for crops – removes salts – but also beneficial ions Ca, Mg