Water ResourcesChapter 9

Water, water, everywhere…• Most (97%) of Earth’s

water is saltwater • Of the 3% that is

freshwater, <1% is available for us

• The rest is frozen or deep underground

Groundwater• Aquifer – groundwater is located in small

spaces within permeable layers of rock and sediment

• Unconfined aquifer – porous rock + soil; water can move in and out freely

• Confined aquifer – surrounded by impermeable layers– Springs or artesian wells

Groundwater…• Water table – the uppermost level of

water saturation in the soil• Groundwater recharge – water from

precipitation that percolates back into the soil

Groundwater…• Pumping water out of the ground faster

than it can be recharged will cause a drop in the water table

• Wells near the coastline can suffer from saltwater intrusion as the freshwater is infiltrated with ocean water

Surface Water• Streams, rivers, ponds, lakes, wetlands• 3 largest rivers based on volume:

1. Amazon in South America2. Congo in Africa3. Yangtze in China

• Human settlement and impacts– Transportation– Irrigation– Agriculture

Surface water…• Lakes – surface area versus depth and

volume determine size• Classification of lakes:

1. Oligotrophic• Low nutrient levels = low productivity

2. Mesotrophic• Moderate productivity

3. Eutrophic• Highly productive

Surface water…• Wetlands – help to offset flooding during

periods of heavy rainfall• Also are very useful at absorbing

pollutants

Atmospheric water• Drought – lack of rainfall

– Harm ecosystems and humans – Also impact soil:

• Harder for nutrients to cycle• Dried soil more vulnerable to wind erosion

• Flooding – too much rainfall– Also cause crop and property damage– Ground has been paved

• Excess water can’t soak in

Humans alter water availability• Flood control/prevention:

– Levees• Mississippi River (New Orleans)• Black Warrior River (Northport)• Floodwaters move downstream• Encourages development of floodplain• Risk of collapse or breach

– Dikes• Levees for ocean waters• The Netherlands

Humans alter water availability…• Dams – cross rivers to produce a

reservoir– Water used for consumption, generation of

electricity, flood control, recreation– Environmental issues:

• Disrupt ecosystems during construction• Interfere with natural flow of water • Silt behind the dam

Humans alter water availability…• Aqueducts – carry water to another place

– New York City & Los Angeles– Environmental issues

• Disruption of ecosystem during construction• Less water available in ecosystem feeding the

aqueduct• Can cause international disputes

Humans alter water availability…• Desalination – making saltwater fresh

– Distillation: boiled water leaves salt behind, steam is captured and cooled to condense• Requires a lot of energy

– Reverse osmosis: water is forced through a membrane which blocks the salt• More efficient and less costly• Brine – super salty water waste

Water use• Agriculture

– Irrigation: considerations – cost, amount of evaporation• Furrow ~ 65% efficient• Flood ~ 70-80% efficient• Spray ~ 75-95% efficient• Drip > 95%

– Hydroponic agriculture

Water Use…• Industry

– Electrical generation:• In the U.S. ~ ½ of all water used goes toward

generating electricity• Hydroelectric generation returns water to source• Thermoelectric power plants use water to cool the

system and it leaves as water vapor– Refining metals and making paper

• Gallons used per kg made:• Copper 116, Aluminum 108, Steel 68, paper 33

Water Use…• Households ~ 10% of all water used in

U.S.