Chapter 13 Water: A Limited Resource

Overview of Chapter 13 Importance of Water Water Use and Resource Problems Water Problems in US and Canada Global Water Problems Water Management Water Conservation

Importance of Water Cooking & washing Agriculture Manufacturing Mining Energy production Waste disposal Demand for water is increasing California Rice

Properties of Water H 2 O (two hydrogen atoms and one oxygen atom) Exists as solid, liquid, or gas High heat capacity Polar Forms Hydrogen bonds between water molecules H bonds define water s physical properties

Properties of Water Water is never completely pure in nature Content of seawater (left) Water dissolves many substances Some cause water pollution

Hydrologic Cycle

Distribution of Water on Earth Only 2.5% of water on earth is freshwater 2% is in the form of ice! Only ~0.5% of water on earth is available freshwater

Freshwater Terminology Surface water Precipitation that remains on the surface and does not seep into soil Runoff Movement of surface water to lakes, rivers, etc. Watershed (drainage basin) Land area that delivers water into a stream or river system Groundwater Freshwater under the earth s surface stored in aquifers Aquifer Underground caverns and porous layers of sand, gravel and rock in which groundwater is stored

Freshwater Aquifer

Water Use and Resource Problems Fall into three general categories Too much water Too little water Poor quality/contamination (Chapter 22)

Too Much Water Flooding Regular natural phenomenon Human activities can alter flood characteristics Floods are highly destructive in developed areas Humans have removed water absorbing plant cover from soil Humans construct buildings on floodplains Floodplain Area bordering a river channel that has the potential to flood

Where does the water go? Natural ground cover

Where does the water go? 10% 20% Impervious surface

Where does the water go? 35% 50% Impervious surface

Where does the water go? 75% 100% Impervious surface

Floodplain Government restrictions on building on floodplains Levees fail Rather than rebuild levees adjacent to rivers, experts suggest allowing some flooding of floodplains during floods

Right: Suggested levee style, set back from river Left: Traditional levees adjacent to river

The Napa River

The Napa River (New Year s Flood)

Too Little Water Typically found in arid land Problems Drought Overdrawing water for irrigation Aquifer depletion Ground subsidence

Water Distribution in North America The U.S. has a plentiful supply of freshwater However, many areas have severe shortages Geographical variations Seasonal variations

Water Distribution in US Water shortages in West and Southwest Water is diverted and transported via aqueducts The Colorado River is diverted so much that the channel goes dry in Mexico before entering the sea

Water Diversion Projects Water diverted to areas that are deficient Much of Southern CA receives its water supply from diverted water from Northern CA Controversial and expensive

California s Aqueduct System

Dams and Reservoirs Benefits: Ensure year round supply of water with regulated flow Generate electricity Provide recreational activities Disadvantages Alter the ecosystem Reduce sediment load

Dams and Reservoirs Glen Canyon Dam Regulated flow has changed ecosystem

Dams and Reservoirs Salmon populations along west coast have been greatly reduced due to dams that block migration Fish ladders help but are not effective enough to compensate for the altered river system

Global Water Problems Water and Climate Change Climate change affects the type and distribution of precipitation Water content in snowpack Timing

Global Water Problems Amount of freshwater on planet can meet current human needs However, it is unevenly distributed and some places lack reliable sources

Desalination Removal of salt from water Two main methods: Distillation saltwater is evaporated and condensed Reverse Osmosis saltwater forced through a selective membrane, which allows water through but not salt Both methods are very expensive and energyintensive Distillation Setup Reverse Osmosis Unit

Water Conservation Reducing Agricultural Water Waste American agriculture has historically been very inefficient with water Drip (or trickle) irrigation greatly improves water efficiency

Water Conservation Reducing Home and Business Water Waste Gray Water Can be used to flush toilets and for irrigation Water efficient fixtures Government incentives Rebates, tax breaks, etc.

Conserving at Home and Work Install water saving shower heads and faucets Install low flow toilets Repair leaky fixtures Purchase high efficiency appliances Modify personal habits Use the dishwasher instead of washing by hand