Movement of water

• Precipitation driven by gravity

• Evaporation driven by solar heating and wind

• Transpiration driven by solar heating, wind, root pressure, cohesion & adhesion

• Advection driven by wind

• Infiltration driven by gravity

• Runoff driven by gravity

• Condensation driven by solar heating and hydrogen bonds

Dynamic Equilibrium

• Evapo-transpiration is equal to Precipitation

Water Behavior

• High Specific Heat due to hydrogen bonding• High specific heat and high boiling point allow

water to be used as a cooling medium• Moderates the temperature of the

atmosphere• Phase transitions in the Hydrologic Cycle– Condensation, Evaporation, sublimation

• Thermal Pollution

Watersheds• A watershed is all of the land drained into a

single river. • The Amazon River Basin is the largest watershed

in the world. • Runoff within a watershed contributes to the

surface water available for human use• Of the forty inches of annual precipitation

received by the earth, approximately 30% of the runoff is available for human use.

• A floodplain is an inland wetland that receives excess water during a heavy rainfall or flood.

Human Effect on the Watershed• Development increases runoff & flooding• Cultivating land reduces infiltration and increases

runoff• Development and poor soil management

increase erosion• Runoff from agricultural land may contain fecal

coliform bacteria that can cause serious human disease.

• Agricultural runoff increases the nutrient load to waterways (eutrophication).

Lakes

• Oligotrophic Lakes– Low nutrient load– Good for recreation– Dark blue due to deep penetration of high

wavelengths of light• Eutrophic lakes– High nutrient load– Brown or green due to organic matter– Affected by nutrient runoff

Water Supply

Water by Color

• Green water: water that is available for plants• Blue water: ground water, surface water too

deep in a stream to be reached by plants, infiltrated water above the aquifer, and runoff

• Grey water: water used for industrial process, domestic uses other than sewage

• Black water: sewage water

Renewal Rates• The retention times for a drop of water on the

mainland (one speaks of renewal rates) are very different. If a drop falls into a creek or river, it takes only a few days or months until it returns to the sea. Should it fall into a lake, however, the process can last a lot longer - depending on the size and depth of the lake, anywhere from a few years to thousands of years. In groundwater the process lasts for hundreds of thousands of years - in the glaciers and at the poles sometimes many millions of years - until the drop returns to the sea. There it can take hundreds of millions of years until the drop commences its journey back to the mainland.

Water Use• US is largest per-capita user

– Domestic use increased• Toilets are the greatest domestic use of fresh water

– Industrial use decreased– Total use quadrupled

• Different countries vary in their per capita usage due to the climate– Virtual water

• Asia has the greatest area of land under irrigation• Agricultural water use is least efficient in less developed countries

– Surface water dependence– Poor ground water management– Water wars

Health and Water

• E. coli and coliform bacteria• BOD and Hypoxia• Oligotrophic & Eutrophic lakes• 44% of US lakes are unsafe for recreational

activity• Bottled water is not regulated by the FDA,

frequently contaminated• Humans require ½ gallon of water a day

Water Sources

• World water demand is approximately twice the population growth rate

• 50% of US relies on groundwater for drinking supply– If recharge rate for ground water is less than

extraction rate• Non-sustainable• Saltwater intrusion

• Desalination – Reverse Osmosis

Water Conservation• Xeriscaping• Micro-irrigation• Cisterns and water farming• Turning off water while shaving & brushing teeth• Gray water irrigation• Low flow toilets• Off peak watering of lawns• Raising the price of water (true cost pricing) • Increase metering for water users

Colorado River

Aral Sea

California Water Project