CHAPTER 9
WATER: HYDROLOGIC CYCLE AND HUMAN USE

I. Unique Properties of Water

A. Water has Unique Properties
1. Superior Solvent
2. High Melting and Boiling Point
3. High Heat Capacity
4. High Heat of Vaporization
5. Capillary Action (from high surface tension and high wetting ability)
6. Liquid Water Density Greater than Solid Water

II. Water Cycle

A. A global cycle by which water flows through terrestrial, aquatic and atmospheric
environments.

B. Helps purify and distribute water around the planet.

C. The cycle
1. Evaporation - energy input (evaporative cooling), the purification process
2. Condensation - energy released (heat is being moved around the planet)
3. Precipitation - air temperature, removal of pollutants from the atmosphere.

Fig. 9.1 Freshwater constitutes only 0.77% of the total Earth's water.
Fig. 9.3 The Earth's fresh waters are replenished as water vapor enters the atmosphere by evaporation or transpiration from vegetation, leaving salts and other impurities behind. As precipitation hits the ground, note that three additional pathways are possible.
Fig. 9.4 As warm, moist air is cooled, the amount of water it can hold decreases. Cooling air beyond the point where relative humidity (RH) reaches 100% forces excess moisture to condense, forming clouds. Further cooling and condensation results in precipitation.
Fig. 9.5a Moist air from the equator rises, dropping its moisture.  The now-dry air descends at 30 degrees north and south latitude producing deserts.
Fig. 9.5b A cell  is a tube of circulating air girdling the planet. The six Hadley cells on either side of the equator indicating general vertical airflow patterns.
Fig. 9.5c This figure shows global trade wind patterns as a result of Earth's rotation. Because of the earth's rotation, the Coriolis Effect occurs which deflect winds from going straight north or south.
Fig. 9.6 Moisture-laden air in a trade wind cools as it rises over a mountain range, resulting in high precipitation on the windward slopes. Desert conditions arise on the leeward side as the descending air warms and tends to evaporate water from the soil.
Fig. 9.7a This figure shows precipitation patterns in North and South America. Note the high rainfall in equatorial regions and the regions of low rainfall to the north and south.
Fig. 9.7b This figure shows precipitation patterns in North and South America. Note the high rainfall in equatorial regions and the regions of low rainfall 30 degrees to the north and south.
III. Where Does Water Go during the Water Cycle?

A. Precipitation results in water infiltration and runoff
1. Water Infiltration
a. Gravitational water
b. Capillary water
2. Most Gravitational Water Results in Groundwater
a. Groundwater
b. Water table

B. Runoff
C. Floodplain
D. Watershed

Fig. 9.8 In this figure, 1. The contribution of water from the oceans to the land via evaporation and then precipitation; 2. Movement of water from the land to the oceans via runoff and seepage; and 3. The net balance of water movement between terrestrial and oceanic regions.
IV. Human Impacts on the Hydrologic Cycle

A. Changing the Earth's Surface
1. Urbanization
2. Overgrazing
3. Overcultivation
4. Deforestation
5. Pavement

B. Polluting the Water Cycle
1. The solution to pollution is not dilution.

C. Overdrawing Water Resources
1. Why are shortages inevitable with our current use patterns?
2. What are the ecological consequences of overdrawing surface water?
3. What are the ecological consequences of overdrawing groundwater?
a. Diminishing surface water
b. Land subsidence
c. Salt water intrusion

Fig. 9.10 Human activities introduce pollution into the water cycle at numerous points as shown.
V. Sources and Uses of Freshwater

A. Quantitative Concerns
B. Qualitative Concerns
C. Consumptive versus Nonconsumptive Use

D. How is Water Used?
1. Agriculture
2. Industry
3. Residential
Fig. 9.11 A dry-climate, less-developed region uses most of its water for irrigation, whereas moist-climate, industrialized countries (e.g., Europe) require the largest percentage for industry (from World Resources Institute, "World Resources 1998-99.")
Fig. 9.13a Water is often taken from a river or reservoir, sent to the treatment plant, used, and returned after waste treatment.
Fig. 9.13b 1) chlorine is added to kill bacteria, (2) alum (aluminum sulfate) is added to coagulate organic particles, and (3) the water is put into a settling basin for several hours to allow the coagulated particles to settle. It is then (4) filtered through sand.
Fig. 9.14 Droughts occur on an average of every 20 years and may reduce normal water flows by 70%. Therefore no more than 30% of the average surface-water flow can be counted on to be continuously available.
Fig. 9.16 Pumping up water from the Ogallala aquifer has made this arid region of the United States into some of the most productive farmland in the country.
Fig. 9.18a Where aquifers open into the ocean, fresh water is maintained in the aquifer by the head of fresh water inland.
Fig. 9.18b Excessive removal of water may reduce the pressure, so that salt water moves into the aquifer.
VI. How Do We Obtain More Water?

A. Dams and Water Division Projects

B. Conservation
1. Irrigation
2. Urban

C. Technological Solutions
1. Desalinization
2. Cleanup of Polluted Water

VII. Managing Stormwater

A. Reducing Flooding
B. Decreasing Streambank Erosion
C. Decreasing Water Contamination from Pollutants on Paved Surfaces
D. Streamside Ecology - Stop and Remove Channelization
Fig. 9.21 Curves, in this figure, are for similar storms on Brays Bayou in Houston, Texas, before, during, and after development in the early 1950s. Note the increasing height of the surge occurring with the storm and the decreasing volume of flow that occurs later in the cycle.
Fig. 9.22 Different regions of the world vary in their ability to obtain safe fresh water.