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Water Resources
About the Hydrologic Cycle• Hydrology is the study of movements
and characteristics of water.
• The hydrologic cycle has a profound
effect upon climate prediction.
• Water is vital so we must understand
where to find water and how water
supplies cycle through the Earth.
FIGURE 11.2 The distribution of water on Earth. [Data from J. P. Peixoto and M. Ali Kettani, “The Control of the Water Cycle.” Scientific American (April 1973): 46; E. K. Berner and R. A. Berner, Global Environment. Upper Saddle River, N.J.: Prentice Hall, 1996, pp. 2–4.]
Where ’s the Water?
Where’s the Water?
(C & R p. 228)
Renewal time: the time required for the complete replacement of the water in a specific part of the cycle.
Flows and Reservoirs• Precipitation: water vapor condenses into tiny
drops that form clouds, eventually fall as rain or snow
• Infiltration: when precipitation soaks into the ground through particles of soil or cracks
• Runoff: precipitation that doesn’t infiltrate moves over the land surface, eventually collecting in streams and rivers
• Evaporation: liquid water transforming into gaseous water (water vapor)
• Sublimation: solid water (ice) transforming directly into gaseous water (without becoming liquid)
Key Parts of The Water CycleOceans
Reservoirs of liquid waterPrecipitation
Water falling on earth in liquid (rain) or solid (snow) form
Evaporation and TranspirationThe drawing of water into the atmosphere from
water bodies (evaporation) or plants (transpiration)
Surface WaterPonds, lakes, and streams
GroundwaterSubsurface water storage
The Water Cycle
Figure 10.1 The water cycle. This illustration shows the flow of water through the water cycle.(C & R p. 227)
The Hydrologic Cycle
Numbers indicate thousands of km3/year
Precipitation
Figure 10.3 Average annual precipitation in the United States.(C & R p. 229)
GroundwaterInfiltration
Precipitation (rainfall and snowfall) seep into the soil
Zone of aerationPore spaces between soil grains contain air and
waterSoil moisture in this zone is known as
Capillary waterZone of Saturation
Pore spaces between soil grains are filled with water
Soil moisture here is Groundwater
Impervious Surface
Groundwater
Groundwater
Capillary water
Groundwater
Figure 10.5 Fate of water that has fallen on the ground as precipitation. This drawing also shows how an aquifer is formed. (C & R p. 231)
GroundwaterAquifer
Underground body of water
Water tablethe boundary between
the unsaturated and saturated zones
Aquifer recharge zonesAreas where
precipitation can infiltrate the soil and add water to the aquifers
Figure 10.6 An aquifer serves as a source of well water. Continued withdrawal of water would eventually deplete the supply if the rate of withdrawal exceeded the rate of recharge.(C & R p. 231)