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Precipitation in North America
Figure 9.5
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Potential Evapotranspiration
Figure 9.6
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Figure 9.10
U.S. Drought Monitor
Water Year: October ~September
A commonly used drought index: P/PET
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Sample Water Budget
Figure 9.11
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Sample Water
Budgets
Figure 9.12
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Annual River Runoff
Figure 9.13
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Water resources that lie below the soil moisture root zone. It is the largest potential freshwater resources in the hydrologic cycle.
Groundwater is not an independent sources of water, but recharged by surplus water at surface.
Some groundwater accumulation takes millions of years, thus not easily replenished if overdrawn.
Groundwater Resources
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Surface Water Profile
Root zone
Capillary fringe layer
Ground water
Zone of Aeration:Part of the pore space is filled with air.
Water table
Zone of saturationAll pore space is filled with water
Capillary rise: liquid water rises through fine linear space
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Groundwater Characteristics
Figure 9.17
Aquifer: a rock layer that is permeable to groundwater flow adequate for wells and springs. Confined: bounded above and below with impermeable layers, thus high water pressure and easy to extract. Unconfined: permeable layer on top and impermeable layers below, thus easily recharged from above, but need pump to draw water.
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Forming a Cone of Depression
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Groundwater Characteristics
Figure 9.17
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Groundwater and Streamflow
Figure 9.19
Humid climate (e.g. Mississippi River) Dry climate (e.g. Colorado River)
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Figures FS 9.2.1a, 9.2.3
Two Problems
1. Overdrawn. Due to demand for agricultural, industrial and urban use, groundwater table is decreasing .
2. Pollution: groundwater is recharged with surface water. Pollution of ground water will lead to pollution of groundwater, including, septic tank outflows, land fills, pestcides, herbcides, fertilizers, industrial waste injections etc.
point sources non-point sources
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Water Supply in the United States
Instream, Nonconsumptive, and Consumptive Uses
Desalination
Future Considerations
Our Water Supply
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U.S. Water Budget
Figure 9.20
Navigation, hydroeclectric power, fishing, recreation etc.
Water quality changes:
Toxic pollutantsTo much nitrogenHigher temperature
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Water Withdrawal by Sector
Figure 9.21