Precipitation in North America

Figure 9.5

Potential Evapotranspiration

Figure 9.6

Figure 9.10

U.S. Drought Monitor

Water Year: October ~September

A commonly used drought index: P/PET

Sample Water Budget

Figure 9.11

Sample Water

Budgets

Figure 9.12

Annual River Runoff

Figure 9.13

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  

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

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.

Forming a Cone of Depression

Groundwater Characteristics

Figure 9.17

Groundwater and Streamflow

Figure 9.19

Humid climate (e.g. Mississippi River) Dry climate (e.g. Colorado River)

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

Water Supply in the United States  

Instream, Nonconsumptive, and Consumptive Uses 

Desalination 

Future Considerations

Our Water Supply 

U.S. Water Budget

Figure 9.20

Navigation, hydroeclectric power, fishing, recreation etc.

Water quality changes:

Toxic pollutantsTo much nitrogenHigher temperature

Water Withdrawal by Sector

Figure 9.21