Water Resources

Section #1:Chapter 11

Water

•“The Water Planet” - abundant

•found in three phases•fresh & salt•essential to life on Earth•renewable resource

The Hydrologic Cycle

The Water Cycle

• water molecules travel between Earth’s surface & the atmosphere continuously

• evaporation, condensation, & precipitation

• involves all bodies of water (especially the ocean), clouds, soil, plants through transpiration, etc.

The Water Cycle

Distribution

• 71% of Earth’s surface is covered with water

• of all water– 97% is salt water– 3% is fresh water

• most fresh water is frozen in ice caps & glaciers

• only a little is actually available for human use (less than 1%)

This photograph

tries to show what an iceberg might look like if you could see the entire

thing.

Surface Water• fresh water found in lakes, rivers,

streams, & wetlands• has played a vital role in the

development of human societies • cities, towns, & farms have been

built near reliable sources of surface water

• provides drinking water, water for crops, food (fish/shellfish), power for industry, means of transportation

Rice paddies built to trap water from the monsoon

rains.

River Systems

• as streams & rivers move across the land, they form a flowing network of water

• from above, it looks like the roots feeding the trunk of a tree

• Mississippi, Amazon*, & Nile are the largest systems because of the # of streams that drain into these river systems

Watersheds

Watersheds

Watersheds

• the area of land that is drained by a river

• pollution anywhere in the watershed may end up polluting the river

• water entering a watershed varies throughout the year (seasons, snow melts, droughts, growing crops, etc.)

Watershed Area

Groundwater

• fresh water found under the ground that is available for human use

• some precipitation flows directly into lakes & rivers while some soaks into the soil & moves down into the rocks beneath – called PERCOLATION

• water moves down until it reaches a level where the rocks & soil are saturated – called the WATER TABLE

Water Table Levels

•has peaks & valleys that match the shape of the land

•water table can be close to the surface in wet regions or 100s of meters below the surface in desert regions

•always in flux

Factors that Cause the Water Table Depth to Vary

• Amount of rainfall

• Time between rainfalls

• Seasonal changes

• Climate

• Slope of the ground surface

• Excessive pumping from wells

Water Table Fluxuations

Water Table Fluxuations

Aquifers

•an underground formation that contains groundwater

•most consist of materials such as rock, sand, & gravel that have lots of spaces where water can accumulate, like water filling up a sponge

Ogallala Aquifer

Ogallala Aquifer

•formed at the end of the last Ice Age about 12,000 years ago

•makes up 1/3 of all groundwater in the U.S.

•used extensively for irrigation of the Great Plains since the 1940s

•starting to show its limits – wetlands are starting to disappear

•fighting for its preservation

Porosity = % of pore space

Porositypores space between grains can hold

air & water

Water

Pore spaces can also be filled by the cements that hold the rock

particles together

Permeablity

The rate at which water (or other liquids) pass through the pore spaces of a rock

Permeability Rates• Water passes easily through materials

with large pore spaces – like sands & gravels

• Water passes slowly through silts• Clays are considered impermeable –

water cannot pass through• Some rocks can be highly porous but

have a low permeability rates (like pumice) because the pores are NOT CONNECTED!

The Recharge Zone

•the area of Earth’s surface where water percolated down into the aquifer

•environmentally sensitive areas – any pollution that enters will move into the aquifer

•water cannot reach the aquifer in places that are covered with impermeable layers – including buildings & parking lots!

•people must manage recharge zones

Recharge

Recharge -- Water Travel Time

Confined vs. Unconfined Aquifers

Artesian Formation

Wells

•if you dig the hole deep enough anywhere on Earth, you will find water

•well water is more reliable than surface water, and usually cleaner because it has been naturally filtered by passing through the rock layers

Excessive pumping from wells creates a

CONE of DEPRESSION by drawing down the water table

Can the Water Table Survive:

OverpumpingOverpopulation

UrbanizationIndustrialization