4The Water Cyclewater molecules travel between Earth’s surface & the atmosphere continuouslyevaporation, condensation, & precipitationinvolves all bodies of water (especially the ocean), clouds, soil, plants through transpiration, etc.
7Distribution 71% of Earth’s surface is covered with water of all water 97% is salt water3% is fresh watermost fresh water is frozen in ice caps & glaciersonly a little is actually available for human use (less than 1%)
8This photograph tries to show what an iceberg might look like if you could see the entire thing.
9Surface Water fresh water found in lakes, rivers, streams, & wetlands has played a vital role in the development of human societiescities, towns, & farms have been built near reliable sources of surface waterprovides drinking water, water for crops, food (fish/shellfish), power for industry, means of transportation
10Rice paddies built to trap water from the monsoon rains.
11River Systemsas streams & rivers move across the land, they form a flowing network of waterfrom above, it looks like the roots feeding the trunk of a treeMississippi, Amazon*, & Nile are the largest systems because of the # of streams that drain into these river systems
14Watersheds the area of land that is drained by a river pollution anywhere in the watershed may end up polluting the riverwater entering a watershed varies throughout the year (seasons, snow melts, droughts, growing crops, etc.)
16Groundwaterfresh water found under the ground that is available for human usesome precipitation flows directly into lakes & rivers while some soaks into the soil & moves down into the rocks beneath – called PERCOLATIONwater moves down until it reaches a level where the rocks & soil are saturated – called the WATER TABLE
17Water Table Levelshas peaks & valleys that match the shape of the landwater table can be close to the surface in wet regions or 100s of meters below the surface in desert regionsalways in flux
18Factors that Cause the Water Table Depth to Vary Amount of rainfallTime between rainfallsSeasonal changesClimateSlope of the ground surfaceExcessive pumping from wells
23Ogallala Aquiferformed at the end of the last Ice Age about 12,000 years agomakes up 1/3 of all groundwater in the U.S.used extensively for irrigation of the Great Plains since the 1940sstarting to show its limits – wetlands are starting to disappearfighting for its preservation
25Porosity pores space between grains can hold air & water
26Pore spaces can also be filled by the cements that hold the rock particles together
27PermeablityThe rate at which water (or other liquids) pass through the pore spaces of a rock
28Permeability RatesWater passes easily through materials with large pore spaces – like sands & gravelsWater passes slowly through siltsClays are considered impermeable – water cannot pass throughSome rocks can be highly porous but have a low permeability rates (like pumice) because the pores are NOT CONNECTED!
29The Recharge Zonethe area of Earth’s surface where water percolated down into the aquiferenvironmentally sensitive areas – any pollution that enters will move into the aquiferwater cannot reach the aquifer in places that are covered with impermeable layers – including buildings & parking lots!people must manage recharge zones
34Wellsif you dig the hole deep enough anywhere on Earth, you will find waterwell water is more reliable than surface water, and usually cleaner because it has been naturally filtered by passing through the rock layers
35Excessive pumping from wells creates a CONE of DEPRESSION by drawing down the water table
36Can the Water Table Survive: Overpumping Overpopulation Urbanization Industrialization