THE WATER CYCLE AND HUMAN USE
THE SUN DRIVES EVAPORATION AND CONVECTION.
ONCE WATER IS EVAPORATED, AIR CURRENTS MOVE THE
MOISTURE.
AS AIR RISES, IT COOLS, AND PRECIPITATION CAN
OCCUR.
WATER CONDENSES ON VERY FINE PARTICLES OF DUST.
AS THE PARTICLES GROW, THEY CAN BECOME HEAVIER
THAN AIR, AND RAIN CAN OCCUR.
OR, IF TEMPERATURES ARE LOW ENOUGH, SNOW CAN
OCCUR.
ONCE, RAIN OR SNOW FALLS, GRAVITY STARTS THE FLOW
OF WATER BACK TO THE OCEAN.
THE AVERAGE SURFACE HEIGHT OF LAND IS 875 METERS,
WHICH IS ABOUT 2700 FEET. THIS FLOW OF WATER CAN
CONTRIBUTE TO THE PROCCES OF WEATHERING AND
EROSION.
MOST GOES INTO GROUND WATER, AND THE REMAINING
FLOWS BACK TO THE OCEAN IN THE FORM OF SURFACE
WATER.
SUPPLIES OF WATER EXIST IN DIFFERENT
PARTS OF THE WORLD AS SURFACE WATER
AND GROUND WATER.
THESE SUPPLIES ARE BASED ON CLIMATE AND
NATURAL GEOGRAPHY.
THESE SUPPLIES CAN CHANGE BASED ON
CHANGES IN CLIMATE AND HUMAN
INTERVENTION.
FOR EXAMPLE, DURING THE LAST ICE AGE
MUCH OF AFRICA WAS UNDER A DROUGHT.
AREAS THAT WERE RAINFOREST BECAME
SAVANAH.
A LARGE PERCENTAGE OF FRESH WATER IS
TIED UP AS ICE.
ALMOST 90% OF THIS IS PART OF THE
ANTARTIC ICE CAP.
10% IS TIED UP IN THE GREENLAND ICE SHEET.
THE REMAINDER IS IN GLACIERS.
GLACIERS AND SNOW CAPS PLAY A MAJOR
ROLE IN WATER SUPPLIES IN MANY PARTS OF
THE WORLD, ESPECIALLY ASIA AND NORTH
AMERICA.
FOR EXAMPLE, MUCH OF THE WATER IN
WESTERN U.S. RIVERS DEPENDS ON MELT
RUNOFF DURING SUMMER MONTHS.
THE AMOUNT OF WATER TIED UP AS ICE HAS CHANGED
OVER GEOLOGICAL TIME.
RIGHT NOW, 2.5% OF THE WATER, WHICH IS 80% OF THE
FRESH WATER IS ICE.
IF ALL THE ICE MELTED, THE SEA LEVEL WOULD CHANGE
BY ABOUT 75 METERS (230 FEET).
THIS WOULD PUT THE MOUTH OF THE MISSISSIPPI RIVER
NEAR SOUTHERN ILLINOIS.
20,000 YEARS AGO, SEA LEVEL WAS 400 FEET LOWER.
IN TURN, HUMAN INTERVENTION CAN CHANGE
WATER AVAILABILITY.
HUMANS HAVE HARVESTED SO MUCH FIREWOOD
IN SUB SAHARAN AFRICA THAT THE DESERT HAS
REPLACED MUCH OF WHAT WAS ONCE
GRASSLAND.
DEFORESTATION IS OCCURING IN THE AMAZON
BASIN. 50% OF THE MOISTURE IN THIS AREA
COMES FROM TRANSPIRATION OF MOISTURE
FROM TREES. DEFORESTATION COULD RESULT
IN THE AMAZON BECOMING GRASSLAND IN A
SHORT PERIOD OF TIME.
IN MANY AREAS OF THE WORLD, WATER IS BEING
PUMPED OUT OF AQUIFERS FASTER THAN IT CAN
BE REPLINISHED BY RAINFALL AND INFILTRATION.
THIS CAN QUICKLY RESULT IN WATER NOT BEING
AVAILABLE FOR ANY HUMAN USE IN THOSE AREAS.
ANOTHER EXAMPLE IS THE ARAL SEA. SO MUCH
WATER IS TAKEN FROM RIVERS FEEDING THE ARAL
SEA THAT THE VOLUME HAS DRASTICALLY BEEN
REDUCED. THE OLD SEA BED IS DESERT, AND THE
LAND AROUND THE ARAL IS BECOMING COOLER
AND DRYER (MICRO CLIMATE CHANGE) DUE TO
LOSS OF WATER.
GROUNDWATER: THE WATER HELD IN THE
PORES OF SOIL AND ROCK.
AS YOU DID DEEPER, THE SOIL BECOMES
MOISTER.
THE WATER TABLE IS THE TOP OF THE
SATURATED ZONE.
THE WATER TABLE TENDS TO FOLLOW THE
TOPOGRAPHY OF THE LAND.
HOW DOES WATER BECOME GROUNDWATER?
FIRST, IT HAS TO SOAK INTO THE GROUND.
THIS HAPPENS WHEN IT RAINS.
SOME OF THE WATER SOAKS INTO THE
GROUND, AND SOME OF THE WATER BECOMES
RUNOFF.
RUNOFF IS DETERMINED BY THREE FACTORS:
1. AMOUNT OF RAIN
2. TYPE OF SURFACE
3. SLOPE OF LAND
THESE SAME FACTORS WILL DETERMINE HOW
MUCH WATER SOAKS INTO THE GROUND.
SOME SURFACES WILL BE MUCH MORE PERMEABLE
THAN OTHERS.
A PERMEABLE SOIL HAS PORES THAT ARE
CONNECTED THAT WATER CAN FLOW THROUGH.
A MATERIAL LIKE GRANITE WITH NO CRACKS
WOULD BE IMPERMEABLE.
IF YOU HAD PLENTY OF TIME AND DUG DOWN INTO THE
GROUND, THE SOIL WOULD GET WETTER AND WETTER THE
DEEPER YOU DUG.
IF YOU DUG DEEP ENOUGH, THE SOIL WOULD BE SO WET
THAT IT WOULD NOT HOLD ANY MORE WATER.
WE SAY THAT THIS SOIL IS SATURATED.
THE TOP OF THE SATURATED ZONE IS THE WATER TABLE.
IF THE GROUNDWATER IN THE SATURATED ZONE COVERS A
LARGE AREA, WE CALL THIS AN AQUIFER.
SOME AQUIFERS ARE HUGE.
NOTE: IF THE WATER TABLE ON THE SURROUNDING
LAND IS HIGHER THAT A STREAM, FLOW OF
GROUNDWATER INTO THE STREAM WILL KEEP THE
STREAM FLOWING BETWEEN RAINS.
IDEALLY, IF YOU ARE DEPENDING ON GROUND WATER
FOR PERSONAL WATER SUPPLY, YOU WOULD LIKE TO
HAVE A WELL DRILLED IN A VERY TRANSMISSIVE
GEOLOGIC FORMATION.
IF THE FORMATION IS NOT VERY TRANSMISSIVE, A MUCH
DEEPER WELL WOULD HAVE TO BE DRILLED.
WATER HAS A VERY LONG RESIDENCE TIME IN AQUIFERS.
WATER CAN REMAIN IN AQUIFERS FROM THOUSANDS OF
YEARS TO HUNDREDS OF THOUSANDS OF YEARS.
WHAT THIS MEANS IS THAT POLLUTION AND WASTES THAT
HAVE BEEN DUMPED ON THE GROUND IN THE LAST
CENTURY MAY JUST BE REACHING AQUIFERS.
A GOOD EXAMPLE OF AQUIFER CONTAMINATION IS THE USE
OF MTBE IN GASOLINE AS A MEANS OF REDUCING
HYDROCARBON PARTICULATES AND SMOG.
PARTS OF CALIFORNIA ENDED UP WITH GROUND WATER
CONTAMINATION AS A RESULT.
THE OGALLALA AQUIFER COVERS MOST OF THE GREAT
PLAINS AND EXTENDS FROM SOUTH DAKOTA TO TEXAS.
THERE IS A LARGE AQUIFER UNDER MEXICO CITY.
AQUIFERS SUPPLY WATER TO MANY PEOPLE IN THE WORLD.
THE PROBLEM IS THAT IF YOU TAKE OUT WATER FASTER THAN
WATER GOES IN, YOU CAN DRAIN THE AQUIFER.
THIS IS HAPPENING IN MEXICO CITY AND WITH THE OGALLALA
AQUIFER.
IN FLORIDA, SOME OF THE GROUND WATER FLOWS THROUGH
UNDERGROUND CAVES IN THE LIMESTONE.
INCREASE IN SALT LEVELS IN WATER SUPPLIES CAN
ALSO BE A PROBLEM.
IN ARID REGIONS, SUCH AS THE DESERT SOUTH WEST,
WATER USED FOR IRRIGATION CAN EVAPORATE,
LEAVING SALT DEPOSITS BEHIND.
HIGH SALT LEVELS CAN KILL VEGETATION AND CAUSE
SOILS TO BECOME HADR AND MORE COMPACT.
GROUNDWATER IN COASTAL AREAS CAN BECOME
SALINE WHEN THE FRESH WATER IS PUMPED OUT
FASTER THAN IT CAN BE REPLENISHED.
THIS CAUSES SALT WATER TO INTRUDE FROM THE OCEAN
AND FROM ESTUARIES.
THIS IS A PROBLEM IN EASTERN NORTH CAROLINA.
Concern about aquifer depletion and salt
water intrusion.
REVIEW
1) HOW CAN HUMAN INTERVENTION CHANGE
WATER SUPPLIES?
REVIEW
1)HOW CAN HUMAN INTERVENTION CHANGE
WATER SUPPLIES?
A. PUMPING AQUIFERS DRY
B. CONTAMINATING GROUND WATER
C. USING UP SURFACE WATER FOR
IRRIGATION
D. POLLUTING RIVERS AND STREAMS
E. CHANGING THE CLIMATE BY CUTTING
DOWN TREES
2) WHAT COULD CAUSE SEA LEVEL CHANGE?
2) WHAT COULD CAUSE SEA LEVEL CHANGE?
HOW MUCH WATER IS TIED UP AS ICE. THIS IS
DETERMINED BY CLIMATE (AVERAGE GLOBAL SURFACE
TEMPERATURE).
3) WHAT DRIVES THE WATER CYCLE?
3) WHAT DRIVES THE WATER CYCLE?
ENERGY FROM THE SUN
4) WHAT IS AN AQUIFER?
4) WHAT IS AN AQUIFER?
A LARGE COLLECTION OF GROUND WATER
5) WHAT IS THE WATER TABLE?
5) WHAT IS THE WATER TABLE?
THE TOP OF THE SATURATED ZONE
6) WHAT DETERMINES THE AMOUNT OF RUNOFF AFTER A
RAIN?
6) WHAT DETERMINES THE AMOUNT OF RUNOFF AFTER A
RAIN?
A. HOW MUCH IT RAINED
B. THE SLOPE OF THE LAND
C. THE TYPE OF SURFACE