chapter 13 – water resources. water three quarters of our planet is covered by water, but less...
TRANSCRIPT
Chapter 13 – Water Resources
WATER
THREE QUARTERS OF OUR PLANET IS COVERED BY WATER,
BUT LESS THAN 3% OF THE WATER ON EARTH IS FRESH
WATER THAT IS WATER USABLE FOR DOMESTIC, AGRICULTURAL
AND INDUSTRIAL PURPOSES.
WATER IS CRUCIAL FOR MODERN INDUSTRY AND
SOCIETY AS WELL AS EACH INDIVIDUAL: WATER IS USED IN TRANSPORTATION, POWER
GENERATION, FOOD PRODUCTION AND
PROCESSING, MANUFACTURING AND WASTE
DISPOSAL.
OUR BODIES ARE ALSO COMPOSED MAINLY OF
WATER ABOUT 70% OF OUR BODY BY WEIGHT IS WATER. AND WATER IS THE MEDIUM
IN WHICH ALL BIOCHEMICAL REACTIONS OCCUR OR WHERE
THE CHEMISTRY OF LIFE TAKES PLACE.
OUR CONCERNS ABOUT WATER INCLUDE BOTH ITS
QUALITY AND ITS QUANTITY.
FROM PRIMITIVE TIMES UNTIL THE PRESENT,
WATER HAS BEEN ABSOLUTELY ESSENTIAL
TO CIVILIZATION
OUR NEED FOR WATER HAS INCREASED 1000 FOLD
AND, MOST OF THAT INCREASE HAS OCCURRED
DURING THE LAST HUNDRED YEARS.
THE HUMAN BODY ONLY REQUIRES 2 LITER (2
QUARTS) OF WATER A DAY TO PREVENT FATAL
DEHYDRATION.
5,500
5,000
4,500
4,000
3,500
3,000
2,500
2,000
1,500
1,000
500
1900 1920 1940 1960 1980 2000
Wat
er u
se (
cub
ic k
ilom
eter
s p
er y
ear)
Total use
Agricultural use
Industrial use
Domestic use
Year
WATER: WATER OCCURS IN SOLID,
LIQUID AND VAPOR FORMS AND IT IS DISTRIBUTED
AMONG OCEANIC, ATMOSPHERIC, AND
TERRESTRIAL RESERVOIRS.
THE WATER OR HYDROLOGIC CYCLE IS MOVEMENT OF WATER
AMONG OCEANIC, ATMOSPHERIC AND
TERRESTRIAL RESERVOIRS.
EVAPORATION: THE PROCESS BY WHICH WATER CHANGES FROM A LIQUID TO A
VAPOR, AT TEMPERATURE THAT IS BELOW THE BOILING POINT OF WATER.
TRANSPIRATION: THE LOSS OF WATER VAPOR FROM PLANTS.
SUBLIMATION: THE PROCESS BY WHICH WATER CHANGES DIRECTLY FROM A
SOLID TO A VAPOR WITH PASSING THROUGH AN INTERVENING LIQUID
PHASE.
CONDENSATION: THE PROCESS BY WHICH WATER CHANGES FROM A
VAPOR TO A LIQUID.
DEPOSITION: THE PROCESS BY WHICH WATER CHANGES DIRECTLY FROM A
VAPOR INTO A SOLID (ICE CRYSTALS).
PRECIPITATION: THAT PORTION OF THE ATMOSPHERIC WATER THAT RETURNS FROM CLOUDS TO THE
EARTH'S SURFACE IN THE FORM OF RAIN, SNOW, ICE PELLETS, AND HAIL.
THE EVAPORATION CONDENSATION AND
SUBLIMATION DEPOSITION
SEQUENCES PURIFY WATER.
WHEN WATER IS VAPORIZES, THE SUSPENDED AND SOLUBLE
SUBSTANCE, SUCH AS SEA SALTS AND MICROORGANISM ARE LEFT BEHIND. THUS THE CONDENSATE,
WHICH IS ALMOST ENTIRELY FREE OF THOSE SUBSTANCE,
FORMS FRESHWATER PRECIPITATION.
GROUND WATER
MORE THAN 97 PERCENT OF THE UNFROZEN RESOURCES OF FRESH WATER IN THE UNITED STATES IS
CONTAINED IN UNDERGROUND RESERVOIRS. GROUNDWATER
THAT LIES WITHIN 3300 FEET OF THE EARTH'S SURFACE IS
CONSIDERED TO BE ECONOMICALLY RECOVERABLE.
ITS VOLUME IS MORE THAN 9X THAT OF THE GREAT LAKES. !!! AT PRESENT,
ABOUT 50% OF THE UNITED STATES POPULATION OBTAIN
ITS WATER SUPPLY FROM GROUNDWATER SOURCES.
NOT ALL THE PRECIPITATION THAT REACHES THE EARTH'S SURFACE,
HOWEVER FINDS ITS WAY INTO UNDERGROUND RESERVOIRS.
A PORTION OF THE PRECIPITATION EVAPORATES, WHILE THE REMAINDER RUNS OFF INTO STREAMS OR RIVERS.
PRECIPITATION THAT DOES REACH THE EARTH'S SURFACE AND THAT SEEPS
INTO THE GROUND IS CALLED INFILTRATION.
INFILTRATION IS DEPENDED ON :
1. TOTAL AMOUNT OF PRECIPITATION,
2. TOPOGRAPHY.
3. THE CLIMATE AND
4. PHYSICAL PROPERTIES OF THE SOIL.
INFILTRATING WATER TYPICALLY
ACCUMULATES IN TWO ZONES WITHIN THE
UPPER SOIL AND ROCK LAYERS OF THE EARTH'S
CRUST.
IN THE UPPERMOST BAND, THE ZONE OF AERATION, PORES SPACES CONTAIN
BOTH WATER DROPLETS AND AIR.
WATER IN THIS ZONE IS USED BY LAND PLANTS
AND IS EVENTUALLY LOST TO THE
ATMOSPHERE BY EVAPORATION AND
TRANSPIRATION.
UNDER THE INFLUENCE OF GRAVITY, MOISTURE THAT REMAINS IN THE
SOIL IS GRADUALLY DRAWN DOWN AND ACCUMULATES IN A
ZONE OF SATURATION.
PORE SPACES AND FRACTURES IN THE ROCKS AND SOIL IN THE ZONE OF
SATURATION FILL OR SATURATE COMPLETELY
WITH WATER. THIS ZONE OF SATURATION CONSTITUTES
THE GROUNDWATER RESERVOIR.
THE SURFACE THAT SEPARATES THE GROUNDWATER
RESERVOIR AND THE UPPER ZONE OF
AERATION IS CALLED THE WATER TABLE.
LAYERS OF THE GROUNDWATER
RESERVOIR THAT HIGH PERMEABILITY AND
TRANSMIT WATER ARE CALLED AQUIFERS.
LAYERS OF SAND AND GRAVEL ARE GOOD
AQUIFERS, WHEREAS CLAY AND MOST CRYSTALLINE
ROCKS, SUCH AS GRANITE, THAT HAVE LOW
PERMEABILITY ARE POOR AQUIFERS.
GROUNDWATER FLOWS NATURALLY THROUGH
THE PERMEABLE LAYERS TOWARDS VARIOUS
POINTS OF DISCHARGE SUCH AS RIVER LAKE,
AND SEAS.
THE MOVEMENT OF GROUNDWATER IS
EXTREMELY SLOW. A SPEED OF 50 FEET PER YEAR IS TYPICAL, BUT THE SPEED
CAN VARY WIDELY FROM ON LOCATION TO ANOTHER.
POLLUTIONS AND GROUNDWATER
GROUNDWATER MOVES VERY SLOWLY, AND THIS SLOW,
SMOOTH MOVEMENT MIXING AND DILUTION OF POLLUTANTS
IS SEVERELY LIMITED ONCE THEY ARE INTRODUCED INTO A
GROUNDWATER RESERVOIR.
GROUNDWATER DEPLETION
TODAY WE ARE DEPLETING GROUND WATER A RATE THAT
EXCEEDS THE RATE OF NATURAL RECHARGE. SUCH A SITUATION NOW PREVAILS IN THE HIGH PLAINS REGION OF
WESTERN, WHICH ARE IRRIGATED BY WATER THAT IS PUMPED FROM THE GROUND.
BECAUSE EVAPORTRASPIRATION RATES ARE HIGH AND
PRECIPITATION RATES ARE LOW IN THIS AREA, LITTLE SURFACE
WATER IS AVAILABLE FOR GROUNDWATER RECHARGE. AS A
RESULTS WITHDRAWAL IS OCCURRING 50 TIMES FASTER THAN NATURAL RECHARGE.
WYOMING SOUTH DAKOTA
NEBRASKA
COLORADO
KANSAS
OKLAHOMA
NEW MEXICO
TEXAS
0 100Miles
Kilometers
Less than 61 meters (200 ft)
61-183 meters (200-600 ft)
More than 183 meters (600 ft)(as much as 370 meters or 1,200 ft.in places)
0 160
EBBING OF THE
OGALLALA
GroundwaterOverdrafts:
High
Moderate
Minor or none
Acute shortage
Shortage
Adequate supply
Metropolitan regions with populationgreater than 1 million
Withdrawing Groundwater
Advantages Disadvantages
Good source of water for drinking and irrigation
Available year- round
Exists almost everywhere
Renewable if not overpumped or contaminated
No evaporation losses
Cheaper to extract than most surface waters
Aquifer depletion from overpumping
Sinking of land (subsidence) when water removed
Polluted aquifers unusable for decades or centuries
Saltwater intrusion into drinking water supplies near coastal areas
Reduced water flows into streams, lakes, estuaries, and wetlands
Increased cost, energy use, and contamination from deeper wells
Groundwater Depletion
Prevention Control
Waste less water
Subsidize water conservation
Ban new wells in aquifers near surface waters
Buy and retire groundwater withdrawal rights in critical areas
Do not grow water-intensive crops in dry areas
Reduce birth rates
Raise price of water to discourage waste
Tax water pumped from wells near surface waters
Set and enforce minimum stream flow levels
SALT-WATER INTRUSION AND
GROUND SUBSIDENCE
IN REGIONS WHERE FRESH GROUNDWATER IS LOCATED
ADJACENT TO SALTY GROUNDWATER, OVER
WITHDRAWAL OF FRESH WATER CAN CAUSE THE SALT WATER TO MIGRATE TOWARDS THE FRESH
GROUNDWATER RESERVOIR. THE RESULTS IS THAT FRESH WATER IS REPLACED BY SALT WATER IN
THE AQUIFER.
SOMETIMES WHEN GROUNDWATER IS REMOVED, THE EARTH MATERIALS THAT
CONSTITUTE AQUIFERS BECOME COMPACTED, WHICH CAUSES THE OVERLYING LAND
TO SUBSIDE.
WETLANDS:
MARSHES, SPRINGS, AND SOME STREAMS AND LAKES ARE
FORMED WHEN THE WATER TABLE EITHER INTERCEPTS OR
IS HIGHER THAN THE LAND SURFACE IN THOSE
SITUATIONS, NO UPPER ZONE OF AERATION EXISTS.
DURING LONG DRAY SPELLS IN WHICH THE WATER TABLE IS MUCH LOWER THAN A STREAMBED, THE STREAM MAY SUPPLY
WATER DIRECTLY TO THE GROUND WATER RESERVOIR.
STREAMS AND RIVERS
WATER THAT DOES NOT INFILTRATE INTO THE
GROUND OR EVAPORATE REMAINS ON THE SURFACE
OF THE EARTH (AS SURFACE WATER) AND BECOMES
RUNOFF.
THE RUNOFF THEN TRAVELS AS STREAMS AND RIVERS WHICH ARE THE MAJOR
PATHWAYS TAKEN BY THE RUNOFF COMPONENTS OF THE WATER CYCLE IN ITS
JOURNEY FROM THE LAND TO THE SEA.
THE LAND AREA THAT DELIVERS THE WATER TO A COMMON POINT
IS CALLED A DRAINAGE BASIN OR
WATERSHED
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LAKES: DEPRESSIONS IN THE LANDSCAPE
ALLOW LAKES TO EXIST. THE WATER THAT FILLS THOSE DEPRESSIONS
COMES FROM RUNOFF OR GROUNDWATER OR BOTH. SOME
LAKES HAVE RIVERS THAT RUN INTO AND OUT OF THEM, SOME HAVE ONLY
OUTLETS, OTHERS HAVE ONLY INLETS, AND SOME HAVE NEITHER
INLETS NOR OUTLETS. LAKE DEPLETION
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OCEANS: THE SEA, BY FAR THE EARTH'S
LARGEST RESERVOIR OF WATER, IS THE ULTIMATE RECEPTACLE OF THE TERRESTRIAL WATER,
WHETHER IT TRICKLES INTO IT FROM MELTING GLACIAL ICE,
SLOWLY SEEPS THROUGH PERMEABLE ROCK AND SOIL, OR RUSHES DOWN THE COURSES OF
STREAM CHANNELS.
VIEWED FROM SPACE, THE OCEAN IS THE MOST
PROMINENT FEATURE OF THE EARTH'S
SURFACE. IT COVERS 71 PERCENT OF THE TOTAL AREA, TO AN AVERAGE
DEPTH OF 2.5 MILES.
SEAWATER CONTAINS LARGE QUANTITIES OF DISSOLVED SALTS, THE
MOST ABUNDANT OF WHICH ARE SODIUM
CHLORIDE AND MAGNESIUM SULFATE.
WORLD WIDE WATER SHORTAGE
AREAS
WATER USE IN THE UNITED STATES
IRRIGATION TECHNIQUES
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