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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