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Water Resources. Hydrologic Cycle. Hydrosphere: All the water at or near the surface of the earth Amount of water essentially constant and moves between different reservoirs 100 million billion gallons move through Hydrologic Cycle

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hydrologic cycle
Hydrologic Cycle
  • Hydrosphere: All the water at or near the surface of the earth
  • Amount of water essentially constant and moves between different reservoirs
  • 100 million billion gallons move through Hydrologic Cycle
  • Oceans account for ~96%, Fresh water lakes and streams for only 0.016% of all water
hydrologic cycle4
Hydrologic Cycle

Thousands of km3/yr





ground water
Ground water
  • 22% of all fresh water occur underground
  • Aquifer: Underground formation that holds and yields water
  • A good aquifer needs to be both porous and permeable
porosity and permeability
Porosity and Permeability
  • Porosity: Proportion of void space: pore space, cracks, vesicles
    • Gravel : 25-45% (1K - 10K), Clay: 45-55%(<.01)
    • sandstone: 5-30% (0.3 - 3), Granite: <1 to 5%(.003 to .00003)
    • higher porosity in well rounded, equigranular, coarse grained rocks
  • Permeability: Measure of how readily fluid passes through a material
    • Depends on the size of the pores and how well they are interconnected
    • Clay has high porosity but low permeabilty

Less porosity

porosity permeability

Clay 45-55% <0.01 m/day

sand 30-52% 0.01 - 10

gravel 25 - 45% 1000 to 10,000

subsurface water
Subsurface Water
  • Zone of Aeration or Vadose Zone or Unsaturated Zone: Overlies Phreatic Zone. Pore spaces partly filled with water. Contains soil moisture.

Saturated Zone

  • Zone of Saturation or Phreatic Zone: saturated zone overlying impermeable bed rock. Water fills all the available pore spaces
  • Water Table: top of the zone of saturation where not confined by impermeable rock
Water table follows the topography but more gently
  • Intersection of water table and ground surface produces lakes, streams, spring, wetlands…
  • Ground water flows from higher elevation to lower, from areas of lower use to higher use, from wet areas to dry areas.
darcy s law
Darcy’s law
  • Hydraulic Gradient: Slope of the ground water table
  • Rate of flow is proportional to the hydraulic gradient
  • Recharge: Process of replenishment of Ground Water by infiltration, migration and percolation
  • Aquifer: A rock that holds enough water and transmits it rapidly. Porous and Permeable. Sandstone and Coarse Clastic Sedimentary rocks make good aquifers
  • Aquitard and Aquiclude: Rocks of low and very low permeability e.g., shale, slate
  • Perched water table: Local aquifer in Vadose Zone
confined and unconfined aquifer
Confinedand Unconfined Aquifer
  • Unconfined Aquifer: open to atmosphere e.g., overlain by permeable rocks and soils
  • Confined aquifer: sandwiched between aquitards
    • Artesian System: Water rises above the level in aquifer because of hydrostatic pressure
  • Potentiometric surface: Height to which water pressure would raise the water.

Artesian System: Water rises above the level in aquifer because of hydrostatic pressure

  • Potentiometric surface: Height to which water pressure would raise the water.

Consequences of Ground Water Withdrawal

  • Lowering of Water Table
    • Cone of depression: Circular lowering of water immediately around a well
consequences of ground water withdrawal
Consequences of Ground Water Withdrawal
  • overlapping cones of depression causes lowering of regional water table
  • Water mining: rate of recharge too slow for replenishment in human life time
consequences of ground water withdrawal18
Consequences of Ground Water Withdrawal….
  • Compaction and Subsurface subsidence
    • Building damage, collapse
    • flooding and coastal erosion e.g., Venice, Galveston/Houston (80 sq km permanently flooded), San Joaquin Valley (9m subsidence)
    • Pumping in of water no solution
the high plains aquifer
The High Plains Aquifer
  • The High Plains is a 174,000-square-mile area of flat to gently rolling terrain that includes parts of eight States from South Dakota to Texas.
  • moderate precipitation but in general has a low natural-recharge rate to the ground-water system.
  • Unconsolidated alluvial deposits that form a water-table aquifer called the High Plains aquifer underlie the region.
  • Since early 1800s, irrigation water pumped from the aquifer has made the High Plains one of the Nation’s most important agricultural areas.
  • the intense use of ground water for irrigation has caused upto 100m decline in water-level in parts of Kansas, New Mexico, Oklahoma, and Texas.

Changes in ground-water levels in the High Plains aquifer from before ground-water development to 1997. (V.L. McGuire, U.S. Geological Survey, written commun., 1998.)


The Gulf Coastal Plain Aquifer System

  • The Gulf Coastal Plain aquifer system underlie about 290,000 square miles extending from Texas to westernmost Florida, including offshore areas to the edge of the Continental Shelf.
  • Water withdrawals from the aquifer system have caused
    • lowering of hydraulic heads at and near pumping centers;
    • reduced discharges to streams, lakes, and wetlands;
    • induced movement of saltwater into parts of aquifers that previously contained freshwater;
    • and caused land subsidence in some areas as a result of the compaction of interbedded clays within aquifers.

Saltwater Intrusion

    • upconing below cone of depression
    • Aquifer below Brooklyn, NY destroyed
    • Serious problem in Gulf Coast and California

Salt water incursion in caostal aquifer

extent of salt water incursion in miami dade
Extent of salt water incursion in Miami-Dade

Salt water intrusion in Miami-Dade

    • forms in areas with abundant water and soluble bedrock (gypsum or limestone)
    • collapse follows ground water withdrawal



Dripstones in a cavern

urbanisation and ground water
Urbanisation and ground water
  • Loss of Recharge
    • Impermeable cover retards recharge
    • Filling of wetlands kills recharge area
  • Well planned holding pond can help in recharging ground water
water quality
Water Quality
  • Most freshwater contain dissolved substances
  • concentrations are described in ppm or ppb
  • TDS=Total Dissolved Solids
    • 500 to 1000 ppm for drinking water
    • 2000 ppm for livestock
    • some solids (e.g., Iron, Sulfur) more harmful than others (e.g. calcium)
    • synthetic chemicals can be toxic at ppb level
  • Radioactive elements pose special hazard
    • Uranium, Radium, Radon
hard water
Hard water
  • Hard Water:
    • Common in limestone country
    • contains dissolved Ca and Mg; problematic if >100 ppm
    • problem with soap
    • leaves deposits in plumbing and in appliances
    • can be cured with water softener typically ion exchange through zeolites
water use in us
Water Use in US
  • 4200 billion gallons of precipitation
  • 2750 billion gallons lost by evaporation
  • 1400 billion gallons available for consumption
  • Biological need : 1 gal/person/day
  • US consumption: 1800 gal/person/day = 400 billion gallons per day for the entire US
Offstream Use: water diverted from source e.g.,for irrigation or thermal power generation
    • Consumptive: water used up
      • For farming, drinking or lost by evaporation
  • Instream: water returns to flow: e.g., for hydroelectric power generation
water use contd
Water Use …contd
  • Main Uses:
    • Thermoelectric Power
      • Surface: Ground water = 67:33
      • Consumed 2%, Return Flow 98%
    • Irrigation
      • Surface: Ground water = 63:33
      • Consumed 56%, Loss 20%, Return Flow 24%
    • Industrial
      • Surface 67% (saline 12%), Ground water 15% (1% saline), Public Supply 19%
      • Consumption 15%, Return Flow 85%
    • Domestic
      • Public Supply 86%, Ground Water 13%, Surface 1%
      • Consumption 23%, Return Flow 77%
irrigation and ground water
Irrigation and Ground water
  • Thus, irrigation is the major consumer of ground water
  • Western states are the major drawers of ground water causing serious environmental problems

Total withdrawal increased from 1950 to 1980 and has held steady since then although population has increased by 16%

  • Withdrawal for thermoelectric power generation 190,000 Mgal/day: largest of any other category
  • Higher water price, more public awareness, conservation, better farming and industrial techniques will keep water demand in check
water rights
Water Rights
  • Riparian Rights (Eastern USA):
    • Every landowner can make reasonable use of lake or stream or water flowing through or bordering his property
    • Municipalities have the right of eminent domain: at times of scarcity, cities get their requirement first
    • Sale of riparian rights allowed in some states
    • Practical in regions of plentiful water
law of prior appropiation
Law of Prior Appropiation
  • First come, first served
  • Settlers can lay claim to certain amount of water which will be honored for perpetuity
  • The oldest claim are honored first and any left over goes to the next claimant and so on..
  • Los Angeles bought up water rights in 1900 from areas far and wide, some even from Arizona. Now people in those areas are very unhappy about the arrangement

Story of Colorado River

The Colorado River flows through Utah to Lake Powell, thence through the northwest corner of Arizona to Lake Mead. From Hoover Dam it flows southward to Mexico forming the border between Nevada, California and Arizona, and yielding major diversions to central Arizona and southern California. The river is the lifeblood of the southwestern US and its development and management have been the focus of attention by the member states for more than a century. Waters of the Colorado River System have been apportioned by a treaty with Mexico, compacts, and a Supreme Court decree to the seven basin states.

Colorado River basin

colorado river compact
Colorado River Compact
  • The Colorado River Compact of 1922 divided the use of waters of the Colorado River System between the Upper and Lower Colorado River Basin.
  • It apportioned in perpetuity to the Upper and Lower Basin, respectively, the beneficial consumptive use of 7.5 million acre feet (maf) of water per annum.
  • It also provided that the Upper Basin will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 75 maf for any period of ten consecutive years.
  • The Mexican Treaty of 1944 allotted to Mexico a guaranteed annual quantity of 1.5 maf. These amounts, when combined, exceed the river\'s long-term average annual flow.
  • These apportions were decided during a particularly wet climatic period. At present, the flow in Colorado does not add up to all the apportionments

Within Colorado water allocations are based on the Doctrine of Prior Appropriation or the First-in-Time, First-in-Right Doctrine. This doctrine is found in most arid states because when there is too little water to satisfy all users, sharing of the remaining water would be of little value to any user. But a large part of the Colorado river water is diverted to Los Angeles on the basis of this doctrine

  • Shift water-hungry crops to regions with more rainfall
  • Use drip irrigation to reduce evaporation loss
  • Use pipes to reduce transport loss
  • Water lawns in morning and evening or opt for no lawn
  • Direct storm water in recharge basins
interbasinal transfer
Interbasinal transfer
  • Transfer water from water-surplus regions to water-deficient regions
    • California : Los Angeles aqueduct moves 150 million gallons/ day from east of Sierra Nevada to LA
    • New York: Water supply to NYC from Finger Lakes region
    • political problems
  • Desalination
    • Filtration, distillation
    • Expensive, limited