water resarch and ground water

Dharmesh Mishra130070106127

D - 2

Hydrosphere:Hydrosphere: All the water at or All the water at or near the surface of the earthnear the surface of the earth

Amount of water essentially Amount of water essentially constant and moves between constant and moves between different reservoirsdifferent reservoirs

100 million billion gallons move 100 million billion gallons move through Hydrologic Cyclethrough Hydrologic Cycle

Oceans account for ~96%, Fresh Oceans account for ~96%, Fresh water lakes and streams for only water lakes and streams for only 0.016% of all water0.016% of all water

Thousands of km3/yr

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- - +

• 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: 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

• 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:Zone of Saturation or Phreatic Zone: saturated zone overlying impermeable bed saturated zone overlying impermeable bed rock. Water fills all the available pore spacesrock. Water fills all the available pore spacesWater Table:Water Table: top of the zone of saturation top of the zone of saturation where not confined by impermeable rockwhere 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.

• Hydraulic Gradient: Slope of the ground water table

• Rate of flow is proportional to the hydraulic gradient

Q = KiHere,Q = dischargeK = coefficient of discharge i = 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: An impermeable saucer-shaped stratum. These are non rechargeable.

• 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.

Lowering of Water Table Cone of depression: Circular lowering of

water immediately around a well

Consequences of Ground Water Withdrawal

–overlapping overlapping conescones of depression causes of depression causes lowering of regional water tablelowering of regional water table–Water mining: rate of recharge too slow for Water mining: rate of recharge too slow for replenishment in human life timereplenishment in human life time

Compaction and Subsurface subsidenceCompaction and Subsurface subsidence

• 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

Salt water incursion in coastal aquifer

Saltwater Intrusion

–upconing below cone upconing below cone of depressionof depression

• Sinkholes• forms in areas with abundant water and soluble bedrock (gypsum or limestone)

• collapse follows ground water withdrawal

• Loss of Recharge• Impermeable cover retards recharge• Filling of wetlands kills recharge area

• Well planned holding pond can help in recharging ground water

• 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: • 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

• 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

• 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%

• Thus, irrigation is the major consumer of ground water

• Western states are the major drawers of ground water causing serious environmental problems

• Rights :• 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

• 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