environmental engg -i

7/31/2019 Environmental Engg -I

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The main sources of water

Rain

Surface source :

Oceans,

Rivers and streams ,

ponds & lakes, Storage reservoirs


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Subsurface sources

Springs

Infiltration galleries

Infiltration wells

Wells and tube wells


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Rain water is the purest water in nature.

Physically, it is clear, bright and sparkling.

Chemically, it is very soft water containingonly traces of dissolved solids (0.0005percent).

Being soft, it has a corrosive action on leadpipes.

Bacteriologically, rain water from cleandistricts is free from pathogenic agents.


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Rain water tends to become impure as itpasses through the atmosphere.

It picks up suspended impurities from theatmosphere such as

Dust

Soot and microorganisms

Gases such as carbon dioxide, nitrogen,

oxygen and ammonia.


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Gaseous sulphur and nitrogen oxidesthat use fossil fuels.

React with atmospheric water, formingdilute solution of sulphuric and nitricacid.

Precipitation of these acids (acid rain)

has serious impacts on surface waterquality.


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picks up the characteristics of the surfaceover which it passes.

If water flows across a parking lot, gasoline,oil, and other contaminants may be carriedby or dissolved into the water.


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Dependable supply of water.

Grossly polluted

River water is turbid during rainy season

Clarity of water is no guarantee that the riverwater is safe for drinking


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Water may pick up

fertilizers,

road salts,

radioactivity, andbiological contaminant from farms, as well as

countless other biological, physical, and chemical

pollutants


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Contains dissolved and suspended impurities The bacterial count, including the human

intestinal organisms may be very high.

The impurities of river water are derived fromSurface washings,

Sewage and sullage water,

Industrial and trade wastes, and

Drainage from agricultural areas.


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Natural forces of purification such as

Dilution

Sedimentation

Aeration Oxidation

Sunlight, plant and animal life


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Adequate to supply the water demand of thetown

Reasonably surplus

Compensate losses

Evaluated for drought


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Basin constructed across a river or valley tostore water during excess river flow

Created either across the river or off the

riverWater stored can be used for other purposes


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Quantity of water available

Quality of water

Possibility of constructing a water tightreservoir

Distance of the source from the city

Elevation of the site with reference to theelevation of the city

Source of contamination


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Topography of the valley to decide theheight of dam

Length of dam

Value of the land

Need for displacement of people, wildlife etc


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Geology of the catchment area, dam site,reservoir area

Study the nature of the catchment area,

reservoir area and dam site Presence of permeable strata may account

for high percolation losses


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Based on flow expected once in 3 years

Determined from the contour map of thearea


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Evaporation losses

Absorption loss

Percolation loss


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Natural depression

Contribution by small natural streams andG.W springs

Quantity depends by

Size

Catchment area

Annual rainfall

Geological formation


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Ground water is the cheapest and mostpractical means of providing water to smallcommunities.

Ground water is superior to surface water,because the ground itself provides aneffective filtering medium.


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It is likely to be free from pathogenic agents;

It usually requires no treatment

The supply is likely to be certain evenduring dry season

It is less subject to contamination thansurface water.


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It is high in mineral content, e.g., salts ofcalcium and magnesium which increase thewater hard

It requires pumping or some arrangementto lift the water.


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When ground water comes to the surfaceand flows freely under natural pressure, it iscalled a "spring".

Springs may be of two typesShallow springs - Dry up quickly during

summer months

Deep springs - Do not show seasonalfluctuations in the flowof water


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In some geographic areas, springs constitutean important source of water.

Springs are simpler to exploit, as no

pumping is needed to bring the water to thesurface.

Springs are exposed to contamination.


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Quantity of water

Quality Of water

Location of source

Cost of water supply project

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