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Chapter: Environmental Engineering - Sources of water supply

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Classification of sources of water supply

Classification of sources of water supply
The various sources of water available on earth can be classified into the following two categories. 1. Surface sources 2.Sub surface source

CLASSIFICATION OF SOURCES OF WATER SUPPLY

 

The various sources of water available on earth can be classified into the following two categories

PRECIPITATION

Surface sources such as

1.Lakes(natural)

2.Streams and Rivers

3.Storage(impounded)reservoir

4.Oceangenerally not used for water supplies at present

 

Sub surface source ssuch as

1.Springs

2.Infiltration galleries

3.Infiltration wells

4.Wells&Tubewells(Borewells)

 

SURFACE SOURCES are those sources of water in which water flows over the surface of the earth and is thus directly available for water supplies

 

NATURAL PONDS AND LAKES: The quantity of water available from pond or lake is however generally small though they are not considered as principal sources of water supply. It depends on the catchment area of the Lake Basin, annual rainfall and geological formations.

 

The quality of water in lake is generally good and does not need much purification. Larger and older lakes however provide comparatively pure water then smaller and new lakes.

 

Self purification of water due to sedimentation of suspended matter bleaching of colour, etc… makes the lake water pure and better when compared to stream or river waters.

 

STREAMS AND RIVERS: The quantity or discharge of the streams is generally low, sometimes even go dry in summer season. Therefore they may be considered as source of water supply only for small villages. The quality of water in streams is normally good except the first runoff. But sometimes runoff water while flowing over the ground is mixed with silt, clay, sand and other mineral impurities. This can be removed in a sedimentation basin upto certain extent.

 

(Rivers are formed when the discharge of large number of springs and streams. Combine together. Rivers (Perennial) are the most important sources of water for public w.s.s. Therefore most of the cities are situated on the banks of the rivers the rivers may be perennial or non-perennial (seasonal). Perennial rivers flow throughout the year getting their waters during summer from snow and from rain in winter. Perennial rivers may be considered as water supply sources directly where asnon perennial rivers can be used as public water supplies by providing storage barriers across these rivers.

 

IMPOUNDED RESERVOIRS: During summer the water which is flowing in the river may not be sufficient to feed the town and on the other hand during rainy season it may be difficult to operate due to flood waters. Therefore hydraulic structures are constructed across these river valleys forming impounded reservoirs.

 

The quality of water in these reservoirs is not much different from that of lake water while top waters prove to develop algae, bottom layers of water may be high in turbidity Co2, iron and manganese and on occasions H2S.

 

UNDER GROUND SOURCES (OR) SUB-SURFACE SOURCES

 

They are nothing but sub-surface sources with regard to their quantity and quality aspect rainwater percolating into the ground and escaping beyond the reach of vegetation and either collecting in underground basins or flowing underground in sub-surface streams constitutes a ground water source.

 

Generally ground water is clear and colorless but is harder than the surface water of the region in which they occur. In lime stone formation, ground water is very hard and dispositive nature in pipe lines. In granite formations, they are soft. The water as it seeps down comes in contact with organic and inorganic substances during its passage through the ground and acquires chemical characteristics representative of the starter it passes. Bacteria logically, ground water is much better than surface water except where sub-surface pollution exists.

 

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