Surface Sources of Water Supply | Water Engineering

The various surface sources of water supply are briefly described below:

Source # 1. Lakes and Ponds:

A large natural depression or hollow formed in the earth’s surface, which gets filled with water is called a lake. The surface runoff from the catchment area contributing to a lake enters the lake through small natural streams. The ground water may also enter a lake through springs.

The quantity of water available from a lake depends upon its size, catchment area, annual rainfall and geological formations.

The quality of water available from a lake mainly depends upon the characteristics of its catchment. Thus water in a lake would be relatively pure and of good quality if it draws water from uninhabited upland hilly areas free from soluble salts.

On the other hand the water in a lake would be contaminated if it draws from low land areas containing large quantities of soluble salts and other impurities. Moreover, a small lake containing still water may have plenty of algae, weed and other vegetable growth imparting bad smell, taste and colour to the water.

Thus if a sufficient quantity of good quality water is available from a lake then it will be a very useful source of water supply from which water may be supplied without any treatment or with some preliminary treatment. However, if the water in the lake is of relatively poor quality then it should be properly analyzed and treated before supplying to the public.

A pond is a man-made body of standing water smaller than a lake. The ponds are formed by digging of ground and they are filled up with water in rainy season. The quantity of water in a pond is generally very small and often it contains many impurities. As such pond water is generally not suitable for drinking purposes and it can be used only for bathing, washing of clothes or for animals.

Source # 2. Streams or Rivers:

A stream or a river is a natural channel which carries surface runoff received by it from its catchment or drainage basin. It also carries the ground water flow added to it and the runoff resulting from the melted snow. Rivers are the most important sources of water supply.

It is a well-known fact that several big and important cities of the World are situated on the banks of the important rivers. Some of the examples in our country are the cities such as Delhi, Kolkata, Ahmadabad, etc. This is due to the availability of large quantity of water from rivers for water supply throughout the year.

The rivers may be either perennial or non-perennial. Perennial rivers are those in which water is available throughout the year. Such rivers are fed by rains during the rainy season and by melting of snow during the summer season. On the other hand non-perennial rivers are those in which water is not available throughout the year. Generally from perennial rivers water may be utilized directly for public supplies without any arrangement for storage of water.

However, if during dry weather periods the flow in the river is considerably reduced then either the arrangement for raising the water level in the river or the arrangement for storage of water will have to be made to ensure the supply of water in the required quantity. This may be achieved either by constructing a weir or barrage, or by constructing a dam and creating a storage reservoir. Evidently non-perennial rivers can be used for water supply only by providing necessary storage arrangements.

Close to the point of origin in the mountains the river water is fairly pure but as the river approaches plains the quality of its water deteriorates considerably, because it picks up lot of suspended matter, clay, silt, etc., and becomes muddy in appearance. Further the disposal of the untreated or even treated sewage into the river is liable to contaminate the river water. As such the river water must be properly analyzed and treated before supplying to the public.

Source # 3. Storage Reservoirs:

The flow rate of a river or natural stream may vary considerably during different periods of a year. It may carry little or no water during dry weather period and may carry huge amount of water during rainy season. Thus if water is drawn directly from a river then during extremely low flows it may not be possible to meet the demands of the consumers, white during high flows there may be operational problems.

As such it is essential to create a storage reservoir or an artificial lake by constructing a dam across the river, which can store the excess water that flows in the river during the periods of high flows for use during the periods of low flows or droughts.

The quality of water in a storage reservoir mainly depends on the quality of the water flowing in the river on which the reservoir is created. As such the water from a storage reservoir also needs to be properly analyzed and treated before supplying to the public.

The storage reservoirs are the main sources of water supply for big cities. However, the storage reservoirs are created not only for water supply but also for other purposes such as irrigation, hydro-power generation, navigation, flood control, etc. A storage reservoir meant for supplying water for more than one purpose is termed as multipurpose reservoir.

Source # 4. Oceans:

Oceans carry huge amount of water which is estimated to be about 94 to 97% of the total quantity of water available on our planet Earth. However, the ocean water being highly saline it cannot be used for water supply unless the excessive salt content of the water is removed. The process of removing salt from water is known as desalination and the salt free water so obtained is known as fresh water. Several methods of desalination have been developed for the conversion of salt water into fresh water.

However, because of the tremendous cost involved, the procurement of fresh water for water supply by desalination of ocean water has not become common. At present it is being adopted only in a few countries of the World such as Israel, Saudi Arabia, etc., where the other sources of water are scarce. Further some of the developed countries such as U.S.A. have also installed a number of desalination plants for obtaining fresh water from the ocean water.