What are the types of surface waters?
Impounding Reservoirs
Storage or impounded reservoirs are created by construction of a solid barrier (i.e., dam, weir, or barrage) across a flowing river or stream at places where minimum area of land is submerged in the water and the reservoir basin remains cup shaped with a maximum depth of water.
Impounding reservoirs are constructed across rivers, which are not able to provide the required quantity of water all year round. There are three essential parts of a reservoir: (1) a dam to hold the water back, (2) a spillway through which excess stream flow may discharge, and (3) gate chamber containing the necessary values for regulating the flow of water from the reservoir. Impounding reservoirs generally provide a fairly good quality of water.
The water is usually clear, soft, and palatable and ranks next to rainwater in purity. Contamination may occur from human and animal activities; therefore, the catchment area of an impounding reservoir should be free from human and animal intrusion.
Rivers and Streams
Rivers provide a dependable supply of water and streams to a less extent. However, rivers and streams are easily prone to gross pollution and quite unfit for drinking unless properly treated for impurities and pathogens.
The general belief that mountain streams are very pure water is often untrue. Even if there is no human habitation or cattle, there is a possibility of contamination from wild animals.
Tanks, Ponds, and Lakes
Tanks are large excavations in which surface water is stored. They are common in developing countries where they are an important source of water supply. Tanks are prone to a high level of contamination except they are specially protected by construction of elevated platforms, which limit human and animal contacts.
The tank can be subjected to sand filtration and some chlorination to improve their quality. Lakes and ponds arise when the depression of the earth’s surface with impervious beds is filled with water.
Lakes are formed when the size of the depression is very big and ponds are formed when the depression is small; while the former are generally formed in hilly areas, the latter are formed in plain areas.
Ponds are also formed when soil is excavated for constructing earthen dams, embankments, and canals. The quantity of water in the lakes depends upon its basin capacity, soil properties, porosity, annual rainfall, and catchment area.
For public supply, the quantity of water in lakes and ponds is very small and is only suitable for small towns in hilly areas. In some cases, due to the absence of other sources, large lakes become the main and permanent source of water supply.
The quality of water in large lakes is better than that of small lakes. At high altitudes, the water available will be purer due to self-purification action of bleaching, removal of bacteria, and sedimentation of suspended matter. However, stagnation of the water promotes growth of algae, weed, and vegetables with resultant bad smell and taste and impurities.
Groundwater
Groundwater results from rainwater percolating into the ground and constitutes the cheapest and most practical means of providing water to small communities. It has advantages over surface water due to the fact that the ground itself provides an effective filtration medium.
In addition, groundwater is likely to be free from pathogenic agents, therefore usually requiring no treatment. The supply is almost certain even in dry season, but the yield might be reduced.
Furthermore, it is less subject to contamination than surface water. Some disadvantages have been associated with groundwater and these include high mineral content like salts of calcium, magnesium, and iron, which renders it hard. It is also required for the water to be pumped for the purpose of access. The usual groundwater sources are wells and springs.
Wells have been classified into (1) shallow and deep wells and (2) dug and tube wells. It is important to note that once groundwater is contaminated, it is difficult to restore.
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