Sources of Water

Introduction
After estimating the water requirement for a proposed water supply scheme, the planners must search for the water resources which are able to supply the required amount of water. If the available sources near to the scheme (place where the water is needed) Is of sufficient or suitable, planners should search for sources at far distances and provide arrangement for bringing water from there.
Classification of Sources of Water
The various sources of water available on the earth can be classified in to following two categories.
Category 1 »»» Surface Sources
Category 2 »»» Sub-Surface Sources (Underground Sources)
Surface Sources
Surface Sources are those Sources of water in which the water flows over the surface of the earth or accumulated on the surface of the earth and is thus directly available for water supplies. Following are the different types of the surface sources.

Ponds and Lakes
Streams and Rivers
Storage Reservoirs
Oceans

Ponds and Lakes .
A natural large sized depression formed within the surface of the earth, when gets filled up with water, is known as a pond or a lake. The difference between a pond and a lake Is only that of size, If the size of the depression is comparatively small, It may be termed as a pond, and when the size Is larger it may be termed as a lake. Generally, the surface run-off from the catchment area contributing to the particular lake enters the lake through small drains or streams.
The quality of water in a lake is generally good and does not need much purification. Larger and older lakes however provide comparatively purer water than smaller and newer lakes. Self-purification of water due to sedimentation of suspended matter, bleaching of color, removal of bacteria, etc. makes the lake’s water purer and better. On the other hand, in still waters of lakes and pond, the algae, weed and vegetable growth take place freely, imparting bad smells, tastes and colors of their waters.
The quantity of water available from lakes Is, however, generally small. ¡t depends upon the catchment area of the Lake Basin, annual rainfall, and geological formations. Due to the smaller quantity of water available from them, takes are not considered as principal sources of water supplies. They are, therefore, useful for only small towns and hilly areas. However, when no other Sources are available, larger lakes may become the principal sources of supplies,
Streams and Rivers
Small Steam channels feed their waters to the lakes or rivers. Small steams are, therefore generally not suitable for water supply Schemes, because the quantity of water available in them is generally very small, and they may even sometimes go dry. They are, therefore useful as sources of Water only for small villages especially in hilly regions etc. across them.
Rivers are the most important sources of water for public water supply schemes it is a well-known fact that most of the cites are settled near the rivers, and it is generally easy to find a river for Supplying Water to the city. Rivers may be perennial or non-Perennial Perennial rivers are those in which the water IS available through0 the year. Such rivers are generally fed by rains dung rainy season and by Water springs, snow etc. as the case may be, during dry season, Perennial avers can be used as sources of public supplies directly, whereas the non-perennial rivers can be used as sources of public Supplies by Providing storage on the upstream of the intake Works, The concoction of a dam is generally adopted on a highly non Perennial river and may be adopted even on a perennial river when water is used for multiple uses such as irrigation hydropower etc. The head works, such as a barrage or a Weir, may also
be constructed on those perennial rivers, ere supplies are considerably reduced during dry weather periods. The quality of water obtained from rivers is generally not reliable as it contains large amount of sift, Sand and a lot of suspended matter, the disposal of the untreated or treated sewage into the dyers is further liable to contaminate their waters, The river waters must, therefore be properly analyzed and well treated before Supplying to the public.
A water Supply scheme drawing water directly from a river or a stream may fail to satisfy the Consumer’s demands during extremely low flow, while during high flows; ¡t may again become difficult to carry out its operations due to devastating floods. A barrier in the form of a dam may, therefore sometimes be constructed across the river, so as to from a pool of water on the upstream side of the barrier, this pool or artificial lake formed on the upstream side of the dam is known as the storage reservoir, The quality of this reservoir water is not much different from that of a natural lake. .
The water stored in the reservoir can be used easily not only for water supplies but also for other purposes. Generally, multipurpose reservoirs are planned these days and operated so as to get optimum benefits, The subject of design and planning of dams and reservoirs is a big topic in itself, and is not dealt under this subject. However, its salient features such as : Selection of dam site and types of dam; Storage capacity of reservoirs, Reservoir
sedimentation, Reservoir losses, etc. are however being reproduced here, ,
Selection of a Dam Site,

A suitable foundation must be available.
Length of the dam should be as small as possible.
Suitable site for the spillway should be available.
Materials for construction should be easily available.
Reservoir basin should be reasonably water tight.
Value of the land and property submerged by the reservoir should be as low as possible.
Site should be easily accessible.
Site and the reservoir should be environmentally feasible.

Different kinds of Dams

Earth dams
Rock-fill dams
Solid masonry gravity dams ‚

Storage Capacity of Reservoirs.
Whatever be the size or the use of a reservoir, the main function o it is to store water, and thus to stabilize the flow of water. Therefore the most important physical, characteristic of the reservoir is its storage capacity. Storage capacity of a reservoir in a given dam site is calculated and analyzed using Area- Capacity diagrams, Fixing a storage capacity for a given data of available water and the particular requirement of water is done by different methods such as Mass Flow Curves,
Derivation of Reservoir Capacity — Mass Flow Curves

A Mass flow curve is a curve of cumulative reservoir inflow against time and as such it rises continuously. Any point on the curve indicates the total inflow from the beginning of the period up to the given time. The slope of the tangent to the Mass Curve is a measure of Inflow at that time. A steeply rising curve indicates high rate of inflow. Mass Curve of Demand representing accumulated outflow is also plotted. For a uniform rate of demand the Demand Curve is a straight line, rising from the origin.
Reservoir Losses

Evaporation losses
Absorption losses
Percolation losses or Reservoir Leakage

Intakes for Collecting Surface Water
Whenever the water Is withdrawn from a surface water source such as a lake, river or a reservoir, and the entrance of the withdrawal conduit (pipe) Is riot an integral part of the darn or any other related structure, then an intake structure must be conducted at the entrance to the withdrawal conduit (pipe). The water collected at the intake structure could then be taken by gravity flow (if possible) or by pumping up to the treatment plant. It is very important to construct the intake structure site at a proper location. The factors governing the location of an intake structure are as follows,

As far as possible the Intake should be near the treatment plant
The intake must be located in the purer zone of the source.
The Intake must never be located at the downstream or in the vicinity of a point of disposal of waste water
The intake should paver be located near navigation channels
The intake site should be such that it will permit grater withdrawals of water, if required in the future.
The intake must be- located at a place where it can draw water even during driest periods
The intake site should be easily accessible even during floods and should not get flooded.
In meandering rivers, the intake should not be located on curves as much as possible. Even if they have to be located on curves It should be located on the concave banks.