Essay on Sources of Surface Water |Water Engineering

Essay on Sources of Surface Water!

Source # 1. Streams:

In mountainous regions streams are formed by the run off. The discharge in streams is much in rainy season than other seasons. Those streams which dry up in summer and contain water only during rainfall are known as ‘Raining Streams’. The quality of water in streams is normally good except the water of first run-off. But sometimes run-off water while flowing over ground is mixed with clay, sand and mineral impurities.

All the suspended impurities can be removed in settling tanks up to certain extent, but the dissolved impurities require special treatments. The streams generally flow in valleys and are the main source of water supply to villages of hills which are situated near them.

Source # 2. Lakes:

In mountains at some places natural basins are formed with impervious beds. Water from springs and streams generally flows towards these basins and ‘Lakes’ are formed. The quantity of water in the lakes depends on its basin capacity, catchment area, annual rainfall, porosity of the ground etc.

The quality of large lakes is good than that of the small lakes. But lakes which are situated at high altitudes contain almost pure water which can be used without any treatment. Lake water is available only to those towns and cities which are situated near them, such as Naini Tal in U.P.

Source # 3. Rivers:

Rivers are born in the hills, when the discharge of large number of springs and streams combine together. In mountains the quantity of water in rivers remains small, therefore at such places these are called as small rivers. But as the river moves forward more and more streams combine in it and it increases its discharge.

Therefore rivers grow bigger and bigger as they move forward due to increase in their catchment area. Rivers are the only surface sources of water which have maximum quantity of water which can be easily taken, therefore at the very ancient times the town and cities started developing along the banks of rivers.

Mostly all the cities which are situated near rivers discharge their used water of sewage in the rivers, therefore, much care should be taken while drawing water from the river. River water has self-purification action, due to which it automatically becomes clean in some distance travel from the point of disposal of sewage.

In summer the quality of river water is better than that in monsoon, because in rainy season the run-off water also carries with it clay, silt, sand etc., which make the water turbid. River water should always be used after necessary treatment.

Some rivers are snow-fed and perennial, and have water throughout the year; therefore they do not require any arrangement to hold the water. But some rivers dry up wholly or partly in summer; therefore they require special arrangement to meet the water demand during hot weather.

Source # 4. Ponds:

These are depressions in plains like lakes of mountains, in which water is collected during rainy season. Sometimes ponds are formed when much excavation is done for constructing kaccha houses in villages, embankment for road and railways, and manufacture of bricks. Generally the quantity of water in ponds is very small and contains large amount of impurities.

In the villages mostly the used water How towards ponds and further contaminates its water. The water of ponds is used for washing clothes, animals bathing and drinking. In some backward villages people also take bath in the dirty water of ponds. The water of ponds cannot be used for water-supply purposes due to its limited quantity and large amount of impurities.

Source # 5. Imponded Reservoirs:

Mostly it is found that there is great variation in the quantity of river water during monsoon and summer season. The discharge in some rivers remains sufficient to meet the hot weather demand, but in some rivers the flow becomes very small and cannot meet the requirements of hot weather.

In such cases it becomes essential to store the water for summer season. The water can be stored in the river by constructing a bund, a weir or a dam across the river at such places where minimum area of land is submerged in the water and the reservoir basin remains cup-shaped having maximum possible depth of water.

The construction of imponded reservoirs is not feasible under the following conditions:

(a) When the average annual flow is lower than the average demands, as in this ease no extra water is available to meet the hot weather demand.

(b) When the rate of flow in the streams in dry season is more than the demand.

While deciding the site for the location of imponded reservoir the following points should be considered:

(i) Site where the width of river is narrow but rapidly widening upstream should be selected, because at this site the length of the dam will be small and at the same time it can store large quantity of water.

(ii) Site where sufficient quantity of water is available should be selected. This will depend on the intensity of rainfall, run off and catchment area.

(iii) As far as possible the site should be such that water can flow simply under gravity from the reservoir to the treatment plant.

(iv) Site should be such that cultivable land, highways, towns, railways and costly estates should not submerge in its reservoir.

(v) At the site, bed soil should not contain soluble salts, minerals which may affect the quality of water.

(vi) Watershed should be free from swampy areas; otherwise microorganism will grow inside the water and will make its treatment very difficult.

(vii) Site should be such that useful construction materials for the construction of dam and appurtenant should be available nearby.

(viii) The reservoir area in the flood zone should contain little marshland. Important roads, rails should not pass through them otherwise it will be very costly to divert them.

(ix) The reservoir area should not have thick forests or developed towns, because the construction of dam will require the shifting of town and cutting of forest, which will be very costly affair.

(x) The topography should be favourable for sites of spillway and construction of aqueduct or pipe line.

Source # 6. Stored Rain Water:

At some places where neither ground water nor surface water is easily available, the only way is to store the rainwater in cisterns or tanks from roofs of buildings. The rain water from roofs and pucca courtyards is collected in water-tight tanks with the help of channels. Water stored in this way is limited and can never be utilized for water supply schemes on large scale.