Water Resources Engineering Introduction

Elementary Hydrology and Hydrological cycle

Watershed Development, Objectives and Components

Water requirements and its conservation

Sources of Water

Hydraulic structure of storage

Specific terms of Hydrology

Introduction:

Water is an essential requirement for human life, plants and animals. Life cannot exist

without water. It is the natural free gift to the human. It is available in various forms such as

rivers, lakes, streams etc. the demand of water is increase everyday and available sources of

water in form of rain is more or less constant. Therefore now days, it becomes necessary to

maintain, conserve and uses these resources very carefully.

Elementary Hydrology and Hydrological cycle:

Hydrology is referring as a science which deals with rainfall, rainfall losses, surface runoff

and other water surveys.

Hydrology is also referring as deals with behavior and distribution of water in atmosphere

and on the earth.

Hydrological cycle

As shown in fig., Evaporation can be take place from the surface of oceans and clouds

are formed.

Due to condensation of clouds, rain or snow will be fallen over the land.

The few portion of rain or portion of melted snow penetrates into the soil and

remaining portion move across the land as surface runoff.

The surface runoff flows down the slopes and converted into the various streams and

discharge into the river.

The few portion of rain or melted snow which are penetrates into the soil is join with

the underground water and increase the level of underground water.

The river water flows towards the oceans and again evaporation can be take place

from the surface of the oceans as well as the soil moisture which is transpired by

plants and trees enters the atmosphere in form of vapour and this cycle is again

repeated.

The science of hydrology is concerned with the quantity of available water and play

important role in the considerations of water resources.

Hydrological cycle links up all the components of the hydrosphere into the single unit.

Hydrosphere indicates the aqueous envelop of the earth and it includes oceans, rivers,

lakes, well, soil moisture and water vapour in the atmosphere.

Watershed Development, Objectives and Components:

A watershed can be defined as the catchment area of a particular stream or river. It

also refers as the area from where the water to a particular drainage system like a

river, pond and streams comes from.

Catchment area is the area through which the rain water drains from starting point to any

point on the river or stream.

Watershed development refers to the conservation, regeneration and the judicious use

of natural resources like land, water, plants and animals.

People and environment are interdependent to each other. Any change in surrounding

environment directly affects the people living therein.

Watershed development is an art and technique which try to make best possible

balance between natural resources and human being in the environment.

A proper watershed development is very essential in India to meet future requirement

of water for entire year. (As India is an agricultural country and we get rain during

monsoon season only. Hence lots of storage required to meet the requirement for

irrigation as well as domestic purpose.)

Watershed development is comprehensive, integrated approach of land and water

resources management.

The watershed area can be easily found from counter maps.

Objectives of Watershed developments:

Improve the ability of the land to hold the water

To encourage restoration of ecological balance

To conserving soil and water

To control desertification

To promote economic development of village community

To increase crop yield and mitigate the adverse effects of drought on crops and

livestock’s

Components of watershed development:

The main components of watershed development are:

1. Human Resource Development

2. Soil and land management

3. Crop and water management

4. Afforestation

5. Rural energy management

6. Livestock management

Human Resource Development:

Awareness training about watershed development through NGO, VWC (Village water

committee) is provided to farmer.

Soil and land management:

The soil conservation method should be adopted in the catchment area. The soil

erosion can be decreased by intercepting the erosive power of wind, rain etc., by

decreasing the slope of the land, by increasing the roughness of the land surface, by

vegetative covers etc.

Agricultural land should be properly leveled to obtain uniform growth of plants with

optimum quantity of water. Along the slope of the hilly area, contour bunds or terrace

bunds should be constructed at different levels. The deep ploughing by tractor is much

efficient.

Crop and water management:

The crop rotation should be practiced for maintaining fertility of the land for

obtaining maximum yields with minimum supply of water

Water management should be for proper utilization of water by cultivators.

Afforestation:

To reduce soil erosion and greening aspects growth of plantations or tree in water area

or restricted area is preferable

Rural energy management:

By replacing traditional fuel sources, local degradation of environment should be

prevented.

Livestock management:

The livestock (like cows, bullock, sheep, goats etc.) population can be grow by

constructing small structure which provides water availability and by taking steps for

their food and health.

Water requirements and its conservation:

Water requirements for different uses

Domestic purpose Irrigation purpose Hydropower Navigation

Water required for bathing, cooking,

washing etc. for daily uses

Water required for proper growth and

maturity of the crops

Hydropower required to generate the

electricity by using energy of flowing

water

It is the cheapest means of transport

without any consumption of

water

Water required per day per capita Domestic use:

135 lit/day/person Industrial use:

50 lit/day/person Commercial use: 20 lit/day/person

Public utility: 10 lit/day/person

Water losses: 55 lit/day/person

Total: 270 lit/per/person

Certain quantity of water required for every crop

Continuous flow of water required to ensure continuous

production of hydropower

To sustain downstream flow for navigation,

water should be released from

storage reservoir

The water requirement may vary from soil to soil, crop to crop and

from period to period

Total water required for public supplies

=Design population *Per capita

demand*365

Needs for water conservation:

Life on the earth cannot be sustained without water. The demand for fresh water is increased

everyday and an available source of good water is in form of precipitation of rain water only

which is more or less constant. The fresh water available on the land surface is in forms of

rivers, lakes, reservoirs etc. and it is also more or less constant. Therefore, conservation of

fresh water is prime need and hence efforts are required in this area.

Following are general efforts for water conservation

1. New techniques should be found out for reducing water requirements of industries

against high water demand.

2. Local bodies should install water meters to prevent misuse of water. (Like leakage of

water, turn off tape when not in use.)

3. The dumping of sewage in to the natural water resources should be prevented.

4. By reducing evaporation losses, conveyance losses, seepage losses, infiltration losses

etc.

5. To construct a series of small dams on tributary streams.

6. Use drip irrigation method

7. Use lined canals which reduce seepage.

8. Install waste water treatment plant so waste water should be recycled and used for

other purpose.

9. Use such cooling system which uses less water.

Sources of water:

The basic sources of water in India are rainfall or snowfall. About 71% of the earth

surface is covered with water. Total volume of the water in hydrosphere is estimated

to be 1.4 billion km3; out of these 97% are ocean water and 3% fresh water.

The available fresh water is continuously collected, purified and distributed through

hydrological cycle.

The available fresh water comes from:

1. Surface water sources

2. Ground water sources

Surface water sources: 1. Lakes, 2. Ponds, 3. Rivers, 4. Storage Reservoirs.

Lakes:

A natural lake represents a large body of water within the land. The catchment

area of lake is very small and hence quantity of water available is very low. So

lake consider as source of water supply for small towns. The water available

from lake is generally free from undesirable impurities and can be safely used

for drinking purpose.

Pond:

A pond is smaller than a lake and it is manmade body. A pond is formed due

to excessive digging of ground. The quantity of the water stored is very small

compare to lake and contain many impurities, hence not used for drinking

purpose. It only used for washing of clothes, animals etc.

River:

River is important sources of water. The water which does not evaporate it

runs -off the surface through river. Large River is main source of water supply

for many cities. The river water contains silts and suspended impurities so it

required treatment before drinking purpose. The rivers are generally fed by

rains. The dam is constructed over Perennial River when water is used for

multiple uses. The weir is generally constructed on a non perennial river to

store water for water supply in winter and summer season.

Storage reservoirs:

An artificial lakes formed by the construction of dams across a valley or river

is termed as storage reservoir. The water stored in the reservoir can be used for

multiply purpose. The quantity of water stored in the reservoir is same as lake.

It is suitable for drinking and water supply for small cities.

Hydraulic structure of storage (Only dam):

A dam is a hydraulic structure constructed over a river or natural streams to store water on its

upstream side. It is an impervious barrier put across a river.

Gravity dam:

It is a concrete structure with its cross sectional approximately in triangular

shape

The self of the dam resist the forces which are exerted on it

These types of dam is permanent ones, less maintenance and most commonly

used.

It is suitable for any height

The various forces like water pressure, self weight, wave pressure, silt

pressure, uplift pressure, earthquake force etc. are acting on foundation.

Gravity dams are particularly used across narrow openings between hills with

very steep side slopes.

Earthen dam:

It is made of locally available materials such as soils, gravels etc. and

therefore are most economical

These types of dam usually provided for sites where suitable foundation at

reasonable depth may not be available.

Now days, it is more common even for higher height with advance knowledge

of soil mechanics.

Ukai dam or Tapi River is an example of earthen dams.

Rockfill dams:

A rockfill dam is an embankment which uses variable sizes of boulders or

rocks to provide stability and an impervious membrane to provide water

tightness.

Recently composite earth and rockfill type of embankment dams are widely

adopted.

Tehri dam across river Bhagirathi is example of composite dam with height

261m.

Arches dam:

A dam which is constructed in form of an arch supported on abutments is

called arch dam.

It is curved in plan and carries a major part of its water pressure horizontally

to the abutments by arch action. The abutment of an arch should be very

strong.

It is masonry or concrete dam.

It is suitable for V- shaped valley.

Buttress dams:

A buttress dam consists of a number of buttresses or piers dividing the space

into a number of spans.

To store the water between these buttress, panels are constructed of horizontal

arches or flat slabs.

Special Terms:

Precipitation: Condensed water vapour that falls to the earth surface in the form of

rain, snow, sleet etc. is known as precipitation

Run-off: The ways by which water moves across the land is called as runoff

Surface run off: The net quantity of rain water which remains on the surface of the

earth after all rainfall losses ( rainfall losses in form of evaporation, Infiltration,

Evapotranspiration) termed as surface runoff

Infiltration: the rain water which is percolates below ground is known as infiltration.

Evapotranspiration: Evapotranspiration means evaporation+ Transpiration

Evaporation means a process through which water on ground surface or lake can

return to the atmosphere as vapour

Transpiration means water used by plants may return to atmosphere as vapour through

transpiration which occurs when water passes through leaves.