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Chapter: Civil - Water Resources and Irrigation Engineering

Surface and Ground Water Resources

Water in our planet is available in the atmosphere, the oceans, on land and within the soil and fractured rock of one location to another are driven by the solar energy.


Surface and Ground Water Resources


Water in our planet is available in the atmosphere, the oceans, on land and within the soil and fractured rock of one location to another are driven by the solar energy. Moisture circulates from the earth into the atmosphere through evaporation and then back into the earth as precipitation. In going through this process, called the Hydrologic Cycle water is conserved 'that is, it is neither created nor destroyed.It would perhaps be interesting to note that the knowledge of the hydrologic cycle was known at least by about 1000 BC by the people of the Indian Subcontinent. This is reflected by the fact that one verse of Chhandogya Upanishad (the Philosophical reflectionsof the Vedas) points to the following: “The rivers… allwatersdischarginto the sea. They lead from sea to sea, the clouds raise them to the sky as vapour

 

and release them in the form of rain…” Th hydrologic cycle is not equally distributedThe oceans are the largest reservoirs of

 

water, but since it is saline it is not readily usable for requirements of human survival.Again, the fresh water distribution is highly uneven, with most of the water locked in frozen polar ice caps.

 

The hydrologic cycle consists of four key components

 

1. Precipitation

 

2. Runoff

3. Storage

4. Evapotranspiration

 

These are described in the next sections.

Precipitation

 

ü        Precipitation occurs when atmospheric moisture becomes too great to remain suspended in clouds.

 

ü        It denotes all forms of water that reach the earth from the atmosphere, the usual forms being rainfall, snowfall, hail, frost and dew.

 

ü        Once it reaches the earth‟s surfac surface water runoff, surface water storage, glacial ice, water for

 

plants, groundwater, or may evaporate and return immediately to the atmosphere.

 

ü        Ocean evaporation is the greatest source (about 90%) of precipitation.

 

ü        Rainfall is the predominant form of precipitation and its distribution over the world and within a country. India has a typical monsoon climate.

 

ü        At this time, the surface winds undergo a complete reversal from January to July, and cause two types of monsoon.

 

ü        In winter dry and cold air from land in the northern latitudes flows southwest (northeast monsoon), while in summer warm and humid air originates over the ocean and flows in the opposite direction (southwest monsoon), accounting for some 70 to 95 percent of the annual rainfall.

 

ü        The average annual rainfall is estimated as 1170 mm over the country, but varies significantly from place to place.

 

ü        In the northwest desert of Rajasthan, the average annual rainfall is lower than 150 mm/year. In the broad belt extending from Madhya Pradesh up to Tamil Nadu, through Maharastra, parts of Andhra Pradesh and Karnataka, the average annual rainfall is generally lower than 500 mm/year.

 

ü        At the other extreme, more than 10000 mm of rainfall occurs in some portion of the Khasi Hills in the northeast of the country in a short period of four months. In other parts of the northeast (Assam, Arunachal Pradesh, Mizoram, etc.,) west coast

 

ü        and in sub-Himalayan West Bengal the average annual rainfall is about 2500 mm.

ü        Except in the northwest of India, inter annual variability of rainfall in relatively low. The main areas affected by severe droughts are Rajasthan, Gujarat (Kutch and Saurashtra).

 

 

The year can be divided into four seasons:

 

             The   winter   or   northeast   monsoon

February.

 

            The   hot   season  from   March   to   Ma

 

               The    summer    or    south    west   mon

September.

            The'monsoonpost season from October to December.

 

ü        The monsoon winds advance over the country either from the Arabian Sea or from the Bay of Bengal.

ü          In  India,  the  south-west  monsoon  is  the  principal  rainy

 

season, which contributes over 75% of the annual rainfall received over a major portion of the country.

 

ü        The normal dates of onset of monsoon rains provide a rough estimate of the duration of monsoon rains at any region.

 

Runoff

 

ü        Runoff is the water that flows across the land surface after a storm event.

 

ü        As rain falls over land, part of that gets infiltrated the surface as overland flow.

 

ü        As the flow bears down, it notches out rills and gullies which combine to form channels.

ü        These combine further to form streams and rivers.

 

ü        The geographical area which contributes to the flow of a river is called a river or a watershed.

 

ü        The following are the major river basins of our country, and thecorresponding figures, as obtained from the web-site of the Ministry of Water Resources, Government of India is mentioned alongside each.

 

1. Indus

2. Ganges

3. Brahmaputra

 

4. Krishna

 

5. Godavari

6. Mahanandi

7. Sabarmati

8. Tapi

 

9. Brahmani-Baitarani

 

10.Narmada

11.Pennar

12.Mahi

Storage

 

ü     Portion of the precipitation falling on land surface which does not flow out as runoff gets stored as either as surface  water bodies like Lakes, Reservoirs and Wetlands or as sub-surface water body, usually called Ground water.

 

ü        Ground water storage is the water infiltrating through the soil cover of a land surface and traveling further to reach the huge body of water underground.

 

ü        Asmentioned earlier, the amount of ground water storage is much greater than that of lakes and rivers.

 

ü        However, it is not possible to extract the entire groundwater by practicable means. It is interesting to note that the groundwater also is in a state of continuous movement ' flowing from regions of higher potential to lower.

 

ü        The rate of movement, however, is exceptionally small compared to the surface water movement.

 

ü        The following definitions may be useful:

 

 

Lakes: Large, naturally occurring inland body of water

 

Reservoirs: Artificial or natural inland body of water used to store water to meet various demands.

 

Wet Lands: Natural or artificial areas of shallow water or saturated soils that contain or could support water'loving plants.

 

 

Evapotranspiration

 

Ø        Evapotranspiration is actually the combination of two terms ' evaporation and transpiration.

 

Ø        The first of these, that is, evaporation is the process of liquid converting into vapour, through wind action and solar radiation and returning to the atmosphere.

 

Ø        Evaporation is the cause of loss of water from open bodies of water, such as lakes, rivers, the oceans and the land surface.

 

Ø        It is interesting to note that ocean evaporation provides approximately 90 percent of the eart

 

Ø        However, living near an ocean does not necessarily imply more rainfall as can be noted from the great difference in the amount of rain received between the east and west coasts of India

 

Ø        Transpiration is the process by which water molecules leaves the body of a living plant and escapes to the atmosphere.

 

Ø        The water is drawn up by the plant root system and part of that is lost through the tissues of plant leaf (through the stomata).

 

Ø        In areas of abundant rainfall, transpiration is fairly constant with variations occurring primarily in the length of each plants growing season.

 

Ø        However, transpiration in dry areas varies greatly with the root depth.

 

Ø        Evapotranspiration, therefore, includes all evaporation from water and land surfaces, as well as transpiration from plants.

Water resources potential

Surface water potential:

 

Ø        The average annual surface water flows in India has been estimated as 1869 cubic km.

Ø        This is the utilizable surface water potential in India.

 

Ø        But the amount of water that can be actually put to beneficial use is much less due to severe limitations posed by Physiography, topography, inter-state issues and the present state of technology to harness water resources economically.

 

Ø        The recent estimates made by the Central Water Commission, indicate that the water resources is utilizable through construction of structures is about 690 cubic km (about 36% of the total).

 

Ø        One reason for this vast difference is that not only does the whole rainfall occur in about four months a year but the spatial and temporal distribution of rainfall is too uneven due to which the annual average has very little significance for all practical purposes.

 

Ø        Monsoon rain is the main source of fresh water with 76% of the rainfall occurring between June and September under the influence of the southwest monsoon.

 

Ø        The average annual precipitation in volumetric terms is 4000 cubic km.

 

Ø        The average annual surface flow out of this is 1869 cubic km, the rest being lost in infiltration and evaporation.

Ground water potential:

 

Ø        The potential of dynamic or rechargeable ground water resources of our country has been estimated by the Central Ground Water Board to be about 432 cubic km.

 

Ø        Ground water recharge is principally governed by the intensity of rainfall as also the soil and aquifer conditions.

 

Ø        This is a dynamic resource and is replenished every year from natural precipitation, seepage from surface water bodies and conveyance systems return flow from irrigation water, etc.

 

Ø        The highlighted terms are defined or explained as under:

 

Utilizable surface water potential:

 

This is the amount of water that can be purpose fully used, without any wastage to the sea, if water storage and conveyance structures like dams, barrages, canals, etc. are suitably built at requisite sites.

 

Central Water Commission:

 

Ø        Central Water Commission is an attached office of Ministry of Water Resources with Head

 

Quarters at New Delhi. It is a premier technical organization in the country in the field of water resources since 1945.The commission is charged with the general responsibility of initiating, coordinating and furthering, in consultation with the State Governments concerned, schemes for control, conservation and utilization of water resources throughout the country, for purpose of flood control, irrigation, navigation, drinking water supply and water power development.

 

 

 

Central Ground Water Board:

Ø        It is responsible for carrying out nation-wide surveys and assessment of groundwater resources and guiding the states appropriately in scientific and technical matters relating to groundwater.

 

Ø        The Central Ground Water Board has generated valuable scientific and technical data through regional hydro geological surveys, groundwater exploration, resource and water quality monitoring and research and development.

 

Ø        It assists the States in developing broad policy guidelines for development and management of groundwater resources including their conservation, augmentation and protection from pollution, regulation of extraction and conjunctive use of surface water and ground water resources.

 

Ø        The Central Ground Water Board organizes Mass Awareness Programmes to create awareness on various aspects of groundwater investigation, exploration, development and management.

 

Ground water recharge:

 

Ø        Some of the water that precipitates, flows on ground surface or seeps through soil first, then flows laterally and some continues to percolate deeper into the soil.

 

Ø        This body of water will eventually reach a saturated zone and replenish or recharge groundwater supply.

 

Ø        In other words, the recuperation of groundwater is called the groundwater recharge which is done to increase the groundwater table elevation.

 

Ø        This can be done by many artificial techniques, say, by constructing a detention dam called a water spreading dam or a dike, to store the flood waters and allow for subsequent seepage of water into the soil, so as to increase the groundwater table.

 

Ø        It can also be done by the method of rainwater harvesting in small scale, even at individual houses.

 

Ø        The all India figure for groundwater recharge volume is 418.5 cubic km and the per capita annual volume of groundwater recharge is 412.9 cubic m per person.

 

Development of water resources

 

Ø        Due to its multiple benefits and the problems created by its excesses, shortages and quality deterioration, water as a resource requires special attention.

 

Ø        Requirement of technological/engineering intervention for development of water resources to meet the varied requirements of man or the human demand for water, which are also unevenly distributed, is hence essential.

 

Ø        The development of water resources, though a necessity, is now pertinent to be made sustainable.

 

Ø        The concept of sustainable development implies that development meets the needs of the present life, without

compromising on the ability of the future generation to meet their own needs.

Ø        This is all the more important for a resource like water.

 

Ø        Sustainable development would ensure minimum adverse impacts on the quality of air, water and terrestrial environment.

 

Ø        The long term impacts of global climatic change on various components of hydrologic cycle are also important.

 

Ø        India has sizeable resources of water and a large cultivable land but also a large and growing population to feed.

 

Ø        Erratic distribution of rainfall in time and space leads to conditions of floods and droughts which may sometimes occur in the same region in the same year. India has about 16% of the world population as compared to only 4% of the average annual runoff in the rivers

 

Ø        With the present population of more than 1000 million, the per capita water availability comes to about 1170 m3 per person per year.

 

Ø        Here, the average does not reflect the large disparities from region to region in different parts of the country. Against this background, the problems relating to water resources development and management have been receiving critical attention of the Government of India.

 

 

Ø        The country has prepared and adopted a comprehensive National Water Policy in the year 1987, revised in 2002 with a view to have a systematic and scientific development of it water resources.

 

Some of the salient features of the National Water Policy (2002) are as follows:

 

Ø        Since the distribution of water is spatially uneven, for water scarce areas, local technologies like rain water harvesting in the domestic or community level has to be implemented.

 

Ø        Technology for/Artificial recharge of water has also to be bettered.

 

Ø        Desalination methods may be considered for water supply to coastal towns.

 

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Civil - Water Resources and Irrigation Engineering : Surface and Ground Water Resources |


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