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19-03-2013

HYDROLOGY Groundwater Hydrology may be define as the science of the occurrence, distribution, and movement of water below the surface of earth. Geohydrology has an identical association and hydrogeology differs only by its greater importance on geology. Utilization of groundwater datas from ancient times, although an understanding of the occurrence and movement of subsurface water as part of the hydrologic cycle. Hydrology is the science that treats the waters of the earth, their occurrence, circulation, and distribution, their chemical and physical properties, and their reaction with the environment, including the relation to living things. The field of hydrology embraces the full life history of water

and earth.

The Hydrologic Cycle: (the water cycle) It is the journey water takes as it circulates from the land to the sky and back again. This process is powered by the sun's energy, which moves

water between the oceans, the sky, and the land. It is continuous movement of water on, above and below the surface of the Earth. Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go, in and out of the atmosphere. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, runoff, and subsurface flow. In so doing, the water goes through different phases: liquid, solid (ice), and gas (vapor) We can start our

examination of the

hydrologic cycle with the

oceans, which hold over

97% of the planet's

water. The sun causes

evaporation of water on

the surface of the ocean.

The water vapor rises

and condenses into

tiny droplets which

cling to dust particles.

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These droplets form clouds. Water vapor usually remains in the

atmosphere for a short time, from a few hours to a few days until it turns

into precipitation. Some precipitation falls as snow or hail, sleet, and can

accumulate as ice caps and glaciers, which can store frozen water for

thousands of years. Most water falls back into the oceans or onto land as

rain, where the water flows over the ground as surface runoff. A portion of

runoff enters rivers in valleys in the landscape, with streamflow moving

water towards the oceans. Runoff and groundwater are stored as

freshwater in lakes. Not all runoff flows into rivers, much of it soaks into the

ground as infiltration. Some water infiltrates deep into the ground and

replenishes aquifers, which store freshwater for long periods of time.

Some infiltration stays close to the land surface and can seep back into

surface-water bodies (and the ocean) as groundwater discharge. Some

groundwater finds openings in the land surface and comes out as

freshwater springs. Over time, the water returns to the ocean, where our

water cycle started.

20-03-2013

How does the Hydrological Cycle work?

The stages of the cycle are:

Evaporation Transport Condensation Precipitation Infiltration Groundwater Run-off

Here is details of these stages.

Evaporation:

The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere.. The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration. Total annual evapotranspiration amounts to approximately 505,000 km3 (121,000 cu mi) of water, 434,000 km3 (104,000 cu mi) of which evaporates from the

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oceans. Evaporation occurs when the physical state of water is changed from a liquid state to a gaseous state. A considerable amount of heat, about 600 calories of energy for each gram of water, is exchanged during the change of state. Typically, solar radiation and other factors such as air temperature, vapor pressure, wind, and atmospheric pressure affect the amount of natural evaporation that takes place in any geographic area. Evaporation can occur on raindrops, and on free water surfaces such as seas and lakes. It can even occur from water settled on vegetation, soil, rocks and snow. There is also evaporation caused by human activities. Heated buildings experience evaporation of water settled on its surfaces. Evaporated moisture is lifted into the atmosphere from the ocean, land surfaces, and water bodies as water vapor. Some vapor always exists in the atmosphere.

Transport: “The release of water vapor from plants and soil into the air”.

Water vapor is a gas that cannot be seen. Some of the earth’s moisture transport is visible as clouds, which themselves consist of ice crystals and/or tiny water droplets.Clouds are propelled from one place to another by either the jet stream, surface-based circulations like land and sea breezes or other mechanisms. However, a typical cloud 1 km thick contains only enough water for a millimetre of rainfall, whereas the amount of moisture in the atmosphere is usually 10-50 times greater than this. Most water is transported in the form of water vapour, which is actually the third most abundant gas in the atmosphere. Water vapour may be invisible to us, but not to satellites which are capable of collecting data about moisture patterns in the atmosphere.

Condensation:

“The transformation of water vapor to liquid water droplets in the air, creating clouds and fog”.

Condensation is the process by which water vapor changes it's physical state from a vapor, most commonly, to a liquid. Water vapor condenses onto small airborne particles to form dew, fog, or clouds. The most active particles that form clouds are sea salts, atmospheric ions caused by lightning, and combustion products containing sulfurous and nitrous acids. Condensation is brought about by cooling of the air or by increasing the amount of vapor

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in the air to its saturation point. When water vapor condenses back into a liquid state, the same large amount of heat (600 calories of energy per gram) that was needed to make it a vapor is released to the environment.

Precipitation: The primary mechanism for transporting water from the atmosphere to the surface of the earth is precipitation. Most precipitation occurs as rain, but also includes snow, hail, fog drip, graupel, and sleet. .Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year, 398,000 km3 (95,000 cu mi) of it over the oceans. The rain on land contains 107,000 km3 (26,000 cu mi) of water per year and a snowing only 1,000 km3 (240 cu mi)

There are two sub-processes that cause clouds to release precipitation, the coalescence process and the ice-crystal process. As water drops reach a critical size, the drop is exposed to gravity and frictional drag. A falling drop leaves a turbulent wake behind which allows smaller drops to fall faster and to be overtaken to join and combine with the lead drop. The other sub-process that can occur is the ice-crystal formation process. It occurs when ice develops in cold clouds or in cloud formations high in the atmosphere where freezing temperatures occur. When nearby water droplets approach the crystals some droplets evaporate and condense on the crystals. The crystals grow to a critical size and drop as snow or ice pellets. Sometimes, as the pellets fall through lower elevation air, they melt and change into raindrops. Precipitated water may fall into a waterbody or it may fall onto land. It is then dispersed several ways. The water can adhere to objects on or near the planet surface or it can be carried over and through the land into stream channels, or it may penetrate into the soil, or it may be intercepted by plants. When rainfall is small and infrequent, a high percentage of precipitation is returned to the atmosphere by evaporation. The portion of precipitation that appears in surface streams is called runoff. Runoff may consist of component contributions from such sources as surface runoff, subsurface runoff, or ground water runoff. Surface runoff travels over the ground surface and through surface channels to leave a catchment area called a drainage basin or watershed. The portion of the surface runoff that flows over the land surface towards the stream channels is called overland flow. The total runoff confined in the stream channels is called the streamflow. Infiltration:

The flow of water from the ground surface into the ground. Once infiltrated, the water

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becomes soil moisture or groundwater. Infiltration is the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil. The surface phenomenon is governed by soil surface conditions. Water transfer is related to the porosity of the soil and the permeability of the soil profile. Typically, the infiltration rate depends on the puddling of the water at the soil surface by the impact of raindrops, the texture and structure of the soil, the initial soil moisture content, the decreasing water concentration as the water moves deeper into the soil filling of the pores in the soil matrices, changes in the soil composition, and to the swelling of the wetted soils that in turn close cracks in the soil. Water that is infiltrated and stored in the soil can also become the water that later is evapotranspired or becomes subsurface runoff.

Groundwater: Some of the precipitation soaks into the ground and this is the main source of the formation of the waters found on land - rivers, lakes, groundwater and glaciers. Some of the underground water is trapped between rock or clay layers - this is called groundwater. Water that infiltrates the soil

flows downward until it encounters impermeable rock and then travels laterally. The locations where water moves laterally are called ‘aquifers’. Groundwater returns to the surface through these aquifers, which empty into lakes, rivers and the oceans.

Under special circumstances, groundwater can even flow upward in artesian wells. The flow of groundwater is much slower than run-off with speeds usually measured in centimetres per day, metres per year or even centimetres per year.

Run-off: The variety of ways by which water moves across the land. This includes both surface runoff and channel runoff. Runoff is flow from a drainage basin or watershed that appears in surface streams. It generally consists of the flow that is unaffected by artificial diversions, storages or other works that society might have on or in a stream channel. The flow is made up partly of precipitation that falls directly on the stream , surface runoff that flows over the land surface and through channels, subsurface runoff that infiltrates the surface soils and moves laterally towards the stream, and groundwater runoff from deep percolation through the soil horizons. Part of the subsurface flow enters the stream quickly, while the remaining portion may take a longer period

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before joining the water in the stream. When each of the component flows enter the stream, they form the total runoff. The total runoff in the stream channels is called streamflow and it is generally regarded as direct runoff or base flow

A Water Balance

A considerable portion of river flow does not reach the ocean, having evaporated those areas with no natural surface run-off channels. On the other hand, some groundwater bypasses river systems altogether and goes directly to the ocean or evaporates. Every year, the turnover of water on Earth involves 577,000 km3 of water. This is water that evaporates from the ocean surface (502,800 km3) and from land (74,200 km3). The same amount of water falls as atmospheric precipitation, 458,000 km3 on the ocean and 119,000 km3 on land. The difference between precipitation and evaporation from the land surface (119,000 ?– ?74,200 = 44,800 km3/year) represents the total run-off of the Earth’s rivers (42,700 km3/year) and direct groundwater run-off.

World Water Supply by Location

Oceans - 97.08% Ice Sheets and Glaciers - 1.99% Ground Water - 0.62% Atmosphere - 0.29% Lakes (Fresh) - 0.01%

Inland Seas and Salt Water Lakes - 0.005% Soil Moisture - 0.004% Rivers - 0.001%

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Only during the ice ages are there noticeable differences in the location of water storage on the earth. During these cold cycles, there is less water stored in the oceans and more in ice sheets and glaciers. It can take an individual molecule of water from a few days to thousands of years to complete the hydrologic cycle from ocean to atmosphere to land to ocean again as it can be trapped in ice for a long time.

26-03-2013 Groundwater Flow:

Water occurs and moves within the “Hydrologic Cycle.” Water evaporates and then forms clouds though a process called condensation. Precipitation returns this water to the ground surface in the form of rain, snow, sleet, etc. After falling back to the Earth’s surface, liquid water continues within the Hydrologic Cycle through one or more of these pathways:

Direct evaporation back into the atmosphere :

This water again forms clouds and is eventually precipitated again back to the Earth’s surface.

. Run off flow into surface water bodies:.

This water flows on the land surface into ponds, lakes, streams, or oceans. Water from these bodies may again

be evaporated back into the atmosphere, or in the case of streams, may continue flowing toward the ocean.

Soaking into the ground.:

This water may be taken up by vegetation and then returned to the atmosphere as water vapor through plant transpiration. However, water not used by plants seeps deeper into the ground and saturates rock and soil, and is called groundwater.

27-03-2013

Factor affecting infiltration capecity: Infiltration is the process whereby water enters the surface strata of the soil and moves downward toward the water tabe.This water first replenishes the soil moisture deficiency then thereafter any excess moves on downward and become ground water. Infiltration Capecity: The maximum rate at which a soil in any given condition is capable of absorbing water is called infiltreation capecity..

There are some factors which affect the infiltration capecity of water…

Soil moisture

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Compaction due to rain

Inwash of fine material Compaction due to man and animals Macrostructure of soil Vegetative cover Temperature

These factors are describe below…..

Soil moisture: The effect of soil moisture is twofold.

1)If the soil is quite dry at the beginning of a rain, the wetting of the top layer creates a strong capillary potential just under the surface which supplements the gravitational force in causing infiltration. 2)When subjected to wetting , any colloids present in the soil swell and reduce the infiltration capacity during the initial period of rainfall.Soil moisture is usually high in winter and spring and low in summer.This factor therefore, is responsible for much of the typical seasonal variations.

Compaction due to rain: Mechanical compaction caused by raindrops greatly reduces the infiltration capacity in soil of fine texture .The surface of exposed clay soil can be worked into a virtually impermeable condition in this manner, whereas the infiltration capacity of a clean sandy soil is affected very little by rain compaction.

Inwash of fine material: When a soil becomes very dry, the surface often contains many fine particles. When infiltration begins, these fine particles are carried into the soil, which act as filter, and the fine material is deposited in the

interstitial spaces, thus reducing the infiltration capacity.

Compaction due to man and animals: Where heavy pedestrian or vehicular traffic occurs on a soil, the surface is rendered relatively impervious. This type of area has low infiltration capacity.

Macrostructure of soil: This effect may be caused by several natural phenomena such as burrowing animals and insects, by the decay of vegetable matter, particularly roots, by frost heaving. In this manner higher filtration capacity produce which can often reduce very rapidly by compaction due to rain.

Vegetative cover: The presence of a dense cover of vegetation, such as grass or forest, tend to promote rapid infiltration. The vegetative cover not only provides protection from compaction due to rain, but also provides a layer of

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decaying organic matter which promotes the activity of burrowing insects and animals.

Temperature: Because flow in the interstitial spaces is nearly always laminar, changes in viscosity influence the rate of infiltration. With increasing temperature, viscosity decreases and infiltration increases and vice versa. (REF. Hydrology by CHESTER O. WISLER AND ERNEST F. BRATTER)

02-04-2013 Vertical distribution of Ground water: Conditions: For vertical distribution of ground water, sediments must be homogeneous and isotropic. Aquifer must be unconfined. The subsurface occurrence of ground water may be divided into two

zones. Aeration zone (vadoz zone) Saturation zone

Here these two zones are describes…..

Aeration zone: (vadoz zone) The zone of aeration consists of interstices occupied partially by water and partially by air……… Over most of the land masses of the earth a single zone of aeration overlies a single zone of saturation and expend upward to the ground surface.

03-04-2013

This general zone may be further subdivided into.. Soil water zone Intermediate zone Capillary zone

Here is these sub-zones are describes… Soil water zone:

Water in the soil water zone exists at less than saturation except temporarily when excessive water reaches the ground surface as from rainfall or irrigation. The zone extends from the ground surface down through the major root zone. Its thickness varies with soil type and vegetation.

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Soil water was classified by Briggs into three categories dependent upon its concentration in the soil zone..

Hygroscopic water adsorbed from the air, forms thin film of moisture on soil particle surfaces. The adhesive forces are very

large, so that this water is unavailable to plants. Capillary water exists as continuous films around the soil

particles. It is held by surface tension, is moved by capillary action and available to plants.

09-04-2103 Gravitational water is excess soil water which drains through

the soil under the influence of gravity.

The hygroscopic coefficient is the maximum moisture which an initially dry soil will absorb in contact with an atmosphere of 50% relative humidity at 250 C. The wilting point a is that moisture content at which permanent wilting of plants occurs. Experiments have proved that this is not a unique value, but rather depends upon the plants, the climate, the root system, and volume of soil tested. Field capacity is defined as the amount of water held in the soil after the excess gravitational water has drained away and after the rate of downward movement of water has materially decreased. Moisture equivalent is the amount of water which a saturated soil will retain after being centrifuged at a centrifugal force 1000 times that of gravity. The field capacity for sands is higher than the moisture equivalent, but about the same for loams. Because field capacity and wilting point represent the upper and lower limits, respectively, of moisture for plant growth, the difference b/w these points is the available water for plant growth. The water required to saturate all of the soil voids is the maximum possible water content. This is as the maximum water capacity. There are three methods for measuring soil moisture in place and its variations with time.

1) Gravmetric 2) Tensiometer 3) Neutron scattering 10-04-2103

Intermediate zone: The intermediate zone is extends from the lower edge of the

soil water to the upper limit of the capillary zone. This zone may vary in thickness from zero, when the bounding zone merge with a high water table approaching the ground surface, to several hundred ft under deep water table conditions. The zone serves primarily as a region connecting the zone near the ground surface to that near the water table through which water moving vertically downward must pass. Non-moving, or pellicular, water in the intermediate zone is held in place by hgroscopic

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and capillary forces, and is equivalent to field capacity in the soil water zone. Excess water is gravitational water, which moves downward under the influence of gravity.

Capillary zone: The capillary zone extend from the

water table upto the limit of capillary rise of water.

Saturation zone: Ground water fills all of the interstices in

the saturated zone, hence the porosity is a direct measure of the water contained per unit volume. Not all of this water may be removed from ground by drainage or pumping from a well, however , as molecular and surface tension forces will hold a portion of the water in place.

Thus, retained water is that held in place against gravity.

11-04-2013 The specific retention of a rock or soil is the ratio expressed as a

percentage of the volume of water it will retain after saturation against the force of gravity to its own volume. If Sr is the specific retention then

Sr = 100ωr/V Where ωr is the volume occupied by retained water, and V is the gross

volume of the rock or soil. On the other hand, the water which can be drained is expressed as the

specific yield Sy. The term, effective porosity, has a synonymous meaning. It may be defined as “the ratio expressed as a percentage of the volume of water which, after being saturated, can be drained by gravity to its own volume.

Therefore, SY = 100ωY/V

Where ωy is the volume of water drained. Because ωr + ωy =ω

so α = Sr + Sy

Thus, specific yield is a fraction of the porosity of an aquifer. Values depend on grain size, shape and distribution of pores, and copmpaction of the stratum. For uniform sand, specific yield may equal upto 30%, but most alluvial aquifers give values in the range of 10% to 20%.

Table: Specific yield of water-bearing Deposits in Scramento Valley, California

Material Specific

YIELD

parcentage

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Gravel 25

Sand, including sand and gravel, and gravel and sand

20

Fine sand, hard sand, tight sand, sandstone, and related deposits

10

Clay and gravel, gravel and clay, cemented gravel, and related deposits

5

Clay, silt, sandy clay, lava rock, and related fine-grained deposits

3

(REF. Hygrology by DAVID KEITH TODD) 16-04-2013

Aquifer: Groundwater occurs in many types of geological formations but

aquifer is most important. An aquifer may be define as a formation that contains

sufficient saturated permeable material to yield significant quantities of water to wells and springs.

Or An aquifer is the underdround layer of water-bearing permeable

rock or unconsolidated material (sand,gravel,or clay) from which groundwater can be usefully extracted using a water well.

This implies an ability to store and to transmit water, unconsolidated sands and gravels are a typical example. Aquifer are generally areally extensive and may be overlain or underlain by a confining bed, which may be defined as a relatively impermeable material stratigraphically adjacent to one or more aquifer. There are various types of confining beds, the

following types are well established. 1. Aquiclude: A saturated but relatively impermeable material that does not

yield appreciable quantities of water to wells, e.g clay .

2. Aquifuge: A relatively impermeable formation neither containing nor

transmitting water . e.g solid granite

3. Aquitard: A saturated but poorly permeable stratum that impedes

groundwater movement and does not yield water freely to wells, that may transmit appreciable water to or from adjacent aquifers and, where sufficiently thick, may constitute an important groundwater storge zone . e.g sand clay.

Types of Aquifers

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General. An aquifer is a geologic unit that canstore and transmit water. Aquifers are generallycategorized into four basic formation types dependingon the geologic environment in which they occur:

Unconfined Aquifer Confined Aquifer Semi-confined Aquifer Perched Aquifer Here is the detail of types of aquifer. Unconfined Aquifer: Unconfined aquifers contain a phreatic surface (water

table) as an upper boundary that fluctuates in response to recharge and discharge (such as from a pumping well). Unconfined aquifers are generally close to the land surface, with continuous layers of materials of high intrinsic permeability extending from the land surface to the base of the aquifer. An unconfined aquifer possesses no overlying confining layer, but may sit upon an impermeable or slightly permeable bed. Therefore, the top of the unsaturated zone of an unconfined aquifer is most often the ground surface, and the top of the saturated zone is usually under negative pressure or tension. This latter property gives rise to the definition of the water table which is simply the surface where the relative pressure is zero, i.e., the absolute pressure is atmospheric. Immediately above the water table, the medium is still saturated but the water is held by capillary forces, thus creating a negative pressure head, or tension. This tension can exist even though the pores may be saturated between the water table and the top of the capillary fringe. Below the water table, the water pressure increases with depth.

Confined Aquifer: Confined, or artesian, aquifers are created when groundwater is trapped between two layers of low permeability known as aquitards. In a confined aquifer, the groundwater is under pressure and the water level in a well rises above the upper boundary of the aquifer. Flowing artesian conditions exist when the water level in a well rises above land surface. Recharge to confined aquifers is predomi nantly from areas where the confining bed is breached, either by erosional unconformity, fracturing, or depositional absence.

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If the recharge area for the aquifer is located at a higher elevation than the top of the aquifer, and a well is drilled into the aquifer, the water level will rise above the top as shown. Such an aquifer is known as an artesian aquifer; it is named after Artois, France, where such wells are common. It should be noted, however, that the well does not have to be flowing to be termed “artesian,” although that is the popular conception. A flowing well is known as a “flowing artesian well.” The water level above the top is known as the piezometri surface (pressure surface), which is the locus of the piezometric head, and it is not to be confused with the water table discussed below. The piezometric surface occurs above the ground surface because the higher elevation of the recharge area causes the pressure head to rise to such an elevation. The water within the aquifer will be partly under elastic storage. Pumping a well or allowing it to flow will release the water from storage. Artesian or confined aquifers are common in glaciated regions of the world where a body of outwash sand and gravel may have been covered by clay-rich till or lacustrine sediments from a subsequent glaciation. They may also occur in layered bedrock.

17-04-2013 Semi-confined Aquifer:

Semi-confined, or leaky, aquifers occur when water-bearing strata are confined, either above or below, by a semipermeable layer. When water is pumped from a leaky aquifer,water moves both horizontally within the aquifer and vertically through the semipermeable layer.

Perched Aquifer: A perched aquifer is a special type of unconfined aquifer where a groundwater body is separated above the water table by a layer of unsaturated material. A perched aquifer occurs when water moving down through the unsaturated zone is intercepted by an impermeable formation. Clay lenses in sedimentary deposits often have shallow perched water bodies overlying them Wells tapping perched aquifers generally yield temporary or small quantities of water. (REF. Groundwater engineering by Jacques W Delleur, Groundwater Hydrology by David K Todd, Engineering and Design GROUNDWATER HYDROLOGY)

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18-04-2013 Ground water Recharge: In flow of water system that are near the ground water table is ground water recharge. If rain or precipitation is gentle then chances of infiltration is high and if there is sudden brust then chances of run-off is higher. Ground water recharge depends upon nature of rain fall and topography.

Types of Recharge: Recharge from surface precipitation Irrigation

Inflow from surface water Artificial racharge

Here is the detail of the following. Recharge from surface precipitation:

It depends upon the depth of the ground water. if ground table is deep then it will take more time to recharge and vice versa. If rock is hard then it also take more time to recharge.

23-04-2013 Irrigation:

Water which is used for irrigation purpose is infiltrate and there is no chance for run-off in such condition.

Inflow from surface water: Streams and lakes which is on the surface also contributes for aquifer in the form of infiltration. For seasonal recharge, water is also contriute to the aquifer especially

shallow aquifer. Artificial recharge:

We may contribute to the ground water recharge artificially by draining water from streams into the aquifer. Holes or digs also used for infiltration of water. This is can be done where aquifer is at shallow depth.

24-04-2013 Ground water discharge: Groundwater discharge is the volumetric flow rate of groundwater through an aquifer. Groundwater discharge is the movement of water out of an area of saturated soil. While groundwater discharge usually refers to the water leaving aquifers in the soil, sometimes the term is also used to reference water moving through an aquifer. In either case, the unit of measurement ofgroundwater flow that is typically used is cubic meters per second (m3/s).When ground water meet with aquifer then ultimately water in the form of spring mill be on the surface.

Types of ground water discharge: Spring discharge

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Roots discharge

Stream discharge Groundwater abstraction

A spring is an easily visible point of groundwater discharge, and it is usually happened in mountain areas where ground water intersect the surface, but there are many other places that act as discharge points. Groundwater discharge occurs when water seeps from aquifers into rivers, streams, and lakes. Water may also seep out of the ground into wetlands and marshes. In areas where the water table is close to the top of the ground, groundwater may be mostly discharged through the actions of growing plants as they draw water out of aquifers, and release it into the air as moisture. Near the ocean, groundwater discharge may occur directly into the sea, and in this case, it is called submarine groundwater discharge.

25-04-2013 Geological formation as aquifer: An aquifer is a geologic formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to springs and wells. Use of the term is often restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply for people's uses. Here is some points which is important for identify the aquifer.

By studying the geological history or environment (porosity and permeability) of rock we hit the aquifer.

If we found coarse grained material during drilling then it will be the favorable condition for aquifer.

Commonly aquifer have discharge 50-750 m3/day.

In sedimentary rocks we look for area where loose unconsolidated material or sand are present which has probably 90% chance of aquifer.

Flood plains where gravel or loose material present is the feasible condition for the aquifer.

The valley which are not active these days or buried and active in past, we may met there potential aquifer.

Valley are also potentially important where seasonal water aquifer are common.

Clays, silt, loam and other fine material usually on floodplains, may act as aquifer.

02-05-2013 Volcanic rocks as aquifer: Volcanic rocks have a wide range of chemical, mineralogic, structural, and hydraulic properties, due mostly to variations in rock type and the way the rock was ejected and deposited. Unaltered pyroclastic rocks, for example,

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might have porosity and permeability similar to poorly sorted sediments. Hot pyroclastic material, however, might become welded as it settles, and, thus, be almost impermeable. Silicic lavas tend to be extruded as thick, dense flows, and they have low permeability except where they are fractured. Basaltic lavas tend to be fluid, and, they form thin flows that have considerable pore space at the tops and bottoms of the flows. Numerous basalt flows commonly overlap, and the flows are separated by soil zones or alluvial material that form permeable zones. Columnar joints that develop in the central parts of basalt flows create passages that allow water to move vertically through the basalt. Basaltic rocks are the most productive aquifers in volcanic rocks.

Some importants points …. 1. Aquifer – a geologic formation that is water bearing. A geological formation or structure that stores and /or transmits water, such as to wells and springs. 2. Aquifer (confined) – soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer. 3. Aquifer (unconfined) – an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall. 4. Artificial recharge – a process where water is put back into ground-water storage from surface-water supplies such as irrigation, or induced infiltration from streams or wells. 5. Water table – the top of the water surface in the saturated part of an aquifer 6. Confining Layer - a geologic material with little or no permeability or hydraulic conductivity. Water does not pass through this layer or the rate of movement is extremely slow. 7. Contaminant - (pollutant) any substance that makes water unfit for a given use. 8. Discharge Area - an area where groundwater emerges at the surface; an area where upward pressure or hydraulic head moves groundwater towards the surface to escape as a spring, seep, or base flow of a stream. 9. Groundwater - the water below the water table contained in void spaces (pore spaces between rock and soil particles, or bedrock fractures). 10. Infiltration - the process of water moving from the ground surface vertically downward into the soil.

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11. Surface Water - water found in ponds, lakes, streams, rivers, and inland seas.

The End