際際滷

際際滷Share a Scribd company logo

ground water

Download as PPTX, PDF
Z
zebrhe gebrehiwet

Groundwater is water found below the Earth's surface. It occupies pore spaces in rocks and soil. There are three main types of aquifers - confined, unconfined, and semi-confined. Confined aquifers are bounded above and below by layers of rock that do not allow water to move through them easily. Unconfined aquifers have a layer of permeable rock or soil at the top that allows water to recharge. Semi-confined aquifers have a layer of low permeability at the top. Important properties of aquifers include porosity, specific yield, hydraulic conductivity, and the type and permeability of the rock material.

1 of 13
Download to read offline
ground water
CHAPTER -7 GROUND WATER OUR GROUP PRESENTATION TOPIC INCLUDES GROUND WATER DEFINITION AND CONCEPTS AQUIFER FORMATION TYPES OF AQUIFER PROPERTIES OF AQUIFER
7.1.DEFNITION FOR GROUND WATER WHAT IS GROUND WATER? Groundwater is the water below the ground surface occupying the pore spaces in rocks and soils. Ground water is any water found in or on the ground, it can be distinguished from rain water, which becomes ground water when it hits the fill in the blank. Ground water is a water that occur below the surface of the earth where it occupies all or part of the void spaces in soil or geologic strata. Ground water is the water stored in between the pores in rock and sediment and also known as sub surface water. Groundwater is fresh water (from rain or melting ice and snow) that soaks into the soil and is stored in the tiny spaces (pores) between rocks and particles of soil. ground water is the under groundwater that occurs in saturated zone of variable thickness and depth below the earth surface. GROUND WATER HYDROLOGY defined as a science of the occurrence , distribution and movement of water below the surface of the earth.
Origin of Groundwater The origin of groundwater is primarily one of the following: 他 Groundwater derived from rainfall and infiltration within the normal hydrological cycle. This kind of water is called meteoric water. the name implies recent contact with the atmosphere. Groundwater encountered at great depths in sedimentary rocks as a result of water having been trapped in marine sediments at the time of their deposition. This type of groundwater is referred to as connate waters. These waters are normally saline. It is accepted that connate water is derived mainly or entirely from entrapped sea water as original sea water has moved from its original place. Some trapped water may be brackish. Fossil water if fresh may be originated from the fact of climate change phenomenon, i.e., some areas used to have wet weather and the aquifers of that area were recharged and then the weather of that area becomes dry.
Groundwater and the Hydrologic Cycle The hydrological cycle is the most fundamental principle of groundwater hydrology. The driving force of the circulation is derived from the radiant energy received from the sun. Water evaporates and travels into the air and becomes part of a cloud. It falls down to earth as precipitation. Then it evaporates again. This happens repeatedly in a never-ending cycle. This hydrologic cycle never stops. Water keeps moving and changing from a solid to a liquid to a gas, repeatedly. Precipitation creates runoff that travels over the ground surface and helps to fill lakes and rivers. It also percolates or moves downward through openings in the soil and rock to replenish aquifers under the ground. Some places receive more precipitation than others do with an overview balance. These areas are usually close to oceans or large bodies of water that allow more water to evaporate and form clouds. Other areas receive less. Often these areas are far from seawater or near mountains. As clouds move up and over mountains, the water vapor condenses to form precipitation and freezes. Snow falls on the peaks.
Groundwater and the Hydrologic Cycle
7.2. Aquifer Formation What is aquifer? Let us begin with a definition: Aquifer---from the Latin words aqua, meaning water, and ferre, meaning to bear--- is a term used to designate a porous geological formation that: contains water at full saturation (i.e., the entire interconnected void space is filled with water), and permits water to move through it under ordinary field conditions. Thus, whether a geological formation can be referred to as an aquifer, or not, depends on its ability to store and transport water relative to other formations in the vicinity. An aquifer is a body of saturated rock through which water can easily move. Aquifers must be both permeable and porous and include such rock types as sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel. Fractured volcanic rocks such as columnar basalts also make good aquifers. The rubble zones between volcanic flows are generally both porous and permeable and make excellent aquifers. In order for a well to be productive, it must be drilled into an aquifer. Rocks such as granite and schist are generally poor aquifers because they have a very low porosity. However, if these rocks are highly fractured, they make good aquifers. A well is a hole drilled into the ground to penetrate an aquifer. Normally such water must be pumped to the surface. If water is pumped from a well faster than it is replenished, the water table is lowered and the well may go dry. When water is pumped from a well, the water table is generally lowered into a cone of depression at the well.
An aquifer is a ground-water reservoir composed of geologic units that are saturated with water and sufficiently permeable to yield water in a usable quantity to wells and springs. Sand and gravel deposit ,sandstone ,limestone ,and fractured, crystalline rocks are examples of geological units that form aquifers. Aquifers provide two important functions: (1) they transmit ground water from areas of recharge to areas of discharge, and (2) they provide a storage medium for useable quantities of ground water. The amount of water a material can hold depends upon its porosity. The size and degree of interconnection of those openings (permeability) determine the materials ability to transmit fluid.
7.3.TYPES OF AQUIFER There are all kinds of aquifers. The most commonly used types are the confined (or artesian) aquifer, the unconfined(or free, phreatic) aquifer and the semi-confined aquifer Confined aquifers(artesian) are confined because they have an aquitard above and below the aquifer. These aquifers do not recharge quickly because it takes a long time for water to pass through the top aquitard. In some cases, confined aquifers contain high quality water because they are not directly impacted by human activity on the surface. Confined aquifers can contain groundwater that is very old. Water can stay in a confined aquifer for several millennia. confinedaquiferhaswatertable unconfinedaquifer (free, phreatic) aquifer is an aquifer underlain by an impermeable stratum, but the top of the aquifer consists of soil layers that are permeable enough to provide easy passage of water, at least in vertical sense. Such an aquifer has a free water table or phreatic surface. When perforating a hole into the ground until it fills with water, and letting the water come to rest, the water level in the hole can be observed and it indicates the level of the water table in the aquifer outside the hole. Many alluvial fans and river plains have unconfined aquifers in the upper part of the sediment deposits. The Indus basin in Pakistan provides examples of extensive and deep unconfined aquifers. Where the water quality of the aquifer is acceptable, the aquifer is intensively pumped from wells, mostly for irrigation purposes.
semi-confined aquifer A semi-confined aquifer is an aquifer underlain by an impermeable stratum and bounded at the top by soil layers of relatively low permeability (hydraulic conductivity), especially in horizontal sense. These layers form the semi-confining layer (the aquitard) in which a free water table is found. The flow of water in the top layer is mainly vertical while the horizontal flow is negligible. Semi-confined aquifers are often found in river delta's and coastal plains.
7.4.Properties OF Aquifer The most important properties of the aquifer are porosity and specific yield which in turn give its capacity to release the water in the pores and its ability to transmit the flow with ease. Porosity is a measure of how much water a body of rock can hold. In and , porosity is defined as the ratio of volume of voids to the total volume of porous medium. The significance of the porosity is that it gives the idea of storage capacity of the aquifer. Qualitatively, porosity less than 5% is considered to be small, between 5 and 20% as medium and the percentage exceeding 20% is considered as large. Specific yield &specific retention is a measure of how much an aquifer can yield or produce . the actual amount of water that can be extracted from the unit volume of aquifer by pumping of under the action of gravity. some of the pores may not connect with other pores or they may be so tenuously connected that water can not move readily from one to another. While water molecule are very small and can make their way in to even the tiniest spaces in a rock, they are strongly attracted and held to solids by surface tension. the strength of the attraction b/n the water and the mineral grains is proportional to the distance b/n the water molecule and the surface. the proportion of the water in the rock that does drain out readily is known as the specific yield. specific retention is the opposite of specific yield. the sum of specific retention and specific is porosity.
Aquifer materials Both consolidated and unconsolidated geological material are important as aquifer. Of the consolidated materials(bed rock) sedimentary rocks are the most important b/c they tend to have the highest porosities and permeability. Rock properties- from the perspective of hydrogeology the important characteristics of rocks are how much open space they have, how well connected those open spaces are, how strong the rocks are, and how soluble they are. Hydraulic conductivity(permeability)-is the ability of the rock or unconsolidated material to transmit water. very fine grained rocks and materials or rocks with disconnected porosity tend to have low conductivities. Hydraulic conductivity which is denoted using the symbol K is expressed in velocity units, but it is not a measure of velocity by it self. the hydraulic conductivity is used to estimate the flow of dilute water.
ground water

More Related Content

ground water

  • 2. CHAPTER -7 GROUND WATER OUR GROUP PRESENTATION TOPIC INCLUDES GROUND WATER DEFINITION AND CONCEPTS AQUIFER FORMATION TYPES OF AQUIFER PROPERTIES OF AQUIFER
  • 3. 7.1.DEFNITION FOR GROUND WATER WHAT IS GROUND WATER? Groundwater is the water below the ground surface occupying the pore spaces in rocks and soils. Ground water is any water found in or on the ground, it can be distinguished from rain water, which becomes ground water when it hits the fill in the blank. Ground water is a water that occur below the surface of the earth where it occupies all or part of the void spaces in soil or geologic strata. Ground water is the water stored in between the pores in rock and sediment and also known as sub surface water. Groundwater is fresh water (from rain or melting ice and snow) that soaks into the soil and is stored in the tiny spaces (pores) between rocks and particles of soil. ground water is the under groundwater that occurs in saturated zone of variable thickness and depth below the earth surface. GROUND WATER HYDROLOGY defined as a science of the occurrence , distribution and movement of water below the surface of the earth.
  • 4. Origin of Groundwater The origin of groundwater is primarily one of the following: 他 Groundwater derived from rainfall and infiltration within the normal hydrological cycle. This kind of water is called meteoric water. the name implies recent contact with the atmosphere. Groundwater encountered at great depths in sedimentary rocks as a result of water having been trapped in marine sediments at the time of their deposition. This type of groundwater is referred to as connate waters. These waters are normally saline. It is accepted that connate water is derived mainly or entirely from entrapped sea water as original sea water has moved from its original place. Some trapped water may be brackish. Fossil water if fresh may be originated from the fact of climate change phenomenon, i.e., some areas used to have wet weather and the aquifers of that area were recharged and then the weather of that area becomes dry.
  • 5. Groundwater and the Hydrologic Cycle The hydrological cycle is the most fundamental principle of groundwater hydrology. The driving force of the circulation is derived from the radiant energy received from the sun. Water evaporates and travels into the air and becomes part of a cloud. It falls down to earth as precipitation. Then it evaporates again. This happens repeatedly in a never-ending cycle. This hydrologic cycle never stops. Water keeps moving and changing from a solid to a liquid to a gas, repeatedly. Precipitation creates runoff that travels over the ground surface and helps to fill lakes and rivers. It also percolates or moves downward through openings in the soil and rock to replenish aquifers under the ground. Some places receive more precipitation than others do with an overview balance. These areas are usually close to oceans or large bodies of water that allow more water to evaporate and form clouds. Other areas receive less. Often these areas are far from seawater or near mountains. As clouds move up and over mountains, the water vapor condenses to form precipitation and freezes. Snow falls on the peaks.
  • 7. 7.2. Aquifer Formation What is aquifer? Let us begin with a definition: Aquifer---from the Latin words aqua, meaning water, and ferre, meaning to bear--- is a term used to designate a porous geological formation that: contains water at full saturation (i.e., the entire interconnected void space is filled with water), and permits water to move through it under ordinary field conditions. Thus, whether a geological formation can be referred to as an aquifer, or not, depends on its ability to store and transport water relative to other formations in the vicinity. An aquifer is a body of saturated rock through which water can easily move. Aquifers must be both permeable and porous and include such rock types as sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel. Fractured volcanic rocks such as columnar basalts also make good aquifers. The rubble zones between volcanic flows are generally both porous and permeable and make excellent aquifers. In order for a well to be productive, it must be drilled into an aquifer. Rocks such as granite and schist are generally poor aquifers because they have a very low porosity. However, if these rocks are highly fractured, they make good aquifers. A well is a hole drilled into the ground to penetrate an aquifer. Normally such water must be pumped to the surface. If water is pumped from a well faster than it is replenished, the water table is lowered and the well may go dry. When water is pumped from a well, the water table is generally lowered into a cone of depression at the well.
  • 8. An aquifer is a ground-water reservoir composed of geologic units that are saturated with water and sufficiently permeable to yield water in a usable quantity to wells and springs. Sand and gravel deposit ,sandstone ,limestone ,and fractured, crystalline rocks are examples of geological units that form aquifers. Aquifers provide two important functions: (1) they transmit ground water from areas of recharge to areas of discharge, and (2) they provide a storage medium for useable quantities of ground water. The amount of water a material can hold depends upon its porosity. The size and degree of interconnection of those openings (permeability) determine the materials ability to transmit fluid.
  • 9. 7.3.TYPES OF AQUIFER There are all kinds of aquifers. The most commonly used types are the confined (or artesian) aquifer, the unconfined(or free, phreatic) aquifer and the semi-confined aquifer Confined aquifers(artesian) are confined because they have an aquitard above and below the aquifer. These aquifers do not recharge quickly because it takes a long time for water to pass through the top aquitard. In some cases, confined aquifers contain high quality water because they are not directly impacted by human activity on the surface. Confined aquifers can contain groundwater that is very old. Water can stay in a confined aquifer for several millennia. confinedaquiferhaswatertable unconfinedaquifer (free, phreatic) aquifer is an aquifer underlain by an impermeable stratum, but the top of the aquifer consists of soil layers that are permeable enough to provide easy passage of water, at least in vertical sense. Such an aquifer has a free water table or phreatic surface. When perforating a hole into the ground until it fills with water, and letting the water come to rest, the water level in the hole can be observed and it indicates the level of the water table in the aquifer outside the hole. Many alluvial fans and river plains have unconfined aquifers in the upper part of the sediment deposits. The Indus basin in Pakistan provides examples of extensive and deep unconfined aquifers. Where the water quality of the aquifer is acceptable, the aquifer is intensively pumped from wells, mostly for irrigation purposes.
  • 10. semi-confined aquifer A semi-confined aquifer is an aquifer underlain by an impermeable stratum and bounded at the top by soil layers of relatively low permeability (hydraulic conductivity), especially in horizontal sense. These layers form the semi-confining layer (the aquitard) in which a free water table is found. The flow of water in the top layer is mainly vertical while the horizontal flow is negligible. Semi-confined aquifers are often found in river delta's and coastal plains.
  • 11. 7.4.Properties OF Aquifer The most important properties of the aquifer are porosity and specific yield which in turn give its capacity to release the water in the pores and its ability to transmit the flow with ease. Porosity is a measure of how much water a body of rock can hold. In and , porosity is defined as the ratio of volume of voids to the total volume of porous medium. The significance of the porosity is that it gives the idea of storage capacity of the aquifer. Qualitatively, porosity less than 5% is considered to be small, between 5 and 20% as medium and the percentage exceeding 20% is considered as large. Specific yield &specific retention is a measure of how much an aquifer can yield or produce . the actual amount of water that can be extracted from the unit volume of aquifer by pumping of under the action of gravity. some of the pores may not connect with other pores or they may be so tenuously connected that water can not move readily from one to another. While water molecule are very small and can make their way in to even the tiniest spaces in a rock, they are strongly attracted and held to solids by surface tension. the strength of the attraction b/n the water and the mineral grains is proportional to the distance b/n the water molecule and the surface. the proportion of the water in the rock that does drain out readily is known as the specific yield. specific retention is the opposite of specific yield. the sum of specific retention and specific is porosity.
  • 12. Aquifer materials Both consolidated and unconsolidated geological material are important as aquifer. Of the consolidated materials(bed rock) sedimentary rocks are the most important b/c they tend to have the highest porosities and permeability. Rock properties- from the perspective of hydrogeology the important characteristics of rocks are how much open space they have, how well connected those open spaces are, how strong the rocks are, and how soluble they are. Hydraulic conductivity(permeability)-is the ability of the rock or unconsolidated material to transmit water. very fine grained rocks and materials or rocks with disconnected porosity tend to have low conductivities. Hydraulic conductivity which is denoted using the symbol K is expressed in velocity units, but it is not a measure of velocity by it self. the hydraulic conductivity is used to estimate the flow of dilute water.