IMTS Civil Eng. (Water resource system engineering)

I ns t i t ut eo fMa na g e me nt & Te c hni c a lSt udi e s WATERRESOURCESYSTEM ENGI NEERI NG

Ci v i lEng i ne e r i ng www.imtsinstitute.com

IMTS (ISO 9001-2008 Internationally Certified) WATER RESOURCE SYSTEM ENGINEERING

WATER RESOURCE SYSTEM ENGINEERING

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CONTENTS UNIT I WATER

01-61 RESOURCES,IMPORTANCE

WATER,WATER

OF

WATER,PROPERTIES

CONSERVATION,HYDROLOGICAL

,LAKES,RESERVOIR,DAMS,MARINE RESOURCES

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OF CYCLE

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UNIT I WATER RESOURCES Water resources are sources of water that are useful or potentially useful to humans.

Uses of water include agricultural, industrial, household, recreational and environmental activities. Virtually all of these human uses require fresh water. 97% of water on the Earth is salt water, leaving only 3% as fresh water of which slightly over two thirds is frozen in glaciers and polar ice caps. The remaining unfrozen freshwater is mainly found as groundwater, with only a small fraction present above ground or in the air. Fresh water is a renewable resource, yet the world's supply of clean, fresh water is steadily decreasing. Water demand already exceeds supply in many parts of the world and as the world population continues to rise, so too does the water demand. Awareness of the global importance of preserving water for ecosystem services has only recently emerged as, during the 20th century, more than half the world’s wetlands have been lost along with their valuable environmental services. Biodiversity-rich freshwater ecosystems are currently declining faster than marine or land ecosystems. The framework for allocating water resources to water users (where such a framework exists) is known as water rights.

Sources of water resources 1. Surface water Surface water is water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans, evaporation, and sub-surface seepage. Although the only natural input to any surface water system is precipitation within its watershed, the total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity in lakes, wetlands and artificial reservoirs, the permeability of the soil beneath these storage bodies, the runoff characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water lost.

Human activities can have a large impact on these factors. Humans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase runoff quantities and velocities by paving areas and channelizing stream flow. The total quantity of water available at any given time is an important consideration. Some human water users have an intermittent need for water. For example, many farms require large quantities of water in the spring, and no water at all in the winter. To supply such a farm with water, a surface

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water system may require a large storage capacity to collect water throughout the year and release it in a short period of time. Other users have a continuous need for water, such as a power plant that requires water for cooling. To supply such a power plant with water, a surface water system only needs enough storage capacity to fill in when average stream flow is below the power plant's need.

Nevertheless, over the long term the average rate of precipitation within a watershed is the upper bound for average consumption of natural surface water from that watershed. Natural surface water can be augmented by importing surface water from another watershed through a canal or pipeline. It can also be artificially augmented from any of the other sources listed here, however in practice the quantities are negligible. Humans can also cause surface water to be "lost" (i.e. become unusable) through pollution. Brazil is the country estimated to have the largest supply of fresh water in the world, followed by Russia and Canada.

2. Under river flow Throughout the course of the river, the total volume of water transported downstream will often be a combination of the visible free water flow together with a substantial contribution flowing through sub-surface rocks and gravels that underlie the river and its floodplain called the hyporheic zone. For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow. The hyporheic zone often forms a dynamic interface between surface water and true ground-water receiving water from the ground water when aquifers are fully charged and contributing water to ground-water when ground waters are depleted. This is especially significant in karst areas where pot-holes and underground rivers are common.

3. Ground water Sub-surface water, or groundwater, is fresh water located in the pore space of soil and rocks. It is also water that is flowing within aquifers below the water table. Sometimes it is useful to make a distinction between sub-surface water that is closely associated with surface water and deep sub-surface water in an aquifer (sometimes called "fossil water").

Sub-surface water can be thought of in the same terms as surface water: inputs, outputs and storage. The critical difference is that due to its slow rate of turnover, sub-surface water storage is generally much larger compared to inputs than it is for surface water. This difference makes it easy for humans to use sub-surface water unsustainably for a long time without severe consequences. Nevertheless, over the long term the average rate of seepage above a subsurface water source is the upper bound for average consumption of water from that source.

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The natural input to sub-surface water is seepage from surface water. The natural outputs from sub-surface water are springs and seepage to the oceans. If the surface water source is also subject to substantial evaporation, a sub-surface water source may become saline. This situation can occur naturally under endorheic bodies of water, or artificially under irrigated farmland. In coastal areas, human use of a sub-surface water source may cause the direction of seepage to ocean to reverse which can also cause soil salinization. Humans can also cause sub-surface water to be "lost" (i.e. become unusable) through pollution. Humans can increase the input to a sub-surface water source by building reservoirs or detention ponds.

4. Desalination Desalination is an artificial process by which saline water (generally sea water) is converted to fresh water. The most common desalination processes are distillation and reverse osmosis. Desalination is currently expensive compared to most alternative sources of water, and only a very small fraction of total human use is satisfied by desalination. It is only economically practical for high-valued uses (such as household and industrial uses) in arid areas. The most extensive use is in the Persian Gulf.

IMPORTANCE OF WATER With two thirds of the earth's surface covered by water and the human body consisting of 75 percent of it, it is evidently clear that water is one of the prime elements responsible for life on earth. Water circulates through the land just as it does through the human body, transporting, dissolving, replenishing nutrients and organic matter, while carrying away waste material.

Further in the body, it regulates the activities of fluids, tissues, cells, lymph, blood and glandular secretions.

An average adult body contains 42 litres of water and with just a small loss of 2.7 litres he or she can suffer from dehydration, displaying symptoms of irritability, fatigue, nervousness, dizziness, weakness, headaches and consequently reach a state of pathology. Dr F. Batmanghelidj, in his book 'your body's many cries for water', gives a wonderful essay on water and its vital role in the health of a water 'starved' society. He writes: "Since the 'water' we drink provides for cell function and its volume requirements, the decrease in our daily water intake affects the efficiency of cell activity........as a result chronic dehydration causes symptoms that equal disease..."

1. The history of water

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Water has been used since antiquity as a symbol by which to express devotion and purity. Some cultures, like the ancient Greeks, went as far as to worship gods who were thought to live in and command the waters. Whole cities have been build by considering the location and availability of pure drinking water. The place of gathering was around the wells, which is perhaps the following trend in building fountains in the middle of piazzas.

Traditional and modern medicine have been makings use of the psychological and physiological diverse properties of water, in all forms of hydrotherapy (composite Greek word: hydro, of water and therapy, . We all know of the simple, yet effective, calming qualities of a warm bath or the invigorating qualities of a cold shower. For centuries, numerous healing springs located all around the world have been recognised for their benefits. The famous Belgium spas in the Ardennes is a fine example. Historical records of these cold springs claim 'cures' since the fourteenth century. The hot Californian spas, the healing spas of Loutraki in Greece, the Dalhousie hot springs in the border of South Australia and Northern Territory, Moree in NSW, Hepburn mineral spas in Victoria are just a few examples.

2. Our water today Contrary to the past, our recent developed technological society has become indifferent to this miracle of life. Our natural heritage (rivers, seas and oceans) has been exploited, mistreated and contaminated.

The population decline of the marine and riparian life, the appearance of green algae in the rivers and the stench and slime that comes as a result of putrefaction in the water, are clear signs of the depth and extent of disruption that has been caused to this intricate ecosystem (a composite Greek word: eco, home and systema, a combination of things or parts forming a complex or unitary whole). Government bodies and water authorities will have us believe that it is 'safe' and we should not worry about this global alarm. Awareness and action lies entirely upon us, as we need to become our own educators, physicians and innovators. Socrates had once said: "an unexamined life is not worth living", Jesus took it a step further: "seek, and you shall find the truth shall set you free" So questioning everything and anything that anyone tells you until it makes sense, is of uppemost importance. If it is the truth it will feel right, set you free and lead you on the road of discovery and recovery.

3. The truth about the drinking water Our drinking water today, far from being pure, contains some two hundred deadly commercial chemicals. Add to that bacteria, viruses, inorganic minerals (making the water hard)

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and you have a chemical cocktail that is unsuitable (if not deadly) for human consumption. John Archer in his book 'THE WATER YOU DRINK, HOW SAFE IS IT ?' refers to an estimate of 60,000 tonnes of fifty different chemicals being deliberately added annually to Australia's water.

Some of these are: Chlorine: studies1 indicate that chlorine is involved in heart disease, hardening of the arteries (arteriosclerosis), anaemia, high blood pressure, allergies and cancers2 of the bladder, stomach, liver and rectum. Further, chlorine can destroy protein in the body and cause adverse effects on the skin and hair. The US COUNCIL of environmental quality states that cancer risk among people drinking chlorinated water is 93% higher than among those whose water does not contain chlorine". Chlorine binds and reacts with many other chemicals, forming carcinogens like Trihallomethanes (THMs), with chloroform being the most common one. Furthermore, recent real life evidence in the tap water of Sydney shows that certain viruses and parasites, like giardia and cryptosporidium, are being resistant to chlorine and can survive the long journey from the sewage treatment to your tap. That makes chlorination a even more pointless and dangerous practice.

Giardia and cryptosporidium are protosoa (unicellular organisms) parasitic to the intestines of animals and humans. Once in the body, these parasites then multiply and cause the respective infections of giardiasis and cryptosporidosis, which contribute or are associated to enteric (intestinal) diseases. Other than food, these parasites are transmited from contaminated drinking water. These infested waters are today in most major cities which is a direct result of the unsuccsessful treatment of recycled sewage effluent. These parasites initially venture their way into the sewage effluent, from Hospitals, abattoir and farms waste, which contain blood, intestines and faeces. While immunocompitend (the ability to develope an immune response) people may remain asymptomatic (presenting no symptons) by ingestion of this parasites, immunocompromised (ie malnutrition Cancer and Aids) patients are at risk. U.S Health Officials estimate 900,000 people each year become ill, and possibly 900 die from waterborne disease4. Notable outbreaks occured in Milwauke, Wisconsin, in 1993 when over 400,000 people became ill after drinking water contaminated with the parasite. Symptoms associated with the infection of this parasites are, mild to profuse debilitating diarrhoea, lassitude, nausea, abdominal pain and vomiting with consequent loss of appetite and fever. The threat and danger of outbreaks similar to the dreaded great London epidemic in 1854 (were cholera due to contaminated water took the life of many unaware citizens) is now once again at our door step and unless drastic precautions are taken on these early sign's we could be

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expecting disasters of great magnitude (in the apocalipse it states, that one third of the waters will be contaminated, could this be it?). For now it is about time that water authorities admit to their erroneous ways and start looking for alternatives to maintain and preserve water safety and quality. Water is a living substance and as such it needs the same treatment as all other living forms (poisons can not purify). Germany has been for long now pumping oxygen in its rivers and lakes in an attempt to revitalise its nearly dead waters, while Switzerland is experimenting with ozone treatments.

Aluminium sulphate: that is added to clarify water, has long been associated with Smemory loss, possibly Alzheimers disease and is believed to increase cardiovascular disease.

Sodium fluoride: this is not a water treatment and was initially added as a supplement to 'assumingly' prevent tooth decay5 in children. Its toxicity is high enough that in larger concentrations can be used as a pesticide and rat killer. In humans it can be damaging to the heart, lungs, liver, cause genetic mutations and have long term negative effects on enzyme production and the efficiency of the immune system. In the medical encyclopedia and dictionary

by Miller-Keane, under fluoridation it refers that slight excesses of fluoride are poisonous and it can cause dental fluorosis (mottled discolouration of teeth) and when you look up further down under fluorosis, you can see clearly the irony of the system an enamel hypoplasia resulting from prolonged ingestion of drinking water containing high levels of fluoride". Tests carried out in Victoria in 1976 by the State Water Supply Commission indicated that fluoride is involved in the corrosion of the copper pipes, which causes more poisons leaching into the water. Copper at certain concentrations effects the uptake of essential zinc in the body and can bring on stomach pain, nausea and diarrhoea. Newer office blocks and high stories buildings are more risky, as taps are not regularly used, leaving fluorinated water standing in the copper pipes for longer periods of times, consequently allowing corrosion. As the debate about the safety of fluoride continuous, countries such as Switzerland, Belgium, Holland, Germany and Sweden have terminated its use due to its potential health hazard. lead: is another chemical ingredient found in the water that imposes risks to the nervous, circulatory and digestive systems. It is a teratogen, a substance known to cause physical defects in the developing embryo. Chronic exposure, even in small doses, may have serious implications to your well being. Symptoms to be wary of are irritability, nervousness, weight loss, anaemia, stomach crumps, constipation and mental depression. The main source of lead in the water is the plumbing and its corrosion.

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The list of chemicals continues: sodium sillicofluoride slurry, sulphuric acid, sodium hypochlorite solution, calcium oxide, silt, rust, algae, debris, larvae, asbestos (mostly from corroding cement pipe lines), pesticides, herbicides, fertilisers (from agricultural run offs), moulds, fungi, industrial waste, toxic metals, amoebas, clay and silica have all found their way into the water. As if this is not enough, chemical reactions of the different constituents in our drinking chemical and sewage cocktail make things even worse.

Nitrates from fertilisers when brought in contact with chlorine and ammonia, can turn into nitrites. Nitrites once inside the body combine with amines and form nitrosamines which are highly carcinogenic. Nitrites can interfere with oxygen uptake and since babies are specifically sensitive to this aspect you could not fail to see a possible link between blue baby syndrome and the nitrite factor.

According to studies by the state of California, women who drink tap water have twice as many miscarriages and birth defects as those who have filtering devises or are drinking bottled water. Five studies arrived to the same conclusion, according to State Health, Director Kenneth Kizer. This connection now is such a common knowledge that it even appeared as a passing comment during the movie 'ONE THOUSAND ACRES'.

Inorganic minerals (minerals not suitable for human consumption) such as calcium carbonate, have their effect. Unable to be assimilated they store in between joints, muscles, bones, nerves, inside arteries and become partners in many crippling dis-eases, such as arthritis, hardening of the arteries, gall stones, kidney stones, gout, tinnitus and perhaps even stroke and neuralgia. Dr Paul C. Bragg in his essay and book 'THE SHOCKING TRUTH ABOUT WATER' argues that the human brain and other body structures will become hardened largely through the use of "chemicalized and inorganically mineralised water".

Dr E. Banik, in his book 'THE CHOICE IS CLEAR', explains that inorganic minerals coat the crystalline lens of the eye with a fine film, resulting in cataracts. Glaucoma, the dreadful eye disease, can be another result of hard water. The tiny vessels film up with mineral deposits, which results in a build-up pressure in the eye.

4. What choices have we got?

Dr Batmanghelidj talks about the shrinking of the vital organs due to insufficient hydration. Dr Bragg postulates how inorganic minerals in water turns people into 'stones' and

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advises the use of pure water. John Archer alarms of the dangers and condition of public (sewage) water You are what you drink so make sure what you drink is pure' Ten years ago the prospect of drinking only purified or bottled water was a fiction, or a novelty for most people. Nowadays, it is becoming a necessity in maintaining and preserving good health. Finding pure water is becoming more than just food for thought and with our brain being 85 percent water, we better start thinking of the choices. It is my opinion and as well of others that tap water should not be drunk at all if other sources are available. However, if tap water is your only option, then boil the water for a few minutes, expose it to the sun for a while in a clear glass container and then aerate it by pouring it back and forth from one container to another. Keep in mind that boiling will only kill bacteria and that harmful chemicals and minerals will still remain in the water. Rain water it is no longer the best available option with today's pollution. Water is a hungry solvent and as the rain falls, it begins to collect hundreds of potentially harmful substances, such as radioactive isotopes and their degradation products of atomic fission including barium, caesium and strontium from world wide atomic experiments and "accidents" which travel around the atmosphere (<I style="mso-bidi-font-style: normal">refer to chart). In addition industrial and exhaust fumes including carbon monoxide, sulphuric acid and lead are collected. That is why the sky looks so clean after a good 'acid' rain.

Spring water contains those unwanted inorganic minerals and their purity is debatable if you consider the pollution of the soil. So use it sparingly or when nothing else is available. Don't be mislead by claims about the value of inorganic minerals, the body cannot make use of any minerals unless they are derived from the plant kingdom (organic minerals). A well balanced diet will provide an abundance of organic minerals that water never could. In his book 'New Life Through Nutrition' nutritionist Dr Shelton Deal debates that we should not look to water as our source of minerals. As for the inexpensive supermarket filters they don't eliminate all impurities and toxins (not that it is claimed that they do).

Reverse osmosis is by far the most advanced technology for home installation available to the public. It is based on the process by which the human cells diffuse fluids between the intracellular and extracellular spaces, by separating and selectively preventing the passage of solute molecules (through a semipermeable membrane) and allowing the passage of the solvent H2O. Through this process almost all harmful bacteria, minerals and toxins are eliminated. Professional installation and surveillance is necessary for if the membrane is

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ruptured without your knowledge the final condition of the water could be worse than if it were not filtered.

Distilled water, contrary to the wide held view that it leaches organic essential minerals and micronutrients from your body, its emptiness works in your favour. It dissolves and eliminates harmful inorganic minerals and toxic waste accumulation. Once the organic nutrients have been absorbed by the cells they cannot be taken away. Is there an inherent intelligentsia behind all this? The answer is yes! after all, what is the animating factor behind all things? but far from being just an esoteric answer, the key lies in the inherent 'instructions' of the human body's filtering system. The kidneys make sure that nothing valuable will be lost, there is a constant recycling, so even if nutrients were to be 'stolen' they would be returned by the kidneys. Which explains the dark appearance of urine during times of inadequate hydration.

Distillation is achieved by boiling the water, steam then rises and is collected in a condenser where it is stored and cooled. The problem in this process is that together with the steam, percentage of the pollutant gases such fluorine and chlorine are also evaporated over into the condenser. To overcome this problem scientists developed other methods like fragmented distillation and C.M.D method (Cold Molecular Distillation) amongst others. C.M.D water is available from companies6 specialising in this area and supply water for medical purposes, allergy affected chemical sensitive people, cancer and dialysis patients (were even small traces of contaminants can send the patient into shock) and generally to any one who is seeking good health. C.M.D water contains no solid matter and is solely consisting of two elements, Hydrogen and Oxygen.

5. The amount of water your body needs: Another important factor is the amount of water necessary for our body to function at its peak performance. Bearing in mind again that your body is about 75 percent water it is easy to understand that water must be your body's most essential daily ingredient. Your body looses each day about 2-3 litters of water through elimination, urination, perspiration and respiration.

However, this may increase during illness, high performance, exercise, pregnancy and nursing.

The beverages most people choose to consume are often counter-productive in promoting hydration. Coffee, tea, alcohol, soft and sugary drinks are all diuretics and will cause not only the loss of water the are dissolved in, but they will also draw water the bodies reserves. In normal conditions your body needs to replace the fluids it has lost throughout the day. Most of fluids should be replaced by drinking pure water. The rest you should get from fruit, vegetables and their juices. Attention must be given that the elderly and children are meeting their daily

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requirements. Dry mouth is not the only indication of dehydration, in fact it is the last sign. You need to acquire the habit to drink water even when you think you don't need it and eventually your true thirst mechanisms will be reawaken. Signs to look for that identify with dehydration are constipation, headaches, indigestion, weight gain, fluid retention, dark and pungent urine, and their associated pathologies colitis, kidney stones, bladder and urinary track infections to name only a few.

Water is involved in all bodily functions: digestion, assimilation, elimination, respiration, maintaining temperature (homeostasis) integrity and the strength of all bodily structures. Today, the water is polluted with hundreds of toxins and impurities. Authorities only test for a small number of them. Your body, being primarily water, requires sufficient daily water replacement in order to function efficiently. Water treatments, that are aimed to render our drinking water bacteriologically safe, have been proven ineffective and the presence of certain pathogenic bacteria like giardia and cryptosporidium recently found in Sydney water is just one of the many examples. Viewing the effects of individual chemicals, inorganic minerals and their by-products, you can see a link to today's major diseases. If you drink devitalised, impure water how can you expect vitality and health. Dehydration, due to the offensive taste of the water and the introduction of commercial sugar loaded beverages, has become another contributing factor to dis-ease. The advice of Dr Batmanghelidj to stop treating thirst with medications holds lots of merit. Mineral water may be wonderful to bathe in, however, the presence of inorganic minerals makes it undesirable. Tap water has been proven unsuitable even for showering7. In an article published in the magazine New Scientist, by Ian Anderson 18/9/86, he writes "Showers pose a risk to health". Pure water may become the medicine of the future. 'Oxygen enriched and free of radioactive and chemical compounds' may read on the label of our bottle water in the next millennium.... At this stage Reverse Osmosis and C.M.D water are our best available options.

PROPERTIES OF WATER Water is the chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom.

The major chemical and physical properties of water are: ď ś Water is a tasteless, odorless liquid at standard temperature and pressure. The color of water and ice is, intrinsically, a very light blue hue, although water appears colorless in small quantities. Ice also appears colorless, and water vapor is essentially invisible as a gas.

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 Water is transparent, and thus aquatic plants can live within the water because sunlight can reach them. Only strong UV light is slightly absorbed.  Since oxygen has a higher electronegativity than hydrogen, water is a polar molecule.

The oxygen has a slight negative charge while the hydrogens have a slight positive charge giving the article a strong effective dipole moment. The interactions between the different dipoles of each molecule cause a net attraction force associated with water's high amount of surface tension.  The dipolar nature contributes to water molecules' tendency to form hydrogen bonds which cause water's cohesive properties.  Water has a high surface tension caused by the weak interactions, (Van Der Waals Force) between water molecules because it is polar. The apparent elasticity caused by surface tension drives the capillary waves.  Water also has high adhesion properties because of its polar nature.  Capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.  Water is a very strong solvent, referred to as the universal solvent, dissolving many types of substances. Substances that will mix well and dissolve in water, e.g. salts, sugars, acids, alkalis, and some gases: especially oxygen, carbon dioxide (carbonation), are known as "hydrophilic" (water-loving) substances, while those that do not mix well with water (e.g. fats and oils), are known as "hydrophobic" (water-fearing) substances.  All the major components in cells (proteins, DNA and polysaccharides) are also dissolved in water.  Pure water has a low electrical conductivity, but this increases significantly upon solvation of a small amount of ionic material such as sodium chloride.  The boiling point of water (and all other liquids) is directly related to the barometric pressure. For example, on the top of Mt. Everest water boils at about 68 °C (154 °F), compared to 100 °C (212 °F) at sea level. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.  Water has the second highest specific heat capacity of any known substance, after ammonia, as well as a high heat of vaporization (40.65 kJ mol−1), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual

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properties allow water to moderate Earth's climate by buffering large fluctuations in temperature.  The maximum density of water occurs at 3.98 °C (39.16 °F). Water becomes even less dense upon freezing, expanding 9%. This causes an unusual phenomenon: ice floats upon water, and so water organisms can live inside a partly frozen pond because the water on the bottom has a temperature of around 4 °C (39 °F).  ADR label for transporting goods dangerously reactive with water  Water is miscible with many liquids, for example ethanol, in all proportions, forming a single homogeneous liquid. On the other hand, water and most oils are immiscible usually forming layers according to increasing density from the top. As a gas, water vapor is completely miscible with air.  Water forms an azeotrope with many other solvents.  Water can be split by electrolysis into hydrogen and oxygen.  As an oxide of hydrogen, water is formed when hydrogen or hydrogen-containing compounds burn or react with oxygen or oxygen-containing compounds. Water is not a fuel, it is an end-product of the combustion of hydrogen. The energy required to split water into hydrogen and oxygen by electrolysis or any other means is greater than the energy released when the hydrogen and oxygen recombine.  Elements which are more electropositive than hydrogen such as lithium, sodium, calcium, potassium and caesium displace hydrogen from water, forming hydroxides.

Being a flammable gas, the hydrogen given off is dangerous and the reaction of water with the more electropositive of these elements may be violently explosive.  At ultrahigh pressures found in deep interiors of giant planets Uranus and Neptune water may become metallic, which would have important implications for the generation of the magnetic fields of these planets.

1. Physical properties We live on a planet that is dominated by water. More than 70% of the Earth's surface is covered with this simple molecule. Scientists estimate that the hydrosphere contains about 1.36 billion cubic kilometers of this substance mostly in the form of a liquid (water) that occupies topographic depressions on the Earth. The second most common form of the water molecule on our planet is ice. If all our planet's ice melted, sea-level would rise by about 70 meters.

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Water is also essential for life. Water is the major constituent of almost all life forms.

Most animals and plants contain more than 60% water by volume. Without water life would probably never have developed on our planet.

Water has a very simple atomic structure. This structure consists of two hydrogen atoms bonded to one oxygen atom (Fig.3.1). The nature of the atomic structure of water causes its molecules to have unique electrochemical properties. The hydrogen side of the water molecule has a slight positive charge. On the other side of the molecule a negative charge exists. This molecular polarity causes water to be a powerful solvent and is responsible for its strong surface tension (for more information on these two properties see the discussion below).

Fig. 3.1. The atomic structure of a water (or dihydrogen monoxide) molecule consists of two hydrogen (H) atoms joined to one oxygen (O) atom. The unique way in which the hydrogen atoms are attached to the oxygen atom causes one side of the molecule to have a negative charge and the area in the opposite direction to have a positive charge. The resulting polarity of charge causes molecules of water to be attracted to each other forming strong molecular bonds.

When the water molecule makes a physical phase change its molecules arrange themselves in distinctly different patterns (Fig.3.2). The molecular arrangement taken by ice (the solid form of the water molecule) leads to an increase in volume and a decrease in density.

Expansion of the water molecule at freezing allows ice to float on top of liquid water.

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Fig.3.2. The three diagrams above illustrate the distinct arrangement patterns of water molecules as they change their physical state from ice to water to gas. Frozen water molecules arrange themselves in a particular highly organized rigid geometric pattern that causes the mass of water to expand and to decrease in density. The diagram above shows a slice through a mass of ice that is one molecule wide. In the liquid phase, water molecules arrange themselves into small groups of joined particles. The fact that these arrangements are small allows liquid water to move and flow. Water molecules in the form of a gas are highly charged with energy. This high energy state causes the molecules to be always moving reducing the likelihood of bonds between individual molecules from forming.

Water has several other unique physical properties. These properties are: ď ś Water has a high specific heat. Specific heat is the amount of energy required to change

the temperature of a substance. Because water has a high specific heat, it can absorb

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large amounts of heat energy before it begins to get hot. It also means that water releases heat energy slowly when situations cause it to cool. Water's high specific heat allows for the moderation of the Earth's climate and helps organisms regulate their body temperature more effectively.  Water in a pure state has a neutral pH. As a result, pure water is neither acidic nor basic.

Water changes its pH when substances are dissolved in it. Rain has a naturally acidic pH of about 5.6 because it contains natural derived carbon dioxide and sulfur dioxide.  Water conducts heat more easily than any liquid except mercury. This fact causes large

bodies of liquid water like lakes and oceans to have essentially a uniform vertical temperature profile.  Water molecules exist in liquid form over an important range of temperature from 0 -

100° Celsius. This range allows water molecules to exist as a liquid in most places on our planet.  Water is a universal solvent. It is able to dissolve a large number of different chemical

compounds. This feature also enables water to carry solvent nutrients in runoff, infiltration, groundwater flow, and living organisms.  Water has a high surface tension (Fig.3.3). In other words, water is adhesive and elastic,

and tends to aggregate in drops rather than spread out over a surface as a thin film. This phenomenon also causes water to stick to the sides of vertical structures despite gravity's downward pull. Water's high surface tension allows for the formation of water droplets and waves, allows plants to move water (and dissolved nutrients) from their roots to their leaves, and the movement of blood through tiny vessels in the bodies of some animals.

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Fig.3.3. The following illustration shows how water molecules are attracted to each other to create high surface tension. This property can cause water to exist as an extensive thin film over solid surfaces. In the example above, the film is two layers of water molecules thick.

Fig.3.4. The adhesive bonding property of water molecules allows for the formation of water droplets (Photo © 2004 Edward Tsang).  Water molecules are the only substance on Earth that exist in all three physical states of

matter: solid, liquid, and gas. Incorporated in the changes of state are massive amounts of heat exchange. This feature plays an important role in the redistribution of heat energy in the Earth's atmosphere. In terms of heat being transferred into the atmosphere, approximately 3/4's of this process is accomplished by the evaporation and condensation of water.  The freezing of water molecules causes their mass to occupy a larger volume. When

water freezes it expands rapidly adding about 9% by volume. Fresh water has a maximum density at around 4° Celsius. Water is the only substance on this planet where the maximum density of its mass does not occur when it becomes solidified.

Table 3.1: Density of water molecules at various temperatures Temperature (degrees Celsius)

Density (grams per cubic centimeter)

0 (solid)

0.9150

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0 (liquid)

0.9999

4

1.0000

20

0.9982

40

0.9922

60

0.9832

80

0.9718

100 (gas)

0.0006

2. Chemical Properties of water i) The States of Water

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Water has three states. Below freezing water is a solid (ice or snowflakes), between freezing and boiling water is a liquid, and above its boiling point water is a gas. There are words scientists use to describe water changing from one state to another. Water changing from solid to liquid is said to be melting. When it changes from liquid to gas it is evaporating. Water changing from gas to liquid is called condensation (An example is the 'dew' that forms on the outside of a glass of cold soda). Frost formation is when water changes from gas directly to solid form. When water changes directly from solid to gas the process is called sublimation.

Most liquids contract (get smaller) when they get colder. Water is different. Water contracts until it reaches 4oC then it expands until it is solid. Solid water is less dense that liquid

Gas

Liquid

Solid

water because of this. If water worked like other liquids, then there would be no such thing as an ice berg, the ice in your soft drink would sink to the bottom of the glass, and ponds would freeze from the bottom up.

Water is found on Earth in all three forms. This is because Earth is a very special planet with just the right range of temperatures and air pressures. Earth is said to be at the triple point for water. ii) Surface Tension Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. Try this at home: place a drop of water onto a piece of wax paper. Look closely at the drop. What shape is it? Why do you think it is this shape?

What is happening? Water is not attracted to wax paper (there is no adhesion between the drop and the wax paper). Each molecule in the water drop is attracted to the other water molecules in the drop. This causes the water to pull itself into a shape with the smallest amount of surface area, a bead (sphere). All the water molecules on the surface of the bead are 'holding' each other together or creating surface tension.

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Surface tension allows water striders to 'skate' across the top of a pond. You can experiment with surface tension. Try floating a pin or a paperclip on the top if a glass of water. A metal pin or paper clip is heavier than water, but because of the surface tension the water is able to hold up the metal.

iii) Capillary Action Surface tension is related to the cohesive properties of water. Capillary action however, is related to the adhesive properties of water. You can see capillary action 'in action' by placing a straw into a glass of water. The water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to a the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of the straw.

The thinner the straw or tube the higher up capillary action will pull the water (Can you make up an experiment to test this?).

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WATER CONSERVATION Our ancient religious texts and epics give a good insight into the water storage and conservation systems that prevailed in those days. Over the years rising populations, growing industrialization, and expanding agriculture have pushed up the demand for water. Efforts have been made to collect water by building dams and reservoirs and digging wells; some countries have also tried to recycle and desalinate (remove salts) water. Water conservation has become the need of the day. The idea of ground water recharging by harvesting rainwater is gaining importance in many cities.

In the forests, water seeps gently into the ground as vegetation breaks the fall. This groundwater in turn feeds wells, lakes, and rivers. Protecting forests means protecting water 'catchments'. In ancient India, people believed that forests were the 'mothers' of rivers and worshipped the sources of these water bodies.

1. Some ancient Indian methods of water conservation The Indus Valley Civilization, that flourished along the banks of the river Indus and other parts of western and northern India about 5,000 years ago, had one of the most sophisticated urban water supply and sewage systems in the world. The fact that the people were well acquainted with hygiene can be seen from the covered drains running beneath the streets of the ruins at both Mohenjodaro and Harappa. Another very good example is the well-planned city of Dholavira, on Khadir Bet, a low plateau in the Rann in Gujarat. One of the oldest water harvesting systems is found about 130 km from Pune along Naneghat in the Western Ghats. A large number of tanks were cut in the rocks to provide drinking water to tradesmen who used to travel along this ancient trade route. Each fort in the area had its own water harvesting and storage system in the form of rock-cut cisterns, ponds, tanks and wells that are still in use today.

A large number of forts like Raigad had tanks that supplied water. ď ś In ancient times, houses in parts of western Rajasthan were built so that each had a rooftop water harvesting system. Rainwater from these rooftops was directed into underground tanks. This system can be seen even today in all the forts, palaces and houses of the region. ď ś Underground baked earthen pipes and tunnels to maintain the flow of water and to transport it to distant places, are still functional at Burhanpur in Madhya Pradesh, Golkunda and Bijapur in Karnataka, and Aurangabad in Maharashtra.

2. Rainwater harvesting

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In urban areas, the construction of houses, footpaths and roads has left little exposed earth for water to soak in. In parts of the rural areas of India, floodwater quickly flows to the rivers, which then dry up soon after the rains stop. If this water can be held back, it can seep into the ground and recharge the groundwater supply.

This has become a very popular method of conserving water especially in the urban areas. Rainwater harvesting essentially means collecting rainwater on the roofs of building and storing it underground for later use. Not only does this recharging arrest groundwater depletion, it also raises the declining water table and can help augment water supply. Rainwater harvesting and artificial recharging are becoming very important issues. It is essential to stop the decline in groundwater levels, arrest sea-water ingress, i.e. prevent sea-water from moving landward, and conserve surface water run-off during the rainy season.

Town planners and civic authority in many cities in India are introducing bylaws making rainwater harvesting compulsory in all new structures. No water or sewage connection would be given if a new building did not have provisions for rainwater harvesting. Such rules should also be implemented in all the other cities to ensure a rise in the groundwater level.

Realizing the importance of recharging groundwater, the CGWB (Central Ground Water Board) is taking steps to encourage it through rainwater harvesting in the capital and elsewhere.

A number of government buildings have been asked to go in for water harvesting in Delhi and other cities of India.

All you need for a water harvesting system is rain, and a place to collect it! Typically, rain is collected on rooftops and other surfaces, and the water is carried down to where it can be used immediately or stored. You can direct water run-off from this surface to plants, trees or lawns or even to the aquifer.

Some of the benefits of rainwater harvesting are as follows  Increases water availability  Checks the declining water table  Is environmentally friendly  Improves the quality of groundwater through the dilution of fluoride, nitrate, and salinity  Prevents soil erosion and flooding especially in urban areas

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3. Rainwater harvesting: a success story Once Cherrapunji was famous because it received the largest volume of rainfall in the world It still does but ironically, experiences acute water shortages. This is mainly the result of extensive deforestation and because proper methods of conserving rainwater are not used.

There has been extensive soil erosion and often, despite the heavy rainfall and its location in the green hills of Meghalaya, one can see stretches of hillside devoid of trees and greenery.

People have to walk long distances to collect water.

In the area surrounding the River Ruparel in Rajasthan, the story is different - this is an example of proper water conservation. The site does not receive even half the rainfall received

by Cherrapunji, but proper management and conservation have meant that more water is available than in Cherrapunji.

The water level in the river began declining due to extensive deforestation and agricultural activities along the banks and, by the 1980s, a drought-like situation began to spread. Under the guidance of some NGOs (non-government organizations), the women living in the area were encouraged to take the initiative in building johads (round ponds) and dams to hold back rainwater. Gradually, water began coming back as proper methods of conserving and harvesting rainwater were followed. The revival of the river has transformed the ecology of the place and the lives of the people living along its banks. Their relationship with their natural environment has been strengthened. It has proved that humankind is not the master of the environment, but a part of it. If human beings put in an effort, the damage caused by us can be undone.

4. Agriculture Conservation of water in the agricultural sector is essential since water is necessary for the growth of plants and crops. A depleting water table and a rise in salinity due to overuse of chemical fertilizers and pesticides has made matters serious. Various methods of water harvesting and recharging have been and are being applied all over the world to tackle the problem. In areas where rainfall is low and water is scarce, the local people have used simple techniques that are suited to their region and reduce the demand for water.

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 In India's arid and semi-arid areas, the 'tank' system is traditionally the backbone of agricultural production. Tanks are constructed either by bunding or by excavating the ground and collecting rainwater.  Rajasthan, located in the Great Indian Desert, receives hardly any rainfall, but people have adapted to the harsh conditions by collecting whatever rain falls. Large bunds to create reservoirs known as khadin, dams called johads, tanks, and other methods were applied to check water flow and accumulate run-off. At the end of the monsoon season, water from these structures was used to cultivate crops. Similar systems were developed in other parts of the country. These are known by various local names ¾ jal talais in Uttar Pradesh, the haveli system in Madhya Pradesh, ahar in Bihar, and so on.

5. Reducing water demand Simple techniques can be used to reduce the demand for water. The underlying principle is that only part of the rainfall or irrigation water is taken up by plants, the rest percolates into the deep groundwater, or is lost by evaporation from the surface. Therefore, by improving the efficiency of water use, and by reducing its loss due to evaporation, we can reduce water demand.

There are numerous methods to reduce such losses and to improve soil moisture. Some of them are listed below.  Mulching, i.e., the application of organic or inorganic material such as plant debris, compost, etc., slows down the surface run-off, improves the soil moisture, reduces evaporation losses and improves soil fertility.  Soil covered by crops, slows down run-off and minimizes evaporation losses. Hence, fields should not be left bare for long periods of time.  Ploughing helps to move the soil around. As a consequence it retains more water thereby reducing evaporation.  Shelter belts of trees and bushes along the edge of agricultural fields slow down the wind speed and reduce evaporation and erosion.  Planting of trees, grass, and bushes breaks the force of rain and helps rainwater penetrate the soil.

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 Fog and dew contain substantial amounts of water that can be used directly by adapted plant species. Artificial surfaces such as netting-surfaced traps or polyethylene sheets can be exposed to fog and dew. The resulting water can be used for crops.  Contour farming is adopted in hilly areas and in lowland areas for paddy fields. Farmers recognize the efficiency of contour-based systems for conserving soil and water.  Salt-resistant varieties of crops have also been developed recently. Because these grow in saline areas, overall agricultural productivity is increased without making additional demands on freshwater sources. Thus, this is a good water conservation strategy.  Transfer of water from surplus areas to deficit areas by inter-linking water systems through canals, etc.  Desalination technologies such as distillation, electro-dialysis and reverse osmosis are available.  Use of efficient watering systems such as drip irrigation and sprinklers will reduce the water consumption by plants.

6. Water conservation The most important step in the direction of finding solutions to issues of water and environmental conservation is to change people's attitudes and habits¾this includes each one of us. Conserve water because it is the right thing to do. We can follow some of the simple things that have been listed below and contribute to water conservation.  Try to do one thing each day that will result in saving water. Don't worry if the savings are minimal¾every drop counts! You can make a difference.  Remember to use only the amount you actually need.  Form a group of water-conscious people and encourage your friends and neighbours to be part of this group. Promote water conservation in community newsletters and on bulletin boards. Encourage your friends, neighbours and co-workers to also contribute.  Encourage your family to keep looking for new ways to conserve water in and around your home.  Make sure that your home is leak-free. Many homes have leaking pipes that go unnoticed. Do not leave the tap running while you are brushing your teeth or soaping your face.

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 See that there are no leaks in the toilet tank. You can check this by adding colour to the tank. If there is a leak, colour will appear in the toilet bowl within 30 minutes. (Flush as soon as the test is done, since food colouring may stain the tank.)  Avoid flushing the toilet unnecessarily. Put a brick or any other device that occupies space

to

cut

down

on

the

amount

of

water

needed

for

each

flush.

When washing the car, use water from a bucket and not a hosepipe.  Do not throw away water that has been used for washing vegetables, rice or dals¾use it to water plants or to clean the floors, etc  You can store water in a variety of ways. A simple method is to place a drum on a raised platform directly under the rainwater collection source. You can also collect water in a bucket during the rainy season.

HYDROLOGICAL CYCLE The water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth (Fig.3.5). Since the water cycle is truly a "cycle," there is no beginning or end. Water can change states among liquid, vapor, and ice at various places in the water cycle. Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go.

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Fig. 3.5 Hydrologic Cycle 1. Description The sun, which drives the water cycle, heats water in the oceans. Water evaporates as vapor into the air. Ice and snow can sublimate directly into water vapor. Evapotranspiration is water transpired from plants and evaporated from the soil. Rising air currents take the vapor up into the atmosphere where cooler temperatures cause it to condense into clouds. Air currents move clouds around the globe, cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as snow and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Snowpacks can thaw and melt, and the melted water flows over land as snowmelt. Most precipitation falls back into the oceans or onto land, where the precipitation 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 huge amounts of 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.

2. Different Processes

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Fig. 3.6 Process of hydrologic cycle This is an education module about the movement of water on the planet Earth. The module includes a discussion of water movement in the United States, and it also provides specific information about water movement in Oregon.

The scientific discipline in the field of physical geography that deals with the water cycle is called hydrology. It is concerned with the origin, distribution, and properties of water on the globe. Consequently, the water cycle is also called the hydrologic cycle in many scientific textbooks and educational materials. Most people have heard of the science of meteorology and many also know about the science of oceanography because of the exposure that each discipline has had on television. People watch TV weather personalities nearly every day.

Celebrities such as Jacques Cousteau have helped to make oceanography a commonly recognized science. In a broad context, the sciences of meteorology and oceanography describe parts of a series of global physical processes involving water that are also major components of the science of hydrology. Geologists describe another part of the physical processes by addressing groundwater movement within the planet's subterranean features.

Hydrologists are interested in obtaining measurable information and knowledge about the water cycle. Also important is the measurement of the amount of water involved in the transitional stages that occur as the water moves from one process within the cycle to other processes.

Hydrology, therefore, is a broad science that utilizes information from a wide range of other sciences and integrates them to quantify the movement of water. The fundamental tools of

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hydrology are based in supporting scientific techniques that originated in mathematics, physics, engineering, chemistry, geology, and biology. Consequently, hydrology uses developed concepts from the sciences of meteorology, climatology, oceanography, geography, geology, glaciology, limnology (lakes), ecology, biology, agronomy, forestry, and other sciences that specialize in other aspects of the physical, chemical or biological environment. Hydrology, therefore, is one of the interdisciplinary sciences that is the basis for water resources development and water resources management.

The global water cycle can be described with nine major physical processes which form a continuum of water movement. Complex pathways include the passage of water from the gaseous envelope around the planet called the atmosphere, through the bodies of water on the surface of earth such as the oceans, glaciers and lakes, and at the same time (or more slowly) passing through the soil and rock layers underground. Later, the water is returned to the atmosphere. A fundamental characteristic of the hydrologic cycle is that it has no beginning an it has no end. It can be studied by starting at any of the following processes: evaporation, condensation, precipitation, interception, infiltration, percolation, transpiration, runoff, and storage.

The information presented below is a greatly simplified description of the major contibuting physical processes. They include:

i) Evaporation 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 waterbodies as water vapor. Some vapor always exists in the atmosphere. ii) Condensation

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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 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. iii) Precipitation Precipitation is the process that occurs when any and all forms of water particles fall from the atmosphere and reach the ground. 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 ocurrs 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.

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iv) Interception Interception is the process of interrupting the movement of water in the chain of transportation events leading to streams. The interception can take place by vegetal cover or depression storage in puddles and in land formations such as rills and furrows.

When rain first begins, the water striking leaves and other organic materials spreads over the surfaces in a thin layer or it collects at points or edges. When the maximum surface storage capability on the surface of the material is exceeded, the material stores additional water in growing drops along its edges. Eventually the weight of the drops exceed the surface tension and water falls to the ground. Wind and the impact of rain drops can also release the water from the organic material. The water layer on organic surfaces and the drops of water along the edges are also freely exposed to evaporation.

Additionally, interception of water on the ground surface during freezing and subfreezing conditions can be substantial. The interception of falling snow and ice on vegetation also occurs. The highest level of interception occurs when it snows on conifer forests and hardwood forests that have not yet lost their leaves. v) Infiltration Infiltration is the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil. The surface phenomonon 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. vi) Percolation Percolation is the movement of water though the soil, and it's layers, by gravity and capillary forces. The prime moving force of groundwater is gravity. Water that is in the zone of aeration where air exists is called vadose water. Water that is in the zone of saturation is called groundwater. For all practical purposes, all groundwater originates as surface water. Once underground, the water is moved by gravity. The boundary that separates the vadose and the saturation zones is called the water table. Usually the direction of water movement is changed

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from downward and a horizontal component to the movement is added that is based on the geologic boundary conditions.

Geologic formations in the earth's crust serve as natural subterranean reservoirs for storing water. Others can also serve as conduits for the movement of water. Essentially, all groundwater is in motion. Some of it, however, moves extremely slowly. A geologic formation which transmits water from one location to another in sufficient quantity for economic development is called an aquifer. The movement of water is possible because of the voids or pores in the geologic formations. Some formations conduct water back to the ground surface. A spring is a place where the water table reaches the ground surface. Stream channels can be in contact with an unconfined aquifer that approach the ground surface. Water may move from the ground into the stream, or visa versa, depending on the relative water level. Groundwater discharges into a stream forms the base flow of the stream during dry periods, especially during droughts. An influent stream supplies water to an aquifer while and effluent stream receives water from the aquifer. vii) Transpiration Transpiration is the biological process that occurs mostly in the day. Water inside of plants is transferred from the plant to the atmosphere as water vapor through numerous individual leave openings. Plants transpire to move nutrients to the upper portion of the plants and to cool the leaves exposed to the sun. Leaves undergoing rapid transiration can be significantly cooler than the surrounding air. Transpiration is greatly affected by the species of plants that are in the soil and it is strongly affected by the amount of light to which the plants are exposed. Water can be transpired freely by plants until a water deficit develops in the plant and it water-releasing cells (stomata) begin to close. Transpiration then continues at a must slower rate. Only a small portion of the water that plants absorb are retained in the plants.

Vegetation generally retards evaporation from the soil. Vegetation that is shading the soil, reduces the wind velocity. Also, releasing water vapor to the atmosphere reduces the amount of direct evaporation from the soil or from snow or ice cover. The absorption of water into plant roots, along with interception that occurs on plant surfaces offsets the general effects that vegetation has in retarding evaporation from the soil. The forest vegetation tends to have more

moisture

than

the

soil

beneath

the

viii) Runoff

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trees.

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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 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 stream flow and it is generally regarded as direct runoff or base flow. ix) Storage There are three basic locations of water storage that occur in the planetary water cycle.

Water is stored in the atmosphere; water is stored on the surface of the earth, and water stored in the ground.

Water stored in the atmosphere can be moved relatively quickly from one part of the planet to another part of the planet. The type of storage that occurs on the land surface and under the ground largely depend on the geologic features related to the types of soil and the types of rocks present at the storage locations. Storage occurs as surface storage in oceans, lakes, reservoirs, and glaciers; underground storage occurs in the soil, in aquifers, and in the crevices of rock formations.

The movement of water through the eight other major physical processes of the water cycle can be erratic. On average, water the atmosphere is renewed every 16 days. Soil moisture is replaced about every year. Globally, waters in wetlands are replaced about every 5 years while the residence time of lake water is about 17 years. In areas of low development by society, groundwater renewal can exceed 1,400 years. The uneven distribution and movement of water over time, and the spatial distribution of water in both geographic and geologic areas, can cause extreme phenomena such as floods and droughts to occur.

3. Water resources of India Although India occupies only 3.29 million km2 geographical area, which forms 2.4% of the world’s land area, it supports over 15% of the world’s population. The population of India as on 1 March 2001 stood at 1,027,015,247 persons. Thus, India supports about 1/6th of world population, 1/50th of world’s land and 1/25th of world’s water resources. India also has a

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livestock population of 500 million, which is about 20% of the world’s total livestock population.

More than half of these are cattle, forming the backbone of Indian agriculture. The total utilizable water resources of the country are assessed as 1086 km3. A brief description of surface and groundwater water resources of India is given below. i) Surface water resources In the past, several organizations and individuals have estimated water availability for the nation. Recently, the National Commission for Integrated Water Resources Development estimated the basin-wise average annual flow in Indian river systems as 1953 km3.

Utilizable water resource is the quantum of withdrawable water from its place of natural occurrence. Within the limitations of physiographic conditions and socio-political environment, legal and constitutional constraints and the technology of development available at present, utilizable quantity of water from the surface flow has been assessed by various authorities differently. The utilizable annual surface water of the country is 690 km3. There is considerable scope for increasing the utilization of water in the Ganga–Brahmaputra basins by construction of storages at suitable locations in neighbouring countries. ii) Groundwater resources The annual potential natural groundwater recharge from rainfall in India is about 342.43 km3, which is 8.56% of total annual rainfall of the country. The annual potential groundwater recharge augmentation from canal irrigation system is about 89.46 km3. Thus, total replenishable groundwater resource of the country is assessed as 431.89%. After allotting 15% of this quantity for drinking, and 6 km3 for industrial purposes, the remaining can be utilized for irrigation purposes. Thus, the available groundwater resource for irrigation is 361 km3, of which utilizable quantity (90%) is 325 km3. The basinwise per capita water availability varies between 13,393 m3 per annum for the Brahmaputra–Barak basin to about 300 m3 per annum for the Sabarmati basin.

LAKES A lake (from Latin lacus) is a terrain feature (or physical feature), a body of liquid on the surface of a world that is localized to the bottom of basin (another type of landform or terrain feature; that is, it is not global) and moves slowly if it moves at all. On Earth, a body of water is considered a lake when it is inland, not part of the ocean, is larger and deeper than a pond, and

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is fed by a river. The only world other than Earth known to harbor lakes is Titan, Saturn's largest moon, which has lakes of ethane, most likely mixed with methane. It is not known if Titan's lakes are fed by rivers, though Titan's surface is carved by numerous river beds.

Natural lakes on Earth are generally found in mountainous areas, rift zones, and areas with ongoing or recent glaciation. Other lakes are found in endorheic basins or along the courses of mature rivers. In some parts of the world, there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them.

1. Meaning and usage of "lake" There is considerable uncertainty about defining the difference between lakes and ponds, and no current internationally accepted definition of either term across scientific disciplines or political boundaries. For example, limnologists have defined lakes as waterbodies which are simply a larger version of a pond or which have wave action on the shoreline, or where wind induced turbulence plays a major role in mixing the water column. None of these definitions completely excludes ponds and all are difficult to measure. For this reason there has been increasing use made of simple size-based definitions to separate ponds and lakes. One definition of "lake" is a body of water of 2 hectares (5 acres) or more in area, however others have defined lakes as waterbodies of 5 hectares (12 acres) and above, or 8 hectares (20 acres) and above (see also the definition of "pond"). Charles Elton, one of the founders of ecology, regarded lakes as waterbodies of 40 hectares (99 acres) or more. The term "lake" is also used to describe a feature such as Lake Eyre, which is a dry basin most of the time but may become filled under seasonal conditions of heavy rainfall. In common usage, many lakes bear names ending with the word "pond", and a lesser number of names ending with "lake" are in quasitechnical fact, ponds.

In lake ecology the environment of a lake is referred to as lacustrine. Large lakes are occasionally referred to as "inland seas", and small seas are occasionally referred to as lakes.

Smaller lakes tend to put the word "lake" after the name, as in Green Lake, while larger lakes often invert the word order, as in Lake Ontario, at least in North America. In some places, the word "lake" does not correctly appear in the name at all (e.g., Windermere in Cumbria).

Only one lake in the English Lake District is actually called a lake; other than Bassenthwaite Lake, the others are all "meres" or "waters". Only six bodies of water in Scotland are known as lakes (the others are lochs): the Lake of Menteith, the Lake of the Hirsel,

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Pressmennan Lake, Cally Lake near Gatehouse of Fleet, the saltwater Manxman's Lake at Kirkcudbright Bay, and The Lake at Fochabers. Of these only the Lake of Menteith and Cally Lake are natural bodies of fresh water.

2. Distribution of lakes The majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes. More than 60% of the world's lakes are in Canada; this is because of the deranged drainage system that dominates the country.

Finland is known as The Land of the Thousand Lakes, (actually there are 187,888 lakes in Finland, of which 60,000 are large), and the U.S. state of Minnesota is known as The Land of Ten Thousand Lakes. The license plates of the Canadian province of Manitoba used to claim "100,000 lakes" as one-upmanship on Minnesota, whose license plates boast of its "10,000 lakes."

Most lakes have a natural outflow in the form of a river or stream, but some do not and lose water solely by evaporation or underground seepage or both. They are termed endorheic lakes (see below).

Many lakes are artificial and are constructed for hydro-electric power generation, recreational purposes, industrial use, agricultural use, or domestic water supply.

Evidence of extraterrestrial lakes exists; "definitive evidence of lakes filled with methane" was announced by NASA as returned by the Cassini Probe observing the moon Titan, which orbits the planet Saturn.

Globally, lakes are greatly outnumbered by ponds: of an estimated 304 million standing water bodies worldwide, 91% are 1 hectare (2.5 acres) or less in area (see definition of ponds).

Small lakes are also much more numerous than big lakes: in terms of area, one third of the world's standing water is represented by lakes and ponds of 10 hectares (25 acres) or less.

However, large lakes contribute disproportionately to the area of standing water with 122 large lakes of 1,000 square kilometres (390 sq mi, 100,000 ha, 247,000 acres) or more representing about 29% of the total global area of standing inland water.

3. Origin of natural lakes There are a number of natural processes that can form lakes. A recent tectonic uplift of a mountain range can create bowl-shaped depressions that accumulate water and form lakes.

The advance and retreat of glaciers can scrape depressions in the surface where water

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accumulates; such lakes are common in Scandinavia, Patagonia, Siberia, and Canada. The most notables examples are probably the Great Lakes of North America.

Lakes can also form by means of landslides or by glacial blockages. An example of the latter occurred during the last ice age in the U.S. state of Washington, when a huge lake formed behind a glacial flow; when the ice retreated, the result was an immense flood that created the Dry Falls at Sun Lakes, Washington.

Salt lakes (also called saline lakes) can form where there is no natural outlet or where the water evaporates rapidly and the drainage surface of the water table has a higher-thannormal salt content. Examples of salt lakes include Great Salt Lake, the Caspian Sea, the Aral Sea, and the Dead Sea. Small, crescent-shaped lakes called oxbow lakes can form in river valleys as a result of meandering. The slow-moving river forms a sinuous shape as the outer side of bends are eroded away more rapidly than the inner side. Eventually a horseshoe bend is formed and the river cuts through the narrow neck. This new passage then forms the main passage for the river and the ends of the bend become silted up, thus forming a bow-shaped lake.

Crater lakes are formed in volcanic craters and calderas which fill up with precipitation more rapidly than they empty via evaporation. Sometimes the latter are called caldera lakes, although often no distinction is made. An example is Crater Lake in Oregon, located within the caldera of Mount Mazama. The caldera was created in a massive volcanic eruption that led to the subsidence of Mount Mazama around 4860 BC. Some lakes, such as Lake Jackson in Florida, USA, come into existence as a result of sinkhole activity. Lake Vostok is a subglacial lake in Antarctica, possibly the largest in the world.

The pressure from the ice atop it and its internal chemical composition mean that, if the lake were drilled into, a fissure could result that would spray somewhat like a geyser.

Most lakes are geologically young and shrinking since the natural results of erosion will tend to wear away the sides and fill the basin. Exceptions are those such as Lake Baikal and Lake Tanganyika that lie along continental rift zones and are created by the crust's subsidence as two plates are pulled apart. These lakes are the oldest and deepest in the world. Lake Baikal, which is 25-30 million years old, is deepening at a faster rate than it is being filled by erosion and may be destined over millions of years to become attached to the global ocean. The Red Sea, for example, is thought to have originated as a rift valley lake.

4. Types of lakes

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 Periglacial: Part of the lake's margin is formed by an ice sheet, ice cap, or glacier, the ice having obstructed the natural drainage of the land.  Subglacial: A lake which is permanently covered by ice. They can occur under glaciers, ice caps, or ice sheets. There are many such lakes, but Lake Vostok in Antarctica is by far the largest. They are kept liquid because the overlying ice acts as a thermal insulator retaining energy introduced to its underside by friction, by water percolating through crevasses, by the pressure from the mass of the ice sheet above, or by geothermal heating below.  Glacial lake: a lake with origins in a melted glacier.  Artificial lake: A lake created by flooding land behind a dam, called an impoundment or reservoir; by deliberate human excavation; or by the flooding of an excavation incident to a mineral-extraction operation such as an open pit mine or quarry. Some of the world's largest lakes are reservoirs.  Endorheic, terminal or closed: A lake which has no significant outflow, either through rivers or underground diffusion. Any water within an endorheic basin leaves the system only through evaporation or seepage. These lakes, such as Lake Eyre in central Australia or the Aral Sea in central Asia, are most common in desert locations.  Meromictic: A lake which has layers of water which do not intermix. The deepest layer of water in such a lake does not contain any dissolved oxygen. The layers of sediment at the bottom of a meromictic lake remain relatively undisturbed because there are no living aerobic organisms.  Fjord lake: A lake in a glacially eroded valley that has been eroded below sea level.  Oxbow: A lake which is formed when a wide meander from a stream or a river is cut off to form a lake. They are called "oxbow" lakes due to the distinctive curved shape that results from this process.  Rift lake or sag pond: A lake which forms as a result of subsidence along a geological fault in the Earth's tectonic plates. Examples include the Rift Valley lakes of eastern Africa and Lake Baikal in Siberia.  Underground: A lake which is formed under the surface of the Earth's crust. Such a lake may be associated with caves, aquifers, or springs.

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 Crater: A lake which forms in a volcanic caldera or crater after the volcano has been inactive for some time. Water in this type of lake may be fresh or highly acidic and may contain various dissolved minerals. Some also have geothermal activity, especially if the volcano is merely dormant rather than extinct.  Lava: A pool of molten lava contained in a volcanic crater or other depression. Lava lakes that have partly or completely solidified are also referred to as lava lakes.  Former: A lake which is no longer in existence. Such lakes include prehistoric lakes and lakes which have permanently dried up through evaporation or human intervention.

Owens Lake in California, USA, is an example of a former lake. Former lakes are a common feature of the Basin and Range area of southwestern North America.  Seasonal lake: A lake that exists as a body of water during only part of the year.  Shrunken: Closely related to former lakes, a shrunken lake is one which has drastically decreased in size over geological time. Lake Agassiz, which once covered much of central North America, is a good example of a shrunken lake. Two notable remnants of this lake are Lake Winnipeg and Lake Winnipegosis.  Eolic: A lake which forms in a depression created by the activity of the winds.

5. Characteristics Lakes have numerous features in addition to lake type, such as drainage basin (also known as catchment area), inflow and outflow, nutrient content, dissolved oxygen, pollutants, pH, and sedimentation.

Changes in the level of a lake are controlled by the difference between the input and output compared to the total volume of the lake. Significant input sources are precipitation onto the lake, runoff carried by streams and channels from the lake's catchment area, groundwater channels and aquifers, and artificial sources from outside the catchment area. Output sources are evaporation from the lake, surface and groundwater flows, and any extraction of lake water by humans. As climate conditions and human water requirements vary, these will create fluctuations in the lake level.

Lakes can be also categorized on the basis of their richness in nutrients, which typically affects plant growth. Nutrient-poor lakes are said to be oligotrophic and are generally clear, having a low concentration of plant life. Mesotrophic lakes have good clarity and an average level of nutrients. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and

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possible algal blooms. Hypertrophic lakes are bodies of water that have been excessively enriched with nutrients. These lakes typically have poor clarity and are subject to devastating algal blooms. Lakes typically reach this condition due to human activities, such as heavy use of fertilizers in the lake catchment area. Such lakes are of little use to humans and have a poor ecosystem due to decreased dissolved oxygen.

Due to the unusual relationship between water's temperature and its density, lakes form layers called thermoclines, layers of drastically varying temperature relative to depth. Fresh water is most dense at about 4 degrees Celsius (39.2 째F) at sea level. When the temperature of the water at the surface of a lake reaches the same temperature as deeper water, as it does during the cooler months in temperate climates, the water in the lake can mix, bringing oxygenstarved water up from the depths and bringing oxygen down to decomposing sediments. Deep temperate lakes can maintain a reservoir of cold water year-round, which allows some cities to tap that reservoir for deep lake water cooling.

Since the surface water of deep tropical lakes never reaches the temperature of maximum density, there is no process that makes the water mix. The deeper layer becomes oxygen starved and can become saturated with carbon dioxide, or other gases such as sulfur dioxide if there is even a trace of volcanic activity. Exceptional events, such as earthquakes or landslides, can cause mixing, which rapidly brings up the deep layers and can release a vast cloud of toxic gases which lay trapped in solution in the colder water at the bottom of the lake.

This is called a limnic eruption. An example of such a release is the disaster at Lake Nyos in Cameroon. The amount of gas that can be dissolved in water is directly related to pressure. As the previously deep water surfaces, the pressure drops, and a vast amount of gas comes out of solution. Under these circumstances even carbon dioxide is toxic because it is heavier than air and displaces it, so it may flow down a river valley to human settlements and cause mass asphyxiation.

The material at the bottom of a lake, or lake bed, may be composed of a wide variety of inorganics, such as silt or sand, and organic material, such as decaying plant or animal matter.

The composition of the lake bed has a significant impact on the flora and fauna found within the lake's environs by contributing to the amounts and the types of nutrients available.

A paired (black and white) layer of the varved lake sediments correspond to a year.

During winter, when organisms die, carbon is deposited down, resulting to a black layer. At the same year, during summer, only few organic materials are deposited, resulting to a white layer

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at the lake bed. These are commonly used to track paleontological events which happened in the past.

6. Limnology Limnology is the study of inland bodies of water and related ecosystems. Limnology divides lakes into three zones: the littoral zone, a sloped area close to land; the photic or openwater zone, where sunlight is abundant; and the deep-water profundal or benthic zone, where little sunlight can reach. The depth to which light can reach in lakes depends on turbidity, determined by the density and size of suspended particles. A particle is in suspension if its weight is less than the random turbidity forces acting upon it. These particles can be sedimentary or biological in origin and are responsible for the color of the water. Decaying plant matter, for instance, may be responsible for a yellow or brown color, while algae may cause greenish water. In very shallow water bodies, iron oxides make water reddish brown. Biological particles include algae and detritus. Bottom-dwelling detritivorous fish can be responsible for turbid waters, because they stir the mud in search of food. Piscivorous fish contribute to turbidity by eating plant-eating (planktonivorous) fish, thus increasing the amount of algae (see aquatic trophic cascade). The light depth or transparency is measured by using a Secchi disk, a 20centimeter (8 in) disk with alternating white and black quadrants. The depth at which the disk is no longer visible is the Secchi depth, a measure of transparency. The Secchi disk is commonly used to test for eutrophication. For a detailed look at these processes, see lentic ecosystems.

A lake moderates the surrounding region's temperature and climate because water has a very high specific heat capacity (4,186 J·kg−1·K−1). In the daytime, a lake can cool the land beside it with local winds, resulting in a sea breeze; in the night, it can warm it with a land breeze.

7. How lakes disappear A lake may be infilled with deposited sediment and gradually become a wetland such as a swamp or marsh. Large water plants, typically reeds, accelerate this closing process significantly because they partially decompose to form peat soils that fill the shallows.

Conversely, peat soils in a marsh can naturally burn and reverse this process to recreate a shallow lake. Turbid lakes and lakes with many plant-eating fish tend to disappear more slowly.

A "disappearing" lake (barely noticeable on a human timescale) typically has extensive plant mats at the water's edge. These become a new habitat for other plants, like peat moss when

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conditions are right, and animals, many of which are very rare. Gradually the lake closes, and young peat may form, forming a fen. In lowland river valleys, where a river can meander, the presence of peat is explained by the infilling of historical oxbow lakes. In the very last stages of succession, trees can grow in, eventually turning the wetland into a forest.

Some lakes can disappear seasonally. These are called intermittent lakes and are typically found in karstic terrain. A prime example of an intermittent lake is Lake Cerknica in Slovenia.

Sometimes a lake will disappear quickly. On 3 June 2005, in Nizhny Novgorod Oblast, Russia, a lake called Lake Beloye vanished in a matter of minutes. News sources reported that government officials theorized that this strange phenomenon may have been caused by a shift in the soil underneath the lake that allowed its water to drain through channels leading to the Oka River.

The presence of ground permafrost is important to the persistence of some lakes.

According to research published in the journal Science ("Disappearing Arctic Lakes," June 2005), thawing permafrost may explain the shrinking or disappearance of hundreds of large Arctic lakes across western Siberia. The idea here is that rising air and soil temperatures thaw permafrost, allowing the lakes to drain away into the ground.

Neusiedler See, located in Austria and Hungary, has dried up many times over the millennia. As of 2005, it is again rapidly losing water, giving rise to the fear that it will be completely dry by 2010.

Some lakes disappear because of human development factors. The shrinking Aral Sea is described as being "murdered" by the diversion for irrigation of the rivers feeding it. At present the surface of the planet Mars is too cold and has too little atmospheric pressure to permit the pooling of liquid water on the surface. Geologic evidence appears to confirm, however, that ancient lakes once formed on the surface. It is also possible that volcanic activity on Mars will occasionally melt subsurface ice creating large lakes. Under current conditions this water would quickly freeze and evaporate unless insulated in some manner, such as by a coating of volcanic ash.

Only one world other than Earth is known to harbor lakes, Saturn's largest moon, Titan.

Photographs and spectroscopic analysis by the Cassini-Huygens spacecraft show liquid ethane on the surface, which is thought to be mixed with liquid methane.

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Jupiter's small moon Io is volcanically active due to tidal stresses, and as a result sulfur deposits have accumulated on the surface. Some photographs taken during the Galileo mission appear to show lakes of liquid sulfur on the surface.

There are dark basaltic plains on the Moon, similar to lunar maria but smaller, that are called lacus (singular lacus, Latin for "lake") because they were thought by early astronomers to be lakes of water.

8. Notable lakes  Lake Michigan-Huron is the largest lake by surface area: 117,350 km². It also has the

longest lake coastline in the world: 8,790 km. If Huron and Michigan are considered two lakes, Lake Superior is the largest lake, with 82,414 km². However, Huron is still has the longest coastline at 6,157 km (2980 km excluding the coastlines of its many inner islands). The world's smallest geological ocean, the Caspian Sea, at 394,299 km² has a surface area greater than the six largest freshwater lakes combined, and it frequently cited as the world's largest lake.  The deepest lake is Lake Baikal in Siberia, with a bottom at 1,637 m. Its mean depth is

also the greatest in the world (749 m). It is also the world's largest lake by volume (23,600 km³, though smaller than the Caspian Sea at 78,200 km³), and the second longest (about 630 km from tip to tip).  The longest freshwater lake is Lake Tanganyika, with a length of about 660 km

(measured along the lake's center line). It is also the second deepest in the world (1,470 m) after lake Baikal.  The world's oldest lake is Lake Baikal, followed by Lake Tanganyika (Tanzania).  The world's highest lake is the crater lake of Ojos del Salado, at 6,390 metres

(20,965 ft). The Lhagba Pool in Tibet at 6,368 m (20,892 ft) comes second.  The world's highest commercially navigable lake is Lake Titicaca in Peru and Bolivia at

3,812 m (12,507 ft). It is also the largest freshwater (and second largest overall) lake in South America.  The world's lowest lake is the Dead Sea, bordering Israel, Jordan at 418 m (1,371 ft)

below sea level. It is also one of the lakes with highest salt concentration.  Lake Huron has the longest lake coastline in the world: about 2980 km, excluding the

coastline of its many inner islands.

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 The largest island in a freshwater lake is Manitoulin Island in Lake Huron, with a surface

area of 2,766 km². Lake Manitou, located on Manitoulin Island, is the largest lake on an island in a freshwater lake.  The largest lake located on an island is Nettilling Lake on Baffin Island.  The largest lake in the world that drains naturally in two directions is Wollaston Lake.  Lake Toba on the island of Sumatra is located in what is probably the largest resurgent

caldera on Earth.  The largest lake located completely within the boundaries of a single city is Lake

Wanapitei in the city of Sudbury, Ontario, Canada. Before the current city boundaries came into effect in 2001, this status was held by Lake Ramsey, also in Sudbury.  Lake Enriquillo in Dominican Republic is the only saltwater lake in the world inhabited by

crocodiles.

RESERVOIR A reservoir is, most broadly, a place or hollow vessel where fluid is kept in reserve, for later use. Most often, a reservoir refers to an artificial lake, used to store water for various uses.

Reservoirs are often created by building a sturdy dam, usually out of concrete, earth, rock, or a mixture across a river or stream. Once the dam is completed, the stream fills the reservoir.

When a reservoir is predominantly man-made (rather than being an adaptation of a natural basin) it may be called a cistern. The term reservoir is also often used to describe underground reservoirs such as an oil or water well.

1. Types There are three basic types of reservoir: the commonly-seen dam across a valley,the less-common fully-bounded reservoir and sealed and covered reservoir to store high quality material safe from contamination. In the case of drinking water these covered reservoirs are often termed Service reservoirs.

2. Valley dammed reservoir The more common dam across a valley relies on naturally formed features to form the water tight elements. Generally, engineers look for dam sites which are narrow with a broad area upstream; the valley sides can then act as natural walls and the broad area upstream makes a large reservoir for the height. The best place along the valley for building a dam has to be determined according to where the dam can best be tied into the valley walls and floor to FOR MORE DETAILS VISIT US ON WWW.IMTSINSTITUTE.COM OR CALL ON +91-9999554621

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form a water tight seal. If necessary, humans have to be re-housed or historic sites must be moved. For example, the temples of Abu Simbel were moved before the construction of the Aswan Dam (which created Lake Nasser from the Nile in Egypt).

At the start of construction the river must be diverted, often through a tunnel. Then the foundation is prepared. Once that is done, building of the dam can start. This may take anywhere from a few months to a few years, depending on its size and complexity. After the dam is complete, the diversion is removed or plugged, and the river fills the area upstream of the dam.

3. Bank-side reservoir Where water is taken from a river of variable quality or quantity, it is common to construct bank-side reservoirs to store water pumped or siphoned from the river. Such reservoirs are usually built partly by excavation and partly by the construction of a complete encircling bund or embankment. Both the floor of the reservoir and the bund must have an impermeable lining or core, often made of puddled clay. The water stored in such reservoirs may have a residence time of several months during which time normal biological processes are able to substantially reduce many contaminants and almost eliminate any turbidity. The use of bank-side reservoirs also allows a water abstraction to be closed down for extended period at times when the river is unacceptably polluted or when flow conditions are very low due to drought. The London water supply system is one example of the use of bank-side storage for all the water taken from the River Thames and River Lee with many large reservoirs visible along the approach to Heathrow airport.

4. Service reservoir Many service reservoirs are constructed as water towers, often as elevated structures on concrete pillars where the landscape is relatively flat. Other service reservoirs are entirely underground, especially in more hilly or mountainous country. In the United Kingdom Thames Water has many underground reservoirs beneath London built in the 1800s by the Victorians, most of which are lined with thick layers of brick. Honor Oak Reservoir, which was completed in 1909, is the largest of this type in Europe. The roof is supported using large brick pillars and arches and the outside surface is used as a golf course.

5. Operation

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A raw water reservoir does not simply hold water until it is needed. It is the first part of the water treatment process. The time the water is held for before it is released is known as the retention time. This is a design feature that allows particles and silts to settle out, as well as time for natural biological treatment using algae, bacteria and zooplankton that naturally live within the water.

Water can be released from the reservoir, generally by gravity, to be cleaned for drinking water, generate electricity, or simply maintain the downstream flow. In the event that major rainfall occurs, water can be released via a spillway to avoid over-topping and compromising the integrity of the dam. Most modern reservoirs have a specially designed draw-off tower that can discharge water from the reservoir at different levels both to access water as the reservoir draws down but also to allow water of a specific quality to be discharged into the downstream river as compensation water.

6. Levels The terminology for reservoirs varies from country to country. In the United States the normal maximum level of a reservoir lake is called full pool, while the minimum level it can function at is dead pool. The water below this point is also called the dead pool, while the water in between is called the conservation pool. Full pool may have different levels in summer and winter, or based on the local wet and dry seasons.

Once a reservoir reaches dead pool, it is below the level at which the dam can release it downstream. At this point, the streambed beyond the dam goes nearly or completely dry, and electricity production stops. This is also often the point at which intakes for municipal water systems begin to suck air in, and must be extended into deeper water, where stagnant water quality is much poorer. This can be done either permanently with longer pipes, or temporarily with large hoses floated on small barges, such as until a severe drought or dam repairs are over.

7. Hydroelectricity A hydroelectric power station consists of large turbines at the base of a dam. Water from the reservoir behind the dam is channeled through pipes and delivered to the turbines, which in turn, spin a generator to produce electricity. Generally, reservoirs behind hydroelectric dams are built specifically for electrical power generation and are not used for drinking water or irrigation.

8. Controlling watercourses

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Reservoirs can be used in a number of ways to control how water flows through downstream waterways. i) Irrigation Water in an irrigation reservoir is released into networks of canals mainly for use in farmlands or secondary water systems. Water in an irrigation reservoir is generally not used for drinking water, but in some cases is. ii_ Flood control Commonly known as an "attenuation" or "balancing" reservoir, these are used to prevent flooding to lower lying lands, flood control reservoirs collect water at times of unseasonally high rainfall, then release it slowly over the course of the following weeks or months. Some of these reservoirs are constructed across the river line with the onward flow controlled by an orifice plate. When river flow exceeds the capacity of the orifice plate water builds behind the dam but as soon as the flow rate reduces the water behind the dam slowly releases until the reservoir is empty again. In some cases such reservoirs only function a few times in a decade and the land behind the reservoir may be developed as community or recreational land. iii) Compensation If a standard reservoir is built on a river which is used as a source of power, a compensation reservoir may also be built to guarantee a sufficient flow of water downstream during the working hours of the water-powered industries. iv) Canals Where a natural watercourse's water is not available to be diverted into a canal, a reservoir may be built to guarantee the water level in the canal; for example, where a canal climbs to cross a range of hills through locks. v) Recreation Reservoirs often provide for recreational uses. Most reservoirs are built for a civic purpose, but still allow fishing, boating, and other activities. At most reservoirs, special rules apply for the safety of the public.

vii) Modelling reservoir management

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There is a wide variety of software for modelling reservoirs, from the specialist Dam Safety Program Management Tools (DSPMT) to the relatively simple WAFLEX, to integrated models like the Water Evaluation And Planning system (WEAP) that place reservoir operations in the context of system-wide demands and supplies. viii) History Dry climate and water scarcity in India led to early development of water management techniques, including the building of a reservoir at Girnar in 3000 BC. Artificial lakes dating to the 5th century BC have been found in ancient Greece. An artificial lake in present-day Madhya Pradesh province of India, constructed in the 11th century, covered 650 square meters.

DAMS A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions.

Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to provide clean electricity for millions of consumers.

1. History The word dam can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old cities.

Most of early dam building took place in Mesopotamia and the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers, and could be quite unpredictable.

The earliest known dam is situated in Jawa, Jordan, 100 km northeast of the capital Amman. The gravity dam featured a 9 m high and 1 m wide stone wall, supported by a 50 m wide earth rampart. The structure is dated to 3000 BC. The Ancient Egyptian Sadd Al-Kafara at Wadi Al-Garawi, located about 25 kilometers south of Cairo, was 102 m long at its base and 87 m wide. The structure was built around 2800 or 2600 B.C. as a diversion dam for flood control, but was destroyed by heavy rain during construction or shortly afterwards. The Romans were also great dam builders, with many examples such as the three dams at Subiaco on the river Anio in Italy. Many large dams also survive at MĂŠrida in Spain.

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The oldest surviving and standing dam in the world is believed to be the Quatinah barrage in modern-day Syria. The dam is assumed to date back to the reign of the Egyptian Pharaoh Sethi (1319â&#x20AC;&#x201C;1304 BC), and was enlarged in the Roman period and between 1934-38.

It still supplies the city of Homs with water.

The Kallanai is a massive dam of unhewn stone, over 300 meters long, 4.5 meters high and 20 meters (60 ft) wide, across the main stream of the Kaveri river in India. The basic structure dates to the 2nd century AD. The purpose of the dam was to divert the waters of the Kaveri across the fertile Delta region for irrigation via canals.

Du Jiang Yan is the oldest surviving irrigation system in China that included a dam that directed waterflow. It was finished in 251 B.C. A large earthen dam, made by the Prime Minister of Chu (state), Sunshu Ao, flooded a valley in modern-day northern Anhui province that created an enormous irrigation reservoir (62 miles in circumference), a reservoir that is still present today.

In Iran, bridge dams were used to power a water wheel working a water-raising mechanism. The first was built in Dezful, which could raise 50 cubits of water for the water supply to all houses in the town. Also diversion dams were known. Milling dams were introduced which the Muslim engineers called the Pul-i-Bulaiti. The first was built at Shustar on the River Karun, Iran, and many of these were later built in other parts of the Islamic world. Water was conducted from the back of the dam through a large pipe to drive a water wheel and watermill.

In the Netherlands, a low-lying country, dams were often applied to block rivers in order to regulate the water level and to prevent the sea from entering the marsh lands. Such dams often marked the beginning of a town or city because it was easy to cross the river at such a place, and often gave rise to the respective place's names in Dutch. For instance the Dutch capital Amsterdam (old name Amstelredam) started with a dam through the river Amstel in the late 12th century, and Rotterdam started with a dam through the river Rotte, a minor tributary of the Nieuwe Maas. The central square of Amsterdam, believed to be the original place of the 800 year old dam, still carries the name Dam Square or simply the Dam. 2. Types of dams Dams can be formed by human agency, natural causes, or even by the intervention of wildlife such as beavers. Man-made dams are typically classified according to their size (height), intended purpose or structure. i) By size

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International standards define large dams as higher than 15-20 meters and major dams as over 150-250 meters in height.

The tallest dam in the world is the 300-meter-high Nurek Dam in Tajikistan. ii) By purpose Intended purposes include providing water for irrigation to town or city water supply, improving navigation, creating a reservoir of water to supply industrial uses, generating hydroelectric power, creating recreation areas or habitat for fish and wildlife, retaining wet season flow to minimise downstream flood risk and containing effluent from industrial sites such as mines or factories. Some dams can also serve as pedestrian or vehicular bridges across the river as well. When used in conjunction with intermittent power sources such as wind or solar, the reservoir can serve as pumped water storage to facilitate base load dampening in the power grid. Few dams serve all of these purposes but some multi-purpose dams serve more than one.

A saddle dam is an auxiliary dam constructed to confine the reservoir created by a primary dam either to permit a higher water elevation and storage or to limit the extent of a reservoir for increased efficiency. An auxiliary dam is constructed in a low spot or saddle through which the reservoir would otherwise escape. On occasion, a reservoir is contained by a similar structure called a dike to prevent inundation of nearby land. Dikes are commonly used for reclamation of arable land from a shallow lake. This is similar to a levee, which is a wall or embankment built along a river or stream to protect adjacent land from flooding.

An overflow dam is designed to be over topped. A weir is a type of small overflow dam that are often used within a river channel to create an impoundment lake for water abstraction purposes and which can also be used for flow measurement.

A check dam is a small dam designed to reduce flow velocity and control soil erosion.

Conversely, a wing dam is a structure that only partly restricts a waterway, creating a faster channel that resists the accumulation of sediment.

A dry dam is a dam designed to control flooding. It normally holds back no water and allows the channel to flow freely, except during periods of intense flow that would otherwise cause flooding downstream.

A diversionary dam is a structure designed to divert all or a portion of the flow of a river from its natural course. iii) By structure

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Based on structure and material used, dams are classified as timber dams, arch-gravity dams, embankment dams or masonry dams, with several subtypes. iv) Masonry dams The arch dam, stability is obtained by a combination of arch and gravity action. If the upstream face is vertical the entire weight of the dam must be carried to the foundation by gravity, while the distribution of the normal hydrostatic pressure between vertical cantilever and arch action will depend upon the stiffness of the dam in a vertical and horizontal direction. When the upstream face is sloped the distribution is more complicated. The normal component of the weight of the arch ring may be taken by the arch action, while the normal hydrostatic pressure will be distributed as described above. For this type of dam, firm reliable supports at the abutments (either buttress or canyon side wall) are more important. The most desirable place for an arch dam is a narrow canyon with steep side walls composed of sound rock. The safety of an arch dam is dependent on the strength of the side wall abutments, hence not only should the arch be well seated on the side walls but also the character of the rock should be carefully inspected.

Two types of single-arch dams are in use, namely the constant-angle and the constantradius dam. The constant-radius type employs the same face radius at all elevations of the dam, which means that as the channel grows narrower towards the bottom of the dam the central angle subtended by the face of the dam becomes smaller. Jones Falls Dam, in Canada, is a constant radius dam. In a constant-angle dam, also known as a variable radius dam, this subtended angle is kept a constant and the variation in distance between the abutments at various levels are taken care of by varying the radii. Constant-radius dams are much less common than constant-angle dams. Parker Dam is a constant-angle arch dam.

A similar type is the double-curvature or thin-shell dam. Wildhorse Dam near Mountain City, Nevada in the United States is an example of the type. This method of construction minimizes the amount of concrete necessary for construction but transmits large loads to the foundation and abutments. The appearance is similar to a single-arch dam but with a distinct vertical curvature to it as well lending it the vague appearance of a concave lens as viewed from downstream.

The multiple-arch dam consists of a number of single-arch dams with concrete buttresses as the supporting abutments, has for example the Daniel-Johnson Dam, QuĂŠbec,

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Canada. The multiple-arch dam does not require as many buttresses as the hollow gravity type, but requires good rock foundation because the buttress loads are heavy. v) Gravity dams In a gravity dam, stability is secured by making it of such a size and shape that it will resist overturning, sliding and crushing at the toe. The dam will not overturn provided that the moment around the turning point, caused by the water pressure is smaller than the moment caused by the weight of the dam. This is the case if the resultant force of water pressure and weight falls within the base of the dam. However, in order to prevent tensile stress at the upstream face and excessive compressive stress at the downstream face, the dam cross section is usually designed so that the resultant falls within the middle at all elevations of the cross section (the core). For this type of dam, impervious foundations with high bearing strength are essential.

When situated on a suitable site, gravity dams can prove to be a better alternative to other types of dams. When built on a carefully studied foundation, the gravity dam probably represents the best developed example of dam building. Since the fear of flood is a strong motivator in many regions, gravity dams are being built in some instances where an arch dam would have been more economical.

Gravity dams are classified as "solid" or "hollow". This is called "Zoning". The core of the dam is zoned depending on the availablity of locally available materials, foundation conditions and the material attributes. The solid form is the more widely used of the two, though the hollow dam is frequently more economical to construct. Gravity dams can also be classified as "overflow" (spillway) and "non-overflow." Grand Coulee Dam is a solid gravity dam and Itaipu Dam is a hollow gravity dam. A gravity dam can be combined with an arch dam, an arch-gravity dam, for areas with massive amounts of water flow but less material available for a purely gravity dam. vi) Embankment dams Embankment dams are made from compacted earth, and have two main types, rock-fill and earth-fill dams. Embankment dams rely on their weight to hold back the force of water, like the gravity dams made from concrete. vii) Rock-fill dams

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Rock-fill dams are embankments of compacted free-draining granular earth with an impervious zone. The earth utilized often contains a large percentage of large particles hence the term rock-fill. The impervious zone may be on the upstream face and made of masonry, concrete, plastic membrane, steel sheet piles, timber or other material. The impervious zone may also be within the embankment in which case it is referred to as a core. In the instances where clay is utilized as the impervious material the dam is referred to as a composite dam. To prevent internal erosion of clay into the rock fill due to seepage forces, the core is separated using a filter. Filters are specifically graded soil designed to prevent the migration of fine grain soil particles. When suitable material is at hand, transportation is minimized leading to cost savings during construction. Rock-fill dams are resistant to damage from earthquakes.

However, inadequate quality control during construction can lead to poor compaction and sand in the embankment which can lead to liquefaction of the rock-fill during an earthquake.

Liquefaction potential can be reduced by keeping susceptible material from being saturated, and by providing adequate compaction during construction. An example of a rock-fill dam is New Melones Dam in California. viii) Earth-fill dams Earth-fill dams, also called earthen, rolled-earth or simply earth dams, are constructed as a simple embankment of well compacted earth. A homogeneous rolled-earth dam is entirely constructed of one type of material but may contain a drain layer to collect seep water. A zonedearth dam has distinct parts or zones of dissimilar material, typically a locally plentiful shell with a watertight clay core. Modern zoned-earth embankments employ filter and drain zones to collect and remove seep water and preserve the integrity of the downstream shell zone. An outdated method of zoned earth dam construction utilized a hydraulic fill to produce a watertight core. Rolled-earth dams may also employ a watertight facing or core in the manner of a rock-fill dam. An interesting type of temporary earth dam occasionally used in high latitudes is the frozen-core dam, in which a coolant is circulated through pipes inside the dam to maintain a watertight region of permafrost within it.

Because earthen dams can be constructed from materials found on-site or nearby, they can be very cost-effective in regions where the cost of producing or bringing in concrete would be prohibitive. ix) Asphalt-Concrete Core

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A third type of embankment dam is built with asphalt concrete core. The majority of such dams are built with rock and/or gravel as the main fill material. Almost 100 dams of this design have now been built worldwide since the first such dam was completed in 1962. All asphaltconcrete core dams built so far have an excellent performance record. The type of asphalt used is a viscoelastic-plastic material that can adjust to the movements and deformations imposed on the embankment as a whole, and to settlements in the foundation. The flexible properties of the asphalt make such dams especially suited in earthquake regions. x) Cofferdams A cofferdam is a (usually temporary) barrier constructed to exclude water from an area that is normally submerged. Made commonly of wood, concrete or steel sheet piling, cofferdams are used to allow construction on the foundation of permanent dams, bridges, and similar structures. When the project is completed, the cofferdam may be demolished or removed. See also causeway and retaining wall. Common uses for cofferdams include construction and repair of off shore oil platforms. In such cases the cofferdam is fabricated from sheet steel and welded into place under water. Air is pumped into the space, displacing the water allowing a dry work environment below the surface. Upon completion the cofferdam is usually deconstructed unless the area requires continuous maintenance. xi) Timber dams Timber dams were widely used in the early part of the industrial revolution and in frontier areas due to ease and speed of construction. Rarely built in modern times by humans because of relatively short lifespan and limited height to which they can be built, timber dams must be kept constantly wet in order to maintain their water retention properties and limit deterioration by rot, similar to a barrel. The locations where timber dams are most economical to build are those where timber is plentiful, cement is costly or difficult to transport, and either a low head diversion dam is required or longevity is not an issue. Timber dams were once numerous, especially in the North American west, but most have failed, been hidden under earth embankments or been replaced with entirely new structures. Two common variations of timber dams were the crib and the plank.

Timber crib dams were erected of heavy timbers or dressed logs in the manner of a log house and the interior filled with earth or rubble. The heavy crib structure supported the dam's face and the weight of the water. Splash dams were timber crib dams used to help float logs downstream in the late 19th and early 20th centuries.

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Timber plank dams were more elegant structures that employed a variety of construction methods utilizing heavy timbers to support a water retaining arrangement of planks. Very few timber dams are still in use. Timber, in the form of sticks, branches and withes, is the basic material used by beavers, often with the addition of mud or stones. xii) Steel dams A steel dam is a type of dam briefly experimented with in around the turn of the 19th20th Century which uses steel plating (at an angle) and load bearing beams as the structure.

Intended as permanent structures, steel dams were an (arguably failed) experiment to determine if a construction technique could be devised that was cheaper than masonry, concrete or earthworks, but sturdier than timber crib dams. xiii) Beaver dams Beavers create dams primarily out of mud and sticks to flood a particular habitable area.

By flooding a parcel of land, beavers can navigate below or near the surface and remain relatively well hidden or protected from predators. The flooded region also allows beavers access to food, especially during the winter.

3. Construction elements i) Power generation plant As of 2005, hydroelectric power, mostly from dams, supplies some 19% of the world's electricity, and over 63% of renewable energy. Much of this is generated by large dams, although China uses small scale hydro generation on a wide scale and is responsible for about 50% of world use of this type of power.

Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator; to boost the power generation capabilities of a dam, the water may be run through a large pipe called a penstock before the turbine. A variant on this simple model uses pumped storage hydroelectricity to produce electricity to match periods of high and low demand, by moving water between reservoirs at different elevations. At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. ii) Spillways A spillway is a section of a dam designed to pass water from the upstream side of a dam to the downstream side. Many spillways have floodgates designed to control the flow through

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the spillway. Types of spillway include: A service spillway or primary spillway passes normal flow. An auxiliary spillway releases flow in excess of the capacity of the service spillway. An emergency spillway is designed for extreme conditions, such as a serious malfunction of the service spillway. A fuse plug spillway is a low embankment designed to be over topped and washed away in the event of a large flood. Fusegate elements are independent free-standing block set side by side on the spillway which work without any remote control. They allow to increase the normal pool of the dam without compromising the security of the dam because they are designed to be gradually evacuated for exceptional events. They work as fixed weir most of the time allowing overspilling for the common floods.

The spillway can be gradually eroded by water flow, including cavitation or turbulence of the water flowing over the spillway, leading to its failure. It was the inadequate design of the spillway which led to the 1889 over-topping of the South Fork Dam in Johnstown, Pennsylvania, resulting in the infamous Johnstown Flood (the "great flood of 1889"). Erosion rates are often monitored, and the risk is ordinarily minimized, by shaping the downstream face of the spillway into a curve that minimizes turbulent flow, such as an ogee curve.

4. Dam creation Common purposes Function

Example Hydroelectric power is a major source of electricity in the world. Many

Power generation

countries have rivers with adequate water flow, that can be dammed for power generation purposes. For example, the Itaipu on the Paranรก River in South America generates 14 GW and supplied 93% of the energy consumed by Paraguay and 20% of that consumed by Brazil as of 2005.

Many urban areas of the world are supplied with water abstracted from rivers pent up behind low dams or weirs. Examples include London - with water from

Water supply

the River Thames and Chester with water taken from the River Dee. Other major sources include deep upland reservoirs contained by high dams across deep valleys such as the Claerwen series of dams and reservoirs.

Stabilize water Dams are often used to control and stabilize water flow, often for agricultural

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flow / irrigation purposes and irrigation. Others such as the Berg Strait dam can help to stabilize or restore the water levels of inland lakes and seas, in this case the Aral Sea. Flood

Dams such as the Blackwater dam of Webster, New Hampshire and the Delta

prevention

Works are created with flood control in mind.

Dams (often called dykes or levees in this context) are used to prevent

Land reclamation

ingress of water to an area that would otherwise be submerged, allowing its reclamation for human use.

A typically small dam used to divert water for irrigation, power generation, or

Water

other uses, with usually no other function. Occasionally, they are used to

diversion

divert water to another drainage or reservoir to increase flow there and improve water use in that particular area. See: diversion dam.

Dams built for any of the above purposes may find themselves displaced by

Recreation and aquatic beauty

time of their original uses. Nevertheless the local community may have come to enjoy the reservoir for recreational and aesthetic reasons. Often the reservoir will be placid and surrounded by greenery, and convey to visitors a natural sense of rest and relaxation.

5. Siting (location) One of the best places for building a dam is a narrow part of a deep river valley; the valley sides can then act as natural walls. The primary function of the dam's structure is to fill the gap in the natural reservoir line left by the stream channel. The sites are usually those where the gap becomes a minimum for the required storage capacity. The most economical arrangement is often a composite structure such as a masonry dam flanked by earth embankments. The current use of the land to be flooded should be dispensable. Significant other engineering and engineering geology considerations when building a dam include: ď ś permeability of the surrounding rock or soil ď ś earthquake faults

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 landslides and slope stability  water table  peak flood flows  reservoir silting  environmental impacts on river fisheries, forests and wildlife (see also fish ladder)  impacts on human habitations  compensation for land being flooded as well as population resettlement  removal of toxic materials and buildings from the proposed reservoir area

6. Impact assessment Impact is assessed in several ways: the benefits to human society arising from the dam (agriculture, water, damage prevention and power), harm or benefits to nature and wildlife (especially fish and rare species), impact on the geology of an area - whether the change to water flow and levels will increase or decrease stability, and the disruption to human lives (relocation, loss of archeological or cultural matters underwater).

i) Environmental impact Dams affect many ecological aspects of a river. Rivers depend on the constant disturbance of a certain tolerance. Dams slow the river and this disturbance may damage or destroy this pattern of ecology. Temperature is also another problem that dams create. Rivers tend to have fairly homogeneous temperatures. Reservoirs have layered temperatures, warm on the top and cold on the bottom; in addition often it is water from the colder (lower) layer which is released downstream, and this may have a different dissolved oxygen content than before. Organisms depending upon a regular cycle of temperatures may be unable to adapt; the balance of other fauna (especially plant life and microscopic fauna) may be affected by the change of oxygen content.

Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks; for example, the daily cyclic flow variation caused by the Glen Canyon Dam was a contributor to sand bar erosion.

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Older dams often lack a fish ladder, which keeps many fish from moving up stream to their natural breeding grounds, causing failure of breeding cycles or blocking of migration paths.

Even the presence of a fish ladder does not always prevent a reduction in fish reaching the spawning grounds upstream. In some areas, young fish ("smolt") are transported downstream by barge during parts of the year. Turbine and power-plant designs that have a lower impact upon aquatic life are an active area of research. A large dam can cause the loss of entire ecospheres, including endangered and undiscovered species in the area, and the replacement of the original environment by a new inland lake.

Depending upon the circumstances, a dam can either reduce or increase the net production of greenhouse gases. An increase can occur if the reservoir created by the dam itself acts as a source of substantial amounts of potent greenhouse gases (methane and carbon dioxide) due to plant material in flooded areas decaying in an anaerobic environment. A study for the National Institute for Research in the Amazon found that Hydroelectric dams release a large pulse of carbon dioxide from above-water decay of trees left standing in the reservoirs, especially during the first decade after closing. This elevates the global warming impact of the dams to levels much higher than would occur by generating the same power from fossil fuels.

According to the World Commission on Dams report (Dams And Development), when the reservoir is relatively large and no prior clearing of forest in the flooded area was undertaken, greenhouse gas emissions from the reservoir could be higher than those of a conventional oilfired thermal generation plant. For instance, In 1990, the impoundment behind the Balbina Dam in Brazil(closed in 1987) had over 20 times the impact on global warming than would generating the same power from fossil fuels, due to the large area flooded per unit of electricity generated.

A decrease can occur if the dam is used in place of traditional power generation, since electricity produced from hydroelectric generation does not give rise to any flue gas emissions from fossil fuel combustion (including sulfur dioxide, nitric oxide, carbon monoxide, dust, and mercury from coal). The Tucurui dam in Brazil(closed in 1984) had only 0.4 times the impact on global warming than would generating the same power from fossil fuels. Large lakes formed behind dams have been indicated as contributing to earthquakes, due to changes in loading and/or the height of the water table. ii) Human social impact The impact on human society is also significant. For example, the Three Gorges Dam on the Yangtze River in China, is more than five times the size of the Hoover Dam (U.S.) will create a reservoir 600 km long, to be used for hydro-power generation. Its construction required the

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loss of over a million people's homes and their mass relocation, the loss of many valuable archaeological and cultural sites, as well as significant ecological change. It is estimated that to date, 40-80 million people worldwide have been physically displaced from their homes as a result of dam construction.

7. Economics Construction of a hydroelectric plant requires a long lead-time for site studies, hydrological studies, and environmental impact assessment, and are large scale projects by comparison to traditional power generation based upon fossil fuels. The number of sites that can be economically developed for hydroelectric production is limited; new sites tend to be far from population centers and usually require extensive power transmission lines. Hydroelectric generation can be vulnerable to major changes in the climate, including variation of rainfall, ground and surface water levels, and glacial melt, causing additional expenditure for the extra capacity to ensure sufficient power is available in low water years.

Once completed, if it is well designed and maintained, a hydroelectric power source is usually comparatively cheap and reliable. It has no fuel and low escape risk, and as an alternative energy source it is cheaper than both nuclear and wind power. It is more easily regulated to store water as needed and generate high power levels on demand compared to wind power, although dams have life expectancies while renewable energies do not.

8. Dam failure Dam failures are generally catastrophic if the structure is breached or significantly damaged. Routine deformation monitoring of seepage from drains in and around larger dams is necessary to anticipate any problems and permit remedial action to be taken before structural failure occurs. Most dams incorporate mechanisms to permit the reservoir to be lowered or even drained in the event of such problems. Another solution can be rock grouting - pressure pumping portland cement slurry into weak fractured rock. During an armed conflict, a dam is to be considered as an "installation containing dangerous forces" due to the massive impact of a possible destruction on the civilian population and the environment. As such, it is protected by the rules of International Humanitarian Law (IHL) and shall not be made the object of attack if that may cause severe losses among the civilian population. To facilitate the identification, a protective sign consisting of three bright orange circles placed on the same axis is defined by the rules of IHL.

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The main causes of dam failure include spillway design error (South Fork Dam), geological instability caused by changes to water levels during filling or poor surveying (Vajont Dam, Malpasset), poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava Dam collapse), extreme rainfall (Shakidor Dam), and human, computer or design error (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant).

A notable case of deliberate dam failure (prior to the above ruling) was the British Royal Air Force Dambusters raid on Germany in World War II (codenamed "Operation Chastise"), in which three German dams were selected to be breached in order to have an impact on German infrastructure and manufacturing and power capabilities deriving from the Ruhr and Eder rivers.

This raid later became the basis for several films.

Since 2007, the Dutch IJkdijk foundation is developing, with an open innovation model an early warning system for levee/dike failures. As a part of the development effort, full scale dikes are destroyed in the IJkdijk fieldlab. The destruction process is monitored by sensor networks from an international group of companies and scientific institutions.

MARINE RESOURCES Marine resources defined as the presence materials (biotic or abiotic) in the ocean region.

1. Biotic resources In science, biotic components of ocean region are the living things that shape an ecosystem. They are in entirety, any living component that affects another organism. Such things include animals which consume the organism in question, and the living food that the organism consumes. As opposed to abiotic components (non-living components of an organism's environment, such as temperature, light, moisture, air currents, etc.), biotic components are the living components of an organism's environment, such as predators and prey i) Biotic Factors are the living organisms that make up an ecosystem For example, if one were to examine a tundra ecosystem for biotic and abiotic components, one would observe things like the extreme temperatures of the day and night, the fast winds, the heavy amount of sunlight, and scarcity of water as abiotic (or non-living components) in the environment. One would observe that for a quail living in the desert, living

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elements like the quail's prey (insects, seeds, etc.) and predators (coyotes, sparrow hawk, gold eagles, etc.) make up the biotic components of the quail's environment.

2. Abiotic Resources In biology, abiotic components of marine environment are non-living chemical and physical factors in the environment. Despite being non-living, abiotic components can impact evolution. Things that were once living but now dead are usually considered biotic components rather than abiotic components (for example, corpses and spilled blood). However, depending upon the definition, components from living things that are no longer living can be considered part of the biotic or abiotic component. Generally, things that were once living are considered part of the biotic component, but marine animal wastes such as feces, urine (and carbon dioxide, oxygen, and water from respiration) are considered abiotic because those components were never living in an organism.

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