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    INTRODUCTION    Environment is defined as the surroundings in which we live. It has the living component known as the biotic and the non-living known as the abiotic environment. In the living part all the plants animals, human beings, micro- organisms such as the bacteria, viruses, fungi etc. are there. In the non-living part the materials, temperature, humidity, air, soil, water, fire, energy, sky, noise, solar and other radiations are there. All of these are in dynamic equilibrium with each other. Every action of the nature is cyclic. We have seen so many cycles like the material and nutrient cycles, hydrological cycle etc. These cycles are interrelated and the occurrence of one depends upon other also. As there is a dynamic interrelationship between the components of the environment, so nothing can be dealt in isolation and one has to think in a holistic manner. Holistic means considering others also along with ones development. The oriental practice was to worship the nature. Nature was respected. We felt gratitude to the nature for bestowing its unlimited uniform blessings upon us. The sun shines for each and every one of us with the same intensity. Every natural blessing is impartial and sufficient. It is sufficient for everybody‟s need but not for anybody‟s greed. Forgetting this basic fundamental theory, we have started exploiting the nature. Nature has some power to compensate the loss that is some adjustments it can do. But the situation has come where it has gone beyond its power of assimilation and it has started reacting. The global warming, earthquakes, Tsunami, Al-Nino and other calamities are the recent examples. Some of them may be natural phenomena but generally it is the human beings who are responsible for them. So the time has come that we must wisely check and analyze our activities with respect to the nature or the environment. For any activity in the nature initially the yield is more and waste is less. There is a dynamic balance in nature that when yield increases waste increases. Waste means undesired product. It may be depth of water table which increase due to exploitation of ground water faster rates To maintain the quality of environment it is the sustainable development, in which no waste is accumulated in the nature (time lag may be there), but all the waste is absorbed.    In some conditions the time may be too much, no scavengers are there, and the waste will be remaining there and accumulating. Nature has a capacity to maintain cycle, waste in used, but after some rate it collapses. For example if we keep using fossil fuels, future generations will not use it as it is limited. Where as if we use hydropower we can keep on using it till the sunshines as the water is lifted up and comes back on earth with a new potential energy. So sound development is sustainable one When we look around and see what is going to happen in other areas (take care of others) it is the holistic development. NECESSITY OF ENVIRONMENTAL ASSESSMENT In the holistic and equitable development one takes care of others, means what so ever engineering project we plan or execute we consider its effect on the biotic and abiotic environment in which it is going to be implemented. This is known as environmental impact assessment. Forest as a complete ecosystem is a good example. It provides shelter. It is a habitat for large number of species. The electricity consumption in India, 350 kWh per capita per year, is very less in comparison to other developed countries as we are mainly dependent on firewood which comes from the forests. Nearly 15000 crores of fuel is burnt in India per year, for cooking which comes from forests. Besides firewood it gives us many other products like gum, resins, thorn, timber, medicinal herbs etc. as discussed earlier. So forest is our life line. Whenever, we have a project we have to asses its impact on this lifeline. What will be the effect of navigation on water course? It shall be the spread of oil, grease, noise and water currents. One has to consider all these negative impacts. For a good and exhaustive example let us consider the environmental impact assessment of some big projects like water resources project. First of all in 1970 s Aswan Dam constructed on river Nile had a problem of its impact on environment. The problem may be of seismicity. Earthquakes below 2.5 intensity on the Richter‟s scale goes unnoticed  whereas those more than 4 are felt with discomfort. Kariba and Koina are the places where first of all it was    assumed that earthquakes took place due to construction of dams. But the actual effect is not quantified yet, though a certain correlation is there. Changed water balance is, of course, to be studied. When we have irrigation projects the hydrology of the area changes. In the command area per square meter availability of water is much higher than required so water logging takes place. The consumptive use of water is 4 to 5 mm/day for plants. 90% of water taken by a tree is evaporated and only 5% is used by the body. As lesser water is consumed by plants in a command area so high water vapors will be formed that will increase the humidity. The rise in humidity shall have microclimatic changes like change in temperature. Water logging takes place as a result of supplying more water than required. Flood pattern downstream are changed. Drought characteristics are changed. The filling done in construction of canal embankments blocks the natural water ways. In command area type of crop is changed. Wheat is replaced by cotton, sugarcane etc. Soil is endemic saline if it contains salt. When no water was there to leach salts, it remained at bottom. When the level of water comes up the salt comes up and when it gets evaporated the salt remains there only and the soil becomes saline. So many other impacts are there and as such, before the actual quantification one has to finalize the areas on which the impact assessment is to be done. METHODOLOGY OF ENVIRONMENTAL IMPACT ASSESSMENT The following steps are taken in the overall assessment 1.   Identification 2.   Data collection 3.   Prediction 4.   Assessment Let us discuss them one by one with some specific examples. 1.   Identification of Impact Areas Depending upon the project under study there are so many areas over which the impact assessment may be made. Some of them are common and can be usually applied on all projects. a.   Water Resource Project Let us consider them for a water resource project. It has a dam, reservoir, canal and the distribution system etc. The dams have a large impact on the environment as sometimes they are very large. In Egypt, the Ashwan High Dam is seventeen times heavier than the great pyramid of Cheops. In Ghana the Volta Dam impounds a reservoir of the size of the Lebanon. Construction of dam inundates large areas of the fertile land. It is difficult to assess this loss. It is not only in terms of just the market value of the crops lost but also the top fertile layer
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