Environmental Impact Assessment can be defined as the study of impact on environment of proposed action like policy, plan or project. It is a process of anticipating or establishing the changes in physical, ecological and socio-economic components of the environment before, during and after an impending developmental project so that undesirable effects, if any can be mitigated. Environmental impact assessment has to try to answer the following set of questions.
1. What are the environmental issues associated with the project?
2. What will be extending of changes?
3. Whether the benefits derived from the project are worth the environmental damages sustained?
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4. What can be done about adverse impacts?
A developmental activity is under taken or the state. The socio-economic quality of life cannot be sustained indefinitely if the activity causes adverse changes in the environment however small these changes may be at some point of time in future the entire system could deteriorate. A thorough assessment of the likely impact which a proposed plan or project shall cause, is therefore, essential so that even the minor seemingly insignificant changes are brought to the notice of policy makers.
The process of environmental impact assessment has to be conducted in three stages i.e.
(i) Initial Scrutiny
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(ii) Rapid Assessment
(iii) Comprehensive Assessment
Tungabhadra is considered as a major river of Karnataka state. In Shimoga District, rivers Tunga and Bhadra merge to form this river. The gross capacity of reservoir is 3767 mm3. The main purposes of project are power generation and irrigation. The total area irrigated under this project amounts to 3.63 lac hac. Main environmental impacts observed during the operation of project are water logging and Salinity of water and soil.
By spot visual examination, it is found that the approx, 33,000 hac of land in the area underwent water logging in 35 years of irrigation. Salt efflorescence, water stagnation, poor germination etc. are the systems of land affects from water logging.
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Salinity is several wells in command area is common. The content of soluble salt in the soil moisture varies from 0.036% to 0.20% in root zones and goes beyond 2.5% at salt concentrations zones. The soil electrical conductivity is more than 1 mho/cm, pH greater than 8.5 and exchangeable Sodium higher than 15% indicating saline character. Because of low rainfall (18 to 20 cm) the leaching of salt is difficult and hence salt deposits can be seen on the surface of soil. Other impacts includes change in cropping pattern, rise in ground water table etc.