Environmental Effects of Small Hydropower Projects
Renewable energy can make a significant contribution to carbon dioxide (CO2) emissions reduction.
It should be accepted that although through having no emissions of CO2 and other pollutants, electricity production in small hydro plants is environmentally rewarding, the fact is that due to their location in sensitive areas, local impacts are not always negligible.
It is recommended to establish a permanent dialogue with the environmental authorities as a very first step in the design phase. It would be convenient to provide a few guidelines that will help the designer to propose mitigating measures that can be agreed with the authorities. A high-head SHP project in mountains, being situated in a highly sensitive area, is more likely to generate impact that an integral low head scheme in a valley. The tail water from the power plant reenters the river and entire areas of the river may be bypassed by a large volume of water, when the plant is in operation.
The exhaustive descriptions of possible impacts due to construction of different components of a small hydro-power plant are briefly given. With a well arrangement of system of power plant structures, new environmental impacts will not be introduced.
The impact generated by construction of hydraulic structures include the loss of ground, the construction and maintenance roads, working platforms, excavation works, blasting and concrete manufacturing plants. Other non negligible impacts are the barrier effect and the alteration of flow consequent to river regulation that did not exist before. To mitigate such impacts it is recommended that the excavation work should be undertaken in the dry season and the disturbed ground restored as soon as possible. In any case these impacts are always transitory and do not constitute a serious obstacle to the administrative authorization procedure.
In view of its protective role against river erosion, it is wise to restore and reinforce the river bank vegetation that may have been damaged during construction of the structures. The ground should be re-vegetated with indigenous species, better adapted to the local conditions.
The impact assessment study should take count of the effects of jettisoning excavated material in the stream. Vehicle emissions, excavation dust, the high noise level and other minor burdens contribute to damage the environment, when the scheme is located in sensitive areas. To mitigate the above impacts the traffic operation must be carefully planned.
The allowable level of noise depends on the local population or on isolated house near to the power house. The noise comes mainly from the turbines and Nowadays noise inside the power house can be reduced, if necessary, by insulation of the power house walls and roof.
Each of the components that comprise a hydro scheme has potential to create a change in the visual impact of the site by introducing contrasting forms, lines, color or textures. The design, location, and appearance of any one feature may well determine the level of public acceptance for the entire scheme. Some of these components may be covered by land form or a layer of re-vegetated terrain.
The pen-stock is usually the main cause of nuisance. Its layout must be carefully studied using every natural feature such as rocks, ground and vegetation to shroud it and if there is no other solution, painting it so as to minimize contrast with the background. If the pen stock can be buried, this is usually a good solution from environmental point of view. Expansion joints and concrete anchor blocks could then be reduced or eliminated; the ground is returned to its original state and the pipe does not form a barrier to the passage of wild life especially in forest. All component of a SHP should be skilfully inserted into the landscape. Any mitigation strategies should be incorporated in the project, usually without too much extra cost to facilitate permits approval.
The reduction on flow in the stream bed between the intake and the tail race downstream of the power house may affect the life of fishes if they exist in the river. In high flow period the water spills over the weir and floods the stream-bed. Such frequent changes from semi dry to wet condition can make problem for aquatic life. It must be underlined that if any of the biologic methods for the definition of the residual flow value is implemented, there is a possibility for the developer to decrease the level of the required discharge, by modifying the physical structure of the stream bed. Actually growing trees on the riverbanks to provide shadowed areas, deposit gravel in the stream bed to improve the substratum, reinforce the riverside shrubs to fight erosion, etc.
A fish passage could be designed to reopen fish migration, which is a firm component of their life cycle. Effective fish passage design for a specific site requires good communication between engineers and biologists and thorough understanding of site characteristics.