The goal of this section is to identify the most common impacts resulting from hydropower dam construction and operation.
The construction of hydropower dam belongs to the category of projects, which are universally designed as mandatory EIA projects. During the screening stage of the EIA process, it is necessary to identify the proposed project and the investor. The primary information about the proposed project is the type of activity, the capacity, the location, the character of the activity, and possibility of cumulative effects with other types of anthropogenic activities. The identification of necessity of the project for this type of project is usually very similar; the main reason to construct hydropower dam is generation of power to meet growing national demands for electricity and to ensure reliable sources. The secondary reason for building a hydropower dam is flow regulation downstream from the dam contributing to the flood control and irrigation, another reason is a recreational purpose and drinking water supply. Important part of screening stage is the identification of proposed location as well as identification of alternative options is a part of the primary step, together with a short description of technical and operational solutions. Identification of the proposed starting and ending date of the activity is another important information collected during the first step of EIA. This first step is common for all EIAs and there should be little variation in content of this part.
The second stage of EIA process is the scoping stage. This should take into account all key activities which will be connected to the dam construction at different stages. The development would involve the excavation of construction materials, the construction of the dam, the power station, access roads, and power lines. Environmental, economic, and social impacts would occur both during construction and during operation. There are some key operations during preconstruction, construction, and operational periods, which can be used as a guide for assessing impact.
The preconstruction program will include
• the construction of new roads to the dam site,
• the improvement of existing roads to facilitate delivery of construction plant and materials,
• the identification of stone quarries and borrow pits,
• the building of housing and other facilities for construction workers,
• the building of a site office,
• the identification of villages and hamlets to be relocated and the development of resettlement plans, and
• the harvesting of timber or other type of clearance of the present vegetation, which will otherwise be drowned and may later on cause problems.
All of these activities have the potential to create environmental impacts. Areas of particular concern will relate to the selection of sites for extracting construction materials and the proposals of resettlements. The construction program will include
• the construction of a coffer dam to regulate flow during building,
• the blasting to obtain rock and prepare the dam site,
• the construction of the dam,
• the construction of power station,
• the construction of replacement villages,
• the erection of pylons and power lines, and
• the construction of replacement access roads to the remaining communities.
The operational phase will include
• the generation of electricity;
• the regulation of river flow in the interest of flood control in the wet season and irrigation in dry season;
• the maintenance of the dam, power station, and power lines;
• transportation on the lake; and
• the possible development of fisheries and recreation.
The above-listed activities will follow construction of most hydropower dams; there are some differences which may occur with respect to local conditions.
Even if there is a common consensus on which parameters should be considered while determining environmental sustainability of a hydroproject (Table 1), the EIA process should not rely only on these factors, but should look on all possible impacts.
The next part will provide an assessment of the most common potential impacts resulting from construction of a hydropower dam (there can be local and case variations). For purpose of this article, the prediction of impacts is separated into three main categories:
• Impact upon the physical environment
• Impact upon the biological environment
• Impact upon the socioeconomic environment
The most common impacts of a hydroproject are listed in Tables 2 and 3 and are separated into impacts originated during the construction phase and during the operation phase, which starts with filling the reservoir with water.
Tables 2 and 3 list the most common effects of hydropower dam construction and operation on physical and biological environment, but it is necessary to take into account local conditions and the size of the dam. In the case of large and deep reservoirs the assessment has to take in account the impact of the large water volume and its weight on induced seismicity and possibility of earthquakes occurrence. The construction of hydropower dam also may have an impact on the socioeconomic environment of local communities. The main impact can be identified as necessity of resettlement, loss of social integrity in resettled communities, loss of agricultural land, and impact on or loss of cultural, historical, and archaeological heritage. Conversely new job opportunities are created, usually improvement of transportation occurs, also positive impact on human health and esthetic changes to the landscape are observed. A number of other impacts will be location dependent. The nature and scale of indirect and cumulative impacts as well as impact interactions will also be site specific.
A number of negative impacts may be minimized by proper mitigation measures and best management practices.
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