Long-Term Behaviour and Environmentally Friendly Rehabilitation Technologies of Dams (LTBD 2017) DOI:10.3217/978-3-85125-564-5-023 167 Environmental impact assessment of dams at construction and operation phases Abdolhosein Haddad 1 , Maryam Naeimi 2 , Ghasem Mohammadi 3 1- Associate Professor, Dept. of Civil Engineering, Semnan University, Iran 2-Postdoctoral Research Fellow, Research Institute of Petroleum Industry, Iran 3- Ph.D. Candidate, Dept. of Civil Engineering, Semnan University, Iran Email: Gm.mohammadi@gmail.com Abstract Environmental impact assessment (EIA) in the projects of civil engineering, was not being considered by many countries until recent years. However, in recent decades of 20th century and after observing environmental impacts of some of the projects, it was stated that the environmental factors played a noticeable role in speeding and directing of projects. Dam construction as one of the important civil and developing projects have positive and negative effects on environment. The environmental impacts can be categorized based on different criteria e.g. short and long term, impacts on surface and the ecosystem of the region, upstream and downstream side of dam, and social and economic impacts. Whereas dams have positive effects, it is necessary to minimize the negative impacts of dams toward stable development. At the same time, it is known that the consequences and impacts are different during construction and operation period in terms of intensity, importance and extent. In this paper, at first, the effectible geophysical factors related to river and reservoir water, vegetation and animal, social, economic and cultural factors are studied. Then, as a case study, Gotvand dam for quantifying the environmental impacts using the Iranian matrix are presented. Keywords: Environmental impact assessment, Earth dams, Environmental factors. 1. INTRODUCTION The environmental considerations in the civil and developing projects were not taken in to account by most of the countries until recent years. The environmental consequences of some projects raised notices that environmental factors played an important role in the direction and speed of development in the last decades of 20th century. Nevertheless, development is not in contradiction to environment; but, exceeding extraction of natural resources leads to disturbance and contamination of environment. Development is stable and persistent when it is appropriate from environmental point of view in addition to technical, social and economic justification [1]. At the same time, it is known that the consequences and impacts during construction and operation period in term of intensity, importance and extent are different. In advance of any environmental impact assessment of the project, all other effects should be evaluated. It should be noted that environmental impact assessment depends on many factors e.g. existing records, collected data interpretation, statistics, sampling, and finally analysis of these subjects. The environmental impacts of dam construction are shown in Fig.1 [1]. Also, the impacts of different environmental factors of dam construction is presented in following. 2. STUDY ON THE EFFECTIVE GEOPHYSICAL FACTORS 2.1. THE IMPACT OF TOPOGRAPHY During construction period, the topography is subject to significant change due to rock and soil excavation, backfilling, road construction, temporary and permanent camps, borrow area excavation and etc. [10]. This impact is considered as a negative impact while it changes the region from its intact and natural condition. It would be intense, permanent and unavoidable. However, the impact would be on the ground shape and general view of the region during operation period.