Asian Journal of Water, Environment and Pollution, Vol. 15, No. 2 (2018), pp. 107–114. DOI 10.3233/AJW-180023 Assessment and Estimation of Environmental Costs of Kasilian Dam Mahsa Khodarahmi, Mohammad Javad Amiri* 1 , Abdolreza Karbassi 2 , Sanaz Tajziehchi 2 and Hassan Darabi 3 Department of Assessment and Land Use Planning, Faculty of Environment and Energy, Science and Research Branch, Islamic Azad University, Tehran, Iran 1 Department of Environmental Planning, Management and Education, Graduate Faculty of Environment, University of Tehran, Tehran, Iran 2 Department of Environmental Engineering, Graduate Faculty of Environment, University of Tehran, Tehran, Iran 3 Department of Environmental Design, Graduate Faculty of Environment, University of Tehran, Tehran, Iran * mjamiri@ut.ac.ir Received August 1, 2017; revised and accepted February 15, 2018 Abstract: Despite the benefts of large dams, there are still concerns about their real benefts and environmental costs. Effects on social and natural ecosystems could be one of the most important external costs of dams’ construction. The aim of this study is to identify the environmental and social costs of Kasilian hydropower Dam in Mazandaran Province, Iran, to reduce the negative consequences and move towards sustainable environmental development. In order to estimate the environmental costs, it is necessary to calculate the damaging and negative effects as well as the benefts of dam construction such that to calculate the net proft. Thus, this paper is one of the frst efforts focusing on identifying the most important social and environmental impacts of dams’ construction. Using the HECAM (Hydropower’s Environmental Costs Analysis Model) software and considering the economic, social and environmental indicators, we estimated the beneft ratio to the cost of Kasilian hydroelectric dam to be about 3.5. We also found that land loss and electricity generation have the highest cost and the greatest proft associated with the lack of greenhouse gases, the water and electricity sale. Key words: Environmental cost, hydropower, dam, HECAM. *Corresponding Author Introduction Due to climatic and geographic conditions in Iran, the food events along with their large damage are witnessed every year. The food event in Iran is not specifc to a particular area and the whole country is affected by this phenomenon. For instance, in the northern regions of Iran, which have rivers with steep slopes and short lengths, annual foods lead to high losses of inhabitants and heavy damages (Ministry of Power, 2015). Dams provide reliable water resources, protect the surrounding areas from foods, and provide a clean energy. Although hydroelectric power (power generation by water) provides more advantages than two other major sources of power generation (i.e., fossil fuels and nuclear power), dams and water resources also cause some problems (Brismar, 2004). The water issue has been highlighted in numerous international reports, including Water Security for Better Lives (OECD’S report). This report introduces the water