This project work based on field study and secondary information, intends to study environmental & socio-economic parameters of Arun-III HEP area. The water quality at Arun-III project site is desirable for drinking and aquatic environment, yet it should be treated against E. coli, iron and turbidity for drinking. The five major tributaries downstream of dam site are capable to sustain the ecological health of river during project construction and operation. The soil quality is good for agriculture use with high Organic content, yet it should be treated with lime for acidic character of the soil at Num VDC. As beneficial impact, the Arun-III project implementation will enhance development of the region and nation both, while adverse environmental and socio-economic impacts should be minimized by executing appropriate mitigation measures. The book is complete in its aspect to cover Environmental and Socio-economic impacts of the Hydropower. In addition to this it has got Impact prediction matrix for the assessment of the environment. Book contains a number of facts, figures which would be beneficial for the Environmental, Civil( Engineers), sociologist, and others in profession.