Products (goods) and services are frequently worth a lot, but they are seldom being transacted at the markets. For this reason and likewise, due to impossibility of the subtle and quantitative calculations in taking decisions and huge making policies, is not considered adequately. Creatig a value is an instrument that provides beneficial information as making decision amongst the diverse choices for managers. In this survey, regarding to the economic value of output, water and soil preservation in natural lower part of ecosystem QAREH AGHACH dam river basin, the re-assessment of economic justification of dam construction project has been performed. In this evaluation the B/C ratio of dam construction project was revised and the avoided expenditure of output for water and soil preservation was considered in its calculation. The avoided costs of these two outputs was determined by utilizing the replacement costs occurrence. The essential expenditure for water and soil preservation and preventing their waste is calculated on basis of the artificial structure costs in the region, that here, the data of ACT for symmetrical government in proximity to educational extent, corres ponding to solar year of 1388 is used. In order to determine the effect rate of QAREH AGHACH dam construction over the erosion Keyword : economic justification, Soil and water conservation, QAREH AGHACH dam, Replacement Cost, SCS, MPSIAC.
