Abstract: The environmental impact assessment is intrinsic activity for every long term project and its estimation is usually done qualitatively through an EIA Environmental Impact Assessment matrix. When there are several activities within a river basin, it is beneficial to estimate the indicator of environmental value or impact factor that occurs in an entire basin. However, the IVAFIC methodology allows quantitative estimation of this value through the IF (Impact Factor), using three attributes: duration, reversibility and nature which are associated with all environmental factors and anthropic activities, using the structural language of MATLAB and geographic information systems. This new indicator undoubtedly facilitates the decision-making of the environmental authority and the prioritization of the territorial ordering of watersheds.