Various methods are used for environmental impact assessment (EIA) of development projects, particularly water resource development projects, depending on the project type, scale, and geographic location. River rehabilitation projects, especially those passing through urban and rural areas, require careful consideration of their environmental impacts. This study evaluates the environmental impacts of key activities associated with the Valmarud River rehabilitation project in the southern region of Tonekabon, Mazandaran Province, Iran. To quantify the impacts of constructing a riverbank wall along the Valmarud River, a scoring checklist method was employed, considering the available scientific methods and data. The checklist was developed for different environmental components—including physical, biological, and socio-economic-cultural environments—in both the construction and operational phases. The results indicated that most negative impacts during the construction phase were related to the physical environment, all of which were short-term and reversible. These impacts were significantly reduced or eliminated after the completion of construction. In contrast, during the operational phase, all assessed impacts in the physical, biological, and socio-economic-cultural environments were positive, with long-term benefits. The final quantitative assessment of the Valmarud River rehabilitation project demonstrates that, with proper environmental management measures, the project will lead to improved conditions in the physical, biological, and socio-economic aspects of the region. Moreover, the negative impacts arising during the construction phase can be effectively mitigated through appropriate preventive and corrective measures.