Impacts of riverbed encroachment and construction on flood risk management.

Document Type : Research Paper

Authors

Department of Range and Watershed Management, Faculty of Natural Resources, University of Guilan, Iran

10.22124/cjes.2025.9372

Abstract

Floods are among the most destructive natural disasters, posing serious threats to human life and property. Riverbed encroachment and construction are key factors that have caused significant human and financial losses in flood-prone areas beside rivers. In this study, three rivers: Babolrud, Siahrud, and Haraz located in Mazandaran Province, Iran, were selected as case studies. The maximum instantaneous flood discharges of these rivers were estimated using statistical methods. Riverbed encroachments and constructions were identified through river boundary maps and satellite imagery. The hydraulic behavior of the rivers was then simulated using the HEC-RAS model. For each river, 10 reaches were selected, each consisting of five consecutive cross-sections with the highest levels of encroachment. The geometry of these sections was modified in the model to simulate riverbed restoration. Two scenarios were analyzed: (i) natural conditions (without encroachments) and (ii) existing conditions (with encroachments). The results of both scenarios were compared in terms of flood depth, flood area, flow velocity along the banks, and the flow centerline. The results indicated that after riverbed restoration and improved flow conveyance, Babolrud River (with a 25-year return period) experienced decreases of approximately 5% in flow depth, 58% in flow velocity, and 9% in flood area. In Siahrud River, flow depth, velocity, and flood area decreased by 10%, 36%, and 8.2%, while in Haraz River, these reductions were 13.4%, 30.5%, and 20% respectively. Overall, the findings demonstrate that riverbed occupation and construction significantly increase flood risk. Therefore, restoring the natural riverbed is strongly recommended to enhance flow capacity and reduce flood hazards, especially during high-return-period floods.
 

Keywords

References

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Caspian Journal of Environmental Sciences
Volume 23, Issue 5
Special issue: Biological Researches and Envireonment, Guest Editor: Prof. Hamed Mousavi-Sabet, University of Guilan, Iran
December 2025
Pages 1293-1301

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