Estimating the Volume of Debris Flows along the Sijan Stream Using Topographic Surveys and CIVIL 3D

The awareness of floods and estimating the debris flow is a fundamental step for assessing risk and planning in the watershed. The village of Sijan, located in the Southern Alborz, is one of the areas threatened by debris flows. The research aimed to estimate the volume of debris flows along 700 m of a stream of Sijan Village time range from 2018 to 2021. The study method included surveying the stream in two-time intervals, which involved one concrete and four gabion checkdams, and calculation of erosion and sedimentation happened via debris flow using the Civil-3D software. Results showed that five check dams had 823 m2 and 750 m3 area and volume, respectively. Debris flows covered 25500 m2 after the flood in 2019, in which the estimated erosion and deposition volumes were 7250 m3 and 10100 m3 according to the elevation difference technique. The Sijan stream channel experienced sedimentation and erosion along the northern and southern banks. Implemented watershed management measures have played a vital role in mitigating the risk of debris flows, especially at the concrete check dam.