**3. Methodology**

In this study, a new method is presented to estimate the peak discharge of ephemeral rivers, in which high-resolution UAV data was taken as a primary data source, and the method of initiation of motion was carried out. The detailed workflow of the study is as follows (Figure 2): Step 1, high-resolution UAV data acquired in the field were processed to obtain Digital Orthophoto Maps (DOMs) and Digital Surface Models (DSMs) of the studied channels. Step 2, orthoimages were compared to identify moved stones around selected cross sections, then the critical velocities of these stones were calculated separately using logarithmic and exponential velocity distributions. Step 3, the average velocity of selected cross sections was calculated from the critical velocities of moving stones, and the discharge through cross sections was then obtained with the extracted cross-sectional area taken from the DSM. Step 4, essential hydraulic variables of culverts were extracted from orthoimages and the DSM to calculate the discharge through a culvert for validation.

**Figure 2.** Workflow of the method calculating flood peak discharge of ephemeral rivers.
