## 4 Results
### Dry Beach Slope  
The original 3D point cloud data without filter processing contained obvious noise points, which are evenly distributed on both sides of the non-noise point cloud. This resulted in the actual point cloud model with a certain thickness. To address this, the point cloud profile denoising method proposed in this study was applied to filter out noise. The window width \(W\) was set to 10, the moving step size \(S\) was set to 3, and the threshold \(T\) was set to 0.05. The results are shown in Figure 15. Experimental results demonstrate that the proposed method can effectively remove most of the noise points while keeping the non-noise points, accurately reflecting the real shape of the dry beach profile. Moreover, the thickness of the point cloud was effectively reduced to nearly zero following the application of the denoising process, aligning with the characteristics of an ideal planar point cloud model without thickness.  
To analyze the slope of the whole dry beach, the dry beach point clouds were divided into grid points, and the slope of the grid points was measured. Firstly, point cloud profiles were divided along the longitudinal direction of the dry beach, and the profile interval was set to 50 m. Following the denoising of the point cloud profile, each profile was further divided along the transverse direction of the dry beach, with an interval of 20 m, resulting in the formation of the final grid points.  
Figure 14: Boundary identification at position E. (**a**) Original image. (**b**) De-reflecting results and identification boundary.  
Figure 15: Dry beach point cloud profile filtering.  
According to Section 3.3, the dry beach slope at each grid point was measured, and the results are shown in Figure 16. The dry beach exhibits a steeper slope near the dam and gradually decreases with an increasing distance from the dam. This pattern is consistent with the sedimentation dynamics of tailings. Specifically, the higher water flow velocity near the dam transports tailings further downstream, while the reduced flow velocity near the waterline causes tailings to settle and accumulate, resulting in gentler slopes farther from the dam. It can be seen from Figure 16 that the slopes of the dry beach near the water range between 0.2% and 0.4%, while those near the dam are between 0.6% and 1.1%. This variation reflects the influence of hydrodynamic forces on the formation of the dry beach slope and provides valuable insights into sedimentation processes and topographic characteristics.  
According to the relevant regulations of China on tailings pond monitoring, slope determination involves calculating the weighted average slope of the sedimentary dry beach. The methodology requires the establishment of one to three measurement sections per 100 m of dam length, depending on the flatness of the dry beach surface. Each measuring section should be arranged perpendicular to the dam axis, where feasible, and positioned at locations with significant slope variations to ensure representativeness. Within each measurement section, the intervals between measurement points should be controlled between 10 and 20 m (larger intervals are desirable for longer dry beaches). The average slope of the sedimentary dry beach is measured based on the weighted average of the slope from all measured sections. In this study, the average slope of a dry beach was measured according to the relevant regulations. According to the standard slope measurement method, six representative sections were established for analysis. These six sections were also extracted from the point cloud, as shown in Figure 17, which illustrates the fluctuation of the dry beach along these sections. The slope values from the point cloud are 0.291%, 0.293%, 0.326%, 0.311%, 0.257%, and 0.275%, and the average slope is 0.292%. The actual average slope measured in situ is 0.3%. The relative error of the calculated slope is 2.67%.  
Figure 16: Dry beach point cloud grid point division and slope measurement.