Document Type : Research Paper
Authors
1 Ph.D. Watershed Sciences and Engineering, Department of Nature Engineering, Faculty of Natural Resources, Yasouj University, Yasouj, Iran
2 Yasouj University
3 3- Professor , Department of Reclamation of Arid and Mountainous Regions , Faculty of Natural Resources, University of Tehran, Karaj, Iran
Abstract
In this study, 47 gullies (including 25 gullies with longitudinal cracks and 22 gullies without cracks) were surveyed and analyzed using UAV imagery with a vertical accuracy of 2 cm. The measured variables included wall slope, bank height, crack distance from the gully edge, bottom and top channel width, channel bed slope, gully planform curvature (outer, straight, inner), and vegetation cover status. The statistical analyses included independent t-test, Mann–Whitney U test, Kruskal–Wallis test, Fisher’s exact test, Spearman’s correlation, cluster analysis, and ROC curve analysis, all of which were performed using R and SPSS software. The results showed that wall slope is the most important factor controlling the occurrence of tensile cracks, such that the mean slope in cracked gullies (86.7 degrees) was significantly higher than in non-cracked gullies (50 degrees). Furthermore, outer curvature and lack of vegetation cover, with odds ratios of 4.2 and 4.57 respectively, were identified as the most important factors increasing the likelihood of crack occurrence. The crack distance from the gully edge (mean: 2.67 m) was mainly influenced by the geometric dimensions of the gully and showed a statistically significant positive correlation only with the bottom channel width. ROC analysis determined the critical wall slope threshold as 78.4 degrees (AUC = 0.835), with model sensitivity and specificity of 80% and 86.4%, respectively. Additionally, cluster analysis revealed three distinct patterns of cracked gullies, indicating different stages of instability evolution. The findings of this study have direct implications for gully erosion management. First, wall slope can be used as a rapid and field-measurable indicator for prioritizing conservation measures. Gullies with a slope exceeding the critical threshold of 78.4 degrees should be prioritized for stabilization, as the probability of crack formation and failure propagation is significantly higher in these gullies.
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