Document Type : Research Paper
Authors
1 1 Postdoctoral Researcher, Department of Nature Engineering, Faculty of Agriculture and Natural Resources, Yasouj University, Yasouj, Iran
2 Associate Professor, Department of Nature Engineering, Faculty of Agriculture and Natural Resources, Yasouj University, Yasouj, Iran
3 Professor, Department of Reclamation pf Arid and Mountainous Regions, Faculty of Natural Resources, University of Tehran, Karaj, Iran
Abstract
Introduction
Gully erosion is one of the most important and destructive forms of soil degradation in arid and semi-arid regions of the world, playing a significant role in reducing agricultural land productivity, increasing sediment load in watersheds, and decreasing the useful life of dam reservoirs. Among the different stages of gully evolution, tensile cracks in the gully wall act as early indicators of instability and play a key role in initiating wall collapse, lateral gully expansion, and accelerating erosion processes. Despite the high importance of this phenomenon in geomorphology and erosion management, quantitative and multivariate investigations of the factors controlling the occurrence and location of these cracks at the gully wall scale remain limited, and few field studies have specifically addressed the development of tensile cracks. The aim of this study is to identify the factors affecting the formation of tensile cracks and to determine the critical slope threshold in the gullies of the Kaloocheh Bijar watershed.
Materials and methods
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.
Results and discussion
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.
Conclusions
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. Second, volumetric measures without attention to slope reduction or stress concentration control have limited stability effects; therefore, engineering interventions should focus on reducing the effective wall slope or dissipating flow energy in outer curves. Third, although the role of vegetation cover was statistically weaker, mechanical evidence suggests that its removal can accelerate the failure threshold; thus, biological stabilization of walls should be considered as a complementary tool in gully management.
Keywords
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