تحلیل ارتباط فرسایش پذیری و پارامترهای مورفومتری هورتون- استرالر در حوضه کمه (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
تحلیل مورفومتریک، رویکرد علمی مناسب برای مدیریت حوضه های آبریز، بررسی وضعیت فرسایش حوضه ها و مدیریت منابع طبیعی است که راهبردهایی برای حفاظت از خاک، مدیریت سیل و جلوگیری از فرسایش و به هم خوردن تعادل اکولوژیک منطقه ارائه می کند. فرسایش خاک و تخریب زمین از مهم ترین مسائل در علوم زمین است که سنجش پیامدهای زیست محیطی آن به داده های کمی نیاز دارد. با در نظر گرفتن آب وهوای خشک حاکم بر گستره عظیمی از ایران و نرخ خاک زایی کم، بررسی فرسایش پذیری حوزه های آبریز ایران از اهمیت ویژه ای برخوردار است. هدف از این پژوهش بررسی ویژگی های مورفومتری و پیش بینی میزان فرسایش ازطریق پارامترهای خطی و مساحتی و درنهایت تهیه نقشه فرسایش پذیری در حوضه کمه واقع در شهرستان سمیرم در جنوب استان اصفهان و درکوهپایه های شرقی کوهستان دنا است. برای رسیدن به هدف مزبور، این منطقه با استفاده از روش استرالر (1964) به 9 زیرحوضه تقسیم شده و سپس با محاسبه پارامترهای مورفومتریک توسط روش هورتون، 13 پارامتر اصلی از مقادیر ترکیبی (Cp) در سه گروه متغیرهای خطی، مساحتی و ناهمواری و با استفاده از داده های مکانی سیستم اطلاعات جغرافیایی اولویت بندی شد. نتایج پژوهش حاضر نشان داد که ادغام و تجزیه وتحلیل پارامترهای مورفولوژیک با نرم افزار GIS Pro می تواند ابزاری درخور توجه برای درک ویژگی های زیرحوضه های آبریز به ویژه فرسایش خاک فراهم کند و درنهایت با تهیه نقشه فرسایش پذیری، زیرحوضه 9 به عنوان آسیب پذیرترین منطقه در برابر خطر فرسایش شناسایی شد.Analysis of the Relationship between Erodibility and Horton-Strahler Morphometric Parameters in the Komeh Basin
Morphometric analysis is a vital scientific approach for watershed management, soil erosion assessment, and natural resource management. It offers essential strategies for soil conservation, flood control, and prevention of ecological imbalances. In the context of Iran’s arid climate and limited soil formation rates, assessing erosion susceptibility in watersheds—such as the Komeh Basin in Semirom County (southern Isfahan Province)—is critically important. This study examined linear, areal, and relief parameters using the methods of Strahler and Horton to prioritize sub-basins and predict erosion risk. The findings revealed that Sub-basin 9 was the most vulnerable area to erosion. Keywords : Morphometrics, Horton, Strahler, Komeh Watershed, Erodibility. Introduction The foundational research conducted by Horton (1945) and Strahler (1964) established the basis for modern geomorphology through the development of frameworks for analyzing landforms and drainage systems. This knowledge is essential for identifying geomorphological hazards, such as soil erosion, floods, and landslides, and conducting effective watershed management. Morphometric analyses, which utilize quantitative parameters (linear, areal, and relief), enable the prediction of natural hazards and assessment of watershed vulnerability. In arid regions like Iran characterized by low soil formation rates and high erosion susceptibility, these analyses are crucial for maintaining ecological balance and managing water resources. The Komeh Watershed in southern Isfahan Province, notable for its complex geological topography, climatic conditions, and human activities, is particularly prone to erosion. This study aimed to prioritize soil erosion susceptibility across the Komeh Basin and its nine sub-basins by analyzing morphometric indices and generating an erosion susceptibility map to identify high-risk zones. Literature Review Domestic Studies: Manbari et al. (2023) demonstrated the effectiveness of factor analysis in grouping morphometric parameters in the watersheds of Kurdistan Province, highlighting its utility for hydrological modeling. Negahban (2021) identified 91% of the Dinor Basin as comprising sub-basins with high tectonic activity. Zali et al. (2022) linked elongated basin shapes and gentle slopes to a reduced risk of flooding in the Nekaroud Basin. International Studies: Benzougagh et al. (2022) prioritized 48 sub-basins in Morocco using morphometric parameters and GIS, confirming the method’s effectiveness in natural resource management. Kadam et al. (2019) emphasized the sensitivity of semi-arid watersheds to land degradation and the critical role of morphometric analysis. Study Area The Komeh Watershed spans approximately 165,015 hectares in southern Isfahan Province, which is bordered by the provinces of Fars and Kohgiluyeh-Boyer Ahmad. Situated between latitudes 30°42' and 31°11' north and longitudes 51°21' and 51°56' east, it is part of Semirom County. Elevations within the watershed range from 1,783 m in the northwest to 4,000 m in the southwest, featuring an average slope of 28%. This rugged and complex topography is significantly influenced by the Dena Mountain Range, the highest fold of the Zagros Mountains. The basin experiences a cold climate with an average annual rainfall of 650 mm. Heavy precipitation and resultant runoff are major contributors to soil erosion in the area. Geologically, the basin is characterized by diverse rock formations dating from the Triassic to Quaternary periods, with Cretaceous rocks (limestone, marl, shale) predominating, especially in the southern regions. Its geomorphological features include mountainous karst landforms (such as caves and sinkholes), floodplains, alluvial terraces, and colluvial hills. Fragile lithology, steep slopes, human activities, and high-intensity rainfall—particularly in central areas receiving 640–690 mm of precipitation—combine with calcareous lithology and slopes to render this region highly susceptible to erosion. Annual precipitation data indicate a volume of 946.1 million cubic meters, which plays a critical role in generating runoff and facilitating erosion processes. The interaction of these natural factors with human interventions, such as changes in land use, has increased the erosion potential in the Komeh Basin. By precisely identifying vulnerable areas through the integration of spatial data layers—including rainfall zones, lithology, and slope—targeted management strategies can be developed to mitigate erosion-related damages and enhance the effective utilization of water and soil resources. This approach is not only relevant to the Komeh Basin, but also serves as a replicable model for other regions in Iran with similar climatic and geological conditions. Materials & Methods This study employed a 30-meter resolution Digital Elevation Model (DEM) from ASTER as the primary dataset for analysis. The drainage network of the Komeh Basin was delineated by using Global Mapper software and applying Strahler’s stream ordering method and was subsequently divided into 9 sub-basins. Selection of these sub-basins was based on stream orders of greater than 2 and their direct connectivity to the main river channel. 13 morphometric parameters were calculated and categorized into 3 groups: linear (e.g., area, perimeter, stream length, drainage density), areal (e.g., form factor, elongation ratio, circularity ratio), and relief (e.g., ruggedness index). Standardized formulas were utilized for these calculations, drawing on methodologies from Horton (1945), Strahler (1964), Miller (1953), and Kadam (2019). Parameters, such as bifurcation ratio (Rb) and drainage density (Dd) were processed using spatial data in GIS Pro and integrated with Excel. A composite parameter (Cp) was created for each sub-basin by combining linear and areal parameters, allowing for prioritization based on the lowest Cp values. This analysis indicated that Sub-basin 9 with the lowest Cp exhibited the highest susceptibility to erosion. Key factors contributing to this vulnerability included a high drainage density (due to extensive stream length) and an elongated form factor, which suggests a rapid hydrological response to rainfall. The hydrographic network revealed two dominant patterns: rectangular (with streams of orders 1–3 running perpendicular to orders 4–6) and parallel, featuring irregular tributaries, particularly in the northern sector, which intensified the complexity of erosion dynamics. The integration of classical methods (e.g., Horton and Strahler) with GIS technology facilitated the identification of critical zones, enabling the development of management strategies, such as flood control structures and erosion-resistant vegetation planting. This methodology provides a replicable framework for similar basins in arid and semi-arid regions of Iran that are facing comparable soil erosion challenges. Basin Parameters The linear parameters of the Komeh Basin—including stream order (U), stream number (Nu), stream length (Lu), stream length ratio (RL), bifurcation ratio (Rb), drainage density (Dd), drainage texture (Dt), stream frequency (Fs), form factor (Ff), circularity ratio (Rc), elongation ratio (Re), overland flow length (Lg), and compactness coefficient (Cc)—were calculated based on the methodologies of Horton (1945) and Strahler (1964). These parameters were directly correlated with the erodibility of the basin. Stream order (U) was classified up to the 6 th order, reflecting a complex drainage system shaped by regional tectonics. The stream number (Nu) decreased with higher orders, peaking in 1 st -order streams (ranging from 85 to 220), which underscored the influence of topography, lithology, and soil permeability. Stream length (Lu) reached its maximum in 1 st -order streams (between 97,254 and 290,281 m), declining in higher orders due to gentle to moderate slopes and lithological factors. The bifurcation ratio (Rb) ranged from 0.94 to 1.0 indicating structural control with Sub-basin 4 (Rb = 1.0) demonstrating the highest vulnerability. Drainage density (Dd), which ranged from 754 to 941 m/km², indicated a rapid hydrological response and erosion potential in Sub-basins 4 and 5 linked to impermeable lithology (such as marls and limestone) and steep slopes. Drainage texture (Dt) values ranged from 0.48 to 1.63, identifying Sub-basins 9 (Dt = 1.63) and 4 (Dt = 1.34) as particularly prone to erosion. Stream frequency (Fs) ranged from 0.57 to 0.80, peaking in Sub-basin 2 (Fs = 0.80) due to its high relief and low permeability. The form factor (Ff) ranging from 0.25 to 0.49 confirmed basin elongation, with Sub-basin 3 (Ff = 0.49) being the most susceptible to flooding. The circularity ratio (Rc), which ranged from 0.17 to 0.32, along with the elongation ratio (Re) (0.56 to 0.79), further validated the elongated shapes of the basins. Overland flow length (Lg) was measured between 0.0021 and 0.0026 km, indicating rapid drainage. Sub-basin 4 (Cc = 0.57) exhibited the highest erosion risk according to the compactness coefficient (Cc), which ranged from 0.40 to 0.57. Research Findings Sub-basin 9 demonstrated the highest erosion susceptibility (Cp = 3.2–4.6) attributed to extreme relief, high annual rainfall (~650 mm), and fragile lithology. In contrast, Sub-basin 3 (Cp < 1) exhibited the lowest erosion risk due to its gentle slopes and permeable soils. Key Drivers: Linear Parameters: Metrics, such as drainage density (Dd = 941 m/km²) and bifurcation ratio (Rb = 1.0), showed a direct correlation with erosion susceptibility. Areal Parameters: Values like the circularity ratio (Rc = 0.17) and form factor (Ff = 0.49) indicated a rapid hydrological response. Soil Analysis: Silty loam soils found in the western and northwestern sectors displayed the highest erodibility, aligning with RUSLE maps that emphasized rainfall erosivity (R) and slope (LS). Management Strategies: Urgent Measures: Implementing sediment traps and planting Astragalus in Sub-basins 9, 6, and 4 Conservation Agriculture: Promoting practices in moderate-risk zones, particularly Sub-basins 7 and 1 Land-Use Monitoring: Maintaining oversight in low-risk areas, such as Sub-basins 3 and 8 Technology Integration: The use of GIS and remote sensing significantly enhanced precision in data analysis, providing a transferable model applicable to arid and mountainous basins. Discussion of Results & Conclusion Morphometric and RUSLE analyses identified Sub-basins 9 and 6 as high-risk zones characterized by dense drainage (940 m/km²), steep slopes of 28%, and fragile lithology. RUSLE highlighted the eastern silty loam soils as erosion hotspots. Divergences between the methods arose from Horton-Strahler’s emphasis on drainage structure compared to RUSLE’s focus on climate and soil factors; however, both approaches concurred on the risks present in the central and northern regions. Key factors contributing to erosion included the path of the main river, extreme relief (up to 4,000 m), and loss of vegetation. In contrast, low-risk Sub-basins 3 and 8 exhibited gentle slopes and permeable soils. Recommendations: Implementing sediment traps and plant erosion-resistant vegetation, such as Astragalus Encouraging reduced tillage and contour farming practices Utilizing satellite-based land-use regulation for better management. Integrating morphometric analyses, RUSLE, and local knowledge can optimize management strategies. This comprehensive approach supports decision-making in data-scarce regions, helping to mitigate soil degradation and promote ecological balance.
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