ارزيابي و پهنه‌بندي مخاطره‌ي فرسايش خاك در حوضه‌ي آبريز الشتر

Soil Erosion Risk Assessment and Zoning in the Aleshtar Catchment

در مطالعات آمايش محيطي، بهترين مسير توسعه توجه اصولي به توان ها و تهديدهاي محيطي و، بر اين اساس، استفاده بهينه از سرزمين است. در اين باره، ارتباط تنگاتنگي بين توسعه ي كشاورزي، توسعه روستايي و منابع محيطي وجود دارد. نوع بهره برداري از اراضي عامل بسيار مهمي در فرسايش و توليد رسوب حوضه هاي آبريز به شمار مي رود. در پژوهش حاضر، مطالعه و ارزيابي وضعيت فرسايش خاكِ حوضه ي آبريزدشت الشتر با هدف توسعه ي بهره برداري هاي كشاورزي با استفاده از روش PSIAC صورت گرفته است. اصول روش PSIAC براي تخمين استعداد رسوب زايي اراضي بر پايه ي بررسي نقش و اهميت نُه عامل مؤثر شامل وضعيت زمين سطحي (مقاومت سنگ بستر در برابر عوامل فرساينده)، وضعيت خاك (واحد هاي اراضي)، وضعيت آب وهوا، وضعيت رواناب، وضعيت توپوگرافي (پستي وبلندي)، وضعيت پوشش حفاظتي، نحوه ي استفاده از اراضي، وضعيت فعلي فرسايش، ارزيابي عامل شيب فرسايش رودخانه اي و حمل رسوب در فرسايش خاك طراحي شده است. در فرآيند مطالعه، با استفاده از سامانه ي اطلاعات جغرافيايي (GIS)، اين اطلاعات تجزيه وتحليل، تلفيق و، سرانجام، به صورت لايه هاي اطلاعاتي تهيه گرديدند. در ادامه، با استخراج واحدها و سنجش آن ها با مطالعات طرح جامع احيا و توسعه ي كشاورزي و منابع طبيعي استان لرستان، كه مؤسسه ي پژوهش هاي برنامه ريزي و اقتصاد كشاورزي تهيه كرده است، پهنه بندي نهايي صورت گرفت. نتيجه ي اين پژوهش نشان مي دهد فرسايش در سطح حوضه نسبتاً فراوان است، به نحوي كه حداقل بيش از 62% را از وسعت حوضه كلاس هاي فرسايشي (VI،V) و حدود 37% را از سطح حوضه كلاس هاي فرسايشي كم تا متوسط (III, II, I) در برگرفته است. بنابراين، در نگاه كلي، استفاده از اراضي در اين حوضه با محدوديت فرسايش روبه رو است و كنترل فرسايش خاك و اقدام هايي براي حفاظت خاك و آب در چارچوب طرح هاي حفاظتي اولويت مي يابد. با اين حال، مكان گزيني گذشته سكونتگاه هاي روستايي عمدتاً منطبق بر پهنه هاي فرسايشي كم تا متوسط است كه اين نشان دهنده ي وجود نوعي تفكر آمايشي سنتي نزد پيشينيان است.

The best path to development is the primary focus on the potentials and threats of the environment and accordingly efficient use of the land. In this regard, it has a closely relation between agricultural and rural development and natural resources. The type of land use is a main factor in soil erosion and sediment production in the watersheds. In this research, it has been studied and evaluated the soil erosion in the Aleshtar plain catchment with aim of developing agricultural exploitation. This study is based on PSIAC model. The PSIAC method has been designed based on the estimating of sediment potential with 9 important effective factors contains surface of the earth, soil type, weather conditions, runoff conditions, topography, land cover, Land use, current erosion condition, slope of river erosion and sediment transportation in the soil erosion. In the process of this research using geographical information system (GIS), the mentioned data analyzed, integrated, and finally layers of information were prepared. Followed by extraction of units, erosion zoning of the studied area has been implemented. The total area of the studied area is 80305 hectares and is located in the northern parts of Lorestan province (southwest of Iran) and geomorphologic features are almost mountainous and 39.65% of their area are mountains and hills. The maximum altitude is 3600 meters the minimum is 1500 meters. and the average height of 2116 meters. Its climate type (based on De Marten method) is Mediterranean climatic pattern exists and the average annual rainfall is 506 mm. The Aleshtar City is the only urban center in the area but there are 208 villages. The economy of the settlements is based on agriculture (farming, gardening and animal husbandry). Based on the findings of this research, 37.92% of the total land area of the basin is eroded (classes I, II, III). The land consists mainly of low slope and plain basin and is suitable for plantation (I). In this zone, 98 rural settlements (47.11%) are located. Relatively deep soils and flat are the features of these lands so the rate of erosion is low (II). 84 rural settlements (40.38%) are classified in this class. Shallow soils, these lands need to have conservation measures and can be managed under the operation of arable, rangeland, forest and resorts (III). 1 rural settlement (0.48%) is located in this class of erosion. 62.09% of the total basin land is located in the classes IV and V. A total of 25 rural settlements (12%) are located in this class. These lands under certain conditions can be planted because erosion in the land is relatively high and the limitations in comparison with class III is more. Therefore they need more protection operations for exploitation. Also in these lands that are located in the high topography of the basin erosion is extreme (Class V), which makes arable exploitation impossible. Generally the land use in Aleshtar basin is faced to erosion limitation, so the control of the soil erosion and soil conservation and water resources management are essential. However, the locations of the most rural settlements were based on low to moderate erosion zones which indicates that the ancient has had a traditional preparatory thinking. As a general recommendation, it can be said that in any location, including rural and urban settlements, along with the development of agricultural activities, attention to the erosion and zoning is essential.