طبقه‌بندی لندفرم‌ها با استفاده از شاخص موقعیت توپوگرافی و بررسی ریسک واقعی فرسایش آنها در مناطق کوهستانی (مطالعة موردی: حوضة آبخیز خارستان)

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانش‌آموختة دکتری بیابان‌زدایی، دانشکدة منابع طبیعی و علوم زمین، دانشگاه کاشان

2 دانشیار گروه علوم بیابان، دانشکدة منابع طبیعی و علوم زمین، دانشگاه کاشان

3 دانشیار بخش مرتع و آبخیزداری دانشکدة کشاورزی و منابع طبیعی داراب، دانشگاه شیراز

چکیده

یکی از بخش‌های نوین و کم‌سابقه، به‌ویژه در مطالعات داخلی، بررسی کمّی ناهمواری‌هاست. شناخت علمی و کمّی‌گرایانة موقعیت توپوگرافی همواره از مباحثی بوده که در تحقیقات داخلی، چندان به آن توجه نشده است. این مبحث تأثیر بسزایی در تحلیل‌های ژئومورفولوژیک، هیدرولوژی و محیط‌شناسی دارد. وجود انواع لندفرم‌ها و تنوع آنها معمولاً با تغییر شکل و موقعیت زمین کنترل می‌شود؛ بنابراین طبقه‌بندی و شناسایی مناطق گوناگون، با توجه به ویژگی‌های مورفومتری آنها، ضروری است و ازاین‌رو پژوهش حاضر سعی در طبقه‌بندی لندفرم‌ها در منطقة خارستان، واقع در شمال‌غرب استان فارس و عوامل مؤثر در آن دارد. در همین زمینه، در مرحلة اول، از روش شاخص موقعیت توپوگرافی (TPI) به‌منظور طبقه‌بندی لندفرم‌ها و روش کورین برای تعیین کلاس‌های ریسک واقعی فرسایش استفاده شد. همچنین به‌منظور تعیین شاخص تفاضلی نرمال‌شدة پوشش گیاهی (NDVI) از تصاویر ماهوارة لندست 8، مربوط به خرداد 1396، بهره گرفته شد. در مرحلة بعد، رابطة انواع گوناگون لندفرم با فاکتورهای زمینی ارتفاع، شیب، جهت شیب، شاخص خیسی توپوگرافی (TWI)، شاخص ناهمواری زمین (TRI) و NDVI مشخص شد. در مرحلة آخر، وضعیت لندفرم‌های گوناگون در کلاس‌های متفاوت ریسک فرسایش، تعیین شد. نتایج نشان‌دهندة ده گونه لندفرم در منطقة مورد مطالعه بود. بیشترین نوع لندفرم‌ها در منطقة مورد مطالعه، آبراهه و قله‌های مرتفع، به‌ترتیب با مساحت 71/27 و 48/27% بود؛ درصورتی‌که دشت‌های کوچک کمترین مساحت (18/1%) منطقة مورد مطالعه را شامل می‌شد. کلاس‌های لندفرم با شاخص خیسی توپوگرافی در سطح 95% همبستگی معنی‌داری را نشان داد. از نظر توزیع مکانی، بیشترین سطح (71/91%) منطقه را NDVI کلاس 1/0 تا 3/0 دربر می‌گرفت. NDVI بزرگ‌تر از 4/0 در لندفرم‌های آبراهه و دره‌های Uشکل مشاهده شد. ریسک واقعی فرسایش در سه کلاس کم، متوسط و زیاد با مساحت‌های 14/31%، 11/31% و 78/37% طبقه‌بندی شد. در کلاس فرسایش کم، متوسط و زیاد، لندفرم‌های آبراهه و یال‌های مرتفع و قله به‌ترتیب با 44%، 57% و 59% بیشترین سطح را به خود اختصاص دادند.

کلیدواژه‌ها


عنوان مقاله [English]

Classification of Landforms Using Topographic Location Index and Assessment of their Actual Soil Erosion Risk in Mountainous Areas (Case Study: Kharestan Watershed)

نویسندگان [English]

  • Farideh Taripanah 1
  • Abolfazl Ranjbar 2
  • Abbasali Vali 2
  • Marzieh Mokarram 3
1 Ph.D. of Desertification Combating, Desert Control and Management Department, University of Kashan
2 Associate Prof., Dep. of Desert Management, University of Kashan
3 Associate Prof. Dep. of Range and Watershed Management, Darab Compass, Shiraz University
چکیده [English]

One of the new and unique sections, especially in internal studies, is the quantitative examination of unevenness. The scientific and quantitative study of topographic position has always been one of the topics that have received little attention in domestic research. So, classification and identification of different morphometrically distinct regions are necessary. Thus, the present study aims to classify landforms in the northwest of Fars province, Kharestan region and investigate its factors affecting. In this regard, the Topographic Position Index (TPI) method was used in the first stage to classify landforms, followed by the CORINE method to determine erosion risk classes. Additionally, Landsat 8 satellite images from June 2017 were used to determine the normalized differential vegetation index (NDVI). The next step was to determine the relationship between different types of landforms and terrestrial factors such as height, slope, slope direction, topographic wetness index (TWI), Terrain Ruggedness Index (TRI) and NDVI. Finally, the status of different landforms was determined based on erosion risk classes. Results showed ten different types of landforms existed within the study area. Small plains (1.18%) were the lowest in the study area, while waterways (27.71%) and high peaks (27.48%) were the highest. The TWI was significantly correlated with landform classes at 95% level. Most of the region (91.71%) had NDVI classes of 0.1 to 0.3. Stream and u-shaped valleys were found to have higher NDVI values. Real erosion risk was classified into three classes: low, medium, and high with areas of 31.14, 31.11, and 37.78%. There were 44, 57, and 59% erosion levels in the low, medium, and high erosion classes, respectively.

کلیدواژه‌ها [English]

  • Landform classification
  • Terrain factors
  • NDVI
  • Actual erosion risk
  • Kharestan region
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