تحلیل فرم ریپل مارک‎ها و موانع نبکا در پلایای سیرجان

نوع مقاله: مقاله علمی پژوهشی

نویسندگان

1 استادیار گروه جغرافیا، دانشگاه شهید باهنر، کرمان

2 استادیار ژئومورفولوژی، گروه جغرافیا، دانشگاه کاشان

3 دانشجوی دکترای ژئومورفولوژی، دانشکدة علوم جغرافیایی و برنامه ریزی، دانشگاه اصفهان

4 دانشجوی کارشناسی ارشد ژئومورفولوژی، دانشکدة علوم جغرافیایی و برنامه ریزی، دانشگاه اصفهان

چکیده

این پژوهش تلاش دارد تأثیر خصوصیت‎های مورفومتری نبکاها را روی ویژگی‎های مورفومتری ریپل مارک‎ها در پلایای سیرجان بررسی کند. ابتدا خصوصیت‎های مرفومتری بیست نمونه از نبکاهای گونۀ درختچۀ گز، اشنان و گل گزی، شامل ارتفاع و قطر تاج پوشش گیاه، ارتفاع و قطر قاعدۀ مخروط نبکا، ارتفاع مانع (مجموع ارتفاع نبکا و ارتفاع گیاه) و همچنین طول و عرض محدودۀ تحت تأثیر مانع اندازه‎گیری شد. سپس رابطۀ همبستگی تحلیل رگرسیون بین معیارهای ارتفاع مانع، قطر تاج پوشش گیاه و قطر قاعدۀ نبکا و متغیرهای طول و عرض محدودۀ تحت تأثیر برقرار شد. همچنین با استفاده از این آزمون تأثیر فاصله از مانع روی طول موج و ارتفاع ریپل مارک‎ها سنجیده شد. نتایج پژوهش نشان می‎دهد که در فواصل نزدیک به مانع که سرعت باد کاهش یافته است، ارتفاع و طول موج ریپل مارک‎ها افزایش می‎یابد؛ اما هرچه فاصله از مانع زیاد شود، اندازۀ طول موج و ارتفاع ریپل مارک‎ها کوچکتر می‎شود. همچنین دامنۀ تأثیرگذاری نبکاهای مختلف روی ریپل‎ها تا حد بسیار زیادی وابسته به قطرتاج پوشش گیاه و ارتفاع مانع است؛ به‎طوری که طول محدوده، کمابیش سه برابر ارتفاع مانع و عرض آن، وابسته به قطر تاج پوشش گیاه و بعد از آن قطر قاعدۀ نبکا است.

کلیدواژه‌ها


عنوان مقاله [English]

Analysis of Ripple Mark Forms and Nebkha Barriers in Sirjan Playa

نویسندگان [English]

  • Mohsen Pourkhosravani 1
  • Abbas Vali 2
  • Tayabeh Mahmoudi Mohamadabadi 3
  • Narjes Salari 4
1 Assistant Prof., Dep. of Geography, Shahid Bahonar University of Kerman
2 Assistant Prof., Faculty of Geomorphology, Dep. of Geography, University of Kashan
3 Ph. D. Student of Geomorphology, College of Geography, University of Isfahan
4 M. Sc. Student of Geomorphology, College of Geography, University of Isfahan
چکیده [English]

Extended Abstract
Introduction
Study about quality and characteristics of wind erosion forms and also relationship between
these forms with other environmental landforms is an important criterion in the assessment of
natural resources. When wind blows on sandy beds, sand grains hop and roll into downwind
shaping sand ripples. Morphometry is quantitative analysis of geomorphic characteristics of a
region of landforms (Bayati Khatibi, 2010, 2). Study of surface sand grain size shows that larger
ripples wavelength are created in the sands and coarse wavelength ripples in finer grain sands
(Chorley et al 1985: 434). Ripples are common forms of roughness in desert areas. Ripples are
created when the wind blows on the sand beds and sands move in the wind direction. In the fact
ripples are gathering sand flows into waves on different landforms surface. Ripple marks are
also the smallest and the most common forms of deserts, which are perpendicular to the
direction of the storm winds and their cross-section is asymmetric (Mehrshahy and Nekounam,
2010, 8). Ripple scale is proportional to the wind speed (Tian-De Miao et al, 2001, 1). The wind
velocity decrease in leeward of nebkha and this decrease in the wind velocity
affectmorphometric characteristics of current ripple marks in leeward of nebkha (Danin, 1996,
7). This research tries to survey effects of nebkha morphometric characteristics on
morphometric properties of ripple marks in Sirjan salt desert.
The study area
Sirjan salt desert is in the south west of Sirjan City (located geographical coordinates 28° 46 and
29° 59 north latitude and 54° 57 and 56° 27 east longitude). Sirjan salt desert is one of the most
important deserts in Kerman. This wilderness area with 1,625 square kilometers of the basin is
largest basin in deserts of Isfahan. The basin has a triangular shape of fovea in the southwestern
city of Sirjan. The study area is elongated from south western Sirjan to west of the cityin green
belt (Klinsli D, 2002, 220).
Wind characteristics in the study area
Dominant wind in the area during the year is mainly from south west and its average occurrence
is two times per year and its average speed is 5 meters per second. The weakest wind is east
wind with occurrence of 8.8 times, that its average speeds is 3.8 meters per second. Another
important wind flow in the study area is tropical winds
Methodology
The study was designed by randomly tested for 60 samples of five species of nebkhas in Sirjan
salt desert. At first, morphometry characterization of the five species of nebkhas including
tamarixmascatensis, Seidlitzia Florida and Reaumeriaturcestanica, plant height, plant canopy
cover, nebkha height, nebkha diameter, height barrier (total nebkha height and plant height) and
also height and wave length of ripple marks and were measured. Then, regression analysis used
to examine the correlation between morphometric parameters of nebkha and ripple marks.
Results and Discussion
The results about different nebkhas showed that barrier height has the most impact in length
parameter of the area affected and plant canopy cover diameter has the most impact on a wide
parameter of the area. There is also a strong correlation between the morphometric parameters
of ripple marks and distance of barrier. These results indicate that the effect of distance of
barrier on the ripple wavelength is stronger than the effect of that on the ripple wave height
parameter.
Conclusion
Ripple wavelength and height is strongly related to the distance barrier. As the distance is slight
and near to the barrier,the wind speed has dropped, and the height and the ripple wavelength is
increased. But with increase in distance of barrier, the height and the ripple wavelength
decreases. Moreover, nebkhas affectthe ripples in a domain. The domain is more dependants
upon the plant canopy cover diameter and height of barrier. Almost length of the area is triple
than height barrier and its width depends on canopy cover diameter and further more on nebkha
diameter.

کلیدواژه‌ها [English]

  • Morphometry
  • Nebkha
  • Ripple Mark
  • Sirjan Desert
  • Wave Height
  • Wave Length