عوامل فیزیکی تعیین کننده ضریب رواناب در حوزه‌های آبخیز استان اردبیل

نوع مقاله: مقاله پژوهشی

نویسندگان

گروه علوم خاک، دانشکده کشاورزی، دانشگاه زنجان

چکیده

ضریب رواناب به­عنوان معیاری برای ارزیابی پتانسیل تولید سیل حوزه آبخیز مورد استفاده قرار می­گیرد. این عامل به مشخصات حوزه آبخیز بستگی داشته و طی سال دچار تغییرات زمانی می­شود. آگاهی از حوزه­های آبخیز مستعد تولید بیش‌تر رواناب و زمان وقوع بیش‌ترین رواناب­، در برنامه­ریزی مدیریت حوزه­های آبخیز نقشی اساسی دارد. در این پژوهش مشخصات فیزیکی و وقایع بارش و رواناب طی دوره بیست ساله (1384-1365) در یازده حوزه­ آبخیز رده چهار در استان اردبیل بررسی شد. مساحت آن­ها بین 257 تا 2184 کیلومتر مربع بوده و شیب از 25/16 تا 3/33 درصد تغییر می­کند. تفاوتی معنی­دار بین ماه­ها از نظر بارندگی (001/0>p)، رواناب (01/0>p) و ضریب رواناب (05/0>p) وجود داشت. در برخی حوزه­های آبخیز، رابطه­ای معنی­دار بین رواناب و بارندگی برقرار است که می­تواند به­دلیل ضعف پوشش گیاهی باشد. در اغلب حوزه­های آبخیز، بیش‌ترین ضریب رواناب در فروردین (70 درصد) و کم‌ترین آن در شهریور (صفر) می­باشد. این نتیجه به­دلیل فواصل کوتاه رخدادهای بارندگی و ضعف پوشش گیاهی در اوایل بهار می­باشد. در شهریور به­دلیل پوشش گیاهی مناسب، ضریب رواناب کاهش می­یابد. ضریب رواناب تحت تأثیر خصوصیات فیزیکی حوزه­ آبخیز قرار دارد، همبستگی منفی بین ضریب رواناب و مساحت (80/0-=r)، طول آبراهه (83/0-=r) و ضریب شکل (82/0-=r) وجود دارد. با این وجود، این مشخصه تحت تأثیر شیب، ضریب گراولیوس و تراکم آبراهه­ای قرار نگرفت. نتایج نشان داد که در منطقه نیمه­خشک، بیش‌ترین خطر پتانسیل تولید سیل مربوط به حوزه­های آبخیز با سطح کوچک و غیرکشیده (ضریب گراویلیوس 2/1) به­ویژه در اوایل بهار می­باشد.

کلیدواژه‌ها


عنوان مقاله [English]

Physical Factors Determining Runoff Coefficient in the Watersheds of Ardabil Province

نویسندگان [English]

  • A Alijanpour Shelmani
  • AR Vaezi
چکیده [English]

Runoff coefficient can be used as a measure for assessing the flood generation potential of the watersheds. This factor is depending on the watershed characteristics and may vary temporally during a year. Knowledge on the watersheds with higher potential to runoff production and determining pick time of runoffs is essential for designing watershed management practices in an area. In this study, physical characteristics with rainfall and runoff data for a thirty-year period (1986-2010) were studied in eleven forth order watersheds in Ardabil, Iran. The watersheds surface areas vary from 257 to 2184 km2 and their slopes are between 16.25% and 33.3%. Significant differences were found among their monthly rainfall (p<0.001), runoff (p<0.01), and runoff coefficient (p<0.05). There were significant relationships between runoff and rainfall in some watersheds which could be related to the poor vegetation cover. In most of the watersheds, the highest runoff coefficient (70 percentage) was appeared in April while the lowest value (zero) occurred in September. This result was associated with the shorter intervals between the rainfalls and poor vegetation cover in early spring. Suitable vegetation cover decreased the runoff coefficient in September. Runoff coefficient was significantly affected by the watersheds characteristics: the land surface area (r= -0.80), waterways length (r= -0.83) and form factor (r= -0.83). There were no significant correlations between runoff coefficient and land slope, Gravelious coefficient, and stream density. Results showed that in the semi-arid watersheds areas, the largest flood hazard belonged to the watersheds with lower area and non-elongated shape (Gravelious coefficient= 1.2) especially in early spring.

کلیدواژه‌ها [English]

  • Flood generation potential risk
  • Physical watershed characteristics
  • Rainfall
  • Watershed order
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