تأثیر همزمان وزش باد و بارش باران بر پارامترهای هیدرولیکی جریان ورقه‌ای و شدت فرسایش بین‌شیاری

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری، گروه علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه شهید باهنر کرمان.

2 دانشیار گروه علوم و مهندسی خاک دانشگاه شهید باهنر کرمان

چکیده

چکیده
سابقه و هدف: بسیاری از رگبارهای طبیعی با وزش باد همراه است. این در حالی است که تاکنون پژوهش جامعی در زمینه نقش باد در فرسایش ناشی از باران در شرایط آزمایشگاهی در ایران گزارش نشده است. پژوهش حاضر با هدف بررسی تأثیر سرعت‌های مختلف باد در تقابل با شدت‌های مختلف باران بر پارامترهای هیدرولیکی جریان ورقه‌ای و همچنین شدت فرسایش بین‌شیاری در چند خاک زراعی انجام شد. به این منظور، از یک دستگاه شبیه‌ساز همزمان باد، باران و رواناب که برای اولین بار در کشور طراحی و ساخته شده است، استفاده گردید.
مواد و روش‌ها: ترکیب‌های مختلف از چهار سرعت باد شامل صفر، 6، 9 و 12 متر در ثانیه و سه شدت باران شامل 30، 50 و 75 میلی‌متر در ساعت بر روی سه خاک زراعی با بزرگترین اندازه ذرات 2، 75/4 و 8 میلی‌متر، هر یک در سه تکرار ایجاد شد. پارامترهای هیدرولیکی جریان شامل سرعت جریان، عمق لایه آب، تنش برشی، قدرت جریان و قدرت جریان واحد و همچنین شدت فرسایش بین‌شیاری اندازه‌گیری شد. در ادامه، تأثیر سرعت باد بر پارامترهای هیدرولیکی جریان ورقه‌ای و همچنین اثر این پارامترها بر شدت فرسایش بین‌شیاری مورد ارزیابی قرار گرفت.
یافته‌ها: نتایج این پژوهش نشان داد که بسته به سرعت باد، شدت فرسایش بین‌شیاری بین 021/0 تا 22/0 گرم بر متر مربع در ثانیه متغیر است. در این پژوهش، سرعت 6 تا 9 متر بر ثانیه باد به‌عنوان حد آستانه تعیین شد. با افزایش سرعت باد به‌ویژه در سرعت‌های بیش از این آستانه، سرعت و قدرت جریان واحد افزایش و در مقابل، عمق جریان و تنش برشی کاهش یافتند. همچنین با افزایش سرعت باد تا مقدار آستانه، قدرت جریان ابتدا افزایش و در ادامه کاهش پیدا کرد. نتایج همچنین گویای این مطلب بود که افزایش سرعت باد از طریق تأثیر بر پارامترهای هیدرولیکی جریان ورقه‌ای، شدت فرسایش بین‌شیاری را کنترل می‌کند. با افزایش سرعت و قدرت جریان واحد، شدت فرسایش بین‌شیاری افزایش یافت در حالی که، افزایش عمق لایه آب و همچنین افزایش تنش برشی و قدرت جریان، به دلیل صرف بخشی از انرژی قطرات باران برای عبور از لایه آب، باعث کاهش شدت فرسایش بین‌شیاری شد. در واقع، رابطه عکس سرعت- عمق جریان، سایر پارامترهای هیدرولیکی را نیز تحت تأثیر قرار داد. از طرفی، با افزایش اندازه خاکدانه‌های در معرض فرسایش، عمق لایه آب افزایش و در مقابل، سرعت و قدرت جریان واحد کاهش و در نتیجه شدت فرسایش بین‌شیاری کاهش یافت.
نتیجه‌گیری: یافته‌های این پژوهش نشان داد که در رگبارهای متأثر از وزش بادها به‌ویژه در سرعت‌های بیشتر از سرعت آستانه باد، به دلیل افزایش فرسایندگی باران، افزایش سرعت جریان رواناب و همچنین کاهش عمق لایه آب، شدت فرسایش بین‌شیاری تشدید می‌شود. همچنین مشخص گردید که با اعمال مدیریت صحیح خاک در اراضی کشاورزی در راستای افزایش اندازه و پایداری خاکدانه‌های موجود در سطح و در نتیجه افزایش ضریب زبری، می‌توان سرعت جریان رواناب و همچنین شدت فرسایش را کاهش داد. از منظر دیگر، وجود خاکدانه‌های درشت و پایدار در سطح، با افزایش عمق لایه آب موجود در سطح از برخورد مستقیم قطرات باران و تشدید فرسایش بین‌شیاری جلوگیری می‌کند. یافته‌های این پژوهش اهمیت و لزوم انجام آزمایش‌های بیشتر در زمینه فرآیندها و مکانیسم‌های فرسایش ناشی اثر همزمان وزش باد و بارش باران را نشان می‌دهد.

کلیدواژه‌ها


عنوان مقاله [English]

Simultaneous effects of wind and rain on hydraulic parameters of sheet flow and interrill erosion rate

نویسندگان [English]

  • Ruhollah Rezaei Arshad 1
  • Majid Mahmoodabadi 2
1 Ph.D. Student, Department of Soil Science, Agriculture Faculty, Shahid Bahonar University of Kerman.
2 Department of Soil Science, Shahid Bahonar University of Kerman
چکیده [English]

Abstract
Background and objectives: Many natural rainstorms are accompanied by wind blowing. However, so far no comprehensive research has been reported on the influence of wind on rain-induced erosion under laboratory conditions in Iran. The present study was conducted to investigate the interactive effects of different wind velocities and rain intensities on flow hydraulic parameters and on interrill erosion rate of several agricultural soils. For this purpose, a simultaneous wind, rain and runoff simulator was used, which has been designed and constructed for the first time in the country.
Materials and methods: Various combinations of four wind speeds including 0, 6, 9 and 12 m s-1, three rain intensities of 30, 50 and 75 mm h-1 were introduced on three cropland soils with different aggregate size distributions with the largest particle size of 2, 4.75, and 8 mm, each at three replications. Different flow hydraulic parameters including mean flow velocity, flow depth, shear stress, stream power and unit stream power and also the rate of interrill erosion were measured. Afterwards, the effects of wind velocity on the flow hydraulic parameters and also the influence of these parameters on interrill erosion rate were assessed.
Results: The results showed that depending on the wind velocity, the rate of interrill erosion varied from 0.021 and 0.22 g m-2 s-1. In this research, the wind velocity of 6 m s-1 was introduced as a threshold value. With increasing wind speed particularly those speeds higher than the threshold, the flow parameters of velocity and unit stream power increased, whereas, flow depth and shear stress decreased. In addition, stream power increased as the wind speed increased up to the threshold wind velocity, and at the higher wind speeds, the reverse trend was observed. The result indicated that wind speed can control interrill erosion rate by affecting on flow hydraulic parameters. Interrill erosion increased with increasing velocity and unit stream power of the flow, while it was reduced when flow depth, shear stress and stream power increased, this was attributed to the expenditure of raindrops energy for passing through water depth. In fact, the opposite relationship between flow velocity and water depth affects the other hydraulic parameters. Moreover, the presence of coarser aggregates at the soil surface increased water depth and decreased the velocity and unit stream power of flow, resulting in reduced interrill erosion.
Conclusion: The findings of this study showed that in wind-driven rains particularly at those wind speeds higher than 6 m s-1, interrill erosion rate is intensified because of increasing in rain erosivity and flow velocity and decreasing in flow depth. It was found that with appropriate soil management in agricultural lands for increasing the size and strength of surface aggregates, flow velocity and consequently soil erosion can be reduced. From another point of view, the presence of stable and coarser aggregates at soil surface decreases interril erosion. Overall, the findings of this research revealed the importance and necessity of more studies on soil erosion processes due to wind-driven rain.

کلیدواژه‌ها [English]

  • Wind-driven rain
  • flow velocity
  • Water Depth
  • Wind speed
  • Rain intensity
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