تأثیر بار معلق رسوب بر ضریب زبری و شدت آشفتگی جریان (مطالعه موردی: رودخانه‌های هراز، رستم‌آباد و بهشت‌آباد)

نوع مقاله: مقاله اصلی

نویسندگان

1 استاد، گروه آب و محیط زیست، دانشکده مهندسی عمران و محیط زیست، دانشگاه علم و صنعت ایران، تهران، ایران

2 دانشجوی دکتری، دانشکده مهندسی عمران و محیط زیست، دانشگاه علم و صنعت ایران، تهران، ایران

3 کارشناسی ارشد، دانشکده مهندسی عمران و محیط زیست، دانشگاه علم و صنعت ایران، تهران، ایران

10.22034/jewe.2020.243225.1403

چکیده

برآورد اثر انتقال رسوب به­ویژه بار معلق­ در برنامه­ریزی و مدیریت رودخانه­ها از اهمیت بسیاری برخوردار است. هدف از این پژوهش بررسی تأثیر بار معلق رسوب در برآورد ضریب زبری و شدت آشفتگی جریان در رودخانه­های هراز، رستم­آباد و بهشت­آباد بود. به‌منظور درک بهتر این روابط، اقدام به برداشت مشخصات هندسی مقاطع، اندازه­گیری سرعت جریان و بار معلق در مقاطع گوناگون این رودخانه­ها شد. سپس تنش برشی، ضریب مانینگ و ضریب ون­کارمن با استفاده از روابطی در هر مقطع محاسبه شد. همچنین با اندازه­گیری نوسانات سرعت، شدت آشفتگی تعیین شد.  بررسی تأثیر بار معلق بر ضریب زبری و ضریب ون­کارمن نشان داد که در اکثر مقاطع در اثر وجود بار معلق، ضریب زبری و ضریب ون­کارمن کاهش یافته است. در رودخانه­های هراز، رستم­آباد و بهشت­آباد نسبت ضریب زبری در شرایط وجود بار معلق به ضریب زبری بدون وجود بار معلق به‌طور میانگین به­ترتیب 9/0، 94/0 و 6/0 به­دست آمد. نتایج این پژوهش نشان داد که توزیع شدت آشفتگی مستقل از دبی جریان بوده و همواره شکل حاصل برای این توزیع همگرا است و حداکثر مقدار آن نه در بستر بلکه در بالای بستر رخ داده است. هم­چنین توزیع شدت آشفتگی در حضور بار معلق در رودخانه­های شنی- قلوه‌سنگی به­صورت همگرا بوده و بر اساس معادله لایه‌مرزی قابل تحلیل است. با انجام آنالیز کوادرانت پیشامدهای غالب در سه عمق جریان بررسی شدند. در نواحی نزدیک بستر پدیده­های غالب به ترتیب درونی، بیرونی و پرتاب بودند و سهم پیشامد جاروب در این بخش قابل چشم­پوشی بود. 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Influence of Suspended Sediment Load on Roughness Coefficient and Intensity of Flow Turbulence (Case study: Haraz, Rostamabad and Beheshtabad Rivers)

نویسندگان [English]

  • Hossein Afzalimehr 1
  • Sanaz Hadian 2
  • Ehsan Shahiri Tabarestani 2
  • Meysam Mohammadi 3
1 Professor, Department of Water and Environmental Engineering, Faculty of Civil and Environmental Engineering, Iran University of Science and Technology, Tehran, Iran
2 Ph.D Scholar, Department of Water and Environmental Engineering, Faculty of Civil and Environmental Engineering, Iran University of Science and Technology, Tehran, Iran
3 M.Sc., Department of Water and Environmental Engineering, Faculty of Civil and Environmental Engineering, Iran University of Science and Technology, Tehran, Iran
چکیده [English]

Estimating the effect of sediment transport, especially suspended load, is important in river planning and management. The aim of this study was to investigate the effect of suspended sediment load on the roughness coefficient and the intensity of flow turbulence in Haraz, Rostamabad and Beheshtabad Rivers. In order to better understand these relationships, the geometric characteristics of the sections, the flow velocity and the suspended load were measured in different sections of these rivers. Then shear stress, Manning coefficient and Von karman coefficient were calculated using related equations in each section. The intensity of turbulence was also determined by measuring velocity fluctuations. The study of the effect of suspended load on roughness coefficient and Van Carmen coefficient showed that in most sections roughness coefficient and Van Carmen coefficient have decreased due to the presence of suspended load. In Haraz, Rostamabad and Beheshtabad Rivers, the ratio of roughness coefficient in the presence of suspended load to roughness coefficient without suspended load was 0.9, 0.94 and 0.6, respectively. The results of this study showed that the turbulence intensity distribution is independent from the flow rate and the distribution is always convergent and its maximum value occurred not in the bed but above the bed. Besides, the distribution of turbulence intensity in the presence of suspended load in gravel-boulder rivers is convergent and can be analyzed based on the boundary layer equation. Quadrant analysis was performed on the dominant events at three flow depths. In the areas close to the bed, the predominant phenomena were inward, outward and ejection, respectively, and the contribution of the sweeping event in this section was negligible.

کلیدواژه‌ها [English]

  • Coefficient
  • Quadrant analysis
  • Roughness
  • suspended load
  • Turbulence Intensity
  • Von-Karman coefficient
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