بررسی آزمایشگاهی تأثیر شدت هیدروگراف سیلاب بر فرسایش بستر تحت جریان غیرماندگار واقعی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه مهندسی آب و سازه‌های هیدرولیکی، دانشکده مهندسی عمران، دانشگاه زنجان، زنجان، ایران.

2 دانشیار، گروه مهندسی آب و سازه‌های هیدرولیکی، دانشکده مهندسی عمران، دانشگاه زنجان، زنجان، ایران.

3 گروه مهندسی عمران، دانشکده فنی دانشگاه ارومیه، ارومیه، ایران.

چکیده

رودخانه‌های طبیعی نرخ انتقال رسوب قابل‌توجهی را در خلال وقوع سیلاب تجربه می‌کنند. هدف پژوهش حاضر، بررسی تأثیر پارامتر شدت هیدروگراف سیلاب بر میزان انتقال رسوبات بستر است. بدین منظور، با تعبیه یک بُرد واسط بین رایانه و مبدل پمپ، جریان غیرماندگار واقعی با دقت بالا درون کانال شیب‌پذیر به طول 15 متر ایجاد گردید. رسوبات به قطر 69/2 میلی‌متر در کف کانال به‌صورت یکنواخت تسطیح گردیده و پس از اشباع شدن، هیدروگراف سیلاب بر روی آن اعمال گردیده است. 20 حالت هیدروگراف با پارامتر شدت متفاوت مورد آزمایش قرار گرفته و نرخ فرسایش در طی زمان هیدروگراف به دست آمده است. نتایج حاصل بیانگر آن است که بیشینه نرخ فرسایش همواره نزدیک به اوج هیدروگراف سیلاب رخ می‌دهد و تأخیر زمانی بین اوج هیدروگراف سیلاب و اوج هیدروگراف رسوب، عمدتاً به‌صورت تأخیر مثبت بوده است. نرخ فرسایش در شاخه صعودی هیدروگراف بیشتر از شاخه نزولی بوده که با کاهش پارامتر شدت جریان، فاصله بین آن‌ها در نمودار هیسترزیس رسوب کاهش می‌یابد. تغییرات نرخ انتقال بار بستر (qb) برحسب دبی جریان (Q) به‌صورت هیسترزیس ساعت‌گرد می‌باشد. با کاهش 32، 57، 75 و 87 درصدی پارامتر شدت هیدروگراف، حجم کل رسوبات انتقال یافته به ترتیب 27، 51، 78 و 90 درصد کاهش می‌یابد. کاهش 50 درصدی زمان پایه هیدروگراف در شرایط یکسان، به‌طور میانگین موجب کاهش 46 درصدی حجم کل رسوبات انتقال یافته شده است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Experimental Investigation of the Effects of Flood Hydrograph Intensity on Bed Erosion under Real Unsteady Flow

نویسندگان [English]

  • Bahman Aghazadeh gharebagh 1
  • Jalal Bazarghan 2
  • Mirali Mohammadi 3
1 Department of Water Engineering and Hydraulic Structures, Faculty of Civil Engineering, University of Zanjan, Zanjan, Iran
2 Associate Professor, Department of Water Engineering and Hydraulic Structures, Faculty of Civil Engineering, University of Zanjan, Zanjan, Iran
3 Department of Civil Eng., Faculty of Eng., Urmia University, Urmia, Iran.
چکیده [English]

Natural rivers experience significant sediment transport rates during floods.The purpose of this study was to investigate the effects of flood hydrograph intensity parameter on the amount of bed sediment transport rate. For this purpose, a real unsteady flow hydrograph was created inside a 15 meters long tilting flume by installing an interface board between the computer and the pump inverter. Sediments with a d50 of 2.69 mm have been put uniformly on the bottom of the channel and the flood hydrograph has been applied on it after saturation. 20 cases of hydrographs with different intensity parameters were tested and the erosion rate was obtained during the hydrograph time. The results show that the maximum erosion rate always occurs near the peak of the flood hydrograph and the time delay between the peak of the flood hydrograph and the peak of the sediment hydrograph is mostly positive. The erosion rate in the rising limb of the hydrograph is higher than the falling limb, and the distance between them decreases in the hysteresis diagram as the flow intensity parameter decreases. The changes of bedload transport rate (qb) in terms of flow rate (Q) are clockwise hysteresis. By decreasing the hydrograph intensity parameter by 32, 57, 75 and 87%, the total volume of transferred sediments decreases by 27, 51, 78 and 90%, respectively. A 50% decrease in the base time of the hydrograph under the same conditions has caused a 46% decrease in the total volume of transported sediments.

کلیدواژه‌ها [English]

  • River
  • Unsteady Flow
  • Flood Hydrograph
  • Erosion Rate
  • Experimental study

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