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ملیحه ابراهیمی حسین اسدی آرزو شریفی عیسی ابراهیمی

چکیده

بررسی ویژگی­های فیزیکی ذرات معلق از موضوعات مهم در مطالعه رودخانه­ها است. یکی از این ویژگی­ها، توزیع اندازه ذرات رسوب معلق است، که بیان­گر ارتباط بین منابع رسوب و فرآیندهای رسوب­گذاری می­باشد. هدف این پژوهش، بررسی تغییرات زمانی و مکانی توزیع اندازه ذرات رسوب معلق رودخانه پسیخان در استان گیلان می­باشد. طی دوره زمانی هفت ماهه از مهر 1392 تا فروردین 1393، از دو ایستگاه هیدرومتری (مبارک­آباد در بالادست و نوخاله در پایین­دست) نمونه­برداری صورت گرفت. به این منظور تعدادی نمونه رسوب معلق با فواصل زمانی 15 روزه به روش انتگراسیون عمقی در شرایط عادی و سیلابی دبی رودخانه برداشت و پس از آماده­سازی، توزیع اندازه ذرات رسوب به روش پیپت اندازه­گیری شد. میانگین وزنی قطر ذرات رسوب (MWD) و قطر ذرات با فراوانی 50 درصد (d50) در هر ایستگاه در تاریخ­های نمونه­برداری تعیین و منحنی توزیع اندازه ذرات رسم گردید. نتایج نشان داد که مقدار متوسط MWD و  d50به ترتیب 062/0 و 052/0 میلی­متر در ایستگاه مبارک­آباد و 052/0 و 047/0 میلی­متر در ایستگاه نوخاله بود. حداکثر MWD و  d50به ترتیب 07/0 و 061/0 میلی­متر در ایستگاه مبارک­آباد مشاهده شد. هم­چنین مطالعه توزیع اندازه ذرات رسوب نشان داد که ذرات کوچک­تر از دو میلی­متر در ایستگاه نوخاله بین 99-87 درصد و در ایستگاه مبارک­آباد بین 94-83 درصد است. علاوه بر این در اکثر نمونه‌برداری­ها، بین دبی جریان و اندازه ذرات رسوب معلق ارتباطی وجود نداشت که نشان­دهنده طبیعت غیرهیدرولیکی و تأثیر متغیرهای متفاوت دیگر مثل منشاء رسوبات، تاریخ و انرژی انتقال، توانایی فرسایندگی، فرسایش­پذیری و ته­نشینی در اندازه ذرات رسوبات معلق در جریان رودخانه­ای است. هم‌چنین براساس نتایج اندازه ذرات رسوب در ایستگاه مبارک­آباد درشت­تر از ایستگاه نوخاله می­باشد که این موضوع را می­توان به نوع فرسایش موجود در منطقه و برداشت شن از رودخانه نسبت داد. در نواحی بالادست به دلیل کوهستانی بودن احتمال وقوع فرسایش خندقی و زمین­لغزش بیش­تر، در حالی‌که در پایین­دست فرسایش عمدتا پاشمانی و ورقه­ای است. ضمن اینکه با کاهش شیب عمومی رودخانه، ذرات درشت­تر قبل از رسیدن به ایستگاه نوخاله ته­نشین می­شوند.

جزئیات مقاله

کلمات کلیدی

بار رسوب, روش پی¬پیت, فرسایش, قطر میانه, میانگین وزنی قطر ذرات

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ارجاع به مقاله
ابراهیمی م., اسدی ح., شریفی آ., & ابراهیمی ع. (2019). بررسی تغییرات زمانی و مکانی توزیع اندازه ذرات رسوب¬های معلق در رودخانه پسیخان استان گیلان. آب و خاک, 33(2), 229-243. https://doi.org/10.22067/jsw.v33i2.75427
نوع مقاله
علمی - پژوهشی