بررسی اثراحداث سد بر تغییرات ریخت شناسی پیچان رود های پایین دست با استفاده از بسته آب پویائی CCHE2D(مطا لعه ی موردی : رود کرخه)
محورهای موضوعی : برگرفته از پایان نامهعلی لیاقت 1 , آرش ادیب 2 , حمیدرضا غفوری 3
1 - دانشجوی دکتری عمران آب، گروه عمران، دانشکده مهندسی، دانشگاه شهید چمران اهواز
2 - دانشیار گروه عمران، دانشکده مهندسی، دانشگاه شهید چمران اهواز
3 - استاد گروه عمران، دانشکده مهندسی، دانشگاه شهید چمران اهواز
کلید واژه: فرسایش, سد, خم, زمین ریخت شناسی, بسته آب پویائیCCHE2D,
چکیده مقاله :
برقراری تعادل در رودخانه ها به عوامل مختلفی وابسته بوده و ممکن است تعادل برقرار شده نیز در هر لحظه، و در هر مقطع زمانی به هم بخورد. یکی ازمهمترین این عوامل احداث سد بر روی رودخانه ها است. در این تحقیق، هدف بررسی احداث سد کرخه بر تغییرات ریخت شناسی پیچان رود پایین دست است. در این راستا، شناسائی و بررسی تغییرات ریخت شناسی رودخانه ی کرخه قبل و بعد از احداث سد، تعیین میزان تغییرات طولی و عرضی خم های رودخانه پائین دست با توجه به تصاویر ماهواره ای و با استفاده از یک بسته آب پویائی CCHE2D انجام پذیرفته است. نتایج نشان می دهند که در شرایط طبیعی، عرض بستر رود به طرف پایین دست مسیر، متناسب با کاهش شیب، افزایش می‌یابد. متوسط عرض رودخانه قبل از احداث سد حدود 273 متر، و بعد از آن تقریبا" به60 متر رسیده است. با کاهش عرضی حدود 78% عرض رودخانه تقریبا 21 هکتار اراضی در هر کیلومتر از امتداد آن آزاد می شود. در محدوده مورد مطالعه، متوسط جابه جائی خط القعر رودخانه حدود 340 متر، حداقل و حداکثر جابه جائی 53 و 768 متر می باشد. بالغ بر 56% از جابه جائی ها به سمت راست جریان(غرب) رودخانه بوده و نزدیک بر 59% این جابه جائی ها بیرون از بستر قدیم صورت گرفته است. به طور متوسط، سالانه حدود 34 متر جابه جائی عرضی رودخانه در بازه ی مورد نظر اتفاق افتاده است، که بیانگر ناپایداری این منطقه می باشد.
Stability of streambeds is dependent on different factors some of which maybe destabilized at any moment. Dam erection on the riverbed is the most important among those factors. Some
morphological changes of a meandering river, the most obvious of which are the gradient change and the area deducted or added to the riverbed, were studied downstream of the Karkheh Dam. To delineate the areas, which had been taken from or added to the riverbed due to the lateral and longitudinal displacement of the meanders, morphology of the downstream river bed prior to and after the dam construction were studied employing satellite imagery, and their extent was calculated using the CCHE2D model. Slope reduction, as expected, follows an increase in the riverbed breadth. The average width of the riverbed was reduced from 273 m to 60 m (78% reduction) after the dam construction. The land taken off the streambed was almost 21 hectares for each kilometer of the length of the river. Mean, maximum and minimum horizontal thalweg displacements were 340,768 and 53 meters, respectively; 56% of the displacements were towards right (west) and 59% of the displacement took place out of the original streambed. The mean annual lateral displacement of the riverbed was 34 meters after the dam construction. This finding illustrates the instability of the terrain through which the river flows.
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