تاثیر مفهوم تغییرات درون سلولی، ابعاد شبکه محاسباتی و مقیاس نقشه توپوگرافی بر عملکرد مدل دوبعدی hec-ras در شبیه‌سازی پهنه‌های سیل گیر رودخانه‌ها (مطالعه موردی: رودخانه سرباز)

در ﺣﺎل ﺣﺎﺿﺮ ﺑﺴﯿﺎری از ﻣﺪلﻫﺎی ﻫﯿﺪروﻟﯿﮑﯽ ﻣﻮﺟﻮد ﮐﻪ ﻋﻤﺪه آﻧﻬﺎ در رده ﻣﺪلﻫﺎی ﻣﺘﻮﺳﻂﮔﯿﺮیﺷﺪه در ﻋﻤﻖ (depth-averaged) ﻗﺮار ﻣﯽﮔﯿﺮﻧﺪ، از ﺷﺒﮑﻪﻫﺎی ﻣﺤﺎﺳﺒﺎﺗﯽ ﻣﻨﻈﻢ ﺑﺮای ﮔﺴﺴﺘﻪﺳﺎزی ﻣﯿﺪان ﺣﻞ اﺳﺘﻔﺎده ﻣﯽﻧﻤﺎﯾﻨﺪ و ﻫﻤﯿﻦ ﻣﺴﺎﻟﻪ ﻣﻮﺟﺐ ﮐﺎﻫﺶ ﮐﺎراﺋﯽ آﻧﻬﺎ ﺑﻪ وﯾﮋه در اﺑﻌﺎد ﺳﻠﻮﻟﯽ ﺑﺰرﮔﺘﺮ ﻣﯽﮔﺮدد. ﺑﺮ ﺧﻼف ﻣﺪلﻫﺎی ﻣﺬﮐﻮر، ﻣﺪل دوﺑﻌﺪی hec-ras از ﻣﻔﻬﻮم ﺟﺪﯾﺪی ﺑﻪ ﻧﺎم ﺗﻐﯿﯿﺮات درون ﺳﻠﻮﻟﯽ ﺑﺮای ﻟﺤﺎظ ﻧﻤﻮدن ﺗﻐﯿﯿﺮات ارﺗﻔﺎﻋﯽ داﺧﻞ ﯾﮏ ﺳﻠﻮل ﻣﺤﺎﺳﺒﺎﺗﯽ اﺳﺘﻔﺎده ﻣﯽﻧﻤﺎﯾﺪ و از اﯾﻨﺮو از واﺑﺴﺘﮕﯽ ﺑﺴﯿﺎر ﮐﻤﯽ ﺑﻪ اﺑﻌﺎد ﺳﻠﻮل ﻣﺤﺎﺳﺒﺎﺗﯽ ﺑﺮﺧﻮردار ﻣﯽﺑﺎﺷﺪ. ﭘﮋوﻫﺶ ﺣﺎﺿﺮ ﺑﺎ ﻫﺪف ارزﯾﺎﺑﯽ اﺛﺮ ﮐﺎرﺑﺮد اﯾﻦ ﻣﻔﻬﻮم ﺑﺮ ﭘﻬﻨﻪ ﺳﯿﻼب رودﺧﺎﻧﻪ ﺳﺮﺑﺎز ﺑﻪ اﻧﺠﺎم رﺳﯿﺪه اﺳﺖ. ﻫﻤﭽﻨﯿﻦ ﺑﺮرﺳﯽ ﺗﺎﺛﯿﺮ ﻣﻘﯿﺎس ﻧﻘﺸﻪ ﺑﺮ ﻋﻤﻠﮑﺮد ﻣﺪل ﯾﮏ ﺑﻌﺪی و دوﺑﻌﺪی hec-ras از دﯾﮕﺮ اﻫﺪاف اﯾﻦ ﭘﮋوﻫﺶ ﻣﯽﺑﺎﺷﺪ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ ﺑﺎ اﻓﺰاﯾﺶ اﺑﻌﺎد ﺳﻠﻮل ﻣﺤﺎﺳﺒﺎﺗﯽ، ﻣﯿﺰان ﺧﻄﺎی ﻣﺪل در ﺷﺒﯿﻪﺳﺎزی ﭘﻬﻨﻪﻫﺎی ﺳﯿﻠﮕﯿﺮ ﻧﺴﺒﺖ ﺑﻪ اﺑﻌﺎد ﺳﻠﻮﻟﯽ ﮐﻮﭼﮏ ﻧﺴﺒﺘﺎً ﭘﺎﺋﯿﻦ ﻣﯽﺑﺎﺷﺪ. ﺑﻪ ﻋﻨﻮان ﻣﺜﺎل، در ﺻﻮرت اﺳﺘﻔﺎده از ﯾﮏ ﺷﺒﮑﻪ ﻣﺤﺎﺳﺒﺎﺗﯽ ﺑﺎ اﺑﻌﺎد 500 ﻣﺘﺮ ﺑﻪ ﺟﺎی ﯾﮏ ﺷﺒﮑﻪ ﺑﺎ اﺑﻌﺎد 20 ﻣﺘﺮ، ﻣﯿﺰان ﺧﻄﺎی ﻣﺪل در ﺑﺮآورد ﭘﻬﻨﻪ ﺳﯿﻼب ﺑﻪ ﮐﻤﺘﺮ از 15 درﺻﺪ ﻣﺤﺪود ﻣﯽﮔﺮدد. ﻣﺪت زﻣﺎن اﺟﺮای ﻣﺪل دوﺑﻌﺪی ﻧﯿﺰ در اﺑﻌﺎد ﺳﻠﻮﻟﯽ 500 ﻣﺘﺮ ﺗﻘﺮﯾﺒﺎً45 ﺑﺮاﺑﺮ ﮐﻤﺘﺮ از ﻣﺪت زﻣﺎن اﺟﺮای ﻣﺪل در ﺻﻮرت اﺳﺘﻔﺎده از اﺑﻌﺎد ﺳﻠﻮﻟﯽ 20 ﻣﺘﺮ اﺳﺖ. ﯾﺎﻓﺘﻪﻫﺎی ﻣﺬﮐﻮر ﺑﻪﺧﻮﺑﯽ ﮔﻮﯾﺎی اﯾﻦ ﻣﻄﻠﺐ اﺳﺖ ﮐﻪ اﺳﺘﻔﺎده از ﻣﻔﻬﻮم ﺗﻐﯿﯿﺮات درون ﺳﻠﻮﻟﯽ در ﻣﺪﻟﺴﺎزی ﺗﺎ ﭼﻪ ﺣﺪ ﻣﯽﺗﻮاﻧﺪ در زﻣﺎن اﺟﺮای ﻣﺪلﻫﺎی ﻋﺪدی ﺑﻪ وﯾﮋه در رودﺧﺎﻧﻪﻫﺎی ﺑﺰرگ و ﺑﺎ ﭘﯿﭽﯿﺪﮔﯽ زﯾﺎد ﻣﻮﺛﺮ ﺑﺎﺷﺪ. ﻫﻤﭽﻨﯿﻦ ﻣﺤﺎﺳﺒﺎت ﺻﻮرت ﮔﺮﻓﺘﻪ ﺣﺎﮐﯽ از آن اﺳﺖ ﮐﻪ اﺧﺘﻼف ﺑﯿﻦ دو ﻣﺪل ﯾﮏ ﺑﻌﺪی و دوﺑﻌﺪی در ﺷﺒﯿﻪﺳﺎزی ﭘﺎراﻣﺘﺮﻫﺎی ﻫﯿﺪروﻟﯿﮑﯽ در ﻣﻘﯿﺎسﻫﺎی ﮐﻮﭼﮏ ﻧﺴﺒﺘﺎً ﻧﺎﭼﯿﺰ ﻣﯽﺑﺎﺷﺪ و ﺑﺎ اﻓﺰاﯾﺶ ﻣﻘﯿﺎس ﻧﻘﺸﻪ اﺧﺘﻼف دو ﻣﺪل ﻣﺬﮐﻮر ﻧﯿﺰ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ ﮐﻪ ﻋﻠﺖ اﺻﻠﯽ ﻟﺤﺎظ ﻧﻤﻮدن ﺗﻤﺎﻣﯽ ﺗﻐﯿﯿﺮات ﺗﻮﭘﻮﮔﺮاﻓﯽ ﺑﺴﺘﺮ و ﺳﯿﻼﺑﺪﺷﺖ رودﺧﺎﻧﻪ در ﻣﻘﯿﺎسﻫﺎی ﺑﺎﻻ ﻣﯽﺑﺎﺷﺪ.

Influence of the concept of subgrid variability and computational mesh dimensions on the performance of HEC-RAS 2D model in simulating river floodplains (Case study: Sarbaz River)

The 2D HECRAS model uses a new concept called subgridvariability to include elevation changes within a computational cell and thus has very little dependence on computational cell dimensions. The purpose of this study was to evaluate the effect of the concept of subgridvariability on the simulated flood area in the Sarbaz River. The other purposes of this study is to investigate the effect of map scale on the performance of 1D and 2D HECRAS model. The results showed that with increasing computational cell dimensions, the model error in simulating flood zones was relatively low compared to small cell dimensions. For example, if using a computing grid with dimensions of 500 meters instead of a 20 meters grid, the simulated flood area in different parts of the Sarbaz River would be less than 15 percent. The run time of the 2D model in the cell dimension of 500 meters is approximately 45 times less than the run time of the model in case of using cell dimensions of 20 meters. The findings clearly indicate to what extent the use of the concept of subgrid variability in modeling can be effective when implementing numerical models, especially in large and complex rivers. The calculations also show that the difference between 1D and 2D models in the simulation of hydraulic parameters in small scales is relatively small and by increasing the map scale, the difference between the two models increases.