بررسي اثر فاصله انتقال بر ضريب انتشارپذيري كلريد سديم در خاك ماسه‌اي مطبق‌ افقي و شبيه‌سازي آن با مدل هايدروس دوبعدي

Study of the Effect of Transport Distance on Dispersion Coefficient of Sodium Chloride in Horizontal Stratified Sandy Soils and its Simulation with HYDRUS- 2D

اﻧﺘﺸﺎرﭘﺬﯾﺮي ﯾﮑﯽ از ﻣﻬﻢﺗﺮﯾﻦ ﺧﺎﺻﯿﺖﻫﺎي ﻗﺎﺑﻞ اﻧﺪازهﮔﯿﺮي ﻣﺤﯿﻂ ﻣﺘﺨﻠﺨﻞ اﺳﺖ. اﯾﻦ ﭘﺎراﻣﺘﺮ ﻣﻬﻢ در ﻣﻌﺎدﻻت ﺟﺎﺑﺠﺎﯾﯽ- اﻧﺘﺸﺎر ﻣﺮﺑﻮط ﺑﻪ اﻧﺘﻘﺎل آﻻﯾﻨﺪه در ﻣﻄﺎﻟﻌﻪ آب زﯾﺮزﻣﯿﻨﯽ اﺳﺘﻔﺎده ﻣﯽﺷﻮد. در ﮔﺬﺷﺘﻪ ﺿﺮﯾﺐ اﻧﺘﺸﺎرﭘﺬﯾﺮي ﺑﺮاي ﮐﻞ ﯾﮏ ﻣﺤﯿﻂ ﻣﺘﺨﻠﺨﻞ ﺑﺼﻮرت ﯾﮏ ﺿﺮﯾﺐ ﺛﺎﺑﺖ در ﻧﻈﺮ ﮔﺮﻓﺘﻪ ﻣﯽﺷﺪ، وﻟﯽ ﻣﻄﺎﻟﻌﺎت زﯾﺎدي ﮐﻪ در ﻃﻮل ﭼﻨﺪ دﻫﻪ اﺧﯿﺮ اﻧﺠﺎم ﺷﺪ ﻧﺸﺎن داده اﺳﺖ ﮐﻪ اﻧﺘﺸﺎرﭘﺬﯾﺮي ﺑﻪ ﭘﺎراﻣﺘﺮﻫﺎي زﯾﺎدي از ﺟﻤﻠﻪ ﻓﺎﺻﻠﻪ اﻧﺘﻘﺎل ﺑﺴﺘﮕﯽ دارد. از آن ﺟﺎﯾﯽ ﮐﻪ اﻏﻠﺐ اﯾﻦ ﻣﻄﺎﻟﻌﺎت در ﻣﺤﯿﻂﻫﺎي ﻣﺘﺨﻠﺨﻞ ﻫﻤﮕﻦ اﻧﺠﺎم ﺷﺪه اﺳﺖ. در اﯾﻦ ﭘﮋوﻫﺶ ﺑﻪ ﺑﺮرﺳﯽ اﺛﺮ ﻓﺎﺻﻠﻪي اﻧﺘﻘﺎل 20 ، 50 و 80 ﺳﺎﻧﺘﯽﻣﺘﺮي ﺑﺮ ﺿﺮﯾﺐ اﻧﺘﺸﺎرﭘﺬﯾﺮي در ﯾﮏ ﻣﺤﯿﻂ ﻣﺘﺨﻠﺨﻞ ﻣﻄﺒﻖ ﺑﺎ داﻧﻪﺑﻨﺪي درﺷﺖ، ﻣﺘﻮﺳﻂ و رﯾﺰ ﺑﺼﻮرت آزﻣﺎﯾﺸﮕﺎﻫﯽ ﭘﺮداﺧﺘﻪ ﺷﺪ. ﻧﺘﺎﯾﺞ ﺑﺪﺳﺖ آﻣﺪه در اﯾﻦ ﭘﮋوﻫﺶ ﻧﺸﺎن داد در ﻫﻤﻪ ﻓﻮاﺻﻞ اﻧﺘﻘﺎل، ﺣﺠﻢ آب ﺗﺨﻠﺨﻞ ﻗﺒﻞ از رﺳﯿﺪن ﺑﻪ ﻏﻠﻈﺖ ﻧﺴﺒﯽ 0/5، ﺑﻪ ﯾﮏ رﺳﯿﺪ و ﺳﺮﻋﺖ اﻧﺘﻘﺎل آﻻﯾﻨﺪه ﺑﺎ اﻓﺰاﯾﺶ ﻓﺎﺻﻠﻪ اﻧﺘﻘﺎل ﮐﻤﺘﺮ ﺷﺪ ﮐﻪ ﺑﺎ ﻧﺘﺎﯾﺞ ﺳﺎﯾﺮ ﻣﻄﺎﻟﻌﺎت ﻣﻄﺎﺑﻘﺖ داﺷﺖ. ﻫﻤﭽﻨﯿﻦ ﻣﺪﻟﺴﺎزي ﻋﺪدي ﺑﻪ وﺳﯿﻠﻪي ﻣﺪل ﻋﺪدي ﻫﺎﯾﺪروس ﻧﺸﺎن داد ﮐﻪ اﯾﻦ ﻣﺪل ﺗﻮاﻧﺴﺘﻪ اﺳﺖ ﻣﻘﺪار ﺿﺮﯾﺐ اﻧﺘﺸﺎرﭘﺬﯾﺮي را ﺑﺮاي ﻓﺎﺻﻠﻪﻫﺎي اﻧﺘﻘﺎل 50 ،20 و 80 ﺳﺎﻧﺘﯽﻣﺘﺮي ﺑﺎ ﺧﻄﺎي RMSE ﺑﻪ ﺗﺮﺗﯿﺐ ﺑﺮاﺑﺮ ﺑﺎ 0/063 ،0/061 و 0/057 ﻣﺤﺎﺳﺒﻪ ﮐﻨﺪ ﮐﻪ ﺑﯿﺎﻧﮕﺮ دﻗﺖ ﺑﺎﻻي آن در ﺷﺒﯿﻪﺳﺎزي و ﻧﺤﻮهي ﺣﺮﮐﺖ اﻧﺘﻘﺎل آﻻﯾﻨﺪه در ﻣﺤﯿﻂ ﻣﺘﺨﻠﺨﻞ اﺳﺖ.

Dispersion is one of the most important measurable properties of porous media. This important parameter is used in the Advection–Dispersion transport equation related to pollutant transfer in the study of groundwater resources. In the past studies, the dispersion coefficient was considered a constant coefficient for the whole porous media, but many studies over the last few decades have shown that it depends on many parameters, including the transmission distance. Since most of these studies have been performed in homogeneous porous media, in this study, experimental study was carried out to investigate the effect of transfer distances of 20, 50 and 80 cm on the dispersion coefficient in layered soils which containing coarse, medium and fine sand. The results of this study showed that at all transfer distance, the volume of porous water before reaching to the relative concentration of 0.5, reached to one and the rate of pollutant transfer decreased with increasing transfer distance. This result consistence with finding of other studies. Numerical modeling by HYDRUS- 2D model also showed that this model was able to calculate the value of diffusion coefficient for transmission distances of 20, 50 and 80 cm with RMSE error equal to 0.061, 0.063 and 0.057, respectively, which indicates its high accuracy in simulating and movement of pollutants in the porous media.