شبيه سازي عددي و تجربي پياز رطوبتي در آبياري قطره اي زيرسطحي براي خاك لومي رسي

Numerical and Empirical Simulation of Wetting Pattern in Subsurface Drip Irrigation in Clay Loam Soil

آﺑﯿﺎري ﻗﻄﺮهاي زﯾﺮﺳﻄﺤﯽ ﺑﻪ ﻃﻮر ﮔﺴﺘﺮدهاي در ﻣﻨﺎﻃﻖ ﺧﺸﮏ ﺑﻪ ﻋﻨﻮان ﯾﮏ روش آﺑﯿﺎري ﮐﻢ ﻣﺼﺮف ﻣﻮرد اﺳﺘﻔﺎده ﻗﺮار ﻣﯽﮔﯿﺮد. اﻣﺎ داﺷﺘﻦ اﻃﻼﻋﺎت ﺟﺎﻣﻊ از اﻟﮕﻮي ﺧﯿﺲﺷﺪﮔﯽ در آﺑﯿﺎري ﻗﻄﺮهاي ﺑﺮاي ﻃﺮاﺣﯽ و ﻣﺪﯾﺮﯾﺖ اﯾﻦ ﺳﯿﺴﺘﻢ ﺿﺮوري اﺳﺖ. ﺛﺎﺑﺖ ﺷﺪه ﮐﻪ ﻣﺪلﻫﺎي ﺷﺒﯿﻪﺳﺎزي ﻣﯽﺗﻮاﻧﻨﺪ ﺑﺮاي اﯾﻦ ﻣﻨﻈﻮر ﻣﻔﯿﺪ ﺑﺎﺷﻨﺪ. ﺑﻨﺎﺑﺮاﯾﻦ، اﯾﻦ ﭘﮋوﻫﺶ ﺑﻪ ﻣﻨﻈﻮر ﺑﺮرﺳﯽ اﺑﻌﺎد ﭘﯿﺎز رﻃﻮﺑﺘﯽ در آﺑﯿﺎري ﻗﻄﺮهاي زﯾﺮﺳﻄﺤﯽ در ﯾﮏ ﺧﺎك ﻟﻮﻣﯽرﺳﯽ ﺑﻪ روش ﻣﺪلﺳﺎزي ﻣﻌﮑﻮس ﺑﺎ ﻣﺪلHydrus 2D ﺑﺎ ﺗﮑﯿﻪ ﺑﺮ ﻧﺘﺎﯾﺞ آزﻣﺎﯾﺸﮕﺎﻫﯽ و ﺗﻮﺳﻌﻪ ﻣﺪل ﺗﺠﺮﺑﯽ اﻧﺠﺎم ﺷﺪ. ﻧﺘﺎﯾﺞ ﺣﺎﺻﻞ از ﭘﮋوﻫﺶ در ﭼﻬﺎر ﻗﺴﻤﺖ دﺳﺘﻪﺑﻨﺪي ﺷﺪﻧﺪ: 1- ﻧﺘﺎﯾﺞ آزﻣﺎﯾﺸﮕﺎﻫﯽ ﻧﺸﺎن داد ﮐﻪ ﻓﻘﻂ در آزﻣﺎﯾﺶ ﻣﺮﺑﻮط ﺑﻪ ﻗﻄﺮهﭼﮑﺎنﻫﺎي ﺑﺎ دﺑﯽ 8 ﻟﯿﺘﺮ ﺑﺮ ﺳﺎﻋﺖ و ﻋﻤﻖ ﻧﺼﺐ 15 ﺳﺎﻧﺘﯽﻣﺘﺮ، ﻋﻤﻖ ﺧﯿﺲﺷﺪﮔﯽ زﯾﺮ ﻗﻄﺮهﭼﮑﺎن ﺑﯿﺸﺘﺮ از ارﺗﻔﺎع ﺧﯿﺲﺷﺪﮔﯽ ﺑﺎﻻي ﻗﻄﺮهﭼﮑﺎن ﻣﯽﺑﺎﺷﺪ. 2- آﻧﺎﻟﯿﺰ ﺣﺴﺎﺳﯿﺖ اﻧﺠﺎم ﯾﺎﻓﺘﻪ روي ﭘﺎراﻣﺘﺮﻫﺎي ﻫﯿﺪروﻟﯿﮑﯽ ﺧﺎك ﻧﺸﺎن داد ﮐﻪ ﺣﺴﺎﺳﺘﺮﯾﻦ ﭘﺎراﻣﺘﺮ، رﻃﻮﺑﺖ اﺷﺒﺎع ﺧﺎك )𝜽𝒔( ﺑﻮده وﻟﯽ ﭘﺎراﻣﺘﺮﻫﺎي ﭘﯿﻮﺳﺘﮕﯽ ﻣﻨﺎﻓﺬ ﺧﺎك )l( و رﻃﻮﺑﺖ ﺑﺎﻗﯽ ﻣﺎﻧﺪه )𝜽𝒓( در روﻧﺪ ﺷﺒﯿﻪﺳﺎزي ﭘﯿﺎز رﻃﻮﺑﺘﯽ ﺑﯽﺗﺄﺛﯿﺮ ﺑﻮدﻧﺪ. 3- ﺑﺮاي ﺧﺎك ﻣﻮرد ﺑﺮرﺳﯽ، ﭼﻨﺎﻧﭽﻪ ﻗﻄﺮهﭼﮑﺎن در ﻋﻤﻖ 15 ﺳﺎﻧﺘﯿﻤﺘﺮي ﻧﺼﺐ ﺷﻮد در دﺑﯽﻫﺎي ﺑﯿﺸﺘﺮ از 2 ﻟﯿﺘﺮ ﺑﺮ ﺳﺎﻋﺖ ﺟﺒﻬﻪ رﻃﻮﺑﺘﯽ ﺑﻪ ﺳﻄﺢ ﺧﺎك رﺳﯿﺪه و ﺑﺎﻋﺚ ﻣﺮﻃﻮب ﺷﺪن ﺳﻄﺢ ﺧﺎك ﻣﯽﮔﺮدد، در ﺣﺎﻟﯽ ﮐﻪ در ﻋﻤﻖ اﺳﺘﻘﺮار 30 ﺳﺎﻧﺘﯿﻤﺘﺮ، ﺣﺘﯽ ﺑﺎ دﺑﯽ 8 ﻟﯿﺘﺮ ﺑﺮ ﺳﺎﻋﺖ ﺟﺒﻬﻪ رﻃﻮﺑﺘﯽ ﺑﻪ ﺳﻄﺢ ﺧﺎك ﻧﻤﯽرﺳﺪ. ﺑﻨﺎﺑﺮاﯾﻦ ﺗﻠﻔﺎت ﺗﺒﺨﯿﺮ از ﺳﻄﺢ ﺧﺎك ﻧﯿﺰ ﺑﻪ ﺣﺪاﻗﻞ ﻣﯽرﺳﺪ 4- ﺷﺎﺧﺺﻫﺎي آﻣﺎري ﻧﺸﺎن دادﻧﺪ ﺗﻔﺎوت ﭼﻨﺪاﻧﯽ ﺑﯿﻦ ﻧﺘﺎﯾﺞ ﻣﺪلﻫﺎي ﺗﺠﺮﺑﯽ و ﻋﺪدي و ﻣﻘﺎدﯾﺮ ﻣﺸﺎﻫﺪاﺗﯽ وﺟﻮد ﻧﺪارد ﺑﻪ ﻮرﯾﮑﻪ RMSE ﻧﺮﻣﺎل ﺷﺪه ﺑﺮاي ﻣﺪل ﻋﺪدي و ﺗﺠﺮﺑﯽ ﺑﻪ ﺗﺮﺗﯿﺐ از 4/4 ﺗﺎ 6/2 و 3/4 ﺗﺎ 8 درﺻﺪ ﻣﺘﻐﯿﺮ ﺑﻮد. ﺑﻨﺎﺑﺮاﯾﻦ ﻣﯽﺗﻮان از ﻧﺘﺎﯾﺞ ﻣﺪل ﺗﺠﺮﺑﯽ ﭘﯿﺸﻨﻬﺎد ﺷﺪه و ﻣﺪل ﻋﺪدي Hydrus ﺑﺮاي ﺑﺮآورد ﭘﯿﺎز رﻃﻮﺑﺘﯽ اﺳﺘﻔﺎده ﻧﻤﻮد.

Subsurface drip irrigation has been widely applied in arid area as a water-saving irrigation technology. But, a comprehensive knowledge of wetting pattern in drip Irrigation is essential for designing and managing such system. Simulation models have been proved to be useful method for this purpose. Therefore, this research was carried out to investigate the dimensions of wetting pattern in subsurface drip irrigation in a clay loam soil using invers modeling method with Hydrus 2D and based on experimental results and empirical models. The results were categorized into four sections: 1. Laboratory results showed that only for emitters with 8 liters per hour and installed at 15 cm depth, the wetted dimension below the emitter is more than the one above the emitter. 2. Sensitivity analysis on soil hydraulic parameters showed that the most sensitive parameter is θs, but the soil porosity continuity (l) and the remaining moisture content (θr) are not effective parameters. 3. Wetting front in emitters with discharge rate more than 2 liters per hour and installed at 15 cm depth in the clay loam soil is reached to the soil surface, while it does not reach to the soil surface in the emitters installed at 30 cm depth, even with discharge rate up to 8 liters per hour. Therefore, the evaporation rate from the soil surface is minimized. 4. Statistical indices showed that there is no significant differences among the empirical, numerical and the observation data, so that the normalized RMSE for the numerical and empirical models varied from 4.4 to 6.2 and 3.4 to 8 percent, respectively. Consequently, the results of this study showed that the proposed empirical model and Hydrus model can be used for estimation of wetting pattern in the soil.