入滲試驗是瞭解土壤水力特性的重要試驗方法之ㄧ，而非飽和層水流流動之數值模式則可做為土壤物理特性改變時，瞭解水流流動機制之快速工具。本研究利用HYDRUS-1D數值模式配合自行撰寫之Levenberg-Marquardt(LM)演算法反推估van Genuchten土壤水分特性曲線參數。模式測試乃由HYDRUS-1D模式產生之測試數據為基礎，再利用反推估模式結合HYDRUS-1D針對無觀測數據之土壤層進行參數推估，並對各參數初始猜測值進行敏感性分析。 經測試後之推估模式再應用至實驗室及現地尺度觀測數據，實驗室試驗先利用標準砂進行單層與多層砂樣入滲試驗，由張力計與含水量計量測土壤入滲過程。本研究先以HYDRUS-1D數值模式利用試誤法調整參數模擬土壤入滲情形，並且與實驗室砂柱所得觀測數據進行套疊，所獲得土壤參數再與本研究開發之LM反推估模式推估之土壤參數進行比較。現地試驗則於濁水溪河岸進行多深度雙環入滲試驗，記錄其土壤入滲量與入滲率，使用LM推估Horton經驗公式參數，求得不同深度飽和土壤入滲率(fc) 、初始入滲率(f0)與入滲參數( )。同時由現地取樣土壤，帶回實驗室進行管柱入滲試驗，配合現地飽和入滲參數再推估實驗室尺度van Genuchten土壤水分特性曲線參數。 研究結果顯示，本研究開發之LM模式配合HYDRUS-1D可以正確地推估van Genuchten非飽和土壤參數，由測試例結果顯示，殘餘含水量(θr) 與α值需從較低的測試例中才可以得到較好的反推估結果，而n值則對初始猜測值較不敏感，飽和水力傳導係數(Ks) 值為推估過程中最敏感參數。 實驗室分析結果顯示，本研究開發之LM模式配合HYDRUS-1D可以較精確地推估非飽和土壤參數。由現地尺度多深度雙環入滲試驗及實驗室砂樣入滲試驗顯示，濁水溪西螺河段，飽和入滲率在一公尺內的不同深度就有一個級數(order)的差異(f0分別為0.0014及0.00015 cm/s)，由帶回砂樣進行實驗室試驗結果顯示，其Ks亦有一個級數差異(介於0.00061至0.00118 cm/sec)，現地實驗與砂樣試驗差異不大。至於van Genuchten公式中其他參數，θr為0.01(-)、θs是0.2601至0.3227、α則介於0.01688至0.09289(cm-1)，n值介於2.528至5.886(-)之間，河床沉積土壤主要為為砂與粉砂。Infiltration test is an important technique to investigate the hydrologic properties in soils, while the unsaturated flow numerical models can be an efficient tool to understand flow mechanism when the physical properties and conditions of soils are changed. This study employs HYDRUS-1D model and self developed Levenberg-Marquardt algorithm to inversely estimate parameters in the van Genuchten formula. The developed LM model was tested based on the synthetically generated data from HYDRUS-1D model. Additionally, the initial guesses of soil parameters in LM model were systematically analyzed to obtain general insight into the laboratory and field scale applications. The tested model was then used to estimate soil parameters of laboratory sand box under different infiltration scenarios. During the infiltration tests, the suction or pressure and water content were measured with tensiometers TDR(Time Domain Reflectometry). Such measured data can thus be used in the LM model to estimate the soil parameters. The estimated parameters were compared with those based on trial and error approach. Field scale double-ring infiltration was tested on the river bank of Zhuoshui river near His-Luo. The saturated infiltration rate(fc), initial infiltration rate (f0), and infiltration parameter by using the in Horton formula were estimated by the developed LM model. The objective of the field scale test is to obtain the saturated infiltration rate(f0) to compare with the results of laboratory experiment. Estimate Van Genuchten parameters by combining the laboratory infiltration experiment of field soil sample and saturated infiltration parameters. The results of the study reveal that the developed LM model associated with HYDRUS-1D model can accurately estimate van Genuchten soil parameters. The results of model test shows that the lower initial guess values would lead to better estimations of residual water content (θr) and α values. The saturated hydraulic conductivity (Ks) is the most sensitive parameter while the initial guess n values are relatively insignificant. The LM inversion of tests show that LM model associated with HYDRUS-1D model can estimate accurately van Genuchten for laboratory scale tests soil parameters. The field scale multiple depth double-ring infiltration tests reveals that the saturated infiltration rates(f0) of Zhuoshui river near His-Luo have one order of magnitude difference for different depths such depth difference of hydraulic conductivity (Ks) (0.0014 and 0.00015 cm/s) were also shown in laboratory scale tests. Based on the soil sample from Zhuoshui river the sand box experiment data were then used in LM model to estimate soil parameters. This simulation results showed that the value of α is from 0.01688 to 0.09289(cm-1), the value of n from 2.528 to 5.886(-), the material of the soil can be classified as sand and silt.
