Study on rainfall-seepage flow on hillslope by saturated-unsaturated groundwater model combined with parameter estimation process

• Main Authors: XU, RONG-TING, 許榮庭
• Other Authors: LIU, CHANG-LING
• Format: Others
• Language: zh-TW
• Published: 1990
• Online Access: http://ndltd.ncl.edu.tw/handle/73101065977108480189

博士 === 國立成功大學 === 水利及海洋工程研究所 === 79 === The purpose of this paper is to analyze the seepage flow of hillslope groundwater with the consideration of rainfall. To build the numerical model, this research used finite element method wit a nonlinear iteration and parameter estimation algorithm. The sand tand model as well as the fog-maker method were used to simulate the seepage process on hillslope. The content of this paper can be divided into four part: In the first part, the saturated-unsaturated groundwater flow model was developed by finite element with a nonlinear iteration algorithm, nad was verified by a one dimensional analytic solution. Consistent results were obtained. To estimate the convergence property of the compuataional scheme and the difference among various nonlinear iteration schemes, three types of grid systems and three iteration algorithms were adopted and analyzed. the results showed that the iteration algorithm using damping parameter method waas better than the others. In the second part, to build an influence coefficient matrix parameter estimation method, the soil hydraulic function of van Genuchten equation was adopted for model calibration. Sensitivity analysis showed that it is better to use heads than soil drainages as objective function. Within this part, parameter estimations were done by combining one-dimensionsl rainfall-seepageexperiments and dour soil hydraulic empirical formulas were chosen and analyzed. In the third part, the numerical model was combined with parameter estimation process to estimate soil hydraulic function from two-dimensional hillslope recession period, then the hillslope seepage flow was calculated by numerical model with estimated soil hydraulic function. The results showed that the computed seepage flow was closed to observations. The influence of unsaturration zone within hillslope recession period was also analyzed by numerical and experimental methods and the results we found to be insensitive. In the last part, according to the analy sis and estimation above, the soil hydraulic function mode(2) was chosen to be estimated in the section. Some experimental results were got in layered hillslope rainfall-seepage process, and these results were compared and discussed with computational results of numerical model. From the analysis, it was learne d that the variation of layered soil construction had various influence on layered hillslope seepage flow, and the middle layer could be regarded as impermeable aquifer as the saturated hydraulic conductivity of middle layer was reduced to less 0.1% of upper layer. In this part, the validity of unit hydrograph was also investigated by the numerical model. Further developement approach for combining system analysis model with physical model was suggested. 本文之研究目的在於利用數值方法與實驗方法，分析坡地地下水在降雨條件下之滲流 流況。就數值方法而言，本文結合有限元素法參數推估法以及非線性疊代運算；而實 驗方法係利用砂箱模型配合噴霧方法模擬坡地之滲流過程。本文之內容可以分成四部 份： 第一部份：利用有限元素及非限性疊代運算建立飽和及未飽和地下水流動模式，並利 用一維之解析方法與數值方法相互驗証，而得到一致皂計算結果。其次，針對數值計 算的數斂性及三種非線性疊代運算方法作評估，此結果顯示有限元素法的元素分割形 狀明顯的影響計算結果；在非線性疊代運算方法之評估上，則顯示振盪參數法比另外 兩種方法為佳。 第二部份：利用影響係數矩陣法建立參數推估過程，並利用van Genuchten 的土壤水 分函數作參數推估模式的檢測以及參數推估過程的敏感度分析，此結果說明了以水頭 作為目標函數要比利用土壤排水量作為目標函數為佳。參數推估過程在此一部份配合 了一維降雨滲流實驗結果，並選擇了四種土壤水分函數之經驗式作為不同經驗式對計 算結果差異程度的探討，此結果顯示模式四之經驗式不適合用於本文之參數推估過程 ，其他三種經驗式則可以接受。 第三部份：利用本文之數值模式結合參數推估過程應用於推求二維坡地退水滲流過程 中之土壤水分函數，再利用推求得到的土壤水分函數計算坡面滲流量，結果顯示經過 此一複雜的計算過程後，坡面滲流量的計算值與觀測值相當接近。未飽和層在坡地退 水滲流過程中所具有的影響力，亦經過實驗方法及數值方法加以分析，結果則顯示未 飽和層對滲流量並沒有顯著的影響。 第四部份：將本文所建立之模式，經過第三部份結果的分析並加以評估後，在此一部 份則選擇模式（二）之經驗式作為土壤水分函數。配合多層坡地降雨滲流的實驗結果 ，利用數值計算對實驗結果加以解釋，此結果之分析說明了土壤地質結構的變化對多 層坡地滲流過程具有不等程度的影響，而當夾層之飽和水力傳導度為上層土壤之飽和 傳導度的0.1%時，夾層可以視為不透水層。此一部份亦利用所建立的數值模式解釋了 單位歷線的適當性，並提供一套系統分析模式和物理模式可以相互配合應用的途徑。