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題 名 | 未飽和層土壤水分垂直入滲之數值模擬=Numerical Approximation of Vertical Moisture Movement in Unsaturated Soil |
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作 者 | 許瑞昌; 陳主惠; 劉振宇; | 書刊名 | 農業工程學報 |
卷 期 | 44:4 1998.12[民87.12] |
頁 次 | 頁1-16 |
分類號 | 434.222 |
關鍵詞 | 未飽和土壤; 土壤水分; 入滲; 數值模擬; Unsaturated soil; Soil moisture; Infiltration; Numerical modelling; |
語 文 | 中文(Chinese) |
中文摘要 | 地表水經由土壤入滲進入地下水層之過程十分複雜,因為土層之邊界條件和初始 條件經常不是定值,土壤水力特性亦會隨時間及空間變化。並且在非飽和土壤中土壤水分趨 近飽和時,其水力傳導係數隨變化微小之體積含水比而會有極大之變化。因此,當水分濕潤 前緣經過時,在很小的深度範圍,變化劇烈之水力傳導係數會造成濕潤前緣附近產生一巨大 之水頭梯度,在數值解之發展過程中,水力傳導係數離散化不論選取算數平均、幾何平均、 調和平均,或其他複雜的公式,均無法正確描述其變化,造成質量守恆之問題。本文利用母 體通量位能推導非飽和層流動方程式,以有限差分法離散,發展一維數值程式,在地表之上 層邊界條件可考盧強度隨時間任意變化之降雨型態,下層邊界條件可考慮有無固定之地下水 面,土壤臨前水文條件可考慮土壤任意分佈之體積含水比。模式可用來推估不同土壤在不同 邊界及初始條件下之地表積水時間及土壤體積含水比剖面與地表入滲率曲線。在不同條件下 程式模擬結果,其質量守恆均達99-105%之精度,顯示上述濕潤前緣附近產生之巨大水頭梯 度所造成之質量守恆問題已獲得良好之改善。模擬結果亦顯示地下水面之深淺及土壤臨前之 體積含水比剖面會影響地表積水時間。地下水面越深者,其地表土壤較地下水面淺者越慢到 達飽和,穩態之初始體積含水比剖面最快使地表土壤到達飽和。 |
英文摘要 | It is complicated to predict water infiltration into subsoil because boundary and initial conditions of soil are not often constant. Also, soil hydraulic properties change with time and space. In unsaturated soil, hydraulic conductivity, K, changes much with volumetric water content which changes little while soil is nearly saturated. As wetting front passes, under teeny depth change, hydraulic conductivity will change greatly and near the wetting front exists an enormous head gradient which can not be accurately approximated numerically and causes the mass-balance problem. In development of numerical solutions, there are many methods, such as arithmetic mean, geometric mean, harmonic mean or other complex formula, proposed to approximate hydraulic conductivity, but most of them can not the resolve the problem of mass-conservation. The study adopt matric flux potential concept to construct the unsaturated flow equation. A finite difference computer program is developed which has the upper boundary condition expressed by rainfall intensity changing with time, the lower boundary condition expressed by groundwater table, and the antecedent condition expressed by distribution of volumetric water content. The model can be used to estimate ponding time, Tp, soil volumetric water content profile, infiltration curve and mass balance curve. The simulated result under various condition shows that mass balance is 99~105% and the mass-balance problem caused by the enormous head gradient near wetting front is improved. The depth of groundwater table and soil antecedent profile of volumetric water content will influence on ponding time. The ponding time of deep groundwater table is longer than that of shallow one. The initial volumetric water content profile at steady state has the subsurface soil reach to saturated condition first. |
本系統中英文摘要資訊取自各篇刊載內容。