非飽和區在入滲過程中之等持現象

一般簡單入滲方程如Green-Ampt型者常忽略土中之非飽和區，而僅拮取該區之毛細張力以供求取入滲速率之用，因此所解也就侷限於飽和區段隨時間之變化而已。本文檢視入滲水份在土中之連續和動量方程，並假設非飽和區含水率隨深度成線性遞減，得到一控制非飽和區長度之獨立方程，此方程可將飽和及非飽和區分割，並不需要特別定義各區之邊緣或藉助繪圖之方法以尋求二區之交界即可決定各區之長度，當地表積水厚增加時也可定量地評估此二區之成長速率和相對重要性。由理論推算之結果發現非飽和段幾乎不受地表積水厚之影響，但臨前含水率卻是最重要影響因子；不論土壤種類如何，只要臨前含水率甚低且土壤維持均質，非飽和區總以近於定值之速率相對於飽和區成長，此現象可維持相當長之一段時間而不消退，本文對此發展出一模式將之定量化，明確地標示出所有影響因子並預測兩區之相對成長速率，同時定義一指標值來說明此現象發生之原因和時機。

關鍵字

Green-Ampt入滲方程；非飽和區；毛細水頭；等持現象

並列摘要

Infiltration equations, such as the type of Green-Ampt functions, usually neglect the unsaturated zone in porous media, and use only the capillary pressure of the zone for analyzing infiltration rates. Therefore, solutions of these equations are restricted to the variation of the saturation length with respect to time. This paper examines the continuity and momentum equations of infiltrating water and assumes a linear variation of water content in the unsaturated zone. By this assumption, an independent equation controlling the length of the zone is obtained. This equation enables the division of the unsaturated zone from the saturated one. It can also calculates their length without any plotting or any special definition of their edge. In addition, this equation can quantifies the relative importance and growth speed of these two zones as the surface water depth is increased. It is found by theoretical estimations that the length of the unsaturated zone is hardly affected by the surface water depth but most importantly affected by initial water contents. Regardless of soil types, the unsaturated zone always grows up with a constant speed relative to that of the saturated one, as long as initial water content is low and soil matrix remains homogeneous and isotropic. This phenomenon sustains quite a long period without fading, and is quantified by a model developed in this paper. This model clearly labels out all the influencing factors and predicts the relative growth speed of the zones. It also defines an index to illustrate the cause and occurrence time of the phenomenon.

並列關鍵字

Green-Ampt equation ； unsaturated zone ； Capillary head ； Consistent growth phenomenon

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