AIR AND WATER FLOW IN A SEALED, PONDED VERTICAL SOIL COLUMN

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Abstract
We present experimental results of ponded infiltration in a vertical column for two cases: when air is free to escape from the medium, and when air is confined and can escape only through the soil surface. We show that, in the second case, air pressure reaches a constant value, independent of depth and time. The primary effect of this air pressure is to decrease the water potential at the surface and thus to reduce the infiltration rate to about one-third of its value when air is free to escape. The confined air pressure value can be predicted if permeabilities of soil to air and water are known with precision near saturation. A simple analytical model is presented, which predicts the cumulative infiltration with a good precision, if air pressure or water content at the soil surface is predicted or in practice measured directly.

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