The Green-Ampt Model

VIONNET CA

2010-06-07/2010-10-12

1-61

Informática (software)

Rec.Hidr.-Crecidas, inundaciones y sequias

Soils are seldom completely saturated with water, although saturation may occur at certain depths for brief periods of time. Most of the time water flows in soil under unsaturated conditions; i.e., the soil pore space is occupied by both air and water. Neglecting the air movement, the unsaturated flow can be described by generalizing the Darcy’s law. The time-dependent rate of infiltration of water into soil is governed by Richards’ equation. Although numerical methods of solution can be obtained for it, the problem remains a difficult one. A number of simpler approaches have provided ways of obtaining more concise parameterizations for certain aspects of the phenomenon. These have consisted of extensions of the approach of Green and Ampt [2], based on a quasi-steady state approximation to solve the infiltration problem. The Green-Ampt model is consequently based upon several simplifying assumptions on how water moves into soil. These notes summarize the salient futures of water movement in unsaturated soils or rock, with emphasis on the Green-Ampt model. Note: most of these notes are textual citations from the books Elements of Physical Hydrology [3] and Hydrology, An Introduction [1], so care should be exerted before using the following material without introducing appropriate modifications into the text and/or including the proper citation. At the end of this technical report, some additional material freely available in the web is also included for later reference by the reader. Attached, the reader may also find the class notes of Prof. Raúl Pedraza, lecturer of the Surface Hydrology subject at FICH.