On shapes of cumulative infiltration curves

Abstract

Water infiltration into soil is the key process in the water cycle, and understanding and predicting infiltration is essential for water management. Measurements of cumulative infiltration are a common part of soil hydrological characterization. Such measurements provide the cumulative infiltration curve (CIC), i.e. dependence of the amount of infiltrated water on time. The classic, usually anticipated CIC shape is the concave increase section transitioning to the linear section. However, other shapes were also observed. The objectives of this work were (a) to use the unique large international infiltration database SWIG to define distinctly different types of CIC shapes, and (b) to see if basic soil properties, land use, and infiltration measurement method can indicate what type of non-classic CIC shapes can be expected in site-specific conditions. Examination of 5023 CIC led to the definition of 12 types of CIC shapes. About 1/3 of SWIG datasets had non-classic CIC shapes. The shape types were visually discernible in most cases. A technique was suggested to distinguish the shape types if needed. The classification tree divided all datasets with non-classic CIC shapes into most similar inside and most different from each other groups. The infiltration measurement method, the clay content, and the organic carbon content were the most influential predictors of the shape type in this classification. Several non-classic shapes were previously related to soil structure and hydrophobicity. The relatively large fraction of non-classic CIC indicates the need to design infiltration experiments accounting for possible non-classic CIC, and the need for the cautious application of common infiltration equations, most of which were developed to simulate classic CIC shapes.