Characteristics of inverted saturated zone under unclogged streams

Unclogged streams are widespread in nature and can generate dynamic inverted saturated zones (ISZ) underneath the streams above the regional water tables. This study is devoted to investigating the evolutional process of such an ISZ and its frontal movement. It defines a uniform saturation zone by moving the boundary of saturation flow from the inverted water table (IWT) to the end of the capillary saturation zone. Consequently, the conventional concept of specific yield, infiltration rate and governing equation at the ISZ frontal surface (IFS) must be revisited. Two new ISZ models are developed and quantified with great details with infiltration rate being constant and variable. The equations of hydraulic head profile development and the IFS are obtained. This study indicates that classical free surface equations, locating at IWT, is not self-consistent. The water balance requirement is not satisfied at IFS in the Green and Ampt (1911) model or the Polubarinova-Kochina (1962) model, causing physically unrealistic spatial variables. The increase of the IFS with time exhibits three different modes depending on the infiltration rate and the saturated hydraulic conductivity. The maximum depth of an IFS (corresponding to a depth with infiltration rate being stable) is linearly correlated with stream stage and air-entry head. The streambed infiltration flux decreases with time and appears to exhibit three modes similar to the IFS evolution. The findings of this study reconstruct the theoretical basis of the dynamic evolution process of stream-aquifer system and can help for better understanding of physical connotation of free surface equations and basic characteristics of ISZ evolution.

Automated summary

This study focuses on the evolutionary process and frontal movement of inverted saturated zones (ISZ) under unclogged streams. It defines a uniform saturation zone, revisits concepts like specific yield and infiltration rate, and develops two new ISZ models. The study shows that classical free surface equations are not self-consistent, with the ISZ frontal surface (IFS) exhibiting different modes over time. The findings help reconstruct the theoretical basis of stream-aquifer system evolution and better understand the physical meaning of free surface equations.