Influence of Soil Heterogeneity on Water Flow and Solute Transport Characterized by Dye Tracer Experiments
Publication: Journal of Hydrologic Engineering
Volume 28, Issue 2
Abstract
Soil heterogeneity is a key factor affecting horizontal water flow and solute transport in unsaturated soil, in which particle distribution, pore structure, and pore connectivity in the soil all present fractal characteristics. The initial water content of soil has significant influence in the resulting heterogeneity of the soil structure, which can affect the water flow and solute transport. In this study, through a series of horizontal transport laboratory simulation experiments in soil columns, the initial water content dependency of transport was elucidated using the fractal Richards’ equation (FRE) model. We first observed that water flows faster in soil columns with higher initial water content, but the law is opposite in the initial process of water flow. By analyzing the variation of parameter values in the FRE model, we speculated that the abnormal phenomenon of early diffusion is caused by the heterogeneity of the soil structure. To elucidate the mechanisms of the water content’s dependency of the solute transport process and to identify the circumstance of altering of flow regime, a series of dye tracer experiments were conducted. Results show that in soil columns with low water content, the inflow of external fluid leads to the agglomeration of soil particles. Combined with matric suction, the heterogeneity of the soil structure is enhanced, which affects the formation of water flow and solute transport paths. It even leads to preferential flow in unsaturated soil columns with low water content.
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Data Availability Statement
All data included in this study are available upon request by contact with the corresponding author.
Acknowledgments
Our research has been supported by the National Natural Science Foundation of China (Grant No. 11572112) and the Fundamental Research Funds for the Central Universities (No. 2016B44914). The support of the Experiment Center of Mechanics and Materials in Hohai University is also appreciated.
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Received: Dec 22, 2021
Accepted: Oct 14, 2022
Published online: Dec 1, 2022
Published in print: Feb 1, 2023
Discussion open until: May 1, 2023
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