Evidence of Preferential Flow Activation in the Vadose Zone via Geophysical Monitoring

Lorenzo De Carlo,Maria Clementina Caputo,Kimberlie Perkins

doi:10.3390/s21041358

Lorenzo De Carlo, Maria Clementina Caputo + Show 1 more

Open Access

https://doi.org/10.3390/s21041358

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Abstract

Preferential pathways allow rapid and non-uniform water movement in the subsurface due to strong heterogeneity of texture, composition, and hydraulic properties. Understanding the importance of preferential pathways is crucial, because they have strong impact on flow and transport hydrodynamics in the unsaturated zone. Particularly, improving knowledge of the water dynamics is essential for estimating travel time through soil to quantify hazards for groundwater, assess aquifer recharge rates, improve agricultural water management, and prevent surface stormflow and flooding hazards. Small scale field heterogeneities cannot be always captured by the limited number of point scale measurements collected. In order to overcome these limitations, noninvasive geophysical techniques have been widely used in the last decade to predict hydrodynamic processes, due to their capability to spatialize hydrogeophysical properties with high resolution. In the test site located in Bari, Southern Italy, the geophysical approach, based on electrical resistivity tomography (ERT) monitoring, has been implemented to detect preferential pathways triggered by an artificial rainfall event. ERT-derived soil moisture estimations were obtained in order to quantitatively predict the water storage (m3m−3), water velocity (ms−1), and spread (m2) through preferential pathways by using spatial moments analysis.

Highlights

IntroductionPreferential flow occurs in the vadose zone due to different hydraulic processes, often associated with obvious flowpaths such as biopores and fractures [1], and in supposedly homogeneous media [2]
The comprehension of water flow dynamics requires a basic support of innovative, feasible, and low-cost approaches. This is even more important when the flow processes lead to preferential patterns due to the great heterogeneity of the vadose flow and nonlinearities of their properties and processes
The variable hydrological properties at the soil–rock interface, the moisture conditions changing over time, and the character of the weather events contribute to the complexity of such phenomena

Summary

Introduction

Preferential flow occurs in the vadose zone due to different hydraulic processes, often associated with obvious flowpaths such as biopores and fractures [1], and in supposedly homogeneous media [2]. It usually moves water faster and with greater fluxes than other flow modes, driven by gravity with little influence of capillarity for a limited time in response to water input. The capability to identify preferential pathways in the subsurface is fundamental to determining the location and the mass of contaminants, to predict their migration and promptly prevent the spread in the hydrogeologic system This is even more important considering that the critical zone plays a crucial role in several environmental questions. The estimation of travel times of the infiltrated rainfall in the vadose zone can provide significant improvements in water storage management of aquifer recharge

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