Preferential Flow in a Reclamation Cover: Hydrological and Geochemical Response

Abstract

Evapotranspirative covers used for waste containment or land reclamation strategies are intended to function in perpetuity. Pedogenesis of the cover materials caused by biophysical processes may lead to the development of macroporosity (i.e., preferential flow paths), which will alter the hydrological response from the intended design function. Hydrometric and geochemical data were used in this study to examine the contribution of preferential flow to the hydrological response of a reclamation cover on saline-sodic shale mine overburden, in a cold semiarid environment. The hydrometric data suggest that infiltration occurs along preferential flow paths when the ground is frozen or when wet antecedent soil moisture conditions develop prior to precipitation events. Interflow is initiated during the spring snowmelt when the cover thaws and water migrates from the preferential flow paths into the soil matrix, causing a perched water table to form on the cover-shale interface. The cessation of interflow coincides with a recession of the perched water table and an increase in matric suction within the cover in response to elevated evapotranspiration demands. The chemistry and stable isotope signature of the interflow demonstrates that these waters are initially composed of fresher snowmelt water, flowing along preferential flow paths, which then transition to pre-event water dominated by higher concentration water from within the soil matrix. A numerical simulation demonstrates that macroporosity imposes a significant control on the discharge rate and cumulative volume of interflow.