Liliana Di Pietro

Scales and dimensions of momentum dissipation during preferential flow in soils

Momentum dissipation may dominate flow in soils over a considerable distance when input rate and antecedent soil moisture are high enough and when adequate soil structures are present. The concept is derived from momentum balance. It is applied to drainage flow from a column of undisturbed soil and a weighing lysimeter and to water content variations at five depths due to sprinkling. Momentum of input is much lower than momentum during flow in the soil; however, the former is considered important in triggering momentum dissipation within the profile. Drainage flow at a depth of 2.2 m shows flow completely dominated by momentum dissipation, whereas momentum of flow within the soil profile increases with depth, indicating acceleration over a vertical distance from 0.15 to 0.55 m. The Reynolds numbers show laminar flow in all cases.

Predicting preferential water flow in soils by traveling-dispersive waves

Abstract Rapid preferential drainage or by-pass flow of water and pollutants occurs in soil macropores such as burrows and channels formed by earthworm activity in soils. We show that preferential flow through these non-capillary pores can be described by a traveling-dispersive wave. This wave is the solution of a non-linear convective–dispersive equation (KDW model) that depends on three transport parameters: two are related to a convective celerity and the other one is a dispersive coefficient. We show that the flux–mobile water content relation is hysteretic and that it can be described by a non-linear function of the mobile water content and its first time derivative. By combining the latter relation with the continuity equation we derive the KDW model. This model can be viewed as a second-order correction of the purely convective kinematic wave model. The dispersive term incorporates the large-scale effects of dissipative forces without resolving the small-scale conservation equations in detail. We further present numerical solutions for the signaling problem and a direct method for estimating model parameters. The model is validated with data obtained from laboratory infiltration experiments on soil columns. The experiments were carried out in repacked soil columns inoculated with Allolobophora chlorotica earthworms. Varying rainfall intensities were applied at the top surface of the columns with a rainfall simulator. Both the mean of mobile water content within the columns and the drainage hydrograph at the bottom were recorded in time. The parameters of the model were estimated from the experimental flux–mobile water content relation. A very good agreement was found between model prediction and experimental data.

Mobilization and preferential transport of soil particles during infiltration: A core‐scale modeling approach

Understanding particle movement in soils is a major concern for both geotechnics and soil physics with regard to environmental protection and water resources management. This paper describes a model for mobilization and preferential transport of soil particles through structured soils. The approach combines a kinematic-dispersive wave model for preferential water flow with a convective-dispersive equation subject to a source/sink term for particle transport and mobilization. Particle detachment from macropore walls is considered during both the steady and transient water flow regimes. It is assumed to follow first-order kinetics with a varying detachment efficiency, which depends on the history of the detachment process. Estimates of model parameters are obtained by comparing simulations with experimental particle breakthrough curves obtained during infiltrations through undisturbed soil columns. Both water flux and particle concentrations are satisfactorily simulated by the model. Particle mobilization parameters favoring both attachment and detachment of particles are related to the incoming solution ionic strength by a Fermi-type function.

Software, Data and Modelling News: Estimating preferential water flow parameters using a binary genetic algorithm inverse method

KDW-GA is a framework for the simulation of preferential water flow through unsaturated soils. Preferential flow can be described by a Kinematic Dispersive Wave (KDW) equation which depends on three transport parameters. Transport parameters are estimated with the binary genetic algorithm (GA) inverse method by reducing the errors (cost function) between estimated and observed water flux values. Different GA components are discussed in order to find the best strategy that fits our problem. Recommendations concerning the mutation rate, the elite number, and the pairing technique are deduced with regard to the algorithm performance.

Enhanced diffusion in a bounded domain

Abstract There exist disordered media where contaminant dispersion is conveniently described by Levy statistics. The case of enhanced diffusion corresponds to small scale motions, in the form of Continuous Time Random Walks with transition probability densities presenting spatial diverging moments. Such CTRWs in infinite media were shown to correspond, on the macroscopic scale, to diffusion equations involving Riesz-Feller derivatives of non-integer order, which are non-local w.r.t. space. For this reason, introducing boundary conditions sometimes results in modifying the large-scale model. We are studying here the diffusive limit of CTRWs, generalizing symmetric Levy flights in a bounded medium, limited by two reflective barriers. The thus obtained space-fractional diffusion equations differ from the infinite domain case.