Parameterization of theeffective properties as input in hydrogeological models for simulating water flow is a time consuming and costly process, and it is characterized by high uncertainty because of the spatial variability of soil properties. Integrating visible−near-infrared spectroscopy (vis−NIRS) models and a developed pedotransfer function, a hydrogeological tool was suggested by Varvaris et al. in 2019 for estimating the hydraulic properties used in an equilibrium approach. In the current study, the proposed concept was further expanded for assisting on a rapid and inexpensive parameterization of effective parameters in nonequilibrium models. In our approach, the soil-water retention curves for the wet and hyper-dry ends were predicted using existing vis−NIRS calibration models for obtaining the parameters for the Campbell retention model and the Campbell and Shiozawa model, respectively.The HYDRUS-2D software package was used to simulate tile drainage discharge in a loamy structured field using as initial input hydraulic parameters the output from the suggested concept. The estimated parameters were validated based on measured hydraulic properties in the laboratory. Two-dimensional models incorporating nonequilibrium flow were used to evaluate the ability of each approach to predict the tile drainage discharge: a single-porosity with modified van Genuchten function, a dual-porosity model, and a dual-permeability model. All approaches gave a fairly good fit to the hydrograph features for both calibration and validation datasets with dual-porosity to present the highest predictive ability. Finally, the suggested initial parameterization concept proved its potential to be used as an alternative for covering the absence of measured data of soil hydraulic properties.

In this study, a tracer field experiment was conducted to study the temporal dynamics of bromide movement in a loamy tile-drained agricultural landscape. Moreover, tritium leaching experiments were performed on undisturbed soil columns from the same field. The HYDRUS-2D software package was used to model water and solute transport. Three water flow models developed in Part 1-a single-porosity approach with modified soil hydraulic functions (SP), a dual-porosity approach (DP), and a dual-permeability approach (DUP)-were used as a foundation for building solute transport models, of which the initial parameterization was based on a suggested hydrogeological tool from previous studies. The selected solute transport models were an SP, an SP with immobile water, a DP, a DUP, and a DUP with immobile water. The model predictions were compared against measurements of bromide concentrations in soil-water. The DP captured the degree of the initial peaks and predicted well the shape of the observed concentrations. However, DP presented low capability to match the timing of bromide concentration peaks. In contrast, the DUP with immobile water illustrated better predictive ability by introducing an additional pore region into the matrix domain. Validation of field-scale solute transport models was implemented using the data from the following leaching experiments. The already suggested parameterization concept was further evaluated for its capability to provide a sufficient initial representation of the internal pathways. The output from such hydrogeological studies shows that macropores and their interconnection with tile drains are key to understanding the water flow and solute transport processes in loamy structured soils.

Core Ideas Simulating water flow dynamics in a clayey subsurface drained agricultural field. Three two‐dimensional models incorporating preferential water flow were used. All models produced a reasonably good fit to the hydrograph features. Examine models' capabilities and weaknesses for simulating the drainage dynamics. Non‐equilibrium preferential flow has received increasing attention in modeling water flow dynamics across tile‐drained agricultural fields. The HYDRUS‐2D software package was used in this study to generate a hydrogeological model for simulating the water flow dynamics across hydro‐topographical gradients and drainage sequences at drainage subcatchment (western part of Norsminde catchment in Denmark). The selected study area is characterized by spatial variability in the geological, stratified heterogeneity. Three two‐dimensional models incorporating preferential water flow were used to examine the ability of each approach to predict the drainage dynamics and water balance in a clayey subsurface drained agricultural field: (i) a single‐porosity model, (ii) a dual‐porosity model, and (iii) a dual‐permeability model. The initial parameterization of the models relied on in situ observations of soil structure, soil hydraulic property maps of Denmark and pedotransfer functions. The models, once calibrated against observed drainage data, were used for the reproduction of the subsurface drainage water dynamics for different time periods for the specific agricultural landscape. The different conceptual approaches gave a fairly good fit to the hydrograph features for both the calibration and validation datasets. The predictive ability of all models for the calibration dataset was fairly similar, while for the first and second validation datasets better results were obtained with the dual‐porosity and dual‐permeability models, respectively. The calibrated values of the effective parameters had been examined using laboratory data and in situ measurements of the groundwater level to evaluate how well these parameters physically represent the flow domain.