Selected Applications of Hydrus Models for the Numerical Analysis of the Hydrological/Thermal Behavior of Various Engineering Systems.

The HYDRUS models have recently been used to analyze the hydrological behavior of several Low Impact Development (LIDs) techniques. The 1D, 2D, and 3D versions of Hydrus have been used to evaluate the behavior of a permeable pavement, a stormwater filter, and a green roof (Brunetti et al., 2016ab, 2017), respectively. Because of the high computational cost and complexity of such numerical analysis, these systems were traditionally analyzed using only empirical or conceptual models. However, the problem of high computational cost can be overcome using new numerical approaches, such as surrogate-based modeling, which can dramatically lower computational requirements. These approaches include the Model Order Reduction (MOR) technique or the Lower-Fidelity Physically-Based Surrogate models, which reduce the computational complexity of a numerical problems by computing an approximation of the original model.

We will demonstrate the use of this technique to multiple applications, such as for the the numerical analysis of the hydrologic behavior of green roofs, furrow irrigation systems, and thermal response tests. In the first application (a green roof), the surrogate model decouples the subsurface water dynamic of a green roof in one-dimensional (1D) vertical flow through a green roof itself and one-dimensional saturated lateral flow along the impervious rooftop. In the second application (a furrow), the surrogate model decouples a furrow system into a surface flow model and subsurface water dynamics in two-dimensional vertical cross-sections perpendicular to a furrow. Finally, in the analysis of a thermal response test, HYDRUS-2D has been coupled with a one-dimensional advection equation to simulate the heat transfer between a carrier fluid in a pipe and the surrounding soil. All these applications demonstrate the versatility of HYDRUS, and how the contribution of modern numerical techniques could increase its potential in a variety of scientific and engineering problems.