Ecohydrological particle model based on representative domains

Abstract

Abstract. Non-uniform infiltration and subsurface flow in structured soils is observed in most natural settings. It arises from imperfect lateral mixing of fast advective flow in structures and diffusive flow in the soil matrix and remains one of the most challenging topics with respect to match observation and modelling of water and solutes at the plot scale. This study extends the fundamental introduction of a space domain random walk of water particles as an alternative approach to the Richards equation for diffusive flow (Zehe and Jackisch, 2016) to a stochastic–physical model framework simulating soil water flow in a representative, structured soil domain. The central objective of the proposed model is the simulation of non-uniform flow fingerprints in different ecohydrological settings and antecedent states by making maximum use of field observables for parameterisation. Avoiding non-observable parameters for macropore–matrix exchange, an energy-balance approach to govern film flow in representative flow paths is employed. We present the echoRD model (ecohydrological particle model based on representative domains) and a series of application test cases. The model proves to be a powerful alternative to existing dual-domain models, driven by experimental data and with self-controlled, dynamic macropore–matrix exchange from the topologically semi-explicitly defined structures.

How Meaningful are Plot‐Scale Observations and Simulations of Preferential Flow for Catchment Models?

“…Obviously, the choice of a modeling approach for simulating preferential flow processes depends on the underlying question. If one is interested in the spatial patterns of preferential flow or in detailed analyses of exchange processes between macropores and soil matrix, an explicit implementation of macropore or fracture geometries and distributions (e.g., Vogel et al, 2006; Rosenbom et al, 2009; Klaus and Zehe, 2011; Jackisch and Zehe, 2018) and a conceptually different description of the pore‐scale processes (e.g., Beven and Germann, 2013; Scheibe et al, 2015; Jackisch and Zehe, 2018) is necessary. In our case, we aimed to test a direct parameter transfer from plot to catchment scale.…”

“…Beven and Germann, 2013; Jarvis et al, 2016). While numerous plot‐scale studies have focused on advancing accurate descriptions of flow and exchange processes within explicitly implemented macropores and fractures (e.g., Vogel et al, 2006; Scheibe et al, 2015; Jackisch and Zehe, 2018), explicit implementations of discrete macropore and fracture geometries for an entire catchment are (currently) not feasible from a computational and parameterization point of view (Jarvis et al, 2016). Instead, the most common representations of preferential flow processes in existing catchment simulations are dual‐domain approaches, which separate the subsurface into two interacting matrix and preferential flow domains with differing hydraulic properties (e.g., Kordilla et al, 2012; van Schaik et al, 2014; Wang et al, 2014; Yu et al, 2014; De Schepper et al, 2015; Jarvis et al, 2016; Steinbrich et al, 2016; Villamizar and Brown, 2017).…”

Surface water and groundwater: unifying conceptualization and quantification of the two “water worlds”

“…3.1). Such information can generally be inferred from breakthrough curves of tracers that enter and leave the system through well-defined boundaries, as shown for instance by the early work of Simmons (1982) and Jury and Sposito (1986), using transfer functions to model solute transport through soil columns. The transfer function approach is based on the theory of linear systems.…”

“…3). The latter implies that travel time distributions through partially saturated soils are transient and hence constrained by the input time (Jury and Sposito, 1986;Sposito et al, 1986). The wellknown fact that the flow velocity field changes continuously with changing soil water content explains why transfer function approaches have been largely put aside in soil physics and solute transport modelling in the partially saturated zone.…”

A Generalized Analytical Solution for Preferential Infiltration and Wetting

“…Current modeling tools to quantify relative infiltration due to preferential macropore flow are either complex, incorporating numerous parameters and processes (Beven and Germann, 1981; Weiler, 2005; Jackisch and Zehe, 2018) or use simple threshold values to partition rainfall between matrix and preferential flow (McGrath et al, 2009). Complex models can be difficult to parameterize and suffer from problems such as equifinality (Beven, 1993; Clothier et al, 2007).…”