Simulating water flow in variably saturated soils: A comparison of a 3D model with approximation-based formulations Hopp, Luisa Fatichi, Simone Ivanov, Valeriy Y. hillslope hydrology hydrologic modeling parsimonious approximation surface-subsurface hydrology In hydrological models, variably saturated flow is often described using the Richards equation, either in a fully three-dimensional (3D) implementation or using a quasi-3D framework based on the 1D Richards equation for vertical flow and a flow-approximation for the other two dimensions. However, it is unclear in which configuration or under which boundary conditions these approximations can produce adequate estimates. In this study, two formulations with a quasi-3D approach are benchmarked against a fully 3D model (HYDRUS-3D). The formulations are: the Real-time Integrated Basin Simulator + VEGetation Generator for Interactive Evolution (tRIBS + VEGGIE) model that uses the Dupuit–Forchheimer assumption and the Tethys &amp; Chloris (T&amp;C) model that implements the kinematic approach. Effects of domain slope, hillslope size, event size and initial moisture conditions on simulated runoff and soil moisture dynamics are examined in event-based simulations at the hillslope scale. The Dupuit–Forchheimer assumption (tRIBS-VEGGIE) produces deviations from the HYDRUS-3D solutions only for simulations with initially dry soil. Using the kinematic approach (T&amp;C) results in deviations from the 3D solution primarily for the small hillslope domain in combination with a gentle slope angle. This applies especially to the partition between subsurface and surface runoff production, with T&amp;C being biased towards the latter. For all other cases investigated, the simpler formulations provide reasonable approximations of the 3D model. IWA Publishing 2016 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/22523 Hopp L, Fatichi S, Ivanov VY. Simulating water flow in variably saturated soils: A comparison of a 3D model with approximation-based formulations. <i>Hydrology Research</i>. 2016;47(2):274-290. doi:<a href="https://doi.org/10.2166/nh.2015.126">10.2166/nh.2015.126</a> eng info:eu-repo/semantics/altIdentifier/doi/10.2166/nh.2015.126 info:eu-repo/semantics/altIdentifier/issn/1998-9563 info:eu-repo/semantics/altIdentifier/e-issn/2224-7955 info:eu-repo/semantics/openAccess