New insights into the differences between the dual node approach and the common node approach for coupling surface–subsurface flow

Water Resources Research

Kurtz

et al. 2018

Flood events can change the riverbed topography as well as the riverbed texture and structure, which in turn can influence the riverbed hydraulic conductivity (Krb) and river‐aquifer exchange fluxes. A major flood event occurred in the Emme River in Switzerland in 2014, with major implications for the riverbed structure. The event was simulated with the fully integrated hydrological model HydroGeoSphere. The aim was to investigate the effect of the spatial and temporal variability of riverbed topography and Krb on predictions of hydraulic states and fluxes and to test whether data assimilation (DA) based on the ensemble Kalman filter (EnKF) can better reproduce flood‐induced changes to hydraulic states and parameters with the help of riverbed topography changes recorded with an unmanned aerial vehicle (UAV) and through‐water photogrammetry. The performance of DA was assessed by evaluating the reproduction of the hydraulic states for the year 2015. While the prediction of surface water discharge was not affected much by the changes in riverbed topography and in Krb, using the UAV‐derived postflood instead of the preflood riverbed topography reduced the root‐mean‐square error of predicted heads (RMSE [h]) by 24%. If, in addition to using the postflood riverbed topography, also Krb and aquifer hydraulic conductivity (Kaq) were updated through DA after the flood, the RMSE (h) was reduced by 55%. We demonstrate how updating of Krb and Kaq based on EnKF and UAV‐based observations of riverbed topography transience after a major flood event strongly improve predictions of postflood hydraulic states.

“…GW flow is implemented by the three‐dimensional Richards' equation:

\frac{\partial}{\partial t} ((), θ_{s} s_{w}) = - \nabla \cdot boldq + Γ \pm Q

Section: Methodsmentioning

confidence: 99%

“…The residual saturation ( S wr ) was fixed at 0.05. The coupling length ( l exch ) between the SW and the GW domain was set to a very small value of 0.001 m, representing an optimal compromise between head continuity and numerical stability (see de Rooij, ).…”

Section: The River‐aquifer Flow Modelmentioning

confidence: 99%

Simulating Flood‐Induced Riverbed Transience Using Unmanned Aerial Vehicles, Physically Based Hydrological Modeling, and the Ensemble Kalman Filter

Tang

Water Resources Research

Kurtz

et al. 2018

“…Numerical simulator : The ISSHM HGS simulates variably‐saturated GW flow with Richards' equation utilizing the van Genuchten parameterization, and SW flow with the 2‐D diffusion wave approximation to the Saint‐Venant equations (Brunner & Simmons, 2011; Therrien & Sudicky, 1996). SW and GW is fully‐coupled via the dual‐node approach (de Rooij, 2017; Ebel et al., 2009). Water from different origins is tracked throughout the model using a mixing‐cell implementation (Partington et al., 2011), enabling direct comparison between observed and simulated f stream .…”

Section: Methodsmentioning

confidence: 99%

Buried Paleo‐Channel Detection With a Groundwater Model, Tracer‐Based Observations, and Spatially Varying, Preferred Anisotropy Pilot Point Calibration

Geophysical Research Letters

Partington

Doherty

et al. 2022

Alluvial sand and gravel (ASG) aquifers are highly heterogeneous and exhibit strong, spatially variable anisotropy, often interspersed by buried paleo‐channels of increased hydraulic conductivity. Groundwater flow and solute transport is often characterized by preferential flow caused by anisotropic properties in ASG aquifers. Connected ASG subsurface structures such as buried paleo‐channels, however, are difficult to reproduce with commonly used techniques, and anisotropy is rarely considered in applied groundwater models. To ease the notoriously difficult problem of how to consider anisotropy, we propose a novel modeling framework based on calibration of an integrated surface‐subsurface hydrological model via spatially varying, preferred anisotropy pilot point inversion. The inversion leverages hydraulic and tracer‐based observations representing multiple spatial and temporal scales. We demonstrate the applicability of the framework on a real‐world ASG site used for drinking water production, and we quantify the information content of observations to identify connected paleo‐channels and provide guidance for optimal field‐data acquisition.

“…Flow coupling between the surface and the subsurface is achieved by the consistent dual node approach (de Rooij, 2017) and defined as:

d_{0} Γ_{0} = \frac{k_{r} K_{zz}}{l_{exch}} (H - H_{0}),

where K zz [LT −1 ] is the vertical saturated hydraulic conductivity, l exch [L] is the coupling length (optimal when it represents the depression storage (Liggett et al., 2012); 0.01 m in this study), H 0 [L] is the SW head and H [L] the GW head.…”

Section: Conceptual and Numerical Modelmentioning

confidence: 99%

Controls on Interactions Between Surface Water, Groundwater, and Riverine Vegetation Along Intermittent Rivers and Ephemeral Streams in Arid Regions

Water Resources Research

Cook

Grierson

et al. 2021

Intermittent rivers and ephemeral streams (IRES) make up the majority of waterways in arid and semi‐arid regions. While the physical underpinnings of surface water‐groundwater (SW‐GW) flow systems are well understood, how ephemerality, hydraulic properties and vegetation interact along IRES is not clear, posing severe challenges to their sustainable management. This study sought to identify the controls for SW‐GW‐vegetation interactions along IRES. To this end, numerical experiments on a quasi‐hypothetical IRES cross‐section with an integrated surface‐subsurface hydrological model were undertaken. The influence of different degrees of ephemerality on infiltration and riverine transpiration was tested by varying the duration of no‐flow periods. The influence of hydraulic conductivity (K), moisture retention capacity, root density, and local rainfall was also explored. Experiments showed that infiltration is controlled by ephemerality and K, with infiltration decreasing rapidly with increasing ephemerality and decreasing K. Transpiration is influenced by a complex interplay between ephemerality, hydraulic properties, and vegetation. While transpiration is strongly controlled by the degree of ephemerality, the capacity of the subsurface to maintain variably saturated conditions can strongly attenuate the effects of ephemerality. A large moisture retention capacity of the subsurface can partly compensate for the reduced infiltration under increasing ephemerality. Transpiration can be as large under ephemeral as under perennial conditions, especially where water table fluctuations exhibit large amplitudes within the zone of high root density. Overall, the results provide important insights into the complex dynamics of IRES and highlight how changes in flow dynamics can have significant impacts beyond instream processes.