Estimating the Spatial Extent of Unsaturated Zones in Heterogeneous River‐Aquifer Systems

Abstract

The presence of unsaturated zones at the river‐aquifer interface has large implications on numerous hydraulic and chemical processes. However, the hydrological and geological controls that influence the development of unsaturated zones have so far only been analyzed with simplified conceptualizations of flow processes, or homogeneous conceptualizations of the hydraulic conductivity in either the aquifer or the riverbed. We systematically investigated the influence of heterogeneous structures in both the riverbed and the aquifer on the development of unsaturated zones. A stochastic 1‐D criterion that takes both riverbed and aquifer heterogeneity into account was developed using a Monte Carlo sampling technique. The approach allows the reliable estimation of the upper bound of the spatial extent of unsaturated areas underneath a riverbed. Through systematic numerical modeling experiments, we furthermore show that horizontal capillary forces can reduce the spatial extent of unsaturated zones under clogged areas. This analysis shows how the spatial structure of clogging layers and aquifers influence the propensity for unsaturated zones to develop: In riverbeds where clogged areas are made up of many small, spatially disconnected patches with a diameter in the order of 1 m, unsaturated areas are less likely to develop compared to riverbeds where large clogged areas exist adjacent to unclogged areas. A combination of the stochastic 1‐D criterion with an analysis of the spatial structure of the clogging layers and the potential for resaturation can help develop an appropriate conceptual model and inform the choice of a suitable numerical simulator for river‐aquifer systems.

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

“…The Upper Emme catchment in the Northern prealps of Switzerland is home to one of the largest drinking water stations of the Swiss capital Bern (Blau & Muchenberger, ; Käser & Hunkeler, ; Schilling, Irvine, et al, ). The Emme River, which is the primary source of recharge for the alluvial aquifer of the Upper Emme catchment, has an average annual discharge of 4.4 m 3 /s and is characterized by highly dynamic discharge behavior (Käser & Hunkeler, ).…”

Natural Stimuli Calibration with Fining Direction Regularization in an Integrated Hydrologic Model

“…HGS has been successfully applied to a many real‐world studies ranging from basin scale applications (Hwang et al , ); to hillslope studies (Park et al ); to river cross‐section surface water‐groundwater interaction studies (Doble et al ; Liggett et al ; Batlle‐Aguilar et al ; Schilling et al ).…”

“…In recent years, the fully‐integrated surface and subsurface flow and transport model, HydroGeoSphere (HGS) (Aquanty ), has been applied in several studies to investigate surface water‐groundwater interaction along river channels. For example, Batlle‐Aguilar et al () used HGS to simulate the infiltration of surface water from a disconnected stream to groundwater for a river transect in South Australia; Alaghmand et al () used HGS to investigate the potential use of artificial flooding as a short‐term saline groundwater management technique along floodplains in arid and semi‐arid environments; Xie et al () simulated the interaction of saline groundwater with surface water during stream events within an idealized river reach; and Schilling et al () used HGS to investigate the impact of river bed clogging on surface water‐groundwater interaction and the redistribution of water beneath disconnected streams.…”

Integrated Surface and Subsurface Hydrological Modeling with Snowmelt and Pore Water Freeze–Thaw

“…HGS has been successfully applied in many different contexts and at many different spatial and temporal scales. Investigations on the interactions between groundwater, surface water, and vegetation (e.g., Ala‐Aho et al [], Schilling et al [], Schomburg et al []), on the development of unsaturated zones between rivers and aquifers in heterogeneous systems (e.g., Irvine et al [], Schilling et al [], Tang et al []), or on contaminant transport and tile drainage in agricultural contexts (e.g., Bonton et al [], De Schepper et al []) are just some recent examples for which HGS was used. HGS has recently been coupled to the Weather Research and Forecast (WRF) model for the integrated simulation of atmosphere, surface, and subsurface interactions (Davison et al ), to particle tracking and flow tracking tools (Partington et al ; Partington et al ; Chow et al ; Schilling et al ), and to the ensemble Kalman filter (EnKF) data assimilation tool (Kurtz et al ; Tang et al ; Tang et al ).…”