Sources of Surface Water in Space and Time: Identification of Delivery Processes and Geographical Sources With Hydraulic Mixing‐Cell Modeling

Abstract

Knowledge of the sources of surface water in riparian zones and floodplains is critical to understanding its role in runoff generation and impact on biogeochemical and ecological processes. In this study, we demonstrate the potential of integrated surface‐subsurface hydrologic modeling (HydroGeoSphere) in combination with a hydraulic mixing‐cell approach to decipher different sources of surface water and their mixing in space and time. We present a novel approach to processing the model data that allowed us to compare which mechanisms ultimately transferred water to the surface (delivery processes) and from where the surface water originated (geographical sources) for varying wetness states and phases of wetting or drying across 36 test locations within the riparian‐stream continuum of an intensively‐studied, humid‐temperate, forested headwater catchment (45 ha). Consistent with current process understanding for the study site, water exfiltrating from the subsurface was simulated as the dominant source for riparian surface water and intermittent streamflow. The model further helped to specify the relevance of different subsurface stores, revealing a wetness‐dependent activation of upslope source areas. Contributions of riparian overland flow and precipitation were minor during all investigated phases of wetting and drying. Moreover, the spatial variability of surface water sources proved to be smaller than expected for the heterogeneous patterns and frequencies of the surface saturation observed and simulated. Based on these findings, we discuss the value of hydraulic mixing‐cell modeling to complement the planning and interpretation of field investigations and to enhance process understanding regarding the spatio‐temporal sources of surface water.

Impacts of Land Surface Nitrogen Input on Groundwater Quality in the North China Plain

“…In each iteration of the cycle, the incoming water displaces an equivalent amount of water in the unit, which then mixes with the remaining material. Subsequently, the new concentration is calculated for each cell. − The mixing model and equation for calculating the groundwater nitrate concentration are depicted in Figure b. The calculation takes into account groundwater recharge, well exploitation, and interflow between different layers of the aquifer.…”

Analysis of the interaction between surface water and groundwater using gaseous tracers in a dynamic test at a riverbank filtration intake

“…At the same time pumping water directly from the river water reached 60% ±10% after a steady flow net was established. Other interesting examples of surface‐subsurface water interaction studies conducted at different scales, aspects and environmental conditions are presented by, inter alia: Kumar et al, 2009; Xueru et al, 2018; Glaser et al (2021); McCallum et al, 2010; Tang et al, 2015; Schilling et al, 2017.…”

“…At the same time pumping water directly from the river water reached 60% ±10% after a steady flow net was established. Other interesting examples of surface-subsurface water interaction studies conducted at different scales, aspects and environmental conditions are presented by, inter alia: Kumar et al, 2009;Xueru et al, 2018;Glaser et al (2021);McCallum et al, 2010;Tang et al, 2015;Schilling et al, 2017. This study focuses on understanding the interaction between river and groundwater at the scale of influence of an infiltration intake located in the Czarny Dunajec valley. Aquifer systems in river valleys are typical sites for the intake of water as riverbank filtration can often be a cost-effective pre-treatment technology for river water.…”