Improved representation of groundwater at a regional scale – coupling of mesocale Hydrologic Model (mHM) with OpeneGeoSys (OGS)

Abstract

Abstract. Most of the current large scale hydrological models do not contain a physically-based groundwater flow component. The main difficulties in large-scale groundwater modeling include the efficient representation of unsaturated zone flow, the characterization of dynamic groundwater-surface water interaction and the numerical stability while preserving complex physical processes and high resolution. To address these problems, we propose a highly-scalable coupled hydrologic and groundwater model (mHM#OGS) based on the integration of two open-source modeling codes: the mesoscale hydrologic 5 Model (mHM) and the finite element simulator OpenGeoSys (OGS). mHM#OGS is coupled using a boundary condition-based coupling scheme that dynamically links the surface and subsurface parts. Nested time stepping allows smaller time steps for typically faster surface runoff routing in mHM and larger time steps for slower subsurface flow in OGS. mHM#OGS features the coupling interface which can transfer the groundwater recharge and river baseflow rate between mHM and OpenGeoSys.Verification of the coupled model was conducted using the time-series of observed streamflow and groundwater levels. More-10 over, we force the transient model using groundwater recharge in two scenarios: (1) spatially variable recharge based on the mHM simulations, and (2) spatially homogeneous groundwater recharge. The modeling result in first scenario has a slightly higher correlation with groundwater head time-series, which further validates the plausibility of spatial groundwater recharge distribution calculated by mHM in the mesocale. The statistical analysis of model predictions shows a promising prediction ability of the model. The offline coupling method implemented here can reproduce reasonable groundwater head time series 15 while keep a desired level of detail in the subsurface model structure with little surplus in computational cost. Our exemplary calculations show that the coupled model mHM#OGS can be a valuable tool to assess the effects of variability in land surface heterogeneity, meteorological, topographical forces and geological zonation on the groundwater flow dynamics. 1Geosci. Model Dev. Discuss., https://doi

Microbial mediated carbon and nitrogen cycling in the spatially heterogeneous vadose zone: A modeling study

“…Previous field and modeling studies at the subject site exploring biogeochemical zones, geology, and long-term recharge informed the parameterization of the model (Jing et al, 2018;Kohlhepp et al, 2017;Kuesel et al, 2016). At the inlet of the domain, we introduced water that was representative of infiltration from the shallow subsurface The total oxidation capacity of the infiltrated terminal electron acceptor would be sufficient for an oxidation of the entire amount of infiltrated organic carbon even without any aeration of the water phase within the domain.…”

Predicting the impact of spatial heterogeneity on microbial redox dynamics and nutrient cycling in the subsurface

“…We performed simulations for three different flow regimes, each characterized by a specific average flow velocity: for the slow flow regime, the average flow velocity of 3.8 10 -4 m d -1 is given by the estimated 185 recharge rate at the subject site (Kohlhepp et al, 2017;Jing et al, 2017) and represents the slow migration of water through the uppermost part of the saturated aquifer. We increased the average flow velocity by a factor of 10 for the medium flow regime, and by a factor of 100 for the fast flow regime(Table 1).…”

“…Further scenarios considered spatial heterogeneity of the flow field using randomly generated hydraulic conductivity fields (Heße et al, 2014). Each random field was characterized by the same mean value of conductivity (i.e., average conditions at the subject site (Jing et al, 2017)) and correlation length in all realizations. To 195 conceptualize heterogeneity, we used two established geostatistical parameters, variance in the log normal distribution of conductivity and anisotropy, to represent varying porous and fractured media and to also control the degree of channelized flow in the domain.…”

“…CC BY 4.0 License. established tool that allows for the simulation reaction networks of arbitrary size and complexity (Thullner et al, 2005) with OGS (Open Geosys), a state of the art open source thermo-hydro-mechanical-chemical (THMC) simulator (Kolditz et al, 2012) that has also been used for modelling groundwater flow and transport (Jing et al, 2017). We used a constant finite volume discretization of 0.01 m in both directions.…”

Assessment of regional inter-basin groundwater flow using both simple and highly parameterized optimization schemes

“…However, the application of such models, in particular at regional scale, is limited by the understanding of the physical system, data availability, and computational capacity (Barthel and Banzhaf 2016). Another important challenge with regard to integrated-water-resource-management, in particular at the regional scale, is that most of the currently existing hydrological models do not contain dynamic physically based coupling between surface water and groundwater or unsaturated zone and evapotranspiration processes (Jing et al 2017). Even if the groundwater component is included in the models, they are often calibrated using only surfacewater observations (Barthel 2014) or applied under a steadystate assumption (Sonnenborg et al 2003;Meyer et al 2018), mainly due to the high computational burden of transient description.…”