HGS RESEARCH HIGHLIGHT - Analytical Approach to Estimate Salt Release from Tailings Sand Hummocks in Oil Sands Mine Closure


Integrated surface water and groundwater models are well suited for evaluating the long-term performance of oil sands mine closure landscapes to optimize reclamation designs that satisfy performance criteria. However, the scale of the problem makes it difficult to evaluate a large number of design alternatives using numerical models, while at the same time satisfying numerical criteria, such as the courant and peclet numbers. The problem becomes particularly challenging in the design of permeable sand tailings hummocks overlying relatively impermeable composite tailings, where vertical advective flushing of process-affected water through the tailings hummocks is coupled to lateral transport of diffusive release from the underlying composite tailings. We developed an analytical solution that rapidly estimates long-term mass loadings from the sand tailings without the challenges typically associated with numerical modelling. Advection and dispersion in the flushing zones, progressive diffusion into underlying low permeability layers, and purely diffusive release are all considered. A comparison of the analytical solutions to numerical simulations for a series of simple hypothetical cases demonstrated that the analytical solutions provide a reasonable simulation of the mass loadings from the reclaimed landscapes over the design life. Although the approach needs to be further verified and validated for more realistic complex mine reclamation conditions, the analytical framework provides a foundation for hydrologic analysis in mine reclamation and closure in the northern boreal environment.

Link to the published article.

HGS RESEARCH HIGHLIGHT - Full Coupling Between the Atmosphere, Surface, and Subsurface for Integrated Hydrologic Simulation


An ever increasing community of earth system modelers is incorporating new physical processes into numerical models. This trend is facilitated by advancements in computational resources, improvements in simulation skill, and the desire to build numerical simulators that represent the water cycle with greater fidelity. In this quest to develop a state-of-the-art water cycle model, we coupled HydroGeoSphere (HGS), a 3-D control-volume finite element surface and variably saturated subsurface flow model that includes evapotranspiration processes, to the Weather Research and Forecasting (WRF) Model, a 3-D finite difference nonhydrostatic mesoscale atmospheric model. The two-way coupled model, referred to as HGS-WRF, exchanges the actual evapotranspiration fluxes and soil saturations calculated by HGS to WRF; conversely, the potential evapotranspiration and precipitation fluxes from WRF are passed to HGS. The flexible HGS-WRF coupling method allows for unique meshes used by each model, while maintaining mass and energy conservation between the domains. Furthermore, the HGS-WRF coupling implements a subtime stepping algorithm to minimize computational expense. As a demonstration of HGS-WRF's capabilities, we applied it to the California Basin and found a strong connection between the depth to the groundwater table and the latent heat fluxes across the land surface.

Link to the published article.

HGS RESEARCH HIGHLIGHT - Advancing Physically-Based Flow Simulations of Alluvial Systems Through Atmospheric Noble Gases and the Novel 37Ar Tracer Method


To provide a sound understanding of the sources, pathways, and residence times of groundwater water in alluvial river-aquifer systems, a combined multi-tracer and modeling experiment was carried out in an important alluvial drinking water wellfield in Switzerland. 222Rn, 3H/3He, atmospheric noble gases, and for the first time, the novel 37Ar -method were used to quantify residence times and mixing ratios of water from different sources. With a half-life of 35.1 days, 37Ar allowed to successfully close a critical observational time gap between 222Rn and 3H/3He for residence times of weeks to months. Covering the entire range of residence times of groundwater in alluvial systems revealed that, to quantify the fractions of water from different sources in such systems, atmospheric noble gases and helium isotopes are tracers suited for end-member mixing analysis. An updated illustration of available tracer methods, now including the new 37Ar method, is provided below:


The tracer-based mixing ratios were subsequently compared to mixing ratios simulated with the fully-integrated, physically-based flow model HydroGeoSphere. In order to simulate the propagation of the different sources of water in HydroGeoSphere, the Hydraulic Mixing Cell method (HMC) of Partington et al. (2013) was extended for this study to incorporate not only streamflow separation, but also tracking in the subsurface. Simulations of three different scenarios (poorly permeable, permeable and strongly permeable riverbed) are illustrated below. Both the exchange flux pattern on the surface and the fraction of surface water in the subsurface are illustrated.


The comparison between tracer-based and simulated mixing ratios revealed that models, which are only calibrated against hydraulic heads, cannot reliably reproduce mixing ratios or residence times of alluvial river-aquifer systems. However, the tracer-based mixing ratios allowed the identification of an appropriate flow model parametrization. Consequently, for alluvial systems, we recommend the combination of multi-tracer studies that cover all relevant residence times with fully-coupled, physically-based flow modelling using HGS and HMC-based flow tracking to better characterize the complex interactions of river-aquifer systems.

Link to the published article.

HGS RESEARCH HIGHLIGHT - Estimating the Spatial Extent of Unsaturated Zones in Heterogeneous River-Aquifer Systems


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. The three fundamentally different states of connection resulting from the different degrees of saturation underneath the riverbed are conceptually illustrated below, including examples of the probability distributions of hydraulic conductivity of the riverbed and the aquifer that may lead to these states of connection (the saturated parts of the aquifer underneath the riverbed are illustrated in blue):


The investigations were based on a large number of numerical flow experiments using HydroGeoSphere. One of the goals of the study was to develop a simple method to predict the spatial extent of the unsaturated zone underneath a riverbed for heterogeneous river-aquifer systems, without the need to undertake complex numerical simulations. For this purpose, simulations of the following degrees of complexity were carried out:


Based on the results of the numerical simulations with HydroGeoSphere, 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. An example of these simualtions is provided below:


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.

Link to the published article.

HGS RESEARCH HIGHLIGHT - Efficient Uncertainty Quantification in Fully-Integrated Surface and Subsurface Hydrologic Simulations

AUTHORS: K.L. Miller, S.J. Berg, J.H. Davison, E.A. Sudicky, and P.A. Forsyth

Although high performance computers and advanced numerical methods have made the application of fully-integrated surface and subsurface flow and transport models such as HydroGeoSphere common place, run times for large complex basin models can still be on the order of days to weeks, thus, limiting the usefulness of traditional workhorse algorithms for uncertainty quantification (UQ) such as Latin Hypercube simulation (LHS) or Monte Carlo simulation (MCS), which generally require thousands of simulations to achieve an acceptable level of accuracy. In this paper we investigate non-intrusive polynomial chaos for uncertainty quantification, which in contrast to random sampling methods (e.g., LHS and MCS), represents a model response of interest as a weighted sum of polynomials over the random inputs. Once a chaos expansion has been constructed, approximating the mean, covariance, probability density function, cumulative distribution function, and other common statistics as well as local and global sensitivity measures is straightforward and computationally inexpensive, thus making PCE an attractive UQ method for hydrologic models with long run times. Our polynomial chaos implementation was validated through comparison with analytical solutions as well as solutions obtained via LHS for simple numerical problems. It was then used to quantify parametric uncertainty in a series of numerical problems with increasing complexity, including a two-dimensional fully-saturated, steady flow and transient transport problem with six uncertain parameters and one quantity of interest; a one-dimensional variably-saturated column test involving transient flow and transport, four uncertain parameters, and two quantities of interest at 101 spatial locations and five different times each (1010 total); and a three-dimensional fully-integrated surface and subsurface flow and transport problem for a small test catchment involving seven uncertain parameters and three quantities of interest at 241 different times each. Numerical experiments show that polynomial chaos is an effective and robust method for quantifying uncertainty in fully-integrated hydrologic simulations, which provides a rich set of features and is computationally efficient. Our approach has the potential for significant speedup over existing sampling based methods when the number of uncertain model parameters is modest ( ≤ 20). To our knowledge, this is the first implementation of the algorithm in a comprehensive, fully-integrated, physically-based three-dimensional hydrosystem model.

Link to the published article.

Read full manuscript here.



HGS RESEARCH HIGHLIGHT - Wetlands and Flood Mitigation in Ontario: Natural adaptation to extreme rainfall

AUTHOR: MASON MARCHILDON, P. Eng. Oak Ridges Moraine Groundwater Program

Wetlands are often recognized for their flood control value, but little research exists specific to Ontario, where extreme weather causing flooding poses ever-greater threats to urban areas. Ducks Unlimited Canada has undertaken new research to better understand the role of wetlands in storing and attenuating flood flows in an urban/rural watershed. The second phase of this research, reported here, employs advanced hydrologic modelling to address the questions of where and how wetlands are most effective at retaining water, what consequences further wetland loss may have on flooding, and what potential wetland restoration could have to improve flood storage within a watershed. The modelling was accomplished using fully-integrated, three-dimensional variably saturated hydrologic model built for the entire Credit River watershed at a high spatiotemporal resolution.

For more information click here.

HGS RESEARCH HIGHLIGHT - Limits of heat as a tracer to quantify transient lateral river-aquifer exchanges


The application of heat as a tracer for assessing river-aquifer exchanges has been mainly limited to vertical flow through the riverbed. Lateral river-aquifer exchanges may be more important than vertical riverbed exchanges if the river is deeply incised into an aquifer. Few studies have examined lateral river-aquifer exchanges and the ability of heat to constrain such exchanges. This study aims to perform a robust assessment of the limits of heat as a tracer to quantify lateral river-aquifer exchanges. It is largely based on a section of the Meuse River in Belgium (Figure 1), a river predominantly gaining in the studied area that only becomes intermittently losing in the winter time.

Figure 1. Location of the study site adjacent to the Meuse River, monitored wells U5 and U3 (114 and 207 m distance from the river, respectively) and groundwater head contours as measured in April 2006.

Figure 1. Location of the study site adjacent to the Meuse River, monitored wells U5 and U3 (114 and 207 m distance from the river, respectively) and groundwater head contours as measured in April 2006.

A site-based transect model established with HydroGeoSphere was first calibrated using both hydraulic head and temperature time series from two monitoring wells over 100 m away from the river (U5 and U3). However, the temperature time series were not helpful in calibrating the model because of the large distance from the river and the gaining nature of the river.

The best-calibrated model was then utilised as the base case for assessing the usefulness of temperature at closer distances from the river. We extracted both head and temperature time series at a number of locations much closer to the river (i.e. 4, 5, 6, 7, 8, 9, and 10 m from the river) from the best-calibrated model. Then we analysed how the use of different synthetic heat and temperature time series as calibration targets impacts on the uncertainty of integrated river-aquifer exchange volume using the Monte Carlo approach (the river-aquifer exchange volume uncertainty is attributed to parameter uncertainties). Our results suggest that the ability of heat to reduce the uncertainty of lateral river-aquifer exchanges is directly proportional to the distance of the monitoring location from the river. In our case, the uncertainty range of the net exchange volume was reduced by approximately a factor of 3 from 4 m to 9 m (Figure 2a). This ability of course is limited to a certain range. For instance, heat cannot be used at 0 – 4 m in our case because of the occupation of the river bank, and was not useful beyond 8 m as the effect of river temperature becomes insignificant. The optimal distance is where groundwater temperature variation is no longer affected by river temperature (8 m in this study), or temperature variation is below the resolution limit of the temperature sensor. Our study also indicates that heat alone cannot constrain lateral river-aquifer exchanges better than the commonly used hydraulic head (compare Figures 2a and 2c). However, once combined with hydraulic head, heat can reduce the uncertainty of lateral river-aquifer exchanges significantly (compare Figures 2a and 2e). A factor of 3 – 6 reduction in the net exchange volume was observed in our synthetic case.

Figure 2. Net river-aquifer exchange volume statistics for using hydraulic head and temperature time series in different manners. The left panel shows results when time series were used at individual locations (i.e., 4, 5, 6, 7, 8, 9, 10 m from the river), whereas the right panel includes results when time series were used at specific ranges of locations (e.g., 4-5 m indicates locations at both 4 and 5 m, and 4-6 m indicates locations at 4, 5 and 6 m). In each boxplot, the upper and lower bounds show maximum and minimum values, the top and bottom of the box indicate 75 and 25 percentiles, and the red bar within the box is the median value. The dotted lines show the net exchange volume for the base case model.

Figure 2. Net river-aquifer exchange volume statistics for using hydraulic head and temperature time series in different manners. The left panel shows results when time series were used at individual locations (i.e., 4, 5, 6, 7, 8, 9, 10 m from the river), whereas the right panel includes results when time series were used at specific ranges of locations (e.g., 4-5 m indicates locations at both 4 and 5 m, and 4-6 m indicates locations at 4, 5 and 6 m). In each boxplot, the upper and lower bounds show maximum and minimum values, the top and bottom of the box indicate 75 and 25 percentiles, and the red bar within the box is the median value. The dotted lines show the net exchange volume for the base case model.

Job Notice - Intermediate/Senior Numerical Modeller (Hydrology/Hydrogeology)

Aquanty is looking for an intermediate/senior Numerical Modeller to join our growing team in Waterloo, ON. The ideal candidate has a background in hydrogeology and numerical modelling at the regional scale.

Location: Waterloo, ON, Canada

Education: Masters/PhD degree hydrogeology or related field

Experience: Minimum 5 - 10 years

Position Description:

The successful applicant will be involved in all aspects of project delivery including; project management, reporting, data processing, GIS, hydrostratigraphic interpretation, 3D model construction, numerical model setup and simulation.

Desired Skill Set:

·         Demonstrated project management and report writing experience

·         Experience building numerical models for hydrogeology/hydrology applications

·         Experience interpreting regional scale hydrostratigraphy

·         Experience with HydroGeoSphere/FEFLOW/MODFLOW is an asset

·         Experience mentoring junior staff


Please send your resume to hr@aquanty.com

About Aquanty

Aquanty Inc., is a research spin-off company from the University of Waterloo specializing in computer simulations of how water moves through the natural environment. Our best-in-class simulation platform, HydroGeoSphere, is used in a number of industries including; agriculture, oil and gas, mining, watershed management, contaminant remediation, and nuclear storage and disposal to support water related decision making. Check out our Case Studies to see examples.

Statement of Commitment

Aquanty’s is an equal opportunity employer that does not unlawfully discriminate against any employee or applicant on the basis of race, ancestry, place of origin, colour, ethnic origin, citizenship, religion, gender identity, gender expression, creed, sex, sexual orientation, age, record of offences, marital status, family status or disability. Aquanty is committed to a fair and inclusive work environment. We will endeavor to accommodate the needs of qualified applicants in all parts of the hiring process.

Australasian Groundwater Conference 2017

Aquanty is proud to support the Australasian Groundwater Conference this year. Swing by our booth to talk to us. We will also have two talks durring the Wednesday session on Groundwater Modelling.

River basin-scale integrated surface-subsurface hydrologic modelling to support agricultural risk management.

Simulating complex surface water/groundwater interactions during flood events with a fully-integrated physics based hydrologic model.