Groundwater-surface Water Exchange Research Articles

Groundwater–surface water exchange from temperature time series: A comparative study of heat tracer methods

The importance of the interaction between groundwater and surface water is increasingly being recognized for both understanding and managing water systems. Many efforts have been made to characterize and quantify groundwater–surface water exchange. In particular, temperature–based methods have quickly established themselves given their monetary and practical advantages. In the last 15 years, several methods for interpreting passive temperature time series measured in the streambed have been developed. Still, the benchmarking of these methods has only been carried out in specific and distinct hydrological conditions.This article aims to fill this research gap by benchmarking the performance of six commonly used methods for deriving seepage fluxes using a two-year-long temperature time series covering various meteorological and thermal conditions. This work compares three analytical methods that calculate seepage flux using the amplitude and/or phase of the temperature signals, and three numerical methods that use different schemes to inversely solve the one–dimensional heat transport equation in the streambed. The temperature measurements were made in the context of an international dispute between Chile and Bolivia over the status and use of the waters of the Silala River, Northern Chile. Flux estimations are tested against Darcy’s flux derived from measured hydraulic gradient and hydraulic conductivity.Flux estimations from the benchmarked methods ranged from −0.5 to 3.5 m/d (with positive fluxes directed downwards), whereas fluxes estimated using Darcy’s law ranged from 0.5 to 6 m/d. Results show that the amplitude method is the best–performing method. This method is best suited for estimating the direction of the fluxes, while the method using both the thermal amplitude and phase is best suited for monthly flux trends, and the combination of a Local Polynomial (LP) method and a Maximum Likelihood Estimator (MLE) method (LPMLEn) is appropriate for estimating flux in transient conditions.The use of heat as a tracer proved to be an effective tool for monitoring groundwater–surface water exchange in a river reach for two years, and yielded exchange flux estimates with lower point-scale variability than Darcy’s law.

Metal-oxide precipitation influences microbiome structure in hyporheic zones receiving acid rock drainage.

In streams receiving acid-rock and mine drainage, the abundant precipitation of iron minerals can alter how groundwater and surface water mix along streams (in what is known as the "hyporheic zone") and may shape the distribution of microbial communities. The findings presented here suggest that neutral pH streams with large, well-mixed hyporheic zones may harbor and transport diverse microorganisms attached to particles/colloids through hyporheic pore spaces. In acidic streams where metal oxides clog pore spaces and limit hyporheic exchange, iron-oxidizing bacteria may dominate and phylogenetic diversity becomes low. The abundance of iron-oxidizing bacteria in acid mine drainage streams has the potential to contribute to additional clogging of hyporheic pore spaces and the accumulation of toxic metals in the hyporheic zone. This research highlights the dynamic interplay between hydrology, geochemistry, and microbiology at the groundwater-surface water interface of acid mine drainage streams.

A framework for parameter estimation, sensitivity analysis, and uncertainty analysis for holistic hydrologic modeling using SWAT+

Abstract. Parameter sensitivity analysis plays a critical role in efficiently determining main parameters, enhancing the effectiveness of the estimation of parameters and uncertainty quantification in hydrologic modeling. In this paper, we demonstrate an uncertainty and sensitivity analysis technique for the holistic Soil and Water Assessment Tool (SWAT+) model coupled with new gwflow module, spatially distributed, physically based groundwater flow modeling. The main calculated groundwater inflows and outflows include boundary exchange, pumping, saturation excess flow, groundwater–surface water exchange, recharge, groundwater–lake exchange and tile drainage outflow. We present the method for four watersheds located in different areas of the United States for 16 years (2000–2015), emphasizing regions of extensive tile drainage (Winnebago River, Minnesota, Iowa), intensive surface–groundwater interactions (Nanticoke River, Delaware, Maryland), groundwater pumping for irrigation (Cache River, Missouri, Arkansas) and mountain snowmelt (Arkansas Headwaters, Colorado). The main parameters of the coupled SWAT+gwflow model are estimated utilizing the parameter estimation software PEST. The monthly streamflow of holistic SWAT+gwflow is evaluated based on the Nash–Sutcliffe efficiency index (NSE), percentage bias (PBIAS), determination coefficient (R2) and Kling–Gupta efficiency coefficient (KGE), whereas groundwater head is evaluated using mean absolute error (MAE). The Morris method is employed to identify the key parameters influencing hydrological fluxes. Furthermore, the iterative ensemble smoother (iES) is utilized as a technique for uncertainty quantification (UQ) and parameter estimation (PE) and to decrease the computational cost owing to the large number of parameters. Depending on the watershed, key identified selected parameters include aquifer specific yield, aquifer hydraulic conductivity, recharge delay, streambed thickness, streambed hydraulic conductivity, area of groundwater inflow to tile, depth of tiles below ground surface, hydraulic conductivity of the drain perimeter, river depth (for groundwater flow processes), runoff curve number (for surface runoff processes), plant uptake compensation factor, soil evaporation compensation factor (for potential and actual evapotranspiration processes), soil available water capacity and percolation coefficient (for soil water processes). The presence of gwflow parameters permits the recognition of all key parameters in the surface and/or subsurface flow processes, with results substantially differing if the base SWAT+ models are utilized.

Wetlands as integral parts of surface water–groundwater interactions in the Athabasca Oil Sands Area: Review and synthesis

Wetlands comprise unique water storage and conveyance mechanisms that maintain landscape integrity under the sub-humid climate in the Athabasca Oil Sands Area. In addition to their internal function, wetlands support a two-way hydrological connection to adjacent uplands and provide water for downstream water courses. Understanding the role of wetlands as integral parts of surface water (SW)–groundwater (GW) exchange can provide insights into the functioning of the hydrological system as a whole and contribute to thoughtful water management strategies and better coordination of monitoring efforts in the areas affected by oil sands (OS) activities. As such, this study summarizes the current state of hydrological knowledge on the role of wetlands in SW–GW interactions based on studies conducted within the Western Boreal Plains. In particular, the role of wetland soils and their properties in SW–GW interactions, the effects of wetlands on landscape hydrological connectivity and watershed runoff, and features of “wetland–aquifer” and “wetland–open waterbody” interactions were reviewed. Given that alterations of SW–GW interactions in wetlands can occur as a result of anthropogenic disturbances, the coordination of GW, SW, and wetland monitoring efforts and targeting areas where increased SW–GW exchange occurs would be beneficial for the economic and logistical efficiency of the OS monitoring network.

Surface Measure to Depth (SMeTD): a new low-budget system for 3D water temperature measurements for combining with UAV-based thermal infrared imagery

Characterising spatial patterns in water temperature is important for monitoring aquatic habitats and understanding physical and biogeochemical processes to support environmental management decisions. As freshwater bodies exhibit high spatial and temporal variability, high-resolution 3D temperature data are essential to understand local anomalies. The acquisition of simultaneously high spatial and temporal datasets in the field has so far been limited by costs and/or workload associated with commonly used monitoring systems.We present a new, low-cost, spatially and temporally flexible 3D water temperature monitoring system, Surface Measures to Depth (SMeTD). SMeTD can be used to provide information on the relation of water surface temperature to changes with depth, characterise water temperature in 3D and ground truth remotely sensed thermal infrared data. The systems performance was tested under laboratory conditions and under controlled conditions in the field. This revealed an accuracy comparable to established but more expensive monitoring systems. Field testing of SMeTD involved 1-min data collection of 3D water temperature for a full diurnal cycle in a lake. The 3D temperature patterns were supported by a thermal infrared image of the lakes surface. The field dataset demonstrated higher water temperatures and higher water temperature variation at the surface compared to deeper layers. SMeTD can be used to observe a broad range of hydrological processes in natural and artificial aquatic environments and help to understand processes involved with energy budgets, infiltration, limnology, or groundwater surface water exchange.

Groundwater exfiltration pattern determination in the sub-arctic catchment using thermal imaging, stable water isotopes and fully-integrated groundwater-surface water modelling

Groundwater-surface water (GW-SW) interactions play an important function in northern catchments, but their dynamics and role in water, carbon, and nutrient balances are still poorly understood. In this case study, we (1) explored groundwater-surface water dynamics in a sub-arctic headwater watershed in Pallaslompolo, Finnish Lapland. (2) We compared fully-integrated physically-based simulations of the groundwater and surface water and their interactions with unique spatially distributed field datasets of drone-derived thermal infrared imaging (TIR) and surface peat pore stable water isotopes. Simulations and field observations point to similar GW-exfiltration areas, with an agreement between slightly over 50% for stable water isotopes and modeling and more than two thirds for thermal infrared and modeling. The agreement provides evidence that a fully-integrated GW-SW model with a simple parameterization approach can successfully identify the main features of GW-SW interactions in the high-latitude catchment. All methods suggest the complex nature of GW-SW exchange that is focused in topographical lowlands. Our simulation results also highlight how specific locations serve as groundwater exfiltration zones, surface water downwelling zones, or ‘mixed’ zones, where both interaction types occur at different times according to the hydrological state of the system. Modeling results suggest abrupt GW-SW interaction reversals – a phenomenon known to occur in peatland areas. To conclude, the three methods should be treated as complementary when describing and understanding GW-SW interactions within peatlands, but only the fully-integrated physically-based modeling can provide comprehensive estimates for both the spatial and temporal patterns and magnitudes of GW-SW interaction fluxes.

Regional evaluation of groundwater-surface water interactions using a coupled geohydrological model (SWAT+gwflow)

Study regionThe research is conducted for the Scheldt river basin, where seven major watersheds located in Belgium and partly in France are included in the analysis. Study focusA proper representation of groundwater–surface water interactions with (geo)hydrological models is possible via a coupled model. However, such models have disadvantages, such as complex code modifications and new tunings, and are computationally expensive. Therefore, their application on large spatial scales is limited. A newly developed model, SWAT+gwflow integrates the Soil Water Assessment Tool (SWAT+) with the groundwater module gwflow and has the potential to overcome these limitations. However, this coupled model has not yet been evaluated at a regional scale; hence, we present the evaluation of this model for regional studies using a global aquifer data over the seven watersheds in the Scheldt basin. Furthermore, we have investigated and quantified water balance components within the basin, with a focus on groundwater-surface water exchange. New Hydrological Insights for the RegionFrom the results (Nash-Sutcliffe efficiency (NSE) of 0.8–0.9 for all catchments based on monthly average streamflow during calibration and validation periods), we consider the model to be a good simulator of hydrology in the basin. In addition, the simulated groundwater head shows good agreement with observed well data (with a mean absolute error of less than 0.42 m). Also, the rivers in five of the seven watersheds are found to be strongly dependent on groundwater discharge to the streams. We conclude that (1) the SWAT+gwflow model is capable of accurately modeling hydrological processes and state variables in the seven watersheds using global aquifer data and limited computational time, (2) the climate-gridded dataset can successfully be used for (geo)hydrological studies, and (3) the groundwater-surface water interaction increases over the years (from 1975 to 2021) with a strong increment found in the Grote Nete (3.7 fold) and upper Scheldt (2.3 fold) watersheds. These results are, moreover, promising for data-scarce regions where geohydrological modeling relies on the use of global datasets, but the mere success of this modeling application does not guarantee the accuracy of the dataset for other locations, hence, further verification is required. Furthermore, although in this study, the gwflow module is integrated into the SWAT+ model, it could also be integrated into other surface water models for other studies.

Methane cycling in the carbonate critical zone

The carbonate critical zone (CZ) is characterized by extensive groundwater-surface water exchange that leads to highly variable redox states of groundwater. Changes in redox condition may cause either production or consumption of methane (CH4), thereby providing an atmospheric source or sink of this important greenhouse gas. To assess how groundwater-surface water exchange affects redox state and CH4 cycling in the carbonate CZ, we measured CH4 concentrations and 13C isotopes in water from streams, spring systems, and wells in north-central Florida. Sampled groundwater has subsurface residence times ranging from hours at a stream sink-rise system, to months following a flood recharge event into a spring vent, to decades at springs with limited point recharge. Concentrations of CH4 ranged from 0.002 to 89 μM, with an inverse relationship in springs between subsurface residence time and CH4 concentration. Where residence time is short, low CH4 concentrations result from methanotrophy linked to elevated dissolved oxygen (DO) concentrations. Following flooding, methanotrophy occurs soon after recharge and is followed by methanogenesis as groundwater becomes increasingly reducing. Groundwater extracted from wells had CH4 concentrations greater than spring water indicating CH4 is lost during flow to spring vents. CH4 concentrations covary with δ13C-CH4 values, which supports both methanogenesis and methanotrophy with changing residence times. Mean fluxes of CH4 ranged from −0.05 to 1.0 mg m−2 d−1 at spring vents, with negative values caused by CH4 uptake in water undersaturated with respect to atmospheric concentration. Most springs are dominated by methanotrophy, limiting atmospheric evasion of CH4 produced in the carbonate CZ. We estimate CH4 emissions to be 12.6 × 10−6 Tg a−1 across all Florida springs or about two orders of magnitude less than emissions from Floridan aquifer groundwater abstraction (3041 × 10−6 Tg a−1). Although CH4 is produced in the carbonate CZ, natural attenuation limits its effects on the global carbon cycle.

A probabilistic assessment of surface water-groundwater exchange flux at a PCE contaminated site using groundwater modelling

Polluted groundwater discharge at a chlorinated solvent contaminated site in Hagfors, Sweden, is affecting a nearby stream flowing through a sparsely populated area. Because of difficulties related to source zone remediation, decision makers recently changed the short-term site management objective to mitigating discharge of polluted groundwater to the stream. To help formulating targeted remediation strategies pertaining to the new objective, we developed a groundwater numerical decision-support model. To facilitate reproducibility, the modelling workflow was scripted. The model was designed to quantify and reduce the uncertainty of surface water-groundwater (SW-GW) exchange fluxes for the studied period (2016–2020) through the use of history-matching. In addition to classical observations, thermal anomalies detected in fiber optic distributed temperature sensing (FO-DTS) measurements were used to inform the model of groundwater discharge. After assessing SW-GW exchange fluxes, we used measurements of surface water chemistry to provide a probabilistic estimation of mass influx and spatio-temporal distributions of contaminated groundwater discharge. Results show 1) SW-GW exchange fluxes are likely to be significantly larger than previously estimated, and 2) prior estimations of mass influx are located near the center of the posterior probability distribution. Based on this, we recommend decision makers to focus remediation action on specific segments of the stream.

Groundwater–Surface Water Exchange and Spatial Distribution of Arsenic in Arid and Semi-Arid Regions: The Case of Aksu River in Xinjiang, Northwestern China

The Aksu River, a quintessential inland river, exhibits elevated arsenic (As) concentrations in certain sections of its natural waters. Further investigation is necessary to determine the role of surface water and groundwater (SW-GW) exchanges in contributing to these high As concentrations. Both surface water and groundwater constitute crucial components of the basin water cycle, and the interaction between the two has been a central focus in basin water cycle research. In this study, a total of 59 groundwater samples and 41 surface water samples were collected along the river’s course within the basin. Among the groundwater samples, 18.64% exceeded the permissible drinking limit for As concentrations (10 μg/L), while 39.02% of the surface water samples exceeded this threshold. The water bodies in the Aksu River Basin are mildly alkaline, with total dissolved solids (TDSs) in surface water significantly surpassing those in groundwater. The chemical compositions of surface water and groundwater are strikingly similar, with the predominant anions being chloride (Cl−) and sulfate (SO42−) and the principal cations being sodium (Na+). The dissolution of silicate and carbonate minerals primarily influences the water chemistry characteristics of surface water and groundwater in the Aksu River Basin, followed by the dissolution of salt rocks. Human activities also play a major role in affecting the river’s water quality. The distribution of groundwater with elevated As content is entirely encompassed within the spatial distribution of surface water. Groundwater–surface water exchange plays a vital role in As enrichment in surface water.

Contribution of Groundwater to River Discharge in the Mampang Sub-watershed

Water is a necessity of human life. In fulfilling this need, the use of groundwater is often used. Groundwater is a non-renewable resource. Jakarta is a city traversed by many rivers and has a morphological dependence on the upstream watershed (DAS) in the Jabodetabek Region. The research location is in the Mampang Sub-watershed, which is in the Jakarta and Depok areas. The Mampang sub-watershed is geographically located at 106°48'44" - 106°49'59" East Longitude and 6°15'4" - 6°22'17" South Latitude. The problem in the research of the Mampang Sub-watershed often experiences floods every year with a height of between 10 cm - 50 cm. The aim of the study was to determine the groundwater-surface water interaction during a flood event at the study site. The method used is by collecting primary data and secondary data, then simulating using SWAT (Soil and Water Assessment Tools) and SWAT-MODFLOW. The SWAT MODFLOW simulation results obtained 874 river grids with Groundwater Surface Water Exchange Rates (GWSER) values in February 2020 between 52 m3/day to 353 m3/day and in September 2019 between -74 m3/day to 26 m3/day. The contribution of groundwater can be analyzed by comparing the river discharge in a certain month with the GSWER value for that month. The contribution of groundwater to the monthly peak discharge of the river at the study site ranges from 0.24% to 5.27%, and the average contribution of groundwater is 2.48%.

Tidal exchange of dissolved metal(loid)s and organic matters across the sediment–water interface in a salt marsh-mangrove ecotone

Coastal wetlands are considered as efficient barriers for pollutants such as dissolved metal(loid)s between land and sea. However, there remains a challenge in understanding how tidal hydrology regulates the source-sink patterns of metal(loid)s across the sediment–water interface, especially in the salt marsh-mangrove ecotone that commonly exists in subtropical coastlines. In this study, we conducted detailed time-series observations of dissolved metal(loid)s (Cr, Cu, Zn, Ba, Pb, Hg, and As) and organic matter (DOM) characteristics (bulk concentrations, aromaticity, and molecular size) in southeast China over a spring-neap tidal cycle. The results demonstrated that both DOM and metal(loid)s fluctuated with tide levels, and higher concentrations exited in groundwater than that in the surface water. The concentrations of bulk DOM and chromophoric DOM both in surface water varied oppositely with tide levels, suggesting the potential role of groundwater discharge at low tides. DOM aromaticity also had tidal time scale fluctuations, but the molecular weight of DOM was insensitive to tide changes. The dispersion fluxes were one to four orders of magnitude lower than advective fluxes with the ranges of 0.14–24.8 μg m−2 d-1 for Cr, 6.2–22.4 μg m−2 d-1 for Cu, 14.7–387.4 μg m−2 d-1 for Zn, 0.7–25.4 μg m−2 d-1 for As, 259.2–2308 μg m−2 d-1 for Ba, 0.1–6.0 μg m−2 d-1 for Pb, 0–1.7 μg m−2 d-1 for Hg and 3.1–116 mg m−2 d-1 for DOM, respectively. Mangrove sediments tended to be the sources of DOM and all dissolved metal(loid)s, but the salt marsh was only the source of Cu, As, and DOM. These results have implications on the geochemical cycling of DOM and dissolved metal(loid)s in the salt marsh-mangrove ecotone which has contrasting pattern of surface water-groundwater exchange.

Validation of an analytical model of groundwater velocity based on laboratory test and numerical simulation

Surface water–groundwater exchange affects the material and energy transfer of rivers and adjacent riparian zones. As an intuitive carrier of energy, temperature can effectively reflect the spatial and temporal variation of surface water–groundwater exchange process. In this paper, the influence of water head variation and sand sample uniformity on its temperature field and seepage field is studied through a one-dimensional sand column laboratory test. To verify the accuracy of the one-dimensional vertical heat analysis model, the vertical seepage velocity measured in the indoor test is compared with the vertical submerged exchange rate calculated by the four analysis models. The results show that the Hatch analytical solution, Keery analytical solution, McCallum analytical solution and Luce analytical solution calculated by VFLUX2 through MATLAB are reliable for calculating the vertical undercurrent exchange rate of the heterogeneous sand column.

Exploring the Signal Filtering Properties of Idealized Watersheds Using Spectral Analysis

Watersheds act as low-pass filters, damping and attenuating climatic signals as water moves through the surface and subsurface. This is a well observed phenomenon; however, the ways in which watershed properties control the nature of this filtering are less well documented, especially with respect to groundwater surface water interactions. Here, we use a physically based groundwater surface water model to simulate idealized hillslope ensembles with varying watershed properties (hillslope slope, hydraulic conductivity, and precipitation magnitude) to quantitively explore the impact of watershed configuration on temporal filtering in both the surface and subsurface. To limit the complexities of this system an idealized titled-v domain is used. Multi-decadal simulations (95 years) are run, and then power spectral densities and transfer functions are used to quantify the temporal dynamics and damping of each simulation. Overall, we show that the degree of filtering and the degree of signal transformation is controlled by the total time spent in the subsurface and the degree of groundwater surface water exchanges. The ratio of precipitation to hydraulic conductivity controls the partitioning between infiltration and runoff. Greater infiltration results in less filtering in the subsurface and more filtering in streamflow. For a given precipitation conductivity ratio, deeper water table depths lead to greater streamflow filtering for periods less than 5 years. For time periods greater than 5 years the streamflow filtering is most strongly related to hydraulic conductivity which controls the baseflow dynamics. The majority of the input signal is filtered in the subsurface for short periods less than one year. For longer time scales, hydraulic conductivity is found to be the primary control of filtering and power shift taking place in the subsurface with larger conductivities correlated to less filtering and less of a signal transformation. Deeper water table depths lead to more signal transformation in saturated storage but are not correlated to filtering in unsaturated storage. This is likely due to counteracting effects of higher conductivity (which decreases filtering) and deeper water table depths (which increase filtering).

Assessing Integrated Hydrologic Model: From Benchmarking to Case Study in a Typical Arid and Semi-Arid Basin

Groundwater-surface water interactions play a crucial role in hydrologic cycles, especially in arid and semi-arid basins. There is a growing interest in developing integrated hydrologic models to describe groundwater-surface water interactions and the associated processes. In this study, an integrated process-based hydrologic model, ParFlow, was tested and utilized to quantify the hydrologic responses, such as changes in surface runoff and surface/subsurface storage. We progressively conducted a complexity-increasing series of benchmarking cases to assess the performance of ParFlow in simulating overland flow and integrated groundwater-surface water exchange. Meanwhile, the overall performance and the computational efficiency were quantitatively assessed using modified Taylor diagrams. Based on the benchmarking cases, two case studies in the Heihe River Basin were performed for further validation and to diagnose the hydrologic responses under disturbance, named the Bajajihu (BJH) and Dayekou (DYK) cases, respectively. Both cases were 2D transects configured with in-situ measurements in the mid- and downstream of the Heihe River Basin. In the BJH case, simulated soil moisture by ParFlow was shown to be comparable with in-situ observations in general, with Pearson’s correlation coefficient (R) > 0.93 and root mean square difference (RMSD) < 0.007. In the DYK case, seven scenarios driven by remote sensing and reanalysis data were utilized to study hydrological responses influenced by natural physical processes (i.e., precipitation) and groundwater exploitations (i.e., pumping) that are critical to surface and subsurface storage. Results show that subsurface storage is sensitive to groundwater exploitation before an obvious stationary point. Moreover, a correlation analysis was additionally provided demonstrating the impacts of different factors on subsurface storage timeseries. It was found that pumping influences subsurface storage remarkably, especially under short-term but large-volume pumping rates. The study is expected to provide a powerful tool and insightful guidance in understanding hydrological processes’ effects in arid and semi-arid basins.

Stormwater Pond Evolution and Challenges in Measuring the Hydraulic Conductivity of Pond Sediments

Stormwater ponds are intended to be used for mitigating floods, improving water quality, and recharging groundwater. The sediment-water interface (SWI) of stormwater ponds exhibits properties that influence surface water–groundwater exchanges similar to naturally occurring surface water bodies. However, these ponds are rarely monitored over time to account for their functionality. As organic and inorganic sediments accumulate on the pond bed, the ability of the SWI to conduct water is influenced by sediment deposition, accumulation, and compaction, as well as organic matter content and other biological processes. Two augmented methods, a sediment core permeability cell and an in situ aluminum tube and manometer, were evaluated for measuring the hydraulic conductivity of the SWI. The grain size, hydraulic conductivity, and percentage of organic matter were compared between two ponds constructed 22 years apart. Both methods were effective at measuring the hydraulic conductivities, especially in challenging encountered field situations, albeit with some shortcomings. The in situ method yielded data from sediments with low hydraulic conductivities due to thermal heating, expansion of the water, and the release of biogenic-derived gas from the sediments within the aluminum tube. The converted sediment core permeability cells generated the most consistent measurements. Grain size and hydraulic conductivities were correlated to pond age. The mean and effective grain sizes, as well as hydraulic conductivities of the older pond, were statistically lower than the younger pond in both shallow and deeper depths. Measurement of the changes in the SWI of stormwater ponds is important to protect urbanized areas from flood damage, control the quality and quantity of runoff, and maintain their groundwater recharge function.

Analysis of Large-Scale Groundwater-Driven Cooling Zones in Rivers Using Thermal Infrared Imagery and Radon Measurements

The role of groundwater (GW) discharge on surface water (SW) quantity, quality and temperature is known to be important. Moreover, the effect of GW contributions to river thermal budgets is critical in natural rivers considering that water temperature plays a vital role in fish survival during extreme heat events. The identification of zones with GW input in rivers can, thus, help river management plans. However, detecting these zones at the watershed scale can be a challenge. This work combines thermal infrared (TIR) imagery of rivers and water sampling for radon measurements for better documentation of GW in rivers. The Sainte-Marguerite and Berard Rivers, both located in Quebec, Canada, are known for their abundance of salmonids. Their water temperature profiles were plotted using TIR imagery, and five cooling zones in the Berard River and two for the Sainte-Marguerite River were identified in which notable GW–SW exchange was the suspected cause. Radon concentrations measured within the cooling zones showed clear GW contribution to SW. TIR imagery is an effective and fast way to identify GW seepage at the watershed scale. Radon can be used as a complementary natural tracer of GW in rivers at finer scales. The combination of both methods was shown to be reliable for the identification of GW in rivers. This can help for a better anticipation of GW effects in management plans to deal with extreme heat waves that are predicted to occur more frequently under future climate change scenarios.

Springs Emerging along the Elevation Gradient Indicate Intensive Groundwater-Surface Water Exchange in an Alpine Headwater Catchment, Northwestern China

Springs Emerging along the Elevation Gradient Indicate Intensive Groundwater-Surface Water Exchange in an Alpine Headwater Catchment, Northwestern China

Estimation of groundwater contributions to Athabasca River, Alberta, Canada

Study regionThe Athabasca River Basin (ARB), Canada Study focusThis study investigates the dynamic interactions that occur between surface water and groundwater systems within the Athabasca River Basin (ARB). The integrated surface-subsurface model of the ARB was first calibrated under monthly normal transient flow conditions to observed surface water and groundwater data, after which the model was forced with monthly average transient data to evaluate model performance. From these results, groundwater contribution to the Athabasca River system was calculated using simulated surface water-groundwater exchange fluxes. These estimates are compared to those obtained from an isotope-based balance analysis which also estimated groundwater contribution to the Athabasca River. New hydrological insights for the regionThe results from this study suggest that the groundwater system in the basin has a high degree of interaction with the surface water system. Specifically, the groundwater contribution to the surface water system along the Athabasca River ranges from 34% (high flow season) to 63% (low flow season) with an overall average annual groundwater contribution of 45%. These results indicate that the groundwater system needs to be considered when analyzing potential climate change impacts on future water availability and extreme hydroclimatic events.

Augmenting the National agroecosystem model with physically based spatially distributed groundwater modeling

We present an integrated hydrologic modeling approach for the conterminous United States using the SWAT + models of the National Agroecosystem Model (NAM). The NAM is a field-based, national scale hydrologic model to aid in conservation planning and policy. We augment the NAM by simulating groundwater storage and flow in a physically based spatially distributed manner using the gwflow module. We also present a scripting tool that automates the creation of gwflow inputs for each 8-digit hydrologic unit code (HUC8) SWAT + model. Key calculated groundwater inflows and outflows include recharge, pumping, groundwater-lake exchange, groundwater-surface water exchange, transfer to soils, and boundary inflow. We demonstrate the approach for six HUC8 watersheds located in various regions of the United States, focusing on areas of groundwater pumping, tile drainage, intensive groundwater-surface water interactions, and high precipitation. The presented framework can be used to establish models for scenario analysis of climate, management, and land use.