Surface Water Interactions Research Articles

Global analysis of groundwater pumping from increased river capture

In many regions globally, groundwater overuse exceeds natural replenishment, leading to immediate consequences such as reduced river flows and devastating impacts on freshwater ecosystems. In alluvial aquifers in particular, groundwater pumping contributes to river flow reduction in two significant ways: first, by intercepting water that would naturally discharge into the river, and second, by lowering groundwater levels below the riverbed, causing river water to infiltrate. Despite these critical interactions, large-scale water resources assessments often overlook the relationship between groundwater and surface water, hindering a comprehensive understanding of the consequences of groundwater pumping on both the groundwater and surface water systems. Our study, utilizing a coupled global-scale groundwater–surface water model, reveals that approximately 20% of globally pumped groundwater stems from diminished streamflow, while 16% results from reduced storage. Projections for the end of the century, accounting for climate change, suggest potential increases to 30% from reduced streamflow and a decrease to 12% from reduced storage. Notably, our results highlight that the impact on streamflow is more widespread and linked to smaller pumping rates, contrasting with impacts on storage associated with higher pumping rates. This study shows the crucial need to include groundwater–surface water interactions in large-scale water resources assessments, not only for accurate estimates of freshwater availability but also for a comprehensive understanding of the far-reaching impacts of groundwater overuse related to increasing water demands and climate change.

DECOMPOSITION OF RIVER HYDROGRAPHS TAKING INTO ACCOUNT DATA OF HYDROGEOLOGICAL OBSERVATIONS

In the case of absence of reliable information on fluctuations of levels and hydraulic parameters of aquifers within a large catchment, the method of river hydrograph decomposition can be used to assess groundwater component and other constituents of river water recharge. The difficulties and shortcomings of this method, which relies on specific schematizations and assumptions, are analysed and discussed. We propose to take into account the results of calculations of lateral groundwater inflow to the river accomplished using the numerical method based on observations at representative balance sites in order to improve the accuracy of the method of decomposition of the river hydrograph. A proper schematization should also be justified for river catchment (or its part), which describes the interaction of surface water, shallow groundwater, and artesian (deep) interlayer waters, which provides rationale for defining or neglecting groundwater inflow to river during the flood periods. The most disputable issue remains the allocation of the phase of “reverse water inflow to river banks” during flood periods. The groundwater level rise at the beginning of the flood results from the infiltration recharge to the aquifer and from inflow of water from the river. The contribution of inflow to river bank to groundwater level rise is dependent from the distance from the river to the observation well. To establish hydraulic head gradient from the river towards the adjacent groundwater aquifer at flood peak, at least two observation wells are needed, one of which should be located 3–4 m from the river water edge on the elevated part of the bank which is not flooded, and the other should be located 50–70 m from the bank towards the watershed. It is proposed that the phase of maximum groundwater inflow to the river should be adjusted based on the dates of the beginning and ending of the groundwater level decrease during the recession of the river flow during the flood period. The combined application of the described above methods showed that the use of only hydrograph decomposition method underestimates the share of groundwater recharge to the river by 2–5%. Based on the analysis of the Pivdennyi Buh River hydrographs during the 1980–2020 period, general tendencies of changes in the shallow groundwater and deep subsurface recharge of the Pivdennyi Buh River in its upper basin (upstream of the city of Khmilnyk) have been established: deep subsurface recharge prevailed over the shallow groundwater component (33.4 compared to 25.0% of the total). At the same time, the total subsurface runoff constituted on average 58%.

Application and Evaluation of Stage–Storage–Discharge Methodology in Hydrological Study of the Southern Phosphate Mining Model Domain in Southwest Florida

This hydrological study investigated a combined rating methodology tested on a 14,090 km2 area in Southwest Florida. The approach applied the Hydrological Simulation Program-Fortran (HSPF) over a 23-year period and was validated by 28 stream gauging stations. The regional hydrological complexity includes natural and agricultural areas, as well as extensive phosphate mining and urbanizing areas. This application is a novel and efficient methodology for generating stage–storage–discharge relationships using a geographic information system (GIS), empirical equations, and spreadsheets for 148,000 isolated and connected alluvial wetlands within the model domain. The validation metrics used to evaluate the applied methodology for populating the stage–storage–discharge relationship demonstrated the model effectiveness in simulating a range of hydrological events across various regions. For discharge prediction, the Nash–Sutcliffe efficiency values surpassed 0.7 at most stations, with an average of 0.67, and the average R squared was 0.74. This methodology, when applied, achieved a root-mean-square error of 4 m3/s for discharge prediction and 0.47 m for stage prediction. However, limitations emerged in simulating baseflow (low flows), highlighting the need for integrated modeling approaches to accurately capture groundwater–surface water interactions. The research provides an improved means for modeling regional water resources and lays the groundwork for enhanced hydrological modeling in watersheds with complex alluvial and isolated wetland systems.

Assessing the resilience of stormwater ponds under climate change: A case study on Grace Lake, Florida, unveiling flood control and water quality implications

Stormwater ponds have emerged as a crucial solution in Florida to accommodate excess runoff from new developments and mitigate environmental pollution. Climate change affects rainfall and evapotranspiration, likely altering the hydrologic process. It is unclear how effective stormwater ponds will be in a changing climate, especially where surface water and groundwater interaction is highly expected. To address these concerns, this study employs a fully coupled surface water and groundwater model that was calibrated for the Grace Lake, located in central Florida. Utilizing the Multi-Model Ensemble method and GCM data, future rainfall projections were generated for the mid-century (2040–2070). The results indicate a projected 13 % increase in rainfall for the mid-century under the Representative Concentration Pathway 4.5 (RCP 4.5). This increase led to a rise of 13 cm in the seasonal high water elevation of Grace Lake, reducing its reliability as a flood control mechanism by 13 %. Moreover, downstream areas from the lake are expected to experience higher flood stages in the future, with the duration of road flooding extending from less than three days (base period) to approximately seven days (future period). This increase in surface runoff raises concerns for water quality, with nitrogen and phosphorus loads projected to surge up to 67 % in the future period.

Evaluation of buoyant action of groundwater and surface water interaction on pit slope stability using hydrogeological-stratigraphic-structural assessment within the Kawere catchment of the Nsuta mine

ABSTRACT In open-pit mining operations where activities are conducted below water table or close to surface water bodies, the mine is potentially faced with dewatering and slope stability challenges. Appropriate evaluation of slope stability to obtain adequate slope safety factor has continuously been the centre of geotechnical research locally and internationally. This paper evaluates the influence of buoyant action propagated by groundwater and surface (GW-SW) interaction on pit slope designed in multi-layered fractured rock with complex hydrology using Hydrogeological-Stratigraphic-Structural Assessment (HSSA) at the Nsuta Manganese Mine in Ghana. LEM analyses of the Pit C-western slope estimated an overall factor of safety (FOS) of 1.1, probabilities of failure (POF) of 7.5% and the reliability index (RI) of 1.4 in the slope stress field. However, when the groundwater was introduced, the slope FOS was reduced to 0.13, POF of 100.0% and (RI) of 0.00 indicating failure. FEM numerical model points to the location of maximum shear strain and total displacement in the argillite zone within the rock mass. The FEM seepage analysis model estimated groundwater pore pressure data along the critical slide surfaces from the crest of the slope to the bottom of the rock slope ranging between 250 kPa and 4250 kPa with an average pore pressure of 2250 kPa within the pit slope. This proposed HSSA approach used in the study provides innovative insights into the percentage failure contribution of the individual lithologies to the overall combined lithological susceptibility of the slope under stress and groundwater failure mechanisms, pointing out Ru ratio in pit slope stability estimation as inadequate.

Formation processes of groundwater in a non-ferrous metal mining city of China: Insights from hydrochemical and strontium isotope analyses.

Tongling is a significant non-ferrous metal mining city in China, which produces waste that negatively impacts the area's water environment. It is essential to comprehend the hydrochemical properties and formation processes of groundwater to safeguard and utilize it efficiently. We explored major ions, strontium, and its isotopes in water and river-bottom samples from the northern (i.e., A-A' section) and southern (i.e., B-B' section) areas. The hydrochemical facies show the mining activities have a greater impact on surface water than on groundwater. Groundwater hydrochemical formation results from several factors, with water-rock interaction and ion exchange being primary. Additionally, the dissolution of calcite, dolomite, and feldspar, oxidation of pyrite, and hydrolysis of carbonate minerals also impact the formation of groundwater chemistry. Our analysis of strontium and its isotopes indicates that carbonate dissolution primarily occurred in the recharge area; the runoff from the recharge to the discharge area results in the dissolution of certain silicate rocks; calcite dissolution sources account for > 70% contribution in both surface water and groundwater water-rock interactions, whereas silicate rock dissolution sources and dolomite dissolution sources account for < 30%. Due to changed order of dissolved carbonate and silicate minerals during groundwater flow, the distribution of strontium and its isotopes in the A-A' section is opposite to that in the B-B' section. The findings provide a basis for developing, utilizing, managing, and protecting groundwater resources, especially in similar mining areas.

Effects of soil heterogeneity and preferential flow on the water flow and isotope transport in an experimental hillslope

Soil water movement plays vital roles in hillslope runoff generation and groundwater and surface water interaction. However, there are still knowledge gaps about the impacts of soil heterogeneity and preferential flow on the internal water flow and transport process. In this study, the vertical soil heterogeneity focused on the variations in soil retention capacity, and the consideration of lateral preferential flow emphasized the higher hydraulic conductivity. We combined isotopic tracing and numerical modeling in an artificial hillslope, focusing on monitored processes of the artificial rainfall and isotopic tracing experiment. The results showed that the soil moisture quickly accumulated at the bottom of the hillslope during rainfall events, while the 2H enrichment occurred in the topsoil derived from enriched isotope injection in the second artificial rainfall. The evaporation process slowed down the mixing of new water in the topsoil and old water in the lower layer. We found that the vertical soil heterogeneity had significant influences on the internal water and isotope transport paths within the hillslope. The lateral preferential flow played an important role in the water flux and transport time to the seepage face. The coupling of isotopic tracing, which reflects the water transport and mixing with the hillslope, effectively improved the model simulation and mechanism analysis of hillslope water flow. Our findings provide new insights into the mechanisms governing soil water flow and transport dynamics in hillslopes, taking into account vertical soil heterogeneity and lateral preferential flow.

Estimating Riparian Water Movement in an Incipient Karst Landscape—Minnesota, USA

Understanding rain, ground, and surface water interactions in riparian zones is essential for hydrologic and environmental management. The novelty of this study lies in its revelation of isotopic shifts and consequent evaluation of hydrologic pathways and processes within the forested riparian zones of three distinct streams, valleys, and riparian systems in a carbonate-sandstone incipient karst landscape. We collected water samples from three southeastern Minnesota catchments: Trout Brook, Crystal Creek, and Bridge Creek. A Picarro L2130i was used to measure δ18O for oxygen, and δD for deuterium in units of ‰ (per mil). We estimated the global meteoric line for the study sites, built upon aquifer age dating, and explored aquifer transit time for the study sites using a simple seasonal amplitude model. The results showed small amplitudes for 2020 and 2021, suggesting that bedrock aquifer water was the primary source water with a mean core transit time greater than 10 years. All three catchments were different but had similar bedrock valley types and riparian sediment. The primary driving factor was the seasonal precipitation input mixing with existing water. In a normal to wetter year, the isotopic data showed larger amplitude shifts between seasons with trendlines that adjusted depending on the temperature of the new water additions. The proposed approach is valuable in revealing complex hydrologic processes and pathways and can contribute extensively to the planning and management of karst riparian systems.

Evidence of Spontaneous Formation of Two-Dimensional Amorphous Clathrates on Superhydrophilic Surfaces.

Clathrate hydrates reserved in the seabed are often dispersed in the pores of coarse-grained sediments; hence, their formation typically occurs under nanoconfinement. Herein, we show the first molecular dynamics (MD) simulation evidence of the spontaneous formation of two-dimensional (2D) clathrate hydrates on crystal surfaces without conventional nanoconfinement. The kinetic process of 2D clathrate formation is illustrated via simulated single-molecule deposition. 2D amorphous patterns are observed on various superhydrophilic face-centered cubic surfaces. Notably, the formation of 2D amorphous clathrate can occur over a wide range of temperatures, even at room temperature. The strong water-surface interaction, the characteristic properties of guest-gas molecules, and the underlying surface structure dictate the formation of 2D amorphous clathrates. Semiquantitative phase diagrams of 2D clathrates are constructed where representative patterns of 2D clathrates for characteristic gas molecules on prototypical Pd(111) and Pt(111) surfaces are confirmed by independent MD simulations. A tunable pattern of 2D amorphous clathrates is demonstrated by changing the lattice strain of the underlying substrate. Moreover, ab initio MD simulations confirm the stability of 2D amorphous clathrate. The underlining physical mechanism for 2D clathrate formation on superhydrophilic surfaces is elucidated, which offers deeper insight into the crucial role of water-surface interaction.

A Study on the Response of Surface Water and Groundwater Interaction to River Runoff in the Taoer River Alluvial Fan

Understanding the transformation mechanisms of surface water and groundwater positively impacts the rational utilization of water resources and the more scientific allocation of their uses. Many factors affect surface water and groundwater interaction (SGWI), among which river runoff is the most critical variable. Studying the response mechanism of SGWI under changes in river channel volume can help understand the essence of SGWI. Using the Taoer River alluvial fan as the research area, daily runoff data from hydrological stations in the study area from January to March 1961, 1971, 1981, 1991, 2001, and 2011 were collected. The daily SGWI was calculated using the water balance and flow speed difference methods. The results show that river runoff is the main factor controlling the SGWI, and the interaction quantity (IQ) is more stable when the IQ is relatively small.

Surface Water and Groundwater Interaction in The Low Land Area of Parit Raja Johor from Isotope Measurement

The groundwater and surface water were analysed for stable isotopes (18O and 2H) to assess the interaction for water protection and management in the lowland area of Parit Raja, Johor. The plotted graph on the δ2H versus δ18O shows that the compositions of the surface water are seen to be evaporated. Since the compositions of δ2H and δ18O were more depleted than the precipitation, indicating that it had a minimum influence on the surface water. In the study, the δ2H of the groundwater was between −83.66 to –36.74 for δ2H and –11.45 to –4.96 for δ18O. These groundwater compositions were depleted compared to surface water, which indicates that in this area, groundwater sources may not be linked to the surface water. Instead, this groundwater was probably old groundwater that was influenced by ancient groundwater, where the weak connectivity between these sources was due to clay layers and interrupted aquifers. Since the top clay layer also plays some role in impeding the downward movement of water, it plays a role in the recharge process. In addition, the isotopic composition of groundwater was significantly more depleted than that of rainwater, indicating that this source was highly evaporated and could have originated from the seepage of meteoric water in the past. These results were expected to be useful for a better assessment of surface water and groundwater since the interaction is critical for water protection and management.

Unraveling the atomic structure and dissociation of interfacial water on anatase TiO2 (101) under ambient conditions with solid-state NMR spectroscopy.

Anatase TiO2 is a widely used component in photo- and electro-catalysts for water splitting, and the (101) facet of anatase TiO2 is the most commonly exposed surface. A detailed understanding of the behavior of H2O on this surface could provide fundamental insights into the catalytic mechanism. This, however, is challenging due to the complexity of the interfacial environments, the high mobility of interfacial H2O, and the interference from outer-layer H2O. Herein, we investigate the H2O/TiO2 interface using advanced solid-state NMR techniques. The atomic-level structures of surface O sites, OH groups, and adsorbed H2O have been revealed and the detailed interactions among them are identified on the (101) facet of anatase TiO2. By following the quantitative evolution of surface O and OH sites along with H2O loading, it is found that more than 40% of the adsorbed water spontaneously dissociated under ambient conditions on the TiO2 surface at a loading of 0.3 mmol H2O/g, due to the delicate interplay between water-surface and water-water interactions. Our study highlights the importance of understanding the atomic-level structures of H2O on the surface of TiO2 in catalytic reactions. Such knowledge can promote the design of more efficient catalytic systems for renewable energy production involving activation of water molecules.

Anomalous Water Wetting on a Hydrophilic Substrate under a High Electric Field.

Macroscopically, the traditional Young-Lippmann equation is used to describe the water contact angle under a weak electric field. Here we report a new wetting mechanism of deionized water under a strong electric field that defies the conventional Young-Lippmann equation. The contact angle of the deionized water droplet on a model hexagonal lattice with a different initial wettability is extensively modulated by the vertical electric field. The cosine of water contact angle on a hydrophilic substrate displays an anomalous linear relationship with the field, in contrast to the hydrophobic case, which shows an inverse parabolic relationship. Such anomalous wetting is verified by experimental measurements of water droplets on a pyroelectric substrate. Moreover, we identify that this anomaly arises from the linear modulation of the solid-liquid interfacial tension of hydrophilic substrates by the electric field. Our findings provide atomistic insight into the fundamental laws and new phenomena of water-surface interactions under extreme electric fields.

Developing a conceptual model of groundwater – Surface water interactions in a drought sensitive lowland catchment using multi-proxy data

Frequencies and intensities of droughts have increased due to climate change, providing an urgent impetus to improve understanding of ecohydrological fluxes in drought-sensitive areas where water and food security are threatened. We used a multi-proxy approach for assessing the effects of landuse and catchment properties on recharge and groundwater – surface water interactions during a prolonged drought starting in summer 2018 in a 66 km2 lowland, mixed landuse catchment (Demnitzer Mill Creek, Germany). We used water table monitoring, water stable isotopes, tritium isotopes, hydrogeochemical tracers, streamflow observations and geophysical investigations to characterise the spatial and temporal patterns of groundwater recharge in a shallow, unconfined aquifer system. Long-term groundwater levels showed a declining trend since 2011, which accelerated after 2018 resulting in increasingly intermittent streamflow. Geophysical surveys and groundwater monitoring indicated that shallow water tables (typically < 3 m deep) in low to moderate permeability surficial deposits are generally recharged during winter, leading to higher groundwater – surface water connectivity in riparian alluvial aquifers, which is the first order control on streamflow generation. This was supported by similar geochemical characteristics of groundwater and streamflow. Water stable isotopes indicated a high damping in groundwater with a bias towards winter precipitation and direct recharge. Groundwater age estimates using tritium showed high uncertainty but indicated that shallow groundwater was < 10 years old and generally similar to streamflow. Such multi-proxy approaches help understand changes in groundwater recharge and stream-aquifer interactions during droughts and contribute to the development of sustainable land and water management strategies for groundwater systems that are sensitive to climate change.

Hydrogeological Investigations of Groundwater and Surface Water Interactions in the Berg River Catchment, Western Cape, South Africa

The Berg River Catchment based in the Western Cape Province, South Africa services the greater Cape Town area with water, subsequent to supplying the vast agricultural activities that exist in the middle and the lower reaches. This study thus investigates the hydrogeochemical interactions between surface and groundwater in the Berg River Catchment with the aim of establishing trends and transfer of constituents between the surface and groundwater systems, investigates the role that geology plays in water chemistry as well as identifies the geochemical processes controlling surface and groundwater chemistry in the catchment. This study was carried out using three types of research designs namely i) experimental research design; ii) field research design and meta-analysis research design. Furthermore, the study made use of hydrochemical data ranging from 2003 to 2013 obtained from the National Water Monitoring Database owned and maintained by the Department of Water and Sanitation and data that were sampled in 2016 by authors and analyzed using the ICP-MS Technique Ground Water Chart, Arc-GIS and Geosoft (Oasis Montaj) were further employed to model the data. The results indicated that: i) in the Upper Berg there is not much interaction and transfer of constituents between surface and groundwater; ii) the Middle Berg, however, indicated a degree of interaction with the sharing of constituents between the two water systems and iii) the Lower Berg indicated only NaCl water type also noting that the area situated near the river mouth whereby there is the mixing of river and seawater.

Floods in Dinaric Karst fields: a case study of the Dicmanjsko-Bisko Polje (Croatia)

ABSTRACT Karst areas are characterized by extreme heterogeneity and variability of geologic, morphologic, hydrogeologic, hydrologic, hydraulic, ecologic and other parameters in space and time. Therefore, the occurrence of floods under such condition manifests in different forms, intensities, and durations. Heavy precipitation in karst areas leads to a considerable increase in groundwater levels and the activation of temporary springs. Karst fields that have not been properly meliorated are particularly vulnerable to such phenomena and, can remain flooded for several weeks. In Dalmatia, in the southern Croatian region, there are 12 karst poljes with an area larger than 1000 ha, including Dicmanjsko-Bisko polje (1700 ha). Our study presents a conceptual model of the interaction of underground and surface water in the Dicmanjsko-Bisko polje, as well as the process of flooding. The input data were geological mapping and measured precipitation. The paper describes the December 2021 flood in detail. The average 11-day precipitation recorded in the field catchment area was 292 mm, which led to the flooding of 230 ha (approximately 14% of the field area). The main cause of the flooding in the western part of the field was a large amount of surface runoff, resulting in insufficient capacity of the existing drainage channels. In the eastern lowest part of the field, flooding was even more intense due to the insufficient capacity of the sinkhole. The flood caused damage to agricultural lands, infrastructure, and economic facilities. The paper proposes flood mitigation measures. The study is an example of the practical application of karst research, that can be used for different purposes (spatial planning, hydrologic monitoring, modeling hydrogeological processes).

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.

Where the water goes: Partitioning surface flow and streambed infiltration in an ephemeral river laboratory experiment

Ephemeral and intermittent flow in dryland streams plays a vital role in supporting delicate ecosystems and recharging groundwater in underlying aquifers. Despite extensive research, accurately predicting surface runoff, streambed water infiltration, and groundwater recharge during ephemeral streamflow events remains challenging due to the complex physical processes involved. Such processes are logistically difficult to observe in the field and should not be assessed through numerical studies alone. To tackle this complexity, we utilized an 8 m long, 0.25 m wide, and 0.6 m deep laboratory flume filled with fine sand as a physical model for event flows along a dry stream. This flume allowed us to measure both streamflow and streambed infiltration volumetrically as the stream wetting front advanced along its length during 8 steady inflow rates. The flume was divided into separate compartments to measure water across the sediment surface (streamflow) and water exiting through the flume’s bottom (groundwater recharge). To validate our physical tests, we compared them with simulated flows in an integrated surface–subsurface hydrological numerical model. The model results exhibited good agreement with the observed stream and groundwater dynamics. Through a parametric numerical investigation, we identified that hydraulic conductivity significantly controlled the rate of surface infiltration and the advancement of the stream wetting front. Interestingly, we found a linear relationship between surface discharge and stream wetting front location, as well as groundwater recharge, under steady-state conditions, in line with the governing equations. However, our simulations of variable streambed heterogeneity and elevation unveiled the crucial influence of these factors in determining the timing of downstream flow progression. This insight is essential for establishing ecological connectivity along non-perennial rivers and has significant implications for delivering environmental flows in arid regions where ephemeral rivers are prevalent. Our study underscores the value of flume experiments in elucidating the transient physical processes during surface water and groundwater interactions in intermittent streams. By employing a combination of physical modelling and numerical simulations, we advance our understanding of these vital hydrological interactions, contributing to sustainable water management practices in semi-arid and arid environments.

Analysis of nationwide groundwater monitoring networks using lumped-parameter models

Many countries maintain nationwide groundwater networks to monitor the status of their groundwater resources. For effective groundwater resource management, it is fundamental to understand the groundwater dynamics measured in the individual monitoring wells. Nationwide monitoring networks typically cover multiple aquifer systems with different degrees of environmental complexity. The analysis of the data of such networks thus requires flexible modeling approaches. In this study, we assessed the applicability and performance of lumped-parameter models using impulse response functions, as implemented in the Pastas software, to simulate hydraulic head data from the nationwide groundwater monitoring network in Switzerland. The selected 28 monitoring wells in the network are situated in unconsolidated, relatively shallow aquifers across Switzerland. Given the very diverse topography in the study area, snowmelt processes affect some aquifers, while groundwater–surface water interactions are important in the valleys. Different linear and nonlinear models were tested to take precipitation and potential evaporation into account, with a new model developed as part of this study to account for the effect of snow processes on recharge generation. After generally good fits in both the calibration and evaluation were achieved, the models were used to identify and quantify which stresses (e.g., precipitation, river stages) control the groundwater dynamics. The results show that precipitation and evaporation explain large parts of the measured dynamics, and about half of the monitoring wells in the network appear to be influenced by river stages. Explicitly accounting for snow processes in the recharge generating process is found to improve the simulation of the head dynamics across Switzerland, particularly for wells in high-altitude aquifers. This study demonstrates for the first time the applicability of lumped-parameter models using impulse response functions to model heads in Switzerland, and more generally, in climatic settings where snow processes are impacting the head dynamics.

Seasonal scour and siltation induced spatiotemporal variations in riverbed sediment leakage coefficients as measured via the thermal tracer method

Riverbed scour and siltation can change the hydraulic conductivity and thickness of sediments, leading to notable spatiotemporal variations of groundwater–surface water interaction. However, correlated quantitative research on the dynamic leakage coefficient (LC) remains lacking under riverbed scour and siltation. Based on dynamic monitoring and analysis of sediment medium properties, river-groundwater levels, and temperature profiles in the section of Liao River, this study compared the applicable conditions of different thermal analytical models and identified spatiotemporal variations in the LC values induced by riverbed scour and siltation. The results showed that: (1) The thermal tracer method combined with river-groundwater level monitoring can effectively quantify spatiotemporal variations in the LCs of riverbed sediment. Based on the sediment temperature presents diurnal fluctuations and gradient characteristics in different seasons, the LCs in summer, spring, and autumn compared to winter in seasonally frozen regions should be calculated using transient and steady-state analytical solution models, respectively. (2) The LCs ranged from 0.47 to 24.90 × 10-6 s−1, showed larger temporal variability than spatial, increased from the river bank to the center, and had larger values in autumn and winter. (3) Distinct from previous findings, the riverbed underwent a scouring process associated with reductions in the incoming sediment coefficient as the river stage shifted from high to low, eroding the surface 4–8 cm of sediment. During this process, the LC increased by 40 to 420%. Further, the influence of riverbed scour and siltation on the LC varied by river section. Near the riverbank, the sediment LC was primarily controlled by hydraulic conductivity related to the coarsening of sediment lithology; however, it was influenced by variations in both sediment thickness and hydraulic conductivity near the riverbed center. Collectively, these results further understand the mechanisms underlying changes in the sediment LC induced by riverbed scour and siltation, as well as provide a scientific basis for ensuring the sustainable development of riverside water sources under such changes.