Water-soil Interaction Research Articles

Biochar–water–soil interactions: Implications for soil desiccation cracking behavior in subtropical regions

In subtropical regions, soil desiccation cracking often exerts a significant impact on the interactions between soil water and the atmosphere, making it a subject of great interest in the fields of geotechnical and geoenvironmental engineering. Despite the growing utilization of biochar as a sustainable soil amendment, there remains a lack of in-depth understanding of biochar–water–soil interactions, as well as its impact on soil desiccation cracking behavior. To address this gap, this study investigated the influence and mechanism of woody biochar dosages and particle sizes on the cracking behavior of three typical clayey soils in subtropical regions in China, namely Pukou expansive soil (PKE), Xiashu soil (XS), and Zhongshan lateritic soil (ZSL). The quantitative analysis of crack images revealed that the use of biochar was not consistently effective in preventing soil cracking. The application of biochar reduced the crack ratio in PKE and XS by up to 24.03% and 53.89%, respectively. In contrast, ZSL exhibited a 74.57% increase in crack ratio with the addition of 10% biochar. This influence can be further enhanced by increasing the dosage and reducing the particle size of biochar. The microstructural analysis demonstrated that biochar exerts an inhibitory effect on PKE and XS primarily through direct replacement, direct barrier, and indirect physical mechanisms. Moreover, an indirect chemical effect between biochar and clay particles was proposed to explain the exacerbated cracking observed in biochar-amended ZSL. To effectively utilize biochar for soil cracking mitigation in subtropical regions, it is essential to evaluate the initial mineral composition and cation type of the soil.

Influence of drainage conditions on piezocone penetration mechanism in offshore clays

ABSTRACT CPTu (piezocone penetration test) is widely used in engineering practice to determine various parameters of clays under partially drained conditions. However, most existing research is based on undrained or fully drained conditions for clays, leading to underestimation or overestimation of soil strength. By applying the Eulerian-Lagrangian large deformation finite element method to analyse the water-soil interaction, the CPTu driving mechanism in offshore saturated soft clays under different drainage conditions is revealed. An advanced hypoplastic constitutive model for clays is used to simulate the nonlinear behaviour of kaolin under different drainage conditions. The generation, accumulation, and dissipation of excess pore water pressure under different drainage conditions are analysed, as well as the influence of excess pore water pressure on cone tip resistance and the effective stress of the soil during the CPTu penetration process.

Effect of Geosynthetics on Swell Reduction During an Extreme Rainfall Event

Expansive (reactive) soils can swell during rainfall causing damage to engineering structures. This paper seeks to investigate the effect of geosynthetic material on the swell reduction of such soils. A series of large-scale long-term soil column experiments were conducted on a very high plasticity reactive soil under simulated rainfall conditions. Non-woven geosynthetics combined with geogrid and woven geosynthetics were used as primary geosynthetic material to provide reinforcement and drainage for the soil mass. The obtained results revealed that these geosynthetics did not improve the California Bearing Ratio values of the soil. However, when placed in the soil mass, the geosynthetic materials greatly reduced the total swell of the soil. Visual observations and the experimental data on water content, suction, and vertical displacements indicated that the geosynthetics provided better drainage of the soil mass. This limited the time of water–soil interaction, thus reducing the total swell of the soil.

Lateral dynamic responses of coastal group piles considering pile‒water‒soil interactions

In this paper, an analytical framework is developed to investigate the dynamic impedance of pile groups comprising an arbitrary number of cylindrical piles connected with a rigid cap. The solution considers the combination of the secondary ground wave effects transferred by the pile‒soil vibration and the hydrodynamic pressure from the pile‒water interaction. A displacement attenuation function is introduced to define the pile‒to‒pile interaction factor, which describes the relationship between the active and passive piles based on the soil reaction development. The pile is modeled as a Euler‒Bernoulli (EB) beam, and the hydrodynamic pressure is calculated using radiation wave theory. Biot's dynamic poroelastic theory describes the saturated soil around the piles. The rationality and correctness of the proposed theoretical model are verified by degenerating the solution to the existing research results. An extensive parametric analysis is conducted to investigate the effect of various factors on the lateral dynamic impedance of the group pile. Moreover, some interesting findings and meaningful conclusions are obtained.

Environmental controls on observed spatial variability of soil pore water geochemistry in small headwater catchments underlain with permafrost

Abstract. Soil pore water (SPW) chemistry can vary substantially across multiple scales in Arctic permafrost landscapes. The magnitude of these variations and their relationship to scale are critical considerations for understanding current controls on geochemical cycling and for predicting future changes. These aspects are especially important for Arctic change modeling where accurate representation of sub-grid variability may be necessary to predict watershed-scale behaviors. Our research goal is to characterize intra- and inter-watershed soil water geochemical variations at two contrasting locations in the Seward Peninsula of Alaska, USA. We then attempt to identify the key factors controlling concentrations of important pore water solutes in these systems. The SPW geochemistry of 18 locations spanning two small Arctic catchments was examined for spatial variability and its dominant environmental controls. The primary environmental controls considered were vegetation, soil moisture and/or redox condition, water–soil interactions and hydrologic transport, and mineral solubility. The sampling locations varied in terms of vegetation type and canopy height, presence or absence of near-surface permafrost, soil moisture, and hillslope position. Vegetation was found to have a significant impact on SPW NO3- concentrations, associated with the localized presence of nitrogen-fixing alders and mineralization and nitrification of leaf litter from tall willow shrubs. The elevated NO3- concentrations were, however, frequently equipoised by increased microbial denitrification in regions with sufficient moisture to support it. Vegetation also had an observable impact on soil-moisture-sensitive constituents, but the effect was less significant. The redox conditions in both catchments were generally limited by Fe reduction, seemingly well-buffered by a cache of amorphous Fe hydroxides, with the most reducing conditions found at sampling locations with the highest soil moisture content. Non-redox-sensitive cations were affected by a wide variety of water–soil interactions that affect mineral solubility and transport. Identification of the dominant controls on current SPW hydrogeochemistry allows for qualitative prediction of future geochemical trends in small Arctic catchments that are likely to experience warming and permafrost thaw. As source areas for geochemical fluxes to the broader Arctic hydrologic system, geochemical processes occurring in these environments are particularly important to understand and predict with regards to such environmental changes.

Water–soil interactions: Unravelling the processes and stages involved in the wetting of water repellent soils

The water repellent behaviour of soils is a widely studied phenomenon given its implications for infiltration, runoff, erosion and preferential flow. However, the principles underlying the eventual penetration of water into affected soils remain poorly understood. Theoretical considerations of the energetics and kinetics involved as a water drop makes contact with a water repellent soil surface and eventually penetrates into the soil suggest three distinct stages in the overall process. These stages are 1) adhesional wetting as soil and water first make contact, followed by 2) a kinetic barrier transitional stage in which molecular reorganisation of organics on soil reduces the water-soil contact angle to allow the water drop to sit deeper over soil particles of initial contact such that there is contact with particles in directly underlying soil layers, and finally 3) branching interstitial wetting as water penetrates into the bulk soil. Studies presented here of optical microscopy, mass of soil initially wetted, penetration time through layers of soil of different thicknesses, and time-dependent measurements of contact angle, volume of water penetrated, and mass of soil wetted, all give results consistent with this model. However, only for highly water repellent soils can distinct stages in wetting be clearly resolved experimentally, presumably because only these soils have a high enough kinetic barrier in the transitional stage for good separation between stages. For less water repellent soils, while the general time dependent behaviour remains consistent with the model, the distinction between the three stages is not so easy to resolve experimentally. The roles of contact angle, particle size distribution and drop size in determining the rates of these stages is considered, and the implications of the model for understanding soil water repellency are discussed.

Impact of mica on geotechnical behavior of weathered granitic soil using macro and micro investigations

The micaceous weathered granitic soil (WGS) is frequently encountered in civil engineering worldwide, unfortunately little information is available regarding how mica affects the physico-mechanical behaviors of WGS. This study prepares reconstituted WGS with different mica contents by removing natural mica in the WGS, and then mixes it with commercial mica powders. The geotechnical behavior as well as the microstructures of the mixtures are characterized. The addition of mica enables the physical indices of WGS to be specific combinations of coarser gradation and high permeability but high Atterberg limits. However, high mica content in WGS was found to be associated with undesirable mechanical properties, including increased compressibility, disintegration, and swelling potential, as well as poor compactability and low effective frictional angle. Microstructural analysis indicates that the influence of mica on the responses of mixtures originates from the intrinsic nature of mica as well as the particle packing being formed within WGS. Mica exists in the mixture as stacks of plates that form a spongy structure with high compressibility and swelling potential. Pores among the plates give the soil high water retention and high Atterberg limits. Large pores are also generated by soil particles with bridging packing, which enhances the permeability and water-soil interactions upon immersion. This study provides a micro-level understanding of how mica dominates the behavior of WGS and provides new insights into the effective stabilization and improvement of micaceous soils.

Dynamic analysis of the mooring system of a salvage barge:A coupled time-domain method considering seabed resistance during the off-bottom stage

The off-bottom stage of the wreck salvage is a complicated load transfer process involving multi bodies and multi mediums. In order to ascertain the dynamic performance of the barge and the mooring cables in salvage, this paper proposed a novel draught-varying numerical simulation strategy by combining the in-house code with the commercial water–soil interaction solver. The seabed resistance obtained by the finite element method was considered in simulations. It was found that the time history results were complicated by the unique coupling characteristics of the salvage system, exhibiting some abnormal motion or tension excitation during the lifting phase. In addition to further explain the coupling mechanism and gain better motion control, a series of comparative studies were conducted under different mooring configurations and sea states. Recommendations were given for optimizing the mooring line arrangements and minimizing the risk factors in the salvage process. However, the overall motion control effect from the line arrangement optimization was weakened in some extent as the wave height elevated.

Influence of Different Industrial Waste Residues on Engineering Properties of High Liquid Limit Soil and Its Microscopic Mechanism

High liquid limit soil has unfavorable engineering geological characteristics, such as strong disintegration, dry shrinkage and easy cracking, and easy uplift when encountering water, which will cause various problems to the engineering. At present, the relationship between the physical and mechanical properties of high liquid limit soil and the characteristics of water-soil interaction is still not clear enough. In this study, the high liquid limit soil of Zhanjiang Avenue was selected to explore the influence of different ratios of three kinds of industrial waste residues (blast furnace slag, carbide slag, and tailing sand) on the high liquid limit soil. Aiming at the common adverse engineering geological phenomena of high liquid limit soil, such as easy disintegration, dry shrinkage crack, and easy uplift in water, the effects of different industrial waste residues on the water-soil interaction characteristics of high liquid limit soil are explored through disintegration and crack tests. In addition, the effects of different kinds and ratios on the free expansion rate, pH, unconfined compressive strength, and shear strength parameters of high liquid limit soil were studied. The improvement mechanism of different industrial waste residues on the engineering properties of high liquid limit soil is discussed in terms of mineral composition and microstructure. Based on the experimental results of this study and considering the cost and engineering practice, it is suggested that the modified carbide slag optimal ratio of high liquid limit soil of Zhanjiang Avenue is 8%. The results can provide certain guidance for the improvement and application of different industrial waste residues on high liquid limit soil to achieve the effect of sustainable development.

Analysis of fluidized zone in transparent soil under jet induced by pipe leakage

Jets caused by burst tubes erode the surrounding soil, eventually leading to issues such as ground collapse. It is therefore highly important to study the mechanisms of soil erosion caused by jets after pipeline leakage. To investigate the water–soil interaction mechanisms of pipe leakage, this study used transparent soil and developed a three-dimensional experimental device to observe the fluidization process. Changes in the boundary of the fluidization transition area were investigated, and a formula for calculating the soil damage area was derived. The results showed three different shapes of the fluidized cavity appearing in the fluidization process. The particles initially moved upward and then gradually transitioned into a state of backflow. The effects of particle size, upper load, and porosity on fluidization were also analyzed. It was found that soil with a large particle size and a lower porosity under a heavy upper load can effectively restrain fluidization. Therefore, large-diameter and dense soil can be used as pipe-covering material.

A Geotechnical Analysis to Assess the Effect of Slow-Moving Landslides on Historic Masonry Churches

ABSTRACT The protection of cultural heritage from water-soil interaction related threats is a crucial challenge for the scientific community. Among the hazards threatening heritage buildings, slow-moving landslides have been recently found to produce significant damage to historic masonry churches. However, assessing the effects of these phenomena is very challenging, as detailed information about slow-moving landslide movements is not generally available. To tackle this problem, geotechnical analyses can be performed, which enable the landslide-induced soil displacement profiles to be predicted. In view of this, this paper investigates the effects of slow-moving landslides on historic masonry churches by performing geotechnical analyses on two case studies located in the Liguria region (Italy). For each case study, limit equilibrium (LE) and finite element (FE) analyses were carried out with reference to representative sections of the slope on which the building was located. Different scenarios of water table levels were also simulated to evaluate a potential evolution of the slope stability conditions towards failure. Finally, the damage level of the building under study was assessed through a damage criterion available in the literature and compared with the severity of the damage observed on site.

Analytical solution for kinematic response of offshore piles under vertically propagating S-waves

This study develops an analytical framework to investigate the kinematic response of offshore piles under vertically propagating S-waves considering hydrodynamic pressure. The hydrodynamic pressure is calculated by using the radiation wave theory. The offshore pile and saturated soil are described by the Euler-Bernoulli beam theory and Biot's poroelastic theory, respectively. The motion of water, scattered field soil and free field soil are derived from governing equations separately. Neglecting water-soil interaction, the rigorous solution for the translational kinematic response factor and curvature ratio along the pile shaft are then obtained based on the boundary conditions of pile-soil and pile-water interaction. The rationality and accuracy of the proposed mathematical model have been verified by comparing the calculated results with the existing studies. Parametric analyses are finally conducted to investigate the influence of hydrodynamic pressure, water depth, embedment depth, slenderness ratio and soil porosity on the kinematic response of offshore piles. The results show that the frequency corresponding to the strongest kinematic response of piles will be overestimated while curvature ratio along the pile shaft will be underestimated if the hydrodynamic pressure is not taken into consideration.

Phytomanagement of Pb/Zn/Cu tailings using biosolids-biochar or -humus combinations: Enhancement of bioenergy crop production, substrate functionality, and ecosystem services.

The extreme characteristics of mine tailings generally prohibit microbial processes and natural plant growth. Consequently, vast and numerous tailings sites remain barren for decades and highly susceptible to windblown dust and water erosion. Amendment-assisted phytostabilization is a cost-effective and ecologically productive approach to mitigate the potential transport of residual metals. Due to the contrasting and complementary characteristics of biosolids (BS) and biochar (BC), co-application might be more efficient than individually applied. Studies considering BS and BC co-application for multi-metal tailings revegetation are scarce. As tailings revegetation is a multidimensional issue, clearly notable demand exists for a study that provides a comprehensive understanding on the co-application impact on interrelated properties of physicochemical, biological, mineral nitrogen availability, metal immobilization, water-soil interactions, and impacts on plant cultivation and biomass production. This 8-month greenhouse study aimed at investigating the efficacy of co-application strategies targeting BS and carbon-rich amendments (BC or humic substances (HS)) to phytomanage a slightly alkaline Pb/Zn/Cu tailings with bioenergy crops (poplar, willow, and miscanthus). A complementary assessment linking revegetation effectiveness to ecosystem services (ES) provision was also included. Owing to their rich nutrient and organic matter contents, BS had the most pronounced influence on most of the measured properties including physicochemical, enzyme activities, NH4+-N and NO3--N availability, immobilization of Zn, Cu, and Cd, and biomass production. Co-applying with BC exhibited efficient nutrient release and was more effective than BS alone in reducing metal bioavailability and uptake particularly Pb. Poplar and willow exhibited more superior phytostabilization efficiency compared to miscanthus which caused acidification-induced metal mobilization, yet BC and BS co-application was effective in ameliorating this effect. Enhancement of ES and substrate quality index mirrored the positive effect of amendment co-application and plant cultivation. Co-applying HS with BS resulted in improved nutrient cycling while BC enhanced water purification and contamination control services.

Characteristics and predictive models of hillslope erosion in burned areas in Xichang, China, on March 30, 2020

Wildfires often greatly aggravate hillslope erosion, which is a complex, highly dynamic and constantly changing water-soil interaction process. In this study, the remote sensing interpretation, field investigation, in-situ soil erosion pins experiments, and laboratory test were used to examine the controlling factors of post-fire hillslope erosion after the Xichang Fires occurred on March 30, 2020, in southwest Sichuan Province, China. We developed an empirical model to predict predicting post-fire hillslope erosion, and evaluated the model performance at watershed scale combined with the Sediment Delivery Ratio model (SDR). The controlling factors of hillslope erosion (fire severity, soil properties, rainfall, and topography) were collected. The correlations between rainfall events-based hillslope erosion depth (HED) and the controlling factors were examined. The results show that the fire severity has the strongest correlation, followed by soil properties, rainfall, and topography. The new predictive models were developed using multiple linear and non-linear (power law relationship) regression based on the normalized differenced Normalized Burn Ratio (ndNBR), soil erodibility (K), accumulated rainfall erosivity (∑R) and topographic factor (LS). Then, the methods were evaluated by comparing the predicted and observed values on the testing subset based on the statistical coefficients including R-squared, root mean squared error (RMSE) and discrepancy ratio (DR). The results suggest that the developed empirical model based on multiple non-linear (power law relationship) has a better performance (R-squared: 0.600, RMSE: 1.948), and the discrepancy ratio of 87.2% data range from 0.5 to 2. The model was used to estimate the spatial distribution of hillslope erosion depth across the entire study area, and the sediment yield at watershed scale (WSY) combined with the SDR model. The comparison between the observed sediment mobilized by debris flow and the predicted WSY shows that the model combined with the SDR showed an acceptable performance at watershed scale.

Soil-water adaptive management process: The case of on-site wastewater treatment systems in peri-urban areas in France

This paper proposes a contribution to tackle urban sanitation issues giving some hindsight on a place-based science-practice collaborative project. Insights from a French public service in charge of On-site Wastewater Treatment Systems (OWTS) highlighted the need to deepen the understanding of soil infiltration assessments and to clarify their relation to some misunderstandings between actors. The initial aim was to explore how a knowledge based approach can offer an original perspective to historical “septic tanks” and overcome technical and organizational difficulties. In this work we consider OWTS as hybrid infrastructures necessary to collect, transport, treat and dispose of domestic wastewater on the plot where it is generated. We suppose that OWTS adaptive management (sludge not included) offer many opportunities regarding water circulation (ecological function), infrastructure diversity (redundancy), and soil-based decision making (spatial planning). The main objective of this paper is to document the French sociotechnical configuration through the interplay between soil and water actors, OWTS technics and local institutions. The originality is to look at OWTS through the lens systemic perspective of Nature-Based Solutions (NBS). We first contextualize OWTS implementation and planning by presenting technical design studies (water-soil interactions, indicators assessment) and the diversity and capacity of actors. Second, we build on the application of a soil-based methodology in a peri-urban district to provide a place-based outlook on the influence of soil infiltration rates variability in day-to-day management. While the current consideration given to soil infiltration rate in OWTS design studies created a situation of conflicts and contestations between actors, a sociotechnical transition is taking place with new regulations and innovative energy-driven device. Moreover, collective infrastructure for domestic wastewater is currently challenged by densification constraints in metropolitan areas (urban sprawl regulation). As a consequence, resolving binding measures for indicators assessment would support OWTS integration into mainstream urban development. Careful investigation of soil hydraulic functions is thus a steppingstone in the search for an adaptive strategy both at the plot and the neighborhood scales. Not only OWTS are opportunities to support the adaptive management process in the water sector, but OWTS have also the potential to improve soil-based decision-making in urban areas. Finally, valuating OWTS as useful NBS for wastewater management in urban areas supports the evaluation of soil capacities to deliver ecosystem services and contributes to justify land-use changes on a functional knowledge basis.

Hydrothermal and magmatic contributions to surface waters in the Aso caldera, southern Japan: Implications for weathering processes in volcanic areas

The role of hydrothermal fluids in the dissolution of primary minerals in volcanic areas, hotspots of silicate weathering at the global scale, is not well quantified. This study aims to determine the hydrothermal contribution to the lateral export of solutes from the Aso caldera, southern Japan. A set of indicators for the hydrothermally related contribution is systematically discussed. Spring, groundwater and river water samples were collected along the two main rivers of the caldera, and their major and trace element concentrations, as well as the stable isotopic compositions of water (δ2Η and δ18O), dissolved inorganic carbon (δ13C), and sulphate (δ34S and δ18O) were analysed. Hydrothermal springs in the study area are associated with a substantial sulphate contribution of magmatic origin. In contrast, the hydrochemistry of non-hydrothermal springs reflects surface water-soil interactions. In particular, non-hydrothermal waters have significantly higher selenium to sulphate ratios than hydrothermal waters. The selenium to sulphate ratios allow to distinguish two different sulphur sources in the Aso catchment: hydrothermal waters impacted by the oxidation of sulphides or controlled by disproportionation reactions of SO2, and non-hydrothermal sulphate. Overall, the results show that hydrothermal waters strongly influence the sulphur budget, accounting for 67 to 91% of the total sulphate flux at the caldera outlet. The dissolution of magmatic CO2 and SO2 contribute to >60% of the observed weathering fluxes in this volcanic area. This suggests that magmatic gases and hydrothermal fluids should be considered for the estimation of biogeochemical budgets at the regional and global scales. However, the temporal variation of the magmatic activity and its effect on the chemistry of waters have to be investigated in future work.

Dynamic responses of an end-bearing pile subjected to horizontal earthquakes considering water-pile-soil interactions

An analytical solution is developed to investigate the seismic responses of end-bearing piles considering water-pile-soil interactions. The pile is assumed to have a linear viscoelastic and circular cross-section. The soil and water are modelled as linear viscoelastic media and linear acoustic media, respectively. The seismic responses of the free-field soil displacement under horizontal earthquakes are first given. Neglecting water-soil interactions, analytical expressions for the impedance of the soil and water media are further derived. The pile displacements induced by horizontal earthquakes are then obtained based on the continuity conditions of the pile with soil and water. The present solution is compared with the substructure method to verify the rationality of the present analytical solution. Parametric analyses are finally conducted to investigate the effects of the water, soil, and pile parameters on the seismic responses of the pile. The results indicate that it is necessary to consider the water-pile-soil interaction in the design of piles installed in offshore areas.

Geochemical proxies for water-soil interactions in the hyperarid Atacama Desert, Chile

The Atacama Desert is the oldest and driest non-polar desert on Earth. Millions of years of hyperaridity enabled salt accumulations through atmospheric deposition. These salts can serve as proxies to decipher the interaction between water and soil as well as to understand the habitability with changing environmental settings. Therefore, we investigated four soil profiles regarding their mineralogy, salt abundance, and sulfate stable isotopic composition. The profiles were located along an elevation transect in the hyperarid region southeast of Antofagasta, Chile. The two lower sites situated on the distal parts of inactive alluvial fan deposits were subject to occasional fog occurrences. The upper steeper-sloped sites experienced no fog but are subject to minimal erosion. In all soil profiles, sulfates are the dominant salts showing a downward transition from gypsum to anhydrite that is accompanied by an increase of highly soluble salts and a decrease of sulfate δ34S and δ18O values. These trends are consistent with downward directed water infiltration during rare rain events causing salt dissolution followed by precipitation within the deeper soil column. This conclusion is also supported by our Rayleigh fractionation model. We attribute the presence of anhydrite at > 40 cm depth to the cooccurrence of nitrate and chloride salts, which decreases water activity during sulfate precipitation and therefore drives anhydrite formation. Along the elevation transect, the total salt inventories of each profile show a trend for nitrates and chlorides concentration decreasing with elevation. This observation together with the sulfate stable isotopes indicates a fog-independent source and suggests remobilization of soluble salts through enhanced washout from hillslopes to alluvial fans. These findings are essential for assessing the long-term regional habitability of hyperarid environments and have also relevance for Mars.

ANALASIS OF WATER-STRUCTURE-SOIL DYNAMIC INTERACTION UNDER EARTHQUAKES

In this paper, we establish an efficient numerical model of water-structure-soil systems under seismic action based on ABAQUS to analyze the influence of water-structure and water-soil interaction on the response of the structure, soil and water under different water depths. Under the action of horizontal ground motions, the results show that the influence of the water-soil interaction on the response of the system is much less than that of the water-structure interaction, and that the influence on the response of the structure, soil and water is negligible. Under the action of vertical ground motions, the effect of water-structure interaction on system response is much less than that of water-soil interaction, and that the water-structure interaction has little influence on the system response. Therefore, only the water-soil dynamic interaction needs to be considered in theoretical simplification analysis.

Concentration–Discharge Relationships in Runoff Components during Rainfall Events at the Hydrohill Experimental Catchment in Chuzhou, China

Concentration–discharge (C-Q) relationships are a convenient and increasingly popular tool for interpreting the episodic hydrochemical response to the varying discharge in small basins, providing insights into solute transport and streamflow generation. While most studies are focused on total runoff, this study quantified C-Q relationships in four runoff components during precipitation events at the Hydrohill experimental catchment in Chuzhou, China. This unique artificial catchment is carefully engineered, allowing observations of the interacting runoff components that collectively determine total flow issuing from the catchment. The four runoff components, or flow paths, include surface runoff (SR), shallow interflow at 0–30 cm depth (SSR30), deeper interflow at 30–60 cm depth (SSR60), and groundwater flow at 60–100 cm depth (SSR100). Water samples were collected during three consecutive precipitation events to study how the concentrations of primary solutes vary with flow. Analysis of C-Q relationships reveals that concentrations of Na+, Ca2+, Mg2+, SO42−, and HCO3− in the four runoff components had a negative relationship with discharge, while the concentration of K+ and Cl− were negatively correlated with discharge in SR and SSR30 but positively correlated in SSR60 and SSR100. Further insights were gained from principal component analysis. Three eigenvectors explained 92% of the variability in hydrochemistry in surface runoff, while two eigenvectors explained most of the variability in the hydrochemistry of subsurface flows observed at various depths in the soil profile (73% for SSR30, 79% for SSR60, and 76% for SSR100). PC1 (the first Principal Component) can be interpreted as a salinity factor, deriving from carbonate minerals such as dolomites and limestone minerals. Results indicated that leaching and dilution processes, water–soil interaction, and macropore flows in soils are the primary factors controlling the C-Q relationships. Our work sheds light on the coupled processes and streamflow generation mechanisms that control water quality at the catchment scale.