Orals: Mon, 28 Apr | Room 2.44
Studying hydrological responses to rainfall events at the catchment scale is a foundational approach to understanding water and solute mobilization processes because it provides insights into the runoff generation mechanisms. These responses are reflected not only in variations in stream discharge, but also in shifts in groundwater tables, particularly within hydrologically connected near-stream riparian zones. In this context, cross-ecoregional comparisons offer additional value as they can identify both shared and distinct drivers of hydrological responses to rainfall events across diverse system settings. We analysed rainfall events in four forest headwater catchments spanning four different ecoregions: boreal, temperate, subhumid Mediterranean, and semiarid Mediterranean. We aim to evaluate the role of hydroclimatic predictors, including rainfall event characteristics and antecedent hydroclimate (e.g. soil moisture) conditions, in shaping hydrological responses. These responses include variations in stream discharge and riparian groundwater table, as well as the relationship between these two variables, with particular attention to hysteresis patterns. Our results show that drier antecedent soil moisture was linked to anticlockwise hysteresis loops, where stream discharge responded faster than riparian groundwater tables to rainfall events. This observation was particularly prominent at the temperate site. Furthermore, distinct hydrological response patterns at the Mediterranean sites emerged only during larger events, while the responses observed at the boreal and temperate sites remained consistent regardless of storm size. We will discuss these and further findings in the context of hydrological connectivity, wetness state, and the hydrological conductivity of the riparian layers activated during rainfall events. This approach has the potential to offer valuable insights for both scientific assessments and the management of land-water connectivity across ecoregions with contrasting hydroclimates.
How to cite: Ledesma, J. L. J., Bernal, S., and Musolff, A.: Drivers of stream and riparian hydrological responses to rainfall events in forest headwater catchments across ecoregions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2243, https://doi.org/10.5194/egusphere-egu25-2243, 2025.
Hydrologists have long recognized that stream discharge responds almost instantaneously to rainfall or snowmelt events in headwater catchments, even though the water that comprises the discharge may be years or decades old. This rapid mobilization of old water arises from the difference between the celerity (or rate of pressure propagation) and velocity (or rate of water movement) of a wetting front through the subsurface. The ratio of celerity to velocity, known as the kinematic ratio, can vary multiple orders of magnitude between catchments — and across different storm events within the same catchment — but the underlying mechanisms that control variations in kinematic ratio remain poorly understood.
To address this knowledge gap, we present a series of experimentally constrained hydrologic simulations that investigate how watershed properties (e.g., depth to the water table and aquifer transmissivity) and system states (e.g., antecedent soil moisture) control differences in celerity and velocity at the plot, hillslope, and catchment scales. Simulation results are validated against rainfall–runoff experiments that use isotopic tracers to measure residence time. Global sensitivity analyses reveal that, at the plot scale, the kinematic ratio of a wetting front through the vadose zone is predominantly controlled by antecedent water content. At the hillslope and catchment scales, this relationship becomes more complex and largely depends on depth to the water table and aquifer transmissivity. This work provides new insights into the subsurface controls on subsurface flow and pressure propagation, with implications for understanding the hydrologic behavior of catchments during storm events and resultant impacts on water quality.
How to cite: Perzan, Z. and Bauser, H.: Exploring celerity–velocity differences in headwater catchments across scales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2953, https://doi.org/10.5194/egusphere-egu25-2953, 2025.
Subsurface storage is inherently difficult to quantify, but strongly affect the ecohydrological resilience of landscapes, which can be defined as the degree to which catchment can maintain key aspects of physical functionality in terms of water resource provisioning and biomass production in response to climatic and other stressors such as drought. These functions, and in particular storage dynamcis, are commonly studied in small-scale experimental settings, at larger regional scales or from purely modelling perspectives. To move the field forward, we urgently need to better characterise and quantify the 3-dimensional water storage continuum at mesoscale catchment (101-102 km2), as its this scale which is most tangible and relevant for land managers, and where physical process-based evidence can still be obtained to understand how sensitivities change between zones of deficit and storage during periods of drought. We present findings from a long-term, drought sensitive experimental catchment in Germany. We integrated extensive hydrometric and water stable isotope approaches into tracer-aided modelling to quantify spatial and temporal storage dynamics. We argue that a spatially distributed understanding of how underlying ecohydrological processes affect drought evolution at the mesoscale is fundamental for future assessment of water storage dynamics, water availability and provision of wider ecosystem services in a changing climate. As such, this proposed approach can form science-based evidence for new concepts on the regulation of catchment ecosystem services and help building societal resilience to droughts.
How to cite: Tetzlaff, D., Laudon, H., and Soulsby, C.: The concept of the water storage continuum to increase ecohydrological resilience of mesoscale catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3998, https://doi.org/10.5194/egusphere-egu25-3998, 2025.
Eco-hydro-meteorological variables (EHM) are key indicators for assessing the impacts of climate change on ecosystems, affecting hydrological processes and the resilience of forest systems. Meteorological forcing, such as precipitation and vapor pressure deficit, notably determines soil moisture variability, strongly related to tree transpiration and sap flow rate. In turn, soil moisture is affected by tree uptake. Understanding the feedback among these variables is crucial for effectively managing water resources and more robust predictions of the effect of climate change-induced droughts. However, few works have been conducted to disentangle the feedback of EHMs over time, frequency, and space domains in mountain forested catchments, especially in the Mediterranean region. To fill this gap, wavelet transform and coherence analysis were applied to investigate physical processes and their interaction in time and frequency domains.
We monitored EHMs for two years in a small sub-catchment (0.31 km2) of the Re della Pietra experimental catchment, Central Italy. The elevation and slope of the sub-catchment are about 940 m a.s.l and 36°, respectively, with a geological substrate of sandstones that promotes the development of well-drained sandy loam soils with a depth larger than 50-80 cm. The area is classified as a temperate Mediterranean climate with annual averages of 1300 mm for rainfall and 10.5 °C for temperature. The vegetation cover consists of pure beech forest. We monitored climatic variables with a weather station in the upper part of the sub-catchment, while soil moisture and sap flow variation were collected at different positions along a steep hillslope. We performed wavelet transform analysis to explore the EHMs variability over time, frequency, and space, while through wavelet coherence, we investigated the conditions and factors that influence the feedback dynamics of EHMs.
Wavelet transform analysis highlights significant rainy periods exceeding the 1024-h frequency and a strong vapor pressure deficit seasonality, defining the alternation between dry and wet seasons. Soil moisture variability at the bottom slope position significantly differs from the upslope and midslope, and recovery periods following the dry season are more evident in the upperslope position than in the middle. High power values for sap flow at 12/24-h frequencies, revealing the daily tree transpiration, differ for the investigated positions. Wavelet coherence analysis remarks differences depending on the hillslope position. High coherence values between sapflow and soil moisture are shown for frequencies between 12/24-h for most of the tree growing season, with soil moisture driving sap flow. However, in the upslope position, the early stop of tree transpiration caused by sharply reduced soil moisture resulted in low coherence values. High coherence values are also highlighted for frequencies larger than 24-h, showing the sap flow leading to soil moisture. Sap flow strongly correlates with vapor pressure deficit in all frequencies of the monitored period, while coherence with precipitation is significant only for frequencies greater than 64-h.
Through the application of wavelet analysis, this study presents an in-depth investigation of the complex relationships between eco-hydro-meteorological dynamics in forest catchments.
How to cite: Murgia, I., Kaffas, K., Verdone, M., Manca di Villahermosa, F. S., Dani, A., Preti, F., Segura, C., Massari, C., and Penna, D.: Revealing the interrelation among eco-hydro-meteorological variables in a forested Mediterranean catchment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1066, https://doi.org/10.5194/egusphere-egu25-1066, 2025.
Preferential flow (PF) is a key hydrological process that influences water infiltration, soil moisture redistribution, and streamflow generation. In Mediterranean forested catchments, the dynamics of PF and its controls remain largely underexplored. Here, we investigated PF mechanisms and their impact on hydrological response in the Re della Pietra experimental catchment (2 km²) in the Tuscan Apennines, central Italy. Two hillslope transects with soil moisture sensors at shallow (15 cm) and deep (35 cm) layers were monitored for 34 and 18 months, respectively. A supervised Random Forest (RF) classification model was employed to identify the dominant controls on PF initiation across varying hydrological, topographical, and soil conditions.
Results showed that antecedent soil moisture was the primary driver of PF in one of the hillslopes, while dry bulk density dominated in the other, highlighting spatial heterogeneity in PF controls. Precipitation characteristics played a secondary role, with PF more likely during dry periods at both sites. PF events altered streamflow dynamics, producing early hydrograph peaks and sustaining flow during recession phases. Mixed flow events, combining sequential and non-sequential soil moisture responses, generated the highest total streamflow volumes, emphasizing the contribution of PF to catchment connectivity.
These findings underscore the importance of PF in Mediterranean hydrology, where alternating wet and dry periods intensify its effects on water redistribution and streamflow generation. By combining extensive field monitoring with machine learning, this study offers new insights into the interplay between PF and catchment hydrological responses.
How to cite: Verdone, M., Kaffas, K., Murgia, I., Menapace, A., Macchioli Grande, M., Dani, A., Manca di Villahermosa, F. S., Preti, F., Segura, C., Massari, C., Klaus, J., Borga, M., and Penna, D.: Soil properties, topography, and meteorological forcing control preferential flow and streamflow generation in a Mediterranean forested catchment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16458, https://doi.org/10.5194/egusphere-egu25-16458, 2025.
In many natural landscapes, subsurface stormflow (SSF) is a runoff-producing mechanism which can substantially contribute to the storm hydrograph of a stream. Despite its importance, there is a lack of systematic studies exploring SSF across sites with different land uses and hydrogeological characteristics. Thus, we face limitations to properly conceptualize and parametrize hydrological models.
In order to gain a better understanding of the processes governing SSF, multiple SSF-capturing trenches were excavated. The selected trench sites span over different land uses, geology, soils and climates in Germany and Austria. Depending on local boundaries, the trenches were designed with a width of 11–15 m allowing to collect water flowing laterally at depths of up to 1–3 m. Using separate drainage pipes, the trench’s face is divided into an upper and lower flow-capture zone. Combining the measurements of vertically separated SSF outflow with upstream monitored groundwater levels and soil moisture dynamics, allows to estimate flow propagations along the hillslope.
Besides the continuous monitoring, these installations were used to measure SSF events triggered by artificial rainfall. In this study we investigated the SSF response at 11 different trench sites under controlled conditions using a large-scale (200 m²) experimental sprinkling system in combination with deuterated water, which served as an artificial tracer. The irrigation was applied at a rate of ca. 16 mm h-1 for about 3 hours. The analysis focuses on trenchflow dynamics (e.g., timing and magnitude of the peak flow, recession curve analysis) and their relationship with changes in soil moisture and groundwater level. The experiments highlighted the vastly different responses between sites; while some trenches remained dry, others were characterized by extremely high subsurface runoff coefficients and short response times.
How to cite: Thoenes, E., Kohl, B., Lechner, V., Pyschik, J., Weiler, M., and Achleitner, S.: Exploring Subsurface Stormflow through Sprinkling Experiments at Multiple Trenchsites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15757, https://doi.org/10.5194/egusphere-egu25-15757, 2025.
Subsurface storm flow (SSF), also referred to as interflow, plays an important role in runoff generation and flood events at the watershed scale. Its transient and spatially variable nature, however, presents significant challenges in investigating and measuring this subsurface process. Framed within the SSF Forcing research unit, supported by the German Research Foundation (DFG) and Austrian Science Fund (FWF), this study explores several methodologies for detecting and characterizing SSF at the plot scale with a focus on understanding its vertical and lateral flow components. The research unit goal is to enhance the accuracy of SSF representation in hydrological models, enabling better flood predictions and water management practices.
This research employs multiple techniques, including Electrical Resistivity Tomography (ERT), Time-Domain Reflectometry (TDR), and artificial rain simulations (ARS). These methods allow for the detailed examination of hydrological processes under controlled conditions, facilitating a comprehensive understanding of the dynamics of subsurface flow. TDR is used to quantify vertical water movement, providing baseline data for interpreting ERT profiles. Simultaneously, the use of two parallel ERT profiles within the irrigation plot enables continuous monitoring of subsurface flow pathways. These profiles capture both vertical infiltration and lateral interflow, which are key components of SSF.
While ERT and ARS are well-established techniques for tracing infiltrating water, distinguishing between vertical and lateral flow remains a challenge. The strong changes in the surface resistivity created by the artificial rainfall complicates the differentiation between vertical infiltration and lateral flow, due to its intrinsic limitations and the inversion artefacts that are exacerbated especially close to the surface. To address this, an 2D ERT reference line is positioned below the primary plot to isolate lateral flow from the influence of vertical infiltration. This reference line serves as a control, allowing for the validation of vertical and lateral interflow dynamics and ensuring the detection of deeper subsurface flows that are not influenced by direct rainfall input.
In addition, the significant change in the surface resistivity occurring within the ARS plot influences the resistivity measurements outside the irrigation plot in the reference ERT line, due to the tridimensionality of the physical phenomena. Therefore, this study primarily evaluates the effect of the irrigated waterfront on the 2D ERT resistivity measurements using forward modelling to subsequently focus on the lateral component of the subsurface runoff. Hence, it assesses the feasibility of using 2D-ERT data to identify subsurface stormflow in combination with ARS, addressing the challenge of differentiating flow components and mitigating inversion artifacts in the resistivity profiles. Overcoming these challenges is necessary for improving the reliability of subsurface flow detection using ERT in hydrological research.
How to cite: Cordero Perez, V. and Lechner, V.: Investigating Subsurface Stormflow: 2D-ERT and Artificial Rain Simulations for Identifying Vertical and Lateral Flow Components, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10810, https://doi.org/10.5194/egusphere-egu25-10810, 2025.
The depth of the soil profile is a critical factor in irrigation engineering, often estimated as 1–1.5 meters, usually referred to as root zone depth below ground based on crop and soil types, as well as practitioner experience. This traditional approach can lead to errors in irrigation planning. This study combines Richards' equation with the Soil Conservation Service Curve Number (SCS-CN) method and soil column principles from geotechnical engineering to create a formula for determining the adequate soil profile depth that provides the maximum water storage capacity. This soil profile depth depends on the soil's hydraulic and storage properties. The relationship is then linked with the SCS-CN parameter (curve number) for practical applications like irrigation scheduling. Results of this study show that for sandy soil, the proposed method can save 83% and 75% of irrigation water compared to the traditional fixed depths of 1.5m and 1m, respectively. For clayey soil, water savings can reach 94% and 92%, respectively. This method also helps to estimate field capacity, average moisture content, and maximum water storage capacity for various soil types, improving water management and irrigation efficiency in field applications.
How to cite: Sharma, D., Mishra, S. K., and Pandey, R. P.: Role of Soil Profile Depth in Effective Irrigation Scheduling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12775, https://doi.org/10.5194/egusphere-egu25-12775, 2025.
Baseflow constitutes over 50% of streamflow in mountainous regions of the Western United States, making its accurate quantification essential for water management and decision-making. Traditional automated baseflow separation methods are often arbitrary and ambiguous, complicating their validation. This study developed an integrated hydrologic model that integrated the exchange between surface and subsurface flows to physically quantify the baseflow component in a snow dominated catchment. Using the model's simulated baseflow and streamflow as a control, we evaluated four common baseflow separation methods: the Pettyjohn and Henning (PH) graphical, the United Kingdom Institute of Hydrology (UKIH) graphical, the Eckhardt digital filter, and conductance mass balance (CMB) methods. Both UKIH graphical and Eckhardt filter methods performed relatively well with high modified Kling-Gupta Efficiency (mKGE) (0.72 and 0.65, respectively) and Nash-Sutcliffe Efficiency (NSE) (0.58 and 0.62, respectively) values. However, the UKIH graphical method performed poorer than the Eckhardt filter method in average and dry years when stream hydrographs resemble unimodal peaks, common in snow-dominated catchments. Additionally, the Eckhardt digital filter showed better matching of the temporal dynamics. The PH graphical and CMB methods did not perform satisfactorily with low mKGE and NSE values. The PH graphical method has consistently overestimated baseflow with an average baseflow index BFI of 85%, whereas the CMB method has consistently underestimated baseflow with an average BFI of 24%. Our findings suggest that integrated hydrologic models, when calibrated, provide a quantitative way to evaluate and improve existing baseflow separation methods. Additionally, caution should be exercised when applying automated baseflow separation methods in snow-dominated catchments, and future work is needed to thoroughly evaluate these methods in catchments with diverse hydroclimate conditions.
How to cite: Shuai, P. and Othman, J.: Quantitative Evaluation of Baseflow Separation Methods Using an Integrated Hydrologic Model: A Case Study in a Snow-Dominated Watershed, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12434, https://doi.org/10.5194/egusphere-egu25-12434, 2025.
Streamflow loss is a key process for stream drying and has been studied across various environments and scales. However, there has been little effort to systematically organize processes that drive streamflow loss. We introduce a conceptual framework of “streamflow degeneration” and outline how this framework facilitates the organization of the processes based on subsurface characteristics and settings. The underlying principle for organizing is based on subsurface’s capacity to convey water away from the stream. Using this transport capacity to organize processes of streamflow loss is feasible because it relies on the same principle governing streamflow generation processes. The streamflow degeneration framework includes six distinct streamflow loss processes. We compare how these streamflow loss processes modify a hydrograph along a stream reach under idealized conditions. We call for both field and modeling studies to build on this conceptual framework to define key questions on the significance of streamflow loss. Additionally, we propose various approaches the community may use to answer these questions. The streamflow degeneration framework will help identify commonalities in drying regimes across streams, allowing the generalization of findings from field and modeling studies across various contexts. Organizing streamflow loss according to the streamflow degeneration framework might ultimately lead to the discovery of hydrological laws and the transferability of this understanding of streamflow loss to unstudied reaches.
How to cite: Glaser, C., Gannon, J. P., Godsey, S. E., Grande, E., and Klaus, J.: Streamflow (de)generation - how do streams lose flow?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19662, https://doi.org/10.5194/egusphere-egu25-19662, 2025.
The (sub-)surface hydrological processes vary over time and space, and the Baseflow Index (BFI) which is used to characterize aquifer discharge and river sustainability is no exception. BFI is defined as the proportion of stable baseflow come from aquifers to the total streamflow. Previous studies have constructed various models based on climatic and geomorphological characteristics to estimate the BFI, aiming to identify key driving factors and predict hydrological behavior in ungauged regions. However, these studies have two primary limitations: (1) they represent a catchment relied on a single long-term BFI, overlooking inter-annual variability, and (2) they utilized global models that assume constant responses of all catchments to factors. To address these limitations, this study compiled a panel data of 2,953 samples, comprising BFI, climate, and geomorphological characteristics of catchments from 60 gauging stations with more than 30 years of daily streamflow records in Taiwan. The identification of factors through correlation analysis and Geographically and Temporally Weighted Regression (GTWR) model. The results of the spatiotemporal dynamics revealed that the BFI of most stations exhibited a significant increasing trend, as well as notable positive spatial autocorrelation. Model comparisons indicated that the GTWR model outperformed the GWR and OLS models with lower AICc. Moreover, the inclusion or exclusion of spatiotemporal heterogeneity may lead to contradictory outcomes in driving factor identification. Correlation analysis without heterogeneity showed that elevation had the strongest negative correlation with BFI. However, the GTWR model indicated that almost all factors exhibited bi-directional influences on BFI varying across time and space. The importance of elevation was not significant in GTWR. Additionally, the rainfall intensity is the only one-way factor that had a negative influence on BFI. This study underscores the influence of climatic and geomorphological factors on BFI exhibits pronounced spatiotemporal heterogeneity. Neglecting spatiotemporal heterogeneity could lead to overestimation or underestimation of the importance of factors. The findings provide valuable insights into other hydrological processes and highlight the necessity of incorporating spatiotemporal heterogeneity analysis in catchment process and groundwater resource assessments.
How to cite: Chen, H.-Y. and Yeh, H.-F.: Spatiotemporal Dynamic and Drivers of Baseflow Index in Taiwan’s Catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5555, https://doi.org/10.5194/egusphere-egu25-5555, 2025.
Past research on the hydrogeological parameters of the local aquifer has rarely utilized sequential pumping test (SPT) drawdown data collected from multiple tests at the same experimental site to comprehensively characterize the distribution fields of transmissivity (𝑇) and storage coefficient (S), as well as their reciprocity. To address this gap, this study aims to collect sequential SPT drawdown data from an experimental site located at the northeast corner of the well field at Yunlin University of Science and Technology, Douliu City, Yunlin County. The dataset spans five pumping tests conducted in 2010, 2012, 2013, 2018, and 2021, providing a unique opportunity to examine the spatiotemporal characteristics of these hydrogeological parameters.
The study first analyzes the reciprocity of drawdown levels observed at the same monitoring well under varying conditions across the five tests, uncovering the influence of temporal and spatial factors on hydrogeological behavior. Subsequently, the drawdown data is integrated into a hydraulic tomography (HT) numerical approach using the VSAFT2 model—a two-dimensional simulation tool for variably saturated flow and transport based on the modified method of characteristics. Through this method, the distribution fields of 𝑇 and 𝑆 are reconstructed for each case. Finally, the study conducts an in-depth comparison of the distribution fields of 𝑇 and 𝑆 across the five years, exploring their temporal evolution, spatial variability, and reciprocity. This research seeks to provide a clearer understanding of the dynamic characteristics of hydrogeological parameters over time and space, laying a solid foundation for further studies and practical applications in the field.
How to cite: Hsu, Z.-J., Lin, H.-R., and Wen, J.-C.: Exploring Hydrogeological Reciprocity: A Case Study in Temporal and Spatial Variability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8592, https://doi.org/10.5194/egusphere-egu25-8592, 2025.
Traditional temperature sensors often lack the capability for continuous, high-resolution soil temperature monitoring. This study employs Fiber Optic Distributed Temperature Sensing (FO-DTS) to establish a large-scale, horizontal experimental site for observing shallow soil temperature variations with high spatial resolution. The research investigates the spatial distribution of water infiltration in a retention pond by analyzing temperature variations in soil layers. The study site near Douliu Irrigation in Gukeng Township, central Taiwan, encompasses a 2-hectare retention pond comprising a precipitate pool and an infiltration pool. Fiber optic cables were deployed around both pools and buried in three layers to a total depth of 60 cm, with 20 cm intervals between each layer, enabling stratified soil temperature monitoring. By leveraging the phase delay in cyclical temperature variations between surface and subsurface layers, the FO-DTS system assesses water infiltration rates and their contribution to groundwater recharge. The results indicate that water infiltration significantly impacts soil temperature beneath the retention pond, exhibiting daily cyclical variability. The average soil temperature shows a negative correlation with depth, demonstrating that the FO-DTS effectively captures the thermal front caused by water infiltration. This approach highlights the potential of FO-DTS for accurately evaluating infiltration dynamics and its implications for regional groundwater management.
How to cite: Chen, B. C., Lin, H. R., and Wen, J. C.: Unraveling Spatial Water Infiltration Patterns in a Retention Pond Using Fiber Optic Distributed Temperature Sensor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8626, https://doi.org/10.5194/egusphere-egu25-8626, 2025.
Temperature is regarded as an effective natural tracer for analyzing river flow sources through heat budgets. This study investigates the thermal dynamics of the Ai-Liao River, Taiwan, during a dry-season period (December 6–9, 2022). A fiber-optic distributed temperature sensor (FO-DTS) was deployed along a 782-meter river section, and the HFLUX model was employed to analyze the river’s heat budget. Additionally, thermal imagery obtained via drone-assisted surveys was used to identify potential groundwater inflow locations. FO-DTS data revealed high spatial temperature variability, dividing the study area into three segments. In the upper segment, daily temperature differences (DTD) increased downstream. In the middle segment, DTD decreased downstream, while in the lower segment, DTD remained stable. The HFLUX model simulations yielded RMSE values of 0.42°C, 0.33°C, and 0.30°C for the respective segments. Results indicated that the upper segment exhibited high sensitivity to heat budget changes due to low flow. In contrast, the middle segment demonstrated increased groundwater energy contributions, with an average of −83.3 W/m² over three days, moderating DTD. Thermal imagery captured "tongue-shaped" inflow patterns along the middle riverbanks, indicating significant water source inputs. In the lower segment, increased flow stabilized DTD. The integrated analysis from observations, modeling, and thermal imagery suggests that modeled groundwater inflows predominantly enter the river as hyporheic flows.
How to cite: Yu-Cheng, C., Hsiu-Hao, Y., Yung-Chia, C., and Tsung-Yu, L.: Heat Budget Analysis of a Braided River in Taiwan Using the HFLUX Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9082, https://doi.org/10.5194/egusphere-egu25-9082, 2025.
An in-depth understanding of the transport and fate of solutes, nutrients and pollutants within a catchment is crucial to address issues related to water quality and quantity, including the protection and management of water resources. Transit Time Distributions (TTDs) of streamflow can provide useful descriptors of catchment hydrological functioning and can inform on solute transport mechanisms. They can be estimated using StorAge Selection (SAS) functions, which is a time-varying approach that describes how catchments selectively release water of different ages from storage through discharge, thereby regulating the streamflow TTDs and solute composition. For instance, the proportion of young water tends to increase during wet conditions and decrease during dry periods.
In this study, we explore how the dynamics of SAS functions can be linked to the different fluxes and state variables of a conceptual hydrological model. To achieve this, we tested various coupling strategies over the French Orgeval catchment (104 km²) in France, using chloride concentrations as a conservative tracer and the GR6J hydrological model (internal state variables). The modelling results showed that incorporating dynamic (time-varying) SAS functions is essential for accurately capturing the temporal variability observed in the chloride concentration time series. Furthermore, the results showed that the signal of inter-catchment groundwater flow (IGF), conceptually defined as the groundwater inflows and outflows across the topographic boundaries of a catchment, is the best variable for driving the dynamic of the age of the river flow.
How to cite: Rabah, A., de Lavenne, A., and Ramos, M.-H.: Toward understanding transport and chloride dynamics at the catchment scale by combining StorAge Selection functions and a hydrological model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9559, https://doi.org/10.5194/egusphere-egu25-9559, 2025.
In catchments with low permeability soils, near-surface flow pathways can quickly transport water and solutes from the hillslopes to the stream network. Gaining insight into these pathways is essential for predicting changes in stream chemistry and improving flood forecasting. Despite their importance, near-surface flow pathways have rarely been assessed for well vegetated catchments in temperate climate. To better understand the importance of these flow pathways in terms of their ability to transfer water to the stream (celerity), transport solutes (particle velocity), and their flow path lengths, we conducted artificial rainfall simulation experiments on two large (>80 m2) trenched runoff plots in a small headwater catchment underlain by gleysols in the Swiss pre-Alps. One plot is located in a natural clearing in an open mixed forest and the other in a wet pasture. Together they represent the dominant land cover types in the region.
We applied streamwater to the surface of the plots using sprinklers and tracers after overland flow and lateral flow through the topsoil had reached steady state. Deuterium-enriched water was applied to the surface via the sprinklers, while Uranine and NaCl were applied as a line tracer at multiple distances from the trench. NaBr was injected into the topsoil at ~20 cm depth. Samples of overland flow and topsoil interflow were collected for several hours after tracer application, while the sprinklers continued to apply water to the surface. To determine the lengths of the overland flow pathways, we applied brilliant blue dye on the surface at different distances from the trench. The celerity of overland flow and topsoil interflow was determined by temporarily adding more water to the surface of the plots at different distances from the runoff collectors.
The breakthrough curves for both plots highlighted the rapid transport of water and solutes, as well as the high interaction between overland flow and topsoil interflow. The average of the maximum particle velocity (calculated for the different tracers) was 51 ± 14 m h-1 for overland flow and 30 ± 9 m h-1 for topsoil interflow for the plot in the natural clearing. The particle velocity was lower for the plot in the pasture: 24 ± 1 m h-1 for overland flow and 17 ± 6 m h-1 for topsoil interflow. The celerity was 2-3 times higher than the particle velocity for overland flow and similar to the velocity for topsoil interflow. The blue dye experiments highlighted that overland flow pathways are relative short for most locations (< 5m) and confirmed the considerable interaction between overland flow and topsoil interflow. In summary, these results highlight the high connectivity between overland flow and topsoil interflow and the critical role of macropores and soil pipes in rapidly transporting water and solutes from the hillslopes to the streams.
How to cite: Leuteritz, A., Gauthier, V., and van Meerveld, I.: Celerity, velocity and flow path lengths of near-surface flow pathways: insights from tracer experiments during artificial rainfall, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10388, https://doi.org/10.5194/egusphere-egu25-10388, 2025.
Subsurface stormflow (SSF) is an essential process in runoff generation, particularly in headwater catchments where it can contribute for more than 90% of streamflow (Beasley, 1976). However, the fundamental mechanisms of SSF are still inadequately comprehended. Studies based on observing natural rainfall events provide valuable insights, but they introduce uncertainties stemming from uncertain input, particularly in forested sites where throughfall alters both the volume and isotopic composition of precipitation. To address these uncertainties and to allow detailed measurements under controlled conditions, we performed 7 sprinkling experiments with specified amount and intensities and elevated isotopic signatures.
We performed the large-scale (200 m²) artificial rainfall experiments in four low mountain and alpine catchments, each with two trenched slopes. The trenches exceeding 10 m in width were stratified to differentiate between shallow (< 1 m) and deep SSF (1 to max 3 m). We monitored groundwater levels using five wells above each trench and measured soil moisture dynamics in one profile per trench. Irrigation was applied at a rate of ~16 mm h -1 for 3 hours. The initial half served as a wetting phase without tracer, while for the latter half we added deuterated water as an artificial tracer.
Runoff was continuously measured and water samples were analysed for their isotopic composition. Deep soil cores were extracted from one trench to identify deuterated water in the soil matrix after the event. The results showed that deuterated water rapidly reached the trench outlet (within 20-40 minutes), indicating substantial preferential flow. Nevertheless, tracer water was exclusively detected in the topsoil of the soil matrix, indicating limited matrix flow. We applied mixing models that indicated that only 5-20% of the irrigation water was recovered at the outlet, with the remainder being pre-event water. We further analysed groundwater level data and soil moisture profiles to identify activated flow paths and better understand SSF dynamics.
These findings underscore the dominance of preferential flow pathways in SSF and indicate that pre-event water contributions play a major role in SSF.
Beasley, R.S. (1976) ‘Contribution of subsurface flow from the upper slopes of forested watersheds to channel flow’, Soil Science Society of America Journal, 40(6), pp. 955–957. doi:10.2136/sssaj1976.03615995004000060039x.
How to cite: Pyschik, J., Thoenes, E., Achleitner, S., Kohl, B., and Weiler, M.: Tracing Subsurface Stormflow: Insights into Preferential Flow and Pre-Event Water Contributions from Controlled Sprinkling Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10457, https://doi.org/10.5194/egusphere-egu25-10457, 2025.
Seldom observed, rock moisture greatly influences plant water availability and is an important component of the terrestrial water cycle. However, its spatiotemporal dynamics and major influencing factors in a watershed are still unclear. Here, we present the results of a year-long time-lapse electrical resistivity tomography (ERT) survey at a semi-arid watershed, the Dry Creek Experimental Watershed (DCEW) in Idaho, USA. The ERT monitoring was conducted across a ridge at the Treeline site of DCEW, and the results show a clear aspect effect on the dynamics of the subsurface water storage. The northeast-facing slope exhibits an increased weekly sensitivity to precipitation and evapotranspiration compared to the southwest slope, which has a smooth response. It also shows that the thicker regolith on the northeast slope holds more water than the thinner regolith on the southwest slope. Regarding the interaction between soil and rock moisture, the results show that there is an approximately two-week delay for the rock moisture to reach its lowest storage after the soil reaches its minimum storage in mid-August. The same delay is also observed for rock moisture during the wetting process occurring in later spring and early summer. Further work is suggested to develop a conceptual model for soil moisture/rock moisture interactions at the hillslope scale.
How to cite: Kietzmann, J., Bensel, S., McNamara, J., and Niu, Q.: Geophysical Investigation of Slope Aspect Effect on Soil and Rock Moisture Interactions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11960, https://doi.org/10.5194/egusphere-egu25-11960, 2025.
The transport of water-soluble organic matter (WSOM) during stormflow events is an important link between hillslope hydrology and biogeochemical cycling, as it determines the movement of organic carbon from soils to streams. Hydrological dynamics in hillslopes, particularly subsurface stormflow (SSF), exhibit substantial spatial and temporal variability, making quantification and generalization challenging. SSF can account for up to 90% of rainfall input to stream discharge during storm events, highlighting its importance in catchment hydrology. Despite its significance, current research frequently overlooks WSOM dynamics during SSF, which are not only key components of carbon cycling but may also serve as tracers for identifying potential critical source areas.
This emphasizes the importance of studying hillslope hydrological dynamics and determining the factors that contribute to SSF spatial and temporal variability. Furthermore, the specific flow paths within hillslopes remain poorly understood, which complicates the identification of spatial sources and transport mechanisms for organic carbon. To fill these knowledge gaps, we conducted a field study in the Black Forest, Germany, using a trench system to collect lateral subsurface flows at two depths (0-100 cm and 100-200 cm) over several rain events. We analysed WSOM concentration and quality using absorbance and fluorescence properties to assess the variability in critical source areas. We also conducted isotopic analyses of oxygen (δ¹⁸O) and hydrogen (δ²H) of the same water samples to infer flow pathways with a conservative tracer.
This approach provides valuable insights into the temporal dynamics and spatial heterogeneity of SSF. Our findings will contribute to our understanding of flow paths, transit times, and the characteristics of WSOM export, offering a deeper understanding of subsurface flow processes in catchments. Finally, the findings of this study can help to improve biogeochemical models and improve scaling of hillslope processes models, particularly in understanding their contribution to organic carbon transport via SSF.
How to cite: Fasching, C., Pyschik, J., Weiler, M., and Chifflard, P.: Subsurface stormflow transport of water-soluble organic matter in hillslopes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12612, https://doi.org/10.5194/egusphere-egu25-12612, 2025.
Subsurface stormflow (SSF) is a streamflow generation process that is difficult to observe. It has therefore been challenging to evaluate the relevance and magnitude of SSF contributions to streamflow quantity and quality. However, some earlier studies have shown that it can deliver substantial amounts of water to the stream at the time scale of an event. One possible approach for detecting SSF in streamflow has been to sample SSF on hillslopes, characterize it by analyzing various tracers and search for this SSF fingerprint in stream water samples. In this study, we ask the following questions: Does subsurface stormflow generated on hillslopes and moving downslope towards the stream have a typical chemical fingerprint or signature by which we could recognize it in the stream? And does this signature vary over time? Here, we present data from a headwater catchment near Freiburg, Germany, where we installed three trenches to measure SSF flow rates and to obtain SSF samples for chemical analysis. We collected SSF samples from the three trenches over multiple events during spring 2023, fall 2023 and spring 2024 and analyzed them for dissolved organic carbon and major ions. We compared chemical SSF signatures through the events, across seasons and between the three trenches. Preliminary analyses indicate that the SSF signature changed during events, with SSF signatures at the beginning and at the end of events being remarkably similar to each other. Results also hint at a seasonal stability of SSF signatures. In our presentation, we are going to present a detailed analysis of the dynamics of the chemical SSF signature. This dataset provides a unique opportunity to evaluate the chemical composition of subsurface stormflow in sub-daily resolution at three different hillslopes and to improve our capability to recognize contributions of SSF to streamflow.
How to cite: Hopp, L., Kuleshov, A., and Blume, T.: Event-based dynamics of the chemical composition of subsurface stormflow across seasons, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15193, https://doi.org/10.5194/egusphere-egu25-15193, 2025.
Near-surface flow pathways are important for the transfer of water and solutes from the hillslopes to the streams, particularly in head water catchments with low permeability soils. However, the high spatio-temporal variability in the occurrence of runoff makes it difficult to study these flow pathways and to upscale plots based measurements to the catchment scale. Furthermore, it is well known that the amount of overland flow at the bottom of a runoff plot depends on the size of the plot. To better understand the importance of near-surface flow pathways in pre-Alpine headwater catchments underlain by low permeability gleysols, we installed 14 small (1 × 3 m) trenched runoff plots in the Studibach catchment in the Alptal (Switzerland). They cover a range of topographic positions and vegetation covers. We measured the occurrence of overland flow (including biomat flow) and shallow subsurface flow through the topsoil (i.e., the main rooting zone), precipitation, and soil moisture during a snow-free season. In addition, we collected data in a second snow-free season from two large plots (>80 m2) and two nearby small plots. The results from the small plots showed that runoff ratios increase with increasing soil moisture storage and precipitation and are higher for areas with a greater topographic wetness index (TWI). To understand the effect of plot size on near-surface runoff, we compared the runoff characteristics (runoff ratio and runoff generation threshold) for the small and large plots for different events. Additionally, we determined the typical flow path lengths (and thus the effect of plot size) by applying blue dye and tracers to the surface of the plots during rainfall simulation experiments. These experiments showed that overland flow generally infiltrates within a short distance (<5 m, and often <1 m) but also exfiltrates again after flowing a short distance below the ground (<5 m). To better understand the importance of near-surface flow for runoff at the catchment scale, we compare the runoff thresholds and runoff ratios for the small and large plots to those for streamflow. We, furthermore, investigated the spatial pattern in near-surface flow generation across the catchment based on the relation between topography (TWI) and near-surface runoff generation. More specifically, we related the area where near-surface runoff is expected to occur and its connectivity to the stream, to the streamflow response for different sub-catchments and the catchment outlet.
How to cite: Gauthier, V., Leuteritz, A., and van Meerveld, I.: Spatial and temporal variation in near-surface runoff in a pre-Alpine headwater catchment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16757, https://doi.org/10.5194/egusphere-egu25-16757, 2025.
Rainfall runoff contributes to a large proportion of the discharge in streams and therefore, heavily influences stream water quality but also flood generation. Rainfall runoff generation is usually a combination of overland and subsurface flow processes, the latter of which being especially difficult to trace. Here, we explored the viability of environmental DNA (eDNA) for subsurface water flow pathway reconstruction and simultaneous biodiversity assessment. The degree of similarity of community patterns indicates biological and therefore, in principle, also hydrological connectivity. We applied eDNA metabarcoding to characterise 10 drilling cores (0.7-3.2 m depth) on 3 hillslopes (10x50 m) in 4 catchment areas in Germany and Austria. In total, more than 2000 species across taxonomic groups could be identified down to species level. Analysis of alpha and beta diversity in the different catchments showed significant differences in spatial clustering patterns between taxonomic groups, but also between geomorphological and geochemical properties, such as the composition of dissolved organic carbon, of the respective catchment. We could assign indicator species sets in all taxonomic groups to various depth layers and identify habitat-specific communities that can be used as hydrological tracers. Although our results support the potential of eDNA to identify flow pathways and enhance our understanding of subsurface flow processes, we are still at the beginning of understanding the viability of eDNA as a tracer in hydrological research. However, our results show that making use of such naturally occurring tracers can expand our understanding of hydrological phenomena, especially those hidden in the subsurface.
How to cite: Schadewell, Y., Köhler, S., Fasching, C., Chifflard, P., and Leese, F.: Harnessing the Power of eDNA Biodiversity Assessment to Enhance Subsurface Water Flow Pathway Reconstruction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17789, https://doi.org/10.5194/egusphere-egu25-17789, 2025.
Sequential salt dilution measurements of discharge along streams allow us to determine stream gains and losses on a reach-by-reach basis. This information is especially useful in the context of studying the spatial variability of subsurface flow contributions to overall streamflow. However, these sorts of measurements are time-intensive and laborious and therefore usually only carried out during snapshot campaigns. In our study we explore the potential of an automated sequential salt injection method, applying the same methodology in three headwater catchments in typical mountainous regions in Germany (Black Forest, Sauerland, Ore Mountains).
Several automated salt injection units were spaced approximately 200 m apart at each site, set to inject at a scheduled daily interval as well as on rainfall event-based triggers. Electrical conductivity is measured at 5-second intervals both upstream and downstream of each injection point to obtain discharge estimates. This approach opens the possibility of measuring local gains and losses at scales on the order of 200 m but at a much higher temporal frequency than is usually achieved with manual snapshot campaigns. This higher frequency has the advantage of sampling over a larger range of conditions and thus providing a much more detailed picture of runoff generation along the stream.
Given the required need for highly accurate discharge estimates in the here studied small streams the feasibility of using this automated method to quantify subsurface contributions to streamflow along the stream is assessed, with a key focus on evaluating uncertainties.
How to cite: Vis, G., Adeberg, F., Sentlinger, G., Hartmann, A., Hopp, L., and Blume, T.: Automated Sequential Salt Injection to Estimate Subsurface Contributions to Streamflow in Headwater Catchments in Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18321, https://doi.org/10.5194/egusphere-egu25-18321, 2025.
In controlled rainfall experiments conducted across four catchments in Germany and Austria, rainfall simulations were conducted on 200m² large plots and 50m² small plots, all designed to detect subsurface stormflow (SSF). At the larger plots, SSF was captured using a trench located below the irrigated area, as described in the study of Thoenes et al. (2025, hoc loco). The present study focuses on the 50m² plots, which were irrigated with an intensity of 100 mm/h for one hour. Surface runoff was collected at the downslope edge and measured in terms of both time and quantity.
Soil moisture changes were monitored using two methods: electrical resistivity tomography (ERT) along three cross-profiles, two of which intersected the rainfall area, while one was located beneath the surface runoff collection boundary. Measurements were conducted at 15-minute intervals pre-, during, and post-experiment to ensure continuous monitoring. Additionally, time-domain reflectometry (TDR) probes were installed up to a depth of 60 cm at the centre of the two ERT profiles within the rainfall area. Soil samples were collected after the experiment and analysed for physical properties, including texture, bulk density, organic content, and pF curves.
The aim of the study is to assess the potential available for deep percolation and potential SSF during intensive rainfall by employing a flexible arrangement across different hillslopes.
Using two different soil hydraulic models (single porosity model van Genuchten–Mualem and dual porosity/dual permeability model by Durner, dual van Genuchten–Mualem), the laboratory results were prepared for modelling in HYDRUS-1D. The rainfall experiments were simulated using the soil moisture data. Further calibration was performed using the measured surface runoff by adjusting the saturated hydraulic conductivity accordingly. The calibrated model allowed for a water balance calculation of the applied rainfall, partitioning it into surface runoff, soil storage, and the fraction available for deep percolation and potential SSF.
In the next step, the HYDRUS-1D simulation results were compared with the values from the ERT profiles close to the TDR measurements. Initial results confirm the findings of Pyschik et al., indicating that 80–95% of the applied rainfall is stored in the soil. The extent to which the combination of hydrological modelling and ERT profiles allows conclusions to be drawn regarding lateral water movement and SSF will subsequently be examined using HYDRUS-2D simulations in a longitudinal section.
How to cite: Lechner, V., Thoenes, E., Achleitner, S., and Kohl, B.: Tracing Subsurface Stormflow: Combining HYDRUS Modelling and ERT Profiles to Explore Runoff, Storage and Percolation under Intense Rainfall, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14817, https://doi.org/10.5194/egusphere-egu25-14817, 2025.
Posters virtual: Fri, 2 May, 14:00–15:45 | vPoster spot A
EGU25-4662 | ECS | Posters virtual | VPS11
Application of a Composite Model to Estimate Baseflow, Effective Recharge, and Hydraulic ConductivityFri, 02 May, 14:00–15:45 (CEST) | vPA.4