Journal of Hydrology and Hydromechanics Feed

Near-saturated hydraulic conductivity of a sandy-loam soil a few months after incorporating compost or zeolite

Sat, 05 Sep 2026 00:00:00 GMT

Little is known about compost (C) and zeolite (Z) effects on hydrodynamic properties of near-saturated coarse-textured soils. These effects were tested for a sandy-loam soil by a mini-disk infiltrometer at three pressure heads (h0 = -6, -3 and -1 cm) and a wide range of amendment percentages, pa (0-40%). Soil hydraulic conductivity, K-6, K-3 and K-1, depending on h0, was determined 3.5 and 8.0 months after the treatment with C and 5.0 and 10.5 months after that with Z. With the C, more amendment determined smaller K-6 (by 1.7-3.0 times), stable K-3 and larger K-1 (3.4-4.4 times) values on both sampling dates. With the Z, the most frequent result was that the soil hydrodynamic parameters did not change with pa. Time effects were more appreciable with the C (means for the two sampling dates differing by 2.1-3.8 times, depending on h0) than the Z (means differing by 1.1-1.7 times). The soil treated with Z was more permeable than that treated with C in the first sampling date (percentage differences, Δ, between corresponding means = 38% - 103%, depending on h0) but not in the second date (Δ values varying from -61% to 4%). In the first year after the treatment, near-saturated soil hydrodynamic behaviour can change appreciably following C addition but the same effect is not expected for the Z. Future investigations should include independent determination of soil pore and particle size distributions.

Response of severity and persistence of water repellency to thermal heating parameters in eucalyptus and pine forest soils in Sri Lanka

Sat, 05 Sep 2026 00:00:00 GMT

Soil water repellency (SWR) relates to plant species such as conifers and Eucalyptus with high amounts of hydrophobic substances such as resins, waxes, and other oily substances, and are highly vulnerable to wildfires. The heat generated through fire can influence SWR, although the changes can deviate based on soil, climatic, and environmental conditions. This study aims to examine the impact of heating temperature and duration of exposure to heat on the severity and persistence of SWR in eucalyptus and pine forest soils in Sri Lankan highlands. Soils collected from three depths (0–5, 5–10, 10–15 cm) were air dried, passed through a 2 mm sieve, and exposed to six heating temperatures (50, 70, 100, 150, 200, 250°C) and five durations of exposure (20, 40, 60, 90, 120 min). SWR was determined using water drop penetration time (WDPT) and soil-water contact angle. Both eucalyptus and pine soils showed water repellent conditions at the field and at air-dried conditions. Both soils reached completely wettable level (WDPT < 5 s) with very low contact angles when exposed to 200–250°C for 90–120 min, except for the contact angle of the eucalyptus 0–5 cm layer that decreased to a minimum of 40°. SWR showed fluctuations with increasing temperature between 28 and 150°C at all durations of exposure. SWR showed significant positive linear correlation with soil organic matter (SOM) content, of which the strength was moderate (R2 = 0.64 and 0.50, respectively, for eucalyptus and pine), indicating that the heat-induced change in SWR was not strongly dependent on SOM content. Contrasting transitions in SOM due to removal via various processes and structural and molecular rearrangements might explain fluctuations of SWR at lower temperatures (28–150°C). The findings would be useful for understanding the impacts of various heating dynamics that might occur during forest fires. Further research considering the other important factors, such as molecular-level variations in organic substances as well as mineralogical and climatic aspects, would be important for a better understanding of hydrological responses on burnt forest floors.

Does temperature-induced vapor flux trigger desert floods? The Negev example

Sat, 05 Sep 2026 00:00:00 GMT

High-magnitude floods characterize deserts, commonly explained by the high rain intensities coupled with the low vegetation cover, surface smoothness and the sealing capability of biocrusts. Nevertheless, runoff generation and the subsequent high-magnitude floods stand out when considering the high evaporation, the relatively dry desert surfaces and the high stoniness that characterize many of the surfaces. Also, the rain amount that stems from high intensity (convective) rains is not necessarily higher than in subhumid regions, and indeed, based on a study of runoff dynamics over biocrusted sand dunes in the Negev Desert, runoff was generated already at low to medium intensities of 9-12 mm/h, explained by the high-water absorbance of the extracellular polymeric substances (EPS) that is excreted by the variable microorganisms inhabiting the biocrust. In the Negev, convective intensities were found to primarily result from unstable daily atmospheric conditions following by daytime surface heating. Daytime heating, coupled with cool/cold nighttime temperatures, were also found responsible for the occurrence of temperature-induced vapor flux (TIVF) and the subsequent occurrence of wet-dry cycles that may last for up to 1-2 weeks following a rain event. We hypothesize that the wet cycles which stem from an upward vapor movement from the warm subsurface soil towards the cool soil surface during the night result in biocrust saturation, triggering in turn runoff generation. By wetting the surface (commonly already during the late afternoon), TIVF may trigger runoff in deserts. This is supported hereafter following a thorough four year-long analysis (1990-1994) of rain-runoff relationship that took place on a pair of biocrusted plots covering dunes in the Negev. Albeit the ~20% higher intensities measured during daytime that should have resulted in higher runoff, nighttime runoff amount, runoff flow duration, runoff yield per average rain intensities and runoff yield per the average intensity of each event were 1.8-, 1.5-, 1.5- and 3.1-fold higher during nighttime in comparison to daytime. It is suggested that in addition to the role played by runoff intensity and the surface properties, TIVF provides an additional mechanism that explains the high runoff generation already at low- to medium-intensities, also explaining, at least partially, the relatively high runoff yield and potent floods in the Negev and other arid regions.

Deadwood-dominated forests buffer microclimate in exposed mountain areas

Sat, 05 Sep 2026 00:00:00 GMT

Microclimatic buffering is a key process that determines the regeneration potential and ecosystem stability in disturbed mountain spruce forests. Retention of standing and downed deadwood alters the balance of radiation, temperature, and humidity near the surface; however, quantitative evidence from exposed slopes in the Carpathians has been scarce. We therefore compared intact forest, deadwood-dominated forest, and open area on steep southeastern slopes of the Western Tatras (Slovakia) using continuous measurements from 2021 to 2025. Micrometeorological stations recorded global solar radiation, air and soil temperature, and humidity at multiple heights and depths; vapour pressure deficit (VPD) was calculated at 5 cm above ground. Differences among sites were assessed using non-parametric tests. Open areas received the highest radiation loads, resulting in extreme warming of the air near the ground (up to 34 °C at 5 cm) and intense soil heating (absolute maximum of 49 °C at – 2 cm). Intact forest reduced incoming radiation and maintained the most stable conditions. Deadwood-dominated stands represented an intermediate type but repeatedly buffered extremes: summer soil maxima remained below 26 °C, and air temperatures near the ground were several degrees cooler than in the open area. In winter, snow cover largely equalised conditions, while during snow-free episodes intact forest showed stronger nocturnal cooling, whereas deadwood stands preserved milder soil minima. VPD patterns followed the same gradient, with the shortest daily duration above the threshold of 1.5 kPa in intact forest, the longest in open area, and intermediate values in deadwood stands. Overall, deadwood-dominated forest approximates, and under certain circumstances even exceeds, the buffering capacity of intact spruce stands. We conclude that retention of deadwood-dominated forests mitigates heat and drought stress, reduces thermal extremes, and provides a low-cost, ecologically grounded adaptation strategy for mountain forest management in the context of climate change.

Relationship between tree transpiration and soil properties: Do trees with higher water demand promote formation of soils with higher water retention?

Sat, 05 Sep 2026 00:00:00 GMT

Soil water availability influence plant growth, vegetation, particularly trees, can in turn substantially alter soil properties affecting soil water availability. This study investigates whether tree species with higher transpiration rates promote the development of soils with a higher water-holding capacity using common garden experiment in post-mining heap in northwest Czechia, where several tree species were planted directly into bare overburden. We focused on three monocultures of alder (Alnus glutinosa), oak (Quercus robur), and spruce (Picea omorica). Tree sap flow was measured and used to estimate transpiration at both individual and stand levels. At the same time, soil moisture and water-holding capacity were assessed in each stand. Alder and oak showed similarly high transpiration rates, significantly exceeding those of spruce. The alder stand exhibited the highest average annual soil moisture as well as the highest moisture during the vegetation and dormant season, significantly differing from oak and spruce, while oak soils had a significantly higher moisture than spruce. Water-holding capacity was the highest in oak soils, significantly exceeding that of alder and spruce. These results support the hypothesis that tree species with a higher water demand foster the development of soils with an enhanced water retention capacity.

Heating affects properties of forest soils with different texture: 1. Physical and chemical properties

Sat, 05 Sep 2026 00:00:00 GMT

Wildland fires affect physical and chemical properties of forest soils, and the magnitude of their effects depends on the soil temperature achieved during a fire. Laboratory heating of soil samples in muffle furnace was used to simulate a natural fire heating of forest soils, although it does not completely reproduce natural fire conditions. The effect of heating temperature of 100–900°C on particle size distribution, soil water repellency (SWR), soil organic carbon content (SOC) and pH was estimated in three soils differing in texture (sandy soil, silty-clay soil, and clay soil) sampled in coniferous and deciduous forests at Gbely (Areni-Gleyic Umbrisol), Hviezdoslavov (Fluvisol) and Gabčíkovo (Fluvisol), respectively. Decrease in the clay content and increase in the sand content was large in silty-clay and clay soils, but not as large in sandy soils. Surprisingly, heating the soil to 100°C, commonly used in soil moisture measurement, caused a decrease in clay content by half (the average value for all soils). This finding should be confirmed by further measurements on the soils from other regions, because the degree of aggregation depends also on the type of clay and other minerals. The persistence of SWR gradually increased in the heating temperature range 100–300°C in all three soils from coniferous forests and sandy soil from deciduous forest, and was absent in the remaining two soils. The SOC decreased and pH increased with increasing heating temperature.

Linking tillage practices to soil health, crop productivity, and erosion control in maize – wheat rotation

Sat, 05 Sep 2026 00:00:00 GMT

The suitability of conservation tillage in maize–wheat interrow farming in a young plum orchard in Croatia to control runoff, soil, and element loss under natural rainfall was evaluated. Paired runoff plots (20 m2 size) comparing conventional (ploughing and discing) and conservation (chisel and harrow) tillage were implemented in triplicate across Stagnosols (11° slope). Soil physical (bulk density, penetration resistance, mean weight diameter, water stable aggregates) and chemical properties (carbon, nitrogen, phosphorous, potassium and copper) were assessed alongside event-based overland flow formation monitoring. After two years, conservation tillage maintained or improved soil structure, with significantly higher aggregate stability and soil carbon at 0–10 cm depth. Moreover, no clear increase in compaction was documented during the shift to conservation tillage. Conservation tillage exhibited a clear and significant mitigation effect on surface flows of water, sediment, and chemical elements. Sediment concentration decreased from 8.95 to 3.11 g L–1, runoff was 40.5% lower, and cumulative soil loss declined from 8.57 to 2.97 t ha–1 over the two years. Importantly, reduced sediment export translated into markedly lower off-site losses. Conventional tillage increased losses of phosphorus (~3.4×), potassium (~3.2×), copper (~2.6×) and nitrogen (~1.7×) relative to conservation tillage. Overall, non-inversion loosening in orchard inter-rows proved an effective conservation practice for reducing runoff, soil erosion, and chemical export under natural rainfall, supporting on-site soil health and reducing off-site pollution.

Treatment of soil with nanosilica particles derived from rice husk: influence of substrate ageing on soil resistance to detachment

Sat, 05 Sep 2026 00:00:00 GMT

No studies have explored how much ageing of rice husk, used as substrate for nanosilica production, alters apparent particle size distribution in this substrate, and therefore modifies nanosilica-soil interactions. To fill this gap, this study has investigated the effects of nanosilica derived from fresh and aged rice husk on soil physical properties and particle detachment (Dc) in paddy soils through flume experiments on samples collected in Northern Iran. Nanosilica obtained from aged husk showed an increase in mean apparent particle size by 96% compared to the soil amendment derived from fresh residues. Soil treated with fresh husk nanosilica exhibited significantly higher (+106%) water-stable aggregates and lower (–7.4%) bulk density compared to the control, while the differences from aged husk treatments were +86 % and –6.3%, also in this case significant. Flume experiments revealed a significant reduction (–21%) in Dc following application of nanosilica from fresh rice husk, while no effect was found for the soil amendment derived from the aged biomass. Compared to the control, Dc decreased by 8.1% with aged husk and by approximately 21% with fresh husk. Dc can be accurately estimated by hydraulic predictors (shear stress, stream power, and unit stream power) using a shifted power function (R² = 0.80–0.96). These models show that, across treatments, the effective hydraulic threshold parameter generally increases from control to amended soils, indicating enhanced resistance to detachment initiation.

Kinetics of water sorption, EPS swelling and evaporation in biological soil crusts on reclaimed temperate dunes, Brandenburg, Germany

Sat, 05 Sep 2026 00:00:00 GMT

Biological soil crusts (BSCs) play a crucial role in regulating water infiltration into surface substrates; however, their exact hydrological effects remain a subject of ongoing debate. This study quantitatively investigates the kinetics of water immobilization through sorption and the swelling behavior of extracellular polymeric substances (EPS) during the wetting of dry BSCs on recultivated temperate dunes in Brandenburg. Crust samples dominated by the green alga Zygogonium ericetorum were collected from an inland dune in the Lusatian post-mining area. Following a multi-week drying phase, rehydration experiments were conducted using deuterium oxide (D2O) to avoid spectral interference with the O–H groups of the EPS. Using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the time-dependent shift of the O–D stretching vibrations was analyzed to determine the sorption kinetics of the biological crusts relative to an undisturbed mineral control. In parallel, gravimetric measurements monitored evaporation, while the EPS composition was characterized via ATR-FTIR spectroscopy. Spectroscopic analysis identified alginate as the primary organic component of the crust EPS. While the uncoated mineral control showed almost immediate water infiltration, the BSC samples exhibited a pronounced plateau in OD vibrations during the first three minutes, indicating an initial phase of free water at the surface. Between the 3rd and 12th minutes, a distinct redshift toward lower wavenumbers followed, reflecting the ongoing functional group reorganization, hydration, and EPS swelling, until thermodynamic equilibrium was reached after approximately 12 minutes. Gravimetric data also revealed a significantly higher and faster evaporation rate for the BSCs compared to the control. These results demonstrate that the alginate and EPS matrix of the biological soil crust acts as a water reservoir that hydrologically seals the surface, drastically limiting vertical infiltration into deeper soil layers while retaining water in a highly accessible surface pool. Furthermore, it is conceivable that this delayed water immobilization by the swelling EPS matrix provides a vital ecological benefit by buffering the crust microbiome against severe hypo-osmotic shock during rapid rewetting. However, direct microbial analyses are required to confirm this effect. By moving beyond conventional visual assessments or indirect macro-hydraulic inferences, this approach provides unprecedented molecular-scale insights into the rapid physicochemical transition from free to matrix-bound water during EPS hydration. To our knowledge, this study represents the first application of time-resolved diffuse reflectance infrared spectroscopy (DRIFTS) combined with deuterium oxide (D2O) rehydration to directly track water immobilization kinetics in biological soil crusts. By eliminating spectral interference from biopolymer hydroxyl groups, this approach provides unprecedented insights into the rapid physicochemical transition from free to matrix-bound water.

Eco-engineered rice-husk nanosilica enhances soil structural stability and reduces detachment capacity in paddy fields

Sat, 05 Sep 2026 00:00:00 GMT

Previous studies have shown that silica nanomaterials produced from rice residues, such as husk, can influence several soil properties. However, their effects on soil detachment capacity and structural characteristics in rice paddy fields remain poorly quantified. This study evaluated the effects of nanosilica derived from rice husk on wet aggregate stability, plasticity index, and detachment capacity in paddy soils of Northern Iran under different flow discharges simulated in a hydraulic flume. The nanosilica used in this study was produced by acid extraction followed by controlled heating, and was incorporated into field plots at a 2% amendment level. Results showed that wet aggregate stability and plasticity index significantly increased by 32% and 27%, respectively, in the nanosilica-treated soils compared with the untreated control. Conversely, the average soil detachment capacity decreased by 49%, also in this case significantly. Multivariate analysis indicated strong interrelations among the measured properties and distinctly separated the amended soils from the control group. Linear regressions between detachment capacity and shear stress or stream power showed that nanosilica reduced soil erodibility and increased the threshold resistance to particle detachment under increasing flow power. Overall, the findings demonstrate that rice-husk-derived nanosilica enhances aggregate cohesion and substantially reduces soil vulnerability to concentrated flow erosion in paddy systems.

Explainable AI and Ensemble Machine Learning Analysis of River Flow Dynamics: Influence of Key Climatic Variables (Temperature, Humidity, Precipitation)

Sat, 20 Jun 2026 00:00:00 GMT

Accurate short-term river flowrate forecasting is essential for flood risk mitigation and sustainable water management. However, many machine learning (ML) applications in hydrology lack strict temporal validation and interpretability, limiting operational reliability. This study develops a reproducible and explainable framework for one-day-ahead daily flowrate forecasting in the Eşen River Basin (Türkiye) using hydro-meteorological data (2017-2022) from one flowrate station and four meteorological monitoring stations.The workflow integrates the Box-Cox transformation, lag-based feature engineering (up to 3 days, reflecting short-term hydrological memory), Boruta feature selection, and strictly time-aware rolling validation (2017-2021 training; 2022 independent test). Classical time-series models (ARIMA, TBATS), interpretable baselines (DT, LR), and advanced ML algorithms (RF, GBM, XGBoost, SVM, ANN) were benchmarked using RMSE, MAE, R², NSE, and KGE. Ensemble tree-based models consistently outperformed classical and baseline approaches in magnitude-sensitive metrics. XGBoost achieved the highest predictive accuracy (R² = 0.864; NSE = 0.864; RMSE = 6590 dm³ s⁻¹). Although TBATS yielded the highest KGE (0.865), ensemble models better captured nonlinear dynamics and flowrate variability. SHAP and LIME analyses revealed that short-term flow lags dominate predictive structure, while precipitation and temperature exert regime-dependent influence. The complete workflow is openly deployed via a reproducible R-Shiny environment. The results demonstrate that explainable ensemble learning, combined with strict temporal validation, provides a reliable and transparent framework for operational hydrological forecasting.

From decadal runoff depletion to daily streamflow cycles: The role of riparian evapotranspiration in a forested catchment

Sat, 20 Jun 2026 00:00:00 GMT

This study investigates the role of evapotranspiration in the hydrological balance of the small forested Vydrica catchment (Slovakia) by linking long-term climatic trends with short-term streamflow dynamics. A 60-year mass balance analysis (1961–2020) was integrated with high-frequency streamflow observations across nine severe summer drought events (1992–2025). The long-term analysis revealed a paradoxical trend: despite a slight increase in precipitation, annual runoff significantly decreased. This decline is driven by rising air temperatures and increased evaporative demand, causing altered seasonal runoff distribution and more severe summer low flows. The short-term event analysis demonstrated that diurnal streamflow fluctuations are strongly controlled by available baseflow. During moderate droughts, active riparian vegetation generates distinct diurnal streamflow cycles with a typical six-hour lag behind maximum air temperature. However, during extreme low-flow periods, the diurnal amplitude flattens and evapotranspiration losses drop by an order of magnitude, indicating that the groundwater table has fallen below the effective root zone. The findings prove that climate-driven long-term warming continuously depletes baseflow reserves, progressively restricting the daily transpiration capacity and resilience of riparian forests.

Geometric shift–aware uncertainty quantification for discharge coefficient prediction of triangular planform weirs

Sat, 20 Jun 2026 00:00:00 GMT

Reliable estimation of the discharge coefficient Cd is central to sharp-crested weir hydraulics, yet data-driven models are commonly evaluated with random train-test splits that can overstate generalization when experiments are structured by discrete geometries. Using a reconstructed run-level dataset for triangular planform weirs (n=123) spanning vertex angles θ ∈{30o,60 o,90 o,120 o,150 o,180 o }, this study benchmarks tabular regression under (i) random 80/20 splitting, which represents interpolation within a mixed-geometry dataset, and (ii) a leave-one-angle-out (LOAO) protocol that enforces geometric domain shift. Dimensionless predictors are derived from Buckingham-π reasoning and formulated to remain numerically stable as θ →180°. Under random splitting, gradient boosting achieves high accuracy, whereas LOAO reveals substantially weaker generalization, with the largest errors near the θ = 180° regime transition. For uncertainty quantification, global split conformal intervals are near-nominal under random splits but severely under-cover under LOAO, indicating that calibration residuals are not transferable across geometries. CV-pooled residual calibration restores LOAO coverage at the cost of substantially wider intervals. Finally, combining k-nearest-neighbor distance-based out-of-distribution detection with a two-tier interval policy yields intermediate operating points that better balance reliability and sharpness when deploying beyond the calibration envelope. Overall, the results indicate that apparently strong interpolation performance can conceal important geometric extrapolation failures, and that safe deployment on novel weir geometries requires explicitly shift-aware uncertainty quantification.

Monthly and fixed coefficient calibration of empirical reference evapotranspiration equations: A case study for a Mediterranean climate (Izmir Province)

Sat, 20 Jun 2026 00:00:00 GMT

Accurate estimation of reference evapotranspiration (ET₀) is essential for efficient irrigation and water resource management, particularly in water-scarce regions. Although the FAO56 Penman–Monteith (PM-FAO56) equation is widely accepted as the standard method, its application is often constrained by the requirement for comprehensive meteorological data. This study provides a regional evaluation and calibration of three widely used empirical ET₀ models Hargreaves and Samani (temperature-based), Priestley and Taylor (radiation-based), and Mahringer (mass transfer-based) under Mediterranean climatic conditions in İzmir, Türkiye. Daily meteorological data from 40 stations covering the period 2000–2020 were used. Model performance was assessed against PM-FAO56 using the coefficient of determination (R²), mean absolute error (MAE), root mean square error (RMSE), percentage error (PE), Nash–Sutcliffe efficiency (NSE) and mean bias error (MBE). Calibration was performed using least squares (LS) regression and a gradient-based optimization approach, with both fixed and monthly varying coefficients. Before calibration, the Priestley–Taylor model showed the best performance among the empirical equations (R² = 0.932, MAE = 0.68, RMSE = 0.92, PE = 7.32, NSE=0.796, MBE=− 0.65). After calibration, all models improved substantially, with the Mahringer equation achieving the highest accuracy when monthly coefficients were applied (R² = 0.995, MAE = 0.05, RMSE = 0.154, PE = 1.41, NSE=0.992, MBE=0.022). The LS and gradient-based optimization approaches produced nearly identical results. In addition, the reconstruction of missing sunshine duration (ADS) data using a regression-based approach enabled the inclusion of a more spatially representative dataset without introducing significant bias into the calibration results. The findings demonstrate that locally calibrated empirical equations, particularly when temporal variability is accounted for through monthly coefficients, can provide highly accurate ET₀ estimates with relatively limited data requirements. This study provides practical monthly and fixed calibration coefficients for the İzmir region and supports the use of monthly calibrated empirical models for irrigation planning in Mediterranean environments.

Backward analysis of the Bílá Desná dam break outflow

Sat, 20 Jun 2026 00:00:00 GMT

In September 1916, the Austro-Hungarian Empire (today the Czech Republic) experienced the failure of the embankment dam Bílá Desná (historically named Weiße Desse), which at that time was the most disastrous dam failure in central Europe. In this study, available information on the failure of the Bílá Desná dam was gathered and analysed. The initiating cause of the Bílá Desná dam failure was an internal erosion. For the backward analysis of the dam failure, the method of analogy, empirical formulae, and three numerical models, AREBA, DL Breach and HEC-RAS were used. Due to uncertainty in the reservoir volume, the solution was carried out for the originally determined (during the dam design) and newly determined reservoir volumes. The analysis indicates the peak breach outflow range between about 360 and 810 m3/s. The most realistic and probable peak outflow discharge is about 520 m3/s. The comparison of individual methods indicate that the AREBA numerical model using Opendata (2024) provides the most realistic failure hydrograph.

Flow structure in a local meander bend of a gravel-bed river

Sat, 20 Jun 2026 00:00:00 GMT

This study investigates the spatial variability of flow structure in a natural meandering bend of the Kheir- Abad River, a gravel-bed mountain stream in southwestern Iran, with emphasis on velocity distribution, boundary shear stress, and secondary circulation. Field measurements were conducted along a 270 m reach (arc angle 113°) across nineteen cross-sections, revealing a highly heterogeneous flow field characterized by a central high-velocity core and reduced velocities near the banks. Comparison with HEC-RAS simulations shows that the model captures the general spatial organization of velocity and shear stress, but produces a smoothed representation and underestimates localized variations, particularly in downstream sections where field data indicate pronounced acceleration and peak shear stress values (up to 84.1 Pa). The observed shear stress distribution deviates from classical outer-bank dominance, with maximum values frequently occurring in the central channel and downstream regions, reflecting the influence of coarse bed roughness, complex secondary flow structures, and thalweg-controlled momentum concentration. Analysis of the secondary flow coefficient (C) supports this interpretation, with peak values coinciding with zones of increased velocity and shear stress, indicating intensified momentum exchange and enhanced near-bed transport capacity. Overall, the results demonstrate that flow in gravel-bed meanders is governed by strongly non-uniform and three-dimensional processes that cannot be fully captured by simplified hydraulic assumptions, and that integrating field measurements with numerical modeling provides a robust framework for interpreting flow dynamics and their morphodynamic implications.

The effects of ice-water discharge ratio and flow Froude number on local scour around tandem double piers and ice jam thickness in an S-shaped channel

Sat, 20 Jun 2026 00:00:00 GMT

In cold regions, bridge piers in rivers can alter flow characteristics and influence the formation and evolution of ice jams, complicating the local scour around the piers and the distribution of ice jam thickness. This study, based on experiments conducted in an S-shaped flume, examines how the flow Froude number and the ice-water discharge ratio affect the local scour depth around tandem double piers and the ice jam thickness. The results reveal that, while a positive correlation exists between the flow Froude number and the scour depth under both open flow and ice-covered flow conditions, the relationship between the scour depth and the flow Froude number under ice-jammed flow conditions is considerably more complex. Due to the influence of the ice jam on scour depth, there exists a critical Froude number at which the relationship between the flow Froude number and scour depth changes. The results indicate that when the flow Froude number is below the critical value, the ice jam thickness decreases slightly, while the scour depth shows a positive correlation with the flow Froude number. When the flow Froude number reaches the critical Froude number, the scour depth peaks. When the flow Froude number exceeds the critical value, the ice jam thickness decreases significantly, and the scour depth becomes negatively correlated with the flow Froude number. Additionally, when the flow Froude number remains constant, an increase in the ice-water discharge ratio leads to a rise in ice jam thickness, which in turn causes the scour depth to increase.

Time-dependent contact angle and repellency persistence in water-repellent Japanese forest soils in relation to droplet geometry and line tension

Sat, 20 Jun 2026 00:00:00 GMT

Water repellency (WR) restricts the spontaneous wetting of soil and lowers the affinity between soil and water. Studies focused on temporal alteration of droplet contact angles on hydrophobic soil substrates and their relation to persistence of WR are highly limited. This study examined time-dependent contact angle and WR persistence considering geometry and line tension droplets using six hydrophobic forest soils. Soils were collected from Japanese cedar (Cryptomeria japonica, CED1, CED2), Japanese cypress (Chamaecyparis obtusa, CYP1, CYP2), and cedar/cypress mixed (MIX1, MIX2) forests. The time-dependence of apparent and geometric soil-water contact angles (θA and θG, respectively) and repellency persistence, using the water drop penetration time (WDPT), were determined. In all tested soils, both θA and θG showed a gradual continuous decline with increasing time to reach zero within a period of ~5–6 min, with strong negative exponential correlations (R2 ≥ 0.90). The θA showed a strong positive linear correlation with θG (R2 > 0.99; p < 0.05), indicating the preservation of a fair spherical segment shape of droplets during spreading irrespective of the possible roughness on granular soil surfaces. The line tensions at the periphery of the contact circle of the water droplet on the tested hydrophobic soil surfaces were in a range of 200–300 μJ m–1, which was within the previously reported order-of-magnitude range (10−5–102 μJ m−1). The timedependent nature of the contact angle in the present study can most likely be attributed to water molecule adsorption processes or amphiphilic molecular reorientation processes. The soil-water contact time until contact angle receded below 90° (CT-θ90°) was not equivalent to WDPT, emphasizing that the time-dependent decline of contact angle would not correspond with water infiltration into the soil matrix. Still, the strong positive linear correlation between CT-θ90° and WDPT (R2 = 0.926; p < 0.05) indicated a close relation between these two parameters.

A four-year monitoring of beerkan infiltration rates in a sandy-loam soil

Sat, 20 Jun 2026 00:00:00 GMT

Long-term investigations on temporal variability of infiltration rates are important for characterizing the porous medium but they are challenging and infrequent. Infiltration rates were measured in a sandy-loam soil by performing 16 beerkan infiltration runs on 14 sampling dates during a nearly four-year period. The means of the initial infiltration rates (i0) varying by approximately four times, were less variable than the means of both the final (if) and the mean (imed) infiltration rates, varying by 13 and nine times, respectively. The means of all considered parameters decreased as the antecedent soil water content (θi) increased but the θi effect was stronger for i0 (coefficient of determination, R2 = 0.84) than both if and imed (R2 = 0.55-0.68). With reference to these last two parameters, θi effects were significant for the lowest measured values (R2 = 0.63-0.76) but not for the highest ones (R2 = 0.12-0.13). Particularly small if and imed values were obtained in initially very wet soil conditions. The antecedent soil water content can be expected to strongly control infiltration rates in a sandy-loam soil. Sampling the widest possible range of θi values is recommended to obtain the most complete information about temporal variability of infiltration rates.

Rethinking design rainfall estimation under non-stationary extremes and imperfect reanalysis data

Sat, 20 Jun 2026 00:00:00 GMT

Design rainfall return levels are critical inputs for engineering applications such as urban drainage design, flood mitigation, resilient transport infrastructure and climate-sensitive planning. However, their estimation is significanlty challenged by changing rainfall regimes, which can weaken the stationarity assumptions traditionally used in design rainfall analysis. A second challenge is data availability: design estimates rely on long gauge records that are often spatially sparse, while reanalysis products such as ERA5-Land provide spatial continuity but may poorly represent point-scale extremes, especially in convectively active and topographically complex settings. This study develops a reproducible GEE workflow to jointly examine these challenges by assessing temporal changes in extreme precipitation return levels and evaluating the reliability of ERA5-Land for design-oriented rainfall screening. Annual maxima from ERA5-Land daily precipitation are modelled using Gumbel and GEV distributions, with the workflow demonstrated globally and evaluated locally in Thessaloniki, Greece, against a long in-situ gauge record for return periods of 5, 10, 50 and 100 years. Results show that ERA5-Land systematically underestimates gauge-based design rainfall, with discrepancies increasing toward rarer events; consequently, gauge-to-ERA5-Land correction factors range from 1.17 to 1.29 under Gumbel and from 1.13 to 1.46 under GEV. A reference-to-recent period comparison further indicates substantial gauge-inferred intensification, including an approximately 33% increase in the 100-year Gumbel return level, while ERA5-Land shows little corresponding change. The proposed framework is reproducible and transferable for screening applications, but correction factors remain site-specific and require local gauge validation before engineering use.