Search Results (104)

River crossing bridges in low-gradient floodplains can be affected by limited conveyance, backwater control, and scour-related foundation risk. This study evaluates a proposed IL 13 bridge replacement over the Mid Fork Saline River, Illinois, using HEC-RAS 1D steady-flow modeling, hydrologic inputs from USGS StreamStats for a drainage area of 236.45 mi², bridge opening analysis, multiple-opening interpretation, and HEC-18 scour assessment. Natural, existing, and proposed conditions were compared under design floods and Ohio River tailwater scenarios. The proposed bridge increased the effective waterway opening under all evaluated hydraulic scenarios, with increases of approximately 68.5–79.5% under the no-tailwater case, 76.1–76.9% under the 10-year Ohio River tailwater case, and 71.7–72.1% under the 50-year Ohio River tailwater case. Bridge opening velocity decreased by about one-third, indicating lower local hydraulic intensity and improved conveyance through the main opening. Contraction scour was not controlling, while computed pier scour decreased by approximately 8–10% and the controlling right abutment scour decreased slightly. Because empirical HEC-18 scour equations can have large uncertainty, commonly approaching an order of a factor of two in practical scour prediction, these reductions are interpreted only as comparative trends. They do not provide a basis for reducing foundation design requirements, but they indicate that the proposed replacement does not worsen the controlling scour response. Overall, the replacement improves hydraulic compatibility, reduces local hydraulic stress, and does not worsen the governing scour response. The study supports SDG 9, SDG 11, and SDG 13 in a hydraulic-infrastructure sense by promoting resilient bridge serviceability, safer transport connectivity, and adaptation-oriented flood risk assessment; however, full life-cycle carbon, cost, and network-resilience metrics were outside the scope. Full article

Quantifying the net hydrological impact of large dams amidst climatic and anthropogenic influences remains a major challenge. This study isolates the effect of Three Gorges Dam (TGD) regulation on discharge at Jiujiang Station in the middle Yangtze River (2009–2016) using a novel scenario-based framework. A Long Short-Term Memory (LSTM) network, optimized by the Sparrow Search Algorithm (SSA), simulated daily discharge with high accuracy (Nash–Sutcliffe Efficiency coefficient > 0.97). By comparing a “with-TGD” simulation against a “without-TGD” scenario—generated by replacing the dam’s regulated outflow with its reconstructed natural inflow—we quantified the net impact ($\Delta Q$). Results show that $\Delta Q$ is substantially modulated by river–lake interactions. For example, in December, the backwater effect from Poyang Lake amplified the direct flow reduction by an additional −82.5 m³/s. The “peak-shaving” effect was context dependent: TGD regulation increased high flows (>30,870 m³/s) by an average of +372 m³/s while slightly decreasing low flows (<12,711 m³/s) by −31 m³/s. The impact exhibits strong seasonality alongside considerable intra-seasonal variability, reflecting multi-objective operations (flood control, power generation, water supply). This framework provides a transferable approach for attributing hydrological change in large regulated rivers and supports integrated water resources management. Full article

The weir–flume combination facility is a type of river flow-measurement structure consisting of a flow weir and a Crump weir, designed to integrate flow measurement and upstream backwater regulation, while incorporating a central flume intended to provide a potential passage for aquatic organisms. This study proposes a novel combined weir–flume structure and systematically validates its hydraulic performance through integrated physical experimentation and high-fidelity numerical simulation. Laboratory tests across a flow range of 5–79 L/s revealed longitudinal water surface profiles and Froude number (Fr) distributions. The study findings show that: (1) As the flow increases, the flow regime of the combination facility transitions from flume flow to weir flow, with the critical transition point at a relative water depth of 0.885. (2) The RNG k-ε turbulence model in Flow-3D software (v11.2, Flow Science, Inc., Santa Fe, NM, USA) effectively simulates the flow movement in the weir–flume combination facility, with water depth simulation results closely matching the measured values, and the maximum relative error not exceeding 5%. (3) The Fr and flow velocity in the weir–flume combination facility first increase and then decrease along the length, forming a large, thin water layer area downstream of the facility, where both Fr and flow velocity reach their maximum values. (4) Flow measurement formulas for flume flow and weir flow are obtained through data fitting, with relative errors between the calculated values and measured flow rates being less than 3%. The present study focuses on the hydraulic performance and flow measurement capability of the proposed facility. Although the structural configuration is intended to facilitate ecological passage, its ecological effectiveness was not evaluated and requires further investigation in future studies. Full article

The middle–lower Huaihe River Basin faces persistent flood and waterlogging threats, with river–lake interactions being a critical yet underexplored factor constraining flood discharge capacity. This study investigates the flood discharge capacity and erosion–deposition dynamics in the Bengbu–Hongze Lake reach and proposes sustainable management solutions. By analyzing long-term hydrological data (1954–2020) and cross-sectional measurements (1971–2025), we quantified changes in channel morphology and flood behavior. The results reveal that while upstream inflow has remained stable (annual runoff 20.5–33.3 billion m³), sediment concentration has continuously declined by approximately 80%—from 0.474 kg/m³ in the 1950s to 0.094 kg/m³ in the 2020s. The main channel exhibits persistent incision totaling 135.7 × 10⁶ m³, while floodplains have undergone progressive aggradation of 35.1 × 10⁶ m³, reflecting a sediment-starved river system in geomorphic disequilibrium. Critically, the riverbed leading to Hongze Lake exhibits an adverse slope, rising from –10 m at Fushan to over +9 m at Laozishan, while the lake’s sedimentation has reduced its storage capacity by 29% since the 1980s (from 31.27 × 10⁸ m³ to 22.15 × 10⁸ m³). Despite extensive engineering interventions, significant issues persist—including the backwater effect of Hongze Lake, prolonged high water levels during moderate floods (in 2020, water level at Fushan reached 18.34 m at only 61% of the design discharge), and exacerbated waterlogging in riparian lowlands. Therefore, we advocate for a paradigm shift towards a river–lake separation scheme, specifically, an inner-lake embankment approach. This nature-based solution aims to restore the river’s physical structure and harness its self-shaping morphological function for long-term flood management and ecological sustainability. Our findings provide a quantitative basis for re-evaluating the river–lake relationship and offer a strategic direction for sustainable flood management in highly altered alluvial river systems. Full article

In the daily operation of hydropower stations, the tailwater level is a fundamental parameter for calculating hydropower output, and it is essential for reservoir operation and management. Therefore, this study explores the influencing factors of tailwater level prediction, including the reservoir’s own downstream water level and the headwater level of the downstream reservoir as the characteristic factors. A Stacking ensemble model, using Ridge, Random Forest, Light Gradient Boosting Machine, and Support Vector Regression models as base learners and Ridge as the meta-learner, is established to predict the tailwater level of the Xiluodu Reservoir. We analyze results from the stacked ensemble model and the single model among different stacked combination models and across different quarters for each model. The tailwater level derived from the Stacking ensemble model is found to be in closer agreement with the measured water level than that obtained via interpolation. The model proposed in this study delivers superior predictive performance compared to the four baseline models, with the average absolute error achieving a maximum reduction of 38%. This confirms the effectiveness of the stacking ensemble strategy in predicting tailwater levels, thereby providing accurate boundary conditions for reservoir scheduling calculations. Full article

Due to the rapid acceleration of urbanisation and the increasing occurrence of extreme rainfall events, underpasses have become critical hotspots of urban flooding vulnerability. In this study, we investigated 36 underpasses in Hangzhou using the Urban Flood Inundation Model (UFIM) to systematically evaluate their drainage performance. A high-resolution hydraulic simulation framework was developed by integrating terrain data, drainage pipe networks, pumping stations, and land-use information. Based on the maximum tolerable hourly rainfall derived from multi-scenario simulations, the facilities were divided into high-, medium-, and low-vulnerability groups. Our quantitative and spatial analyses reveal a pronounced core–periphery disparity: 41.7% of the underpasses were highly vulnerable (drainage threshold ≈ 61.3 mm/h), exhibiting significant spatial agglomeration in the older urban core. In contrast, facilities in newly developed peripheral areas demonstrated better drainage performance (threshold up to 75.6 mm/h). Furthermore, the backwater effect from downstream rivers at flood stages significantly constrains pump efficiency by increasing the static head requirement. Based on these spatial vulnerabilities and thresholds, targeted infrastructure optimisation and spatial planning strategies are proposed, shifting the focus from uniform engineering upgrades to vulnerability-based drainage capacity enhancements. Full article

The beneficial utilization of small and medium floods requires a clear flood-control safety boundary before floodwater can be moderately stored and regulated as a water resource. For the Three Gorges Reservoir, a large river-type reservoir with long-distance backwater effects and tributary blocking, this boundary cannot be determined solely from the dam-front water level. This study developed a one-dimensional unsteady hydrodynamic model with dynamic roughness calibration to investigate the risk-constrained flood-season operating water level of the Three Gorges Reservoir. Typical flood events and the 20-year return period design flood were used to examine the responses of the maximum dam-front flood-regulation water level, excess flood volume, longitudinal water levels, and exceedance risk at key reservoir-area sections under different initial regulation water levels and release-discharge conditions. The results show that the Changshou reach is the main control section for high-water-level inundation risk under the study scenarios. When the initial regulation water level is at or below 155 m, the dam-front flood-regulation water level, the peak water level at Changshou, and the exceedance duration generally vary only slightly. When the initial regulation water level exceeds 155 m, these risk indicators increase markedly, indicating a reduced flood-control safety margin. Perturbation analysis further shows that the dam-front flood-regulation indicators are relatively insensitive to small roughness and dam-front boundary perturbations, whereas the Changshou water level and exceedance duration are more sensitive to roughness and flood-volume perturbations. Therefore, 155 m should be interpreted as a conservative operational reference boundary under the current design-flood framework, existing operation rules, and the assumption of no forecast-based pre-release, rather than as an absolute safety threshold. Increasing release discharge can reduce high-water-level risk in the reservoir area under preset release limits, but its practical application must remain conditional on downstream flood-control constraints and real-time flood-conveyance capacity. The results provide a hydrodynamic basis for risk-constrained flood-season operation of large river-type reservoirs. Full article

Daily hydropower regulation and mainstem backwater generate complex hydrodynamic conditions in the Min River estuary, posing significant challenges to navigation safety. To analyze the impact of mainstem backwater on tributary navigation safety, this study focuses on the lower Min River reach affected by backwater from the Jinsha River. A depth-averaged 2D hydrodynamic model is established, and a water level difference parameter is used to construct the stage–discharge relationship at the estuary based on long-term measured water level and discharge data. Indicators including backwater distance, water surface slope, hydrodynamic axis migration, flow velocity, and cross-flow are used to delineate navigation risk zones. The results indicate the following: (1) The backwater intensity and extent are primarily governed by the mainstem and tributary discharges and by the distance from the estuary. High discharge and water levels produce significant backwater effects and reduced flow velocity. Empirical formulas for backwater length under various discharge conditions are established to support navigation decision-making, with RMSE values ranging from 0.42 km to 0.92 km. (2) Variations in estuarine water level induce oscillations in the hydrodynamic axis. When the upstream discharge is 900 m³/s and the estuarine water level is 258.4 m, the maximum oscillation amplitude reaches 20.33 m. (3) During periods of medium and low water, the reach exhibits significant navigation-obstructing behavior, with high-risk zones concentrated in Tongluowan, Yangjiaoshi, and other shoals 5–8 km being found from the estuary. (4) Under the design discharge condition, the minimum estuarine water level required to ensure adequate channel depth, appropriate flow velocity, and manageable ship resistance for safe navigation is 267.96 m. This study provides a scientific basis for navigation safety and channel regulation in the Min River estuary and similar reaches affected by mainstem backwater, thereby supporting sustainable waterborne transport. Full article

Sediment accumulates behind dams, thereby reducing their operational efficiency. In response to this issue, hydraulic flushing is considered an effective solution for its removal. A numerical model is used to provide a deep understanding of this process and its dynamics. It acts as a low-cost virtual laboratory that eliminates the need for costly field experiments and provides a precise understanding of sedimentation and flushing behavior. This study used numerical modeling to examine sediment deposition in the Tigris River upstream of the Samarra Barrage. Within the iRIC framework, two models were used: NaysCUBE and Nays2DH. NaysCUBE is a three-dimensional solver that provides detailed simulations of partial gate openings and vertical flow distribution. This capability is crucial for a realistic analysis of the flushing process. Nays2DH is a two-dimensional solver that simulates full gate openings and captures general flow patterns. Results showed that sediment deposits were mostly concentrated within the first kilometer upstream of the dam, particularly when backwater effects caused the outflow to be lower than the inflow. Different gate operation schemes produced varied results: some configurations improved the balance between sediment movement and water flow, whereas others caused local erosion and uneven scouring. Results showed that lowering the water level at the barrage by 1 m increases shear stress on the riverbed by up to 25%, thereby improving the river’s ability to carry sediment without the need for additional discharge. High-discharge flushing operations are no longer feasible because of the reduced flow in the Tigris River since the operation of the Ilisu Dam in Turkey. This study recommends maintaining low water levels at the barrage with frequent and reasonable maintenance operations by partially opening the gates (40–60%). This strategy maintains a balance between the required water storage and sediment control, thereby ensuring the long-term sustainability of the hydraulic structure and the river ecosystem. Full article

In sediment-laden irrigation channels, sediment deposition upstream of hydraulic measuring structures can degrade hydraulic performance, reduce measurement reliability, and increase maintenance demand. To clarify the effects of structural optimization on sediment transport and siltation resistance, physical model experiments were conducted on an airfoil weir-orifice facility under different discharges, structural angles, and sediment concentrations. The analysis focused on sediment deposition patterns, longitudinal water surface profiles, sediment concentration, suspended sediment transport rate, cross-sectional velocity distribution, vertical velocity gradient, and Froude number. The results showed that the optimized configuration produced a flatter and more uniform upstream bed morphology, and the average deposition thickness decreased from 4.83 cm to 4.31 cm, corresponding to a reduction of 10.58%. Under all tested conditions, the optimized configuration reduced upstream backwater, increased local flow velocity, and shifted the hydraulic jump closer to the facility outlet. Sediment concentration and suspended sediment transport rate were consistently higher after optimization, indicating enhanced sediment carrying capacity. In addition, the optimized configuration increased the vertical velocity gradient and Froude number, while all cases remained within the subcritical-flow regime. These findings demonstrate that structural optimization can simultaneously improve hydraulic regulation and siltation resistance, and provide an experimental basis for the application of streamlined hydraulic measuring structures in sediment-laden irrigation channels. Full article

The concentration of inevitable ionic species in regenerated water significantly alters the flotation characteristics of rare earth minerals, thereby hindering the effective extraction of bastnaesite. Therefore, it is of great significance to study the influence and mechanism of inevitable ions on the flotation of bastnaesite. This paper systematically investigated the effects of Ca²⁺, Mg²⁺, and Fe³⁺ on the flotation behavior of bastnaesite using a BHA/OHA combined collector system and studied the mechanism of action using contact angle testing, Raman spectroscopy, and Visual MINTEQ solution chemistry calculations. The results showed that the BHA/OHA combined collector had good collecting performance for bastnaesite, while Ca²⁺, Mg²⁺, and Fe³⁺ all had varying degrees of inhibitory effects on its flotation, with the order of influence being Fe³⁺ > Mg²⁺ > Ca²⁺. Contact angle tests showed that the presence of inevitable ions weakened the effect of the combined collector on improving the hydrophobicity of the bastnaesite surface. Raman spectroscopy results indicated that inevitable ions interfered with the adsorption of the combined collector on the mineral surface, with Fe³⁺ having the most significant effect. Solution chemistry analysis further demonstrated that Ca²⁺ and Mg²⁺ have been the primary ions influencing flotation because of their interactions with the mineral surface and collector molecules, but not Fe³⁺, which is mainly adsorbed on the mineral surface in the form of hydrolyzed species, thereby inhibiting the reagent adsorption and enhancing the surface hydrophilicity. Based on this, this paper revealed the differentiated interference mechanisms of different inevitable ions on the flotation of bastnaesite, and applied the relevant insights to guide the recovery of rare earth resources in molybdenum tailings, providing a theoretical basis and new research ideas for the flotation control of bastnaesite and the efficient utilization of rare earth resources under complex backwater conditions. Full article

Urban water bodies serve as biodiversity hot spots in a human-influenced landscape. We studied the backwater “Alte Donau” (Vienna, Austria), which has been the subject of ongoing management and restoration efforts. We aimed to capture short-term variations in the planktonic and benthic algal community during a vegetation period with a specific focus on Gloeotaenium loitlesbergerianum with its primary distribution in tropical regions. In total, 196 algal taxa were identified, indicating a high and balanced species diversity. Although the waterbody is shallow and densely colonized by macrophytes, phytoplankton and microphytobenthos exhibited significant differences in composition, particularly in spring. Less pronounced differences during summer were probably caused by macrophyte harvesting combined with recreational activities. We found a clear seasonal pattern with spring characterized by blooms of Ochrophyta, followed by a shift towards green algae, Dinophyta, and Cyanobacteria during summer and autumn. We found high variability in spring samples, whereas summer and autumn samples showed increasing similarity. Temperature, silicate, and alkalinity were the primary environmental factors structuring algal community composition. G. loitlesbergerianum was detected during warmer months from May through October across a temperature range of 14 to 28 °C, with highest abundances >20 °C. Warmer water and altered nutrient regimes not only stress native populations but also promote the establishment of new species such as G. loitlesbergerianum, accelerating community shifts. Therefore, sustained monitoring, targeted macrophyte restoration, and effective nutrient management are crucial for preserving both water quality and biodiversity in such systems. Full article

Tsunami-induced scour around coastal embankments and nearshore structures is a primary cause of structural instability and failure. However, the hydrodynamic mechanisms by which coastal vegetation mitigates this scour remain insufficiently understood. This study employs three-dimensional numerical simulations to investigate the influence of rigid and flexible vegetation on overflow-induced scour downstream of embankments and local scour around structures under tsunami-like inundation. The simulations were conducted using Ansys Fluent 2021R2, utilizing the Volume of Fluid (VOF) method to capture the free surface and the RNG k − ε turbulence model within the Reynolds-averaged Navier–Stokes (RANS) framework. Computational geometries were reconstructed from laboratory experiments, and the model’s reliability was validated against measured water surface profiles. The results demonstrated that vegetation significantly alters flow dynamics, velocity distributions, vortex structures, and both the magnitude and patterns of bed shear stress within scour holes. Specifically, in overflow-induced scour, vegetation suppresses scour intensity by inducing backwater effects, enhancing momentum diffusion, attenuating flow impingement on the bed, and reducing peak bed shear stress. Conversely, for local scour around structures, vegetation increases upstream water depth while intensifying downstream wake vortices, leading to scour hole elongation—particularly under dense and tall vegetation. These findings offer novel insights into the hydrodynamics of vegetation-induced scour mitigation and provide guidelines for optimizing vegetation configurations to enhance the tsunami resilience of coastal infrastructure. Full article

A series of generalized fixed-bed physical model experiments were conducted to investigate the hydrodynamic effects of spur dike configuration and permeability. The study was carried out in a rectangular flume at a geometric scale of 1:40. A traditional impermeable spur dike, a novel impermeable spur dike with a curved geometry, and permeable spur dikes with varying porosities (p = 11.8%, 17.6%, and 23.2%) were systematically examined. Surface velocity and flow direction were measured using a large-scale surface flow field measurement system. Additionally, tracer-based experiments were conducted to characterize oil spill spreading pathways, areas, and rates. The results showed that the novel curved-profile spur dike alleviates upstream backwater effects and weakens downstream plunging flow compared to the conventional straight-profile spur dike, resulting in a more uniform surface flow structure. At low porosity (P = 11.8%), hydrodynamic behavior resembled that of impermeable structures. In contrast, at high porosity (P = 23.2%), upstream–downstream hydraulic connectivity was enhanced, and recirculation intensity was reduced. Regarding oil spill dispersion, spur dike promoted oil retention in the upstream region and lateral spreading around the spur dike head. The extent of the spreading area was strongly influenced by both the cross-sectional geometry and the porosity of the spur dike. Among the permeable cases, the largest spreading area was observed at an intermediate porosity (P = 17.6%). However, permeable spur dike generally exhibited smaller overall spreading areas compared to impermeable spur dike. Finally, an empirical model for predicting the oil spreading area was developed by incorporating flow velocity, water depth, and porosity. These findings provide a scientific basis for optimizing spur dike design and mitigating oil spill risks. Given the severe threat that oil pollution poses to aquatic environments, the retention capacity of spur dikes serves as a critical hydraulic barrier, thereby promoting environmental and ecological sustainability. Full article

Ice-jam formation during winter low-flow conditions represents a persistent hydrotechnical hazard in small and medium-sized rivers of Central Europe. Despite extensive monitoring efforts, preventive structural measures remain insufficiently developed and rarely evaluated under real geomorphological constraints. This study proposes and hydraulically verifies a low-profile riverbed sill designed to suppress the initiation and stabilization of frazil and anchor ice during critical winter discharges. The analysis integrates 20 years of hydrological and water-temperature data (2004–2024), 26 detailed cross-sectional surveys, a high-resolution longitudinal profile derived from DMR 3.0, and a newly formulated Ice-Jam Risk Index (Iice) combining flow velocity, depth-to-width ratio and thermal deficit. Application to the Torysa River (rkm 42.8–43.6) revealed a clearly defined high-risk zone (rkm 43.20–43.38), where hydraulic conditions frequently fall below the critical thresholds for ice accumulation (U < 0.35 m·s⁻¹; h/B < (h/B)_crit; ΔT > 0.5 °C), indicating shallow and laterally widened channel sections prone to anchor-ice stabilization. Model simulations demonstrated that the proposed sill increases mean velocity by 22–35% during Q₆₅–Q₈₅ conditions, reducing the local I(ice) by 61%, while preserving the conveyance capacity for discharges above Q₅₀ and avoiding measurable backwater impacts upstream. Field-based morphology, risk index interpolation and hydraulic modeling all confirm that the structure effectively disrupts the formation of stable anchor-ice nuclei, which have historically triggered severe ice-jam floods in this reach (2011/12, 2016/17, 2021/22). The results show that a properly dimensioned low-profile sill provides a passive, low-cost, and transferable engineering solution for winter flood risk mitigation, outperforming reactive ice-management techniques while maintaining ecological and hydraulic compatibility with small natural rivers. The methodology is replicable for other rivers where supercooling, low-flow hydraulics and channel morphology jointly control ice-jam initiation. Full article