Complex Hydraulic Conditions Research Articles

Experimental Investigation Of Open Channel Flow Around A Hemisphere At Different Relative Depths Using 3D-PTV

In regulated rivers and small streams, the presence of large roughness elements like boulders and concrete structures significantly impacts the local flow field and creates complex hydraulic conditions important for aquatic habitats. This study focuses on investigating and analyzing the complex three-dimensional flow field around an idealized stone (represented as a hemisphere) to understand how the flow field changes for different relative depths i.e. water depth relative to boulder height, and flow rates. Time-resolved 3D Particle Tracking Velocimetry was employed in laboratory experiments conducted in an open-channel flume, to mimic varying river conditions and their impact on flow characteristics. Results reveal that the relative depth significantly influences the flow structure behind the hemisphere, impacting recirculation zones and wake characteristics. The flow field behind the hemisphere was found to be more sensitive to changes in relative depth than bulk velocity. The study also highlights the larger regions of lower streamwise velocity that occurred downstream of the hemisphere caused by the lower submergences combined with a higher magnitude of the downward vertical velocity. Furthermore, this study demonstrates the capability of the measurement technique and the time-resolved 3D Particle Tracking Velocimetry system used to effectively capture the complex flow dynamics around the boulder. This approach allowed for detailed visualization and quantification of flow parameters such as streamwise and vertical velocities within the wake region, which are important factors for aquatic habitats. Understanding the underlying flow dynamics around an idealized stone at low relative depths could yield insights into ecohydraulic engineering and ecological restoration in shallow streams. This can contribute to advancing our understanding of riverine flow dynamics and their ecological implications.

Participatory Geomonitoring for Future Mining—Resilience Management in the Cavern Storage Epe (Germany)

Integrated geo- and environmental monitoring in mining represents a high-dimensional challenge (location, altitude/depth, time and sensors). This is challenging for experts but poses great problems for a multitude of participants and stakeholders in building up a complete process understanding. The Epe research cooperation aims to elucidate the ground movement at the Epe cavern storage facility with a public participation process. The research cooperation was founded by the city of Gronau, the citizens’ initiative cavern field Epe, the company EFTAS, Münster, and the Research Center of Post-Mining at the Technische Hochschule Georg Agricola, Bochum. This research cooperation is the first in Germany to involve direct collaboration between science and the public. In the cavern field, which has been in operation since the 1970s, brine is extracted, and at the same time natural gas, crude oil and helium, as well as hydrogen in the future, are stored in the subsurface. The technical focus of this work was the development of a high-resolution spatiotemporal analysis of ground movements. The area is monitored annually by the mining company’s mine surveyor. The complexity of the monitoring issue lies in the fact that the western part is a bog area and a former bog area. Furthermore, the soils in the eastern part are very humus-rich and show strong fluctuations in the groundwater and therefore complex hydraulic conditions. At the same time, there are few fixed scatterers or prominent points in the area that allow high-resolution spatiotemporal monitoring using simple radar interferometry methods. Therefore, the SBAS method (Small Baseline Subset), which is based on an aerial method, was used to analyze the radar interferometric datasets. Using an SBAS analysis, it was possible to evaluate a time series of 760 scenes over the period from 2015 to 2023. The results were integrated with the mine survey maps on the ground movement and other open geodata on the surface, the soil layers and the overburden. The results show complex forms of ground movement. The main influence is that of mining. Nevertheless, the influence of organic soils with drying out due to drought years and uplift in wet years is great. Thus, in dry years, ground subsidence accelerates, and in wet years, ground subsidence not only slows down but in some cases also causes uplift. This complexity of ground movements and the necessary understanding of the processes involved has been communicated to the interested public at several public information events as part of the research cooperation. In this way, an understanding of the mining process was built up, and transparency was created in the subsurface use, also as a part of the energy transition. In technical terms, the research cooperation also provides a workflow for developing the annual mine survey maps into an integrated geo- and environmental monitoring system with the development of a transparent participatory geomonitoring process to provide resilience management to a mining location.

Phreatic Line Calculation of Reservoir Landslide under Complex Hydraulic Conditions—A Case Study

A seepage field, influenced by rainfall and reservoir water level fluctuation, is closely associated with the stability of the reservoir landslide. Understanding the phreatic line variation inside the landslide is of significant importance for the analysis and evaluation of slope stability. Currently, most of the boundaries of phreatic line analytical models and the hydrological conditions are simplified, resulting in discrepancies between the outcomes derived from these models and the actual situation. Given this, the newly proposed analytical model is refined by addressing the following two issues. Firstly, the consideration of variable-speed reservoir level fluctuations is incorporated, and secondly, the reservoir bank within the water-level fluctuation zone is treated as non-vertical. Under the combined effect of reservoir water level fluctuation and rainfall, the Boussinesq Differential Equation of unsteady seepage is established and applied to the Majiagou landslide in Three Gorges reservoir area. The results of the analytical solution are basically consistent with the measured groundwater level results, which has demonstrated the accuracy of the proposed model. Consequently, the proposed model can quickly and accurately calculate the groundwater level of landslides, which provides an effective means for the prediction and early warning of reservoir landslides.

3D-CFD analysis of bedload transport in channel bifurcations

Abstract The aim of this research was to numerically reproduce bedload transport processes in channel bifurcations and thereby evaluate the methodology and feasibility of 3D-computational fluid dynamics (CFD) bedload transport simulations. This was carried out by numerically replicating two physical model investigations of channel bifurcations: research conducted by Bulle in 1926 and a large-scale channel bifurcation investigated at the Kassel University hydraulic laboratory. The numerical results were evaluated by comparing bedload distributions in the channel areas, formations of bedload depositions and development of bedload over time. The numerical simulations of Bulle's model were conducted for different boundary conditions, numerical parameters, sediment grain sizes, flow rates, flow distributions on the two channel branches and for longer running simulations. The investigations of the Kassel University bifurcation were carried out for different sediment types, which influences the numerical parameters, as well as for different flow distributions and channel width/depth ratios. Finally, structures for deflection of bedload into the straight channel were investigated. The results showed that bedload movement can be successfully simulated with 3D-CFD models, even in complex hydraulic conditions. Based on the obtained results, important indicators and recommendations for the application of 3D-CFD bedload transport simulations were acquired.

Modelling Stage-discharge Relationships for Hydrological Stations in the Da River Basin using First-kind Chebyshev Polynomial Approximation

Observed discharge time series is essential data for hydrological analysis, streamflow forecasting, as well as water resources planning and management. Estimation of continuous discharge time series is generally based on the curves (or empirical models) that can properly simulate the relationships between water levels (stages) and concurrent water discharges observed at a particular hydrological station. For stations with complex hydraulic conditions, in addition to gauged stages at the discharge gauging section, another variable such as stage measured at an auxiliary station (to calculate the slope) or rate of change in stage is added to the estimation process. This paper presents the results of applying the first-kind Chebyshev polynomial approximation method in constructing rating curves for three hydrological stations in the Da river basin, each having different basin characteristics and various influencing factors. The analysis results using five evaluation indices (MAE, σ, Pbias, KGE, and MAPE) show that the Chebyshev polynomials are highly effective in modelling both simple and complex stage-discharge relationships. The Chebyshev polynomial approximation method is suggested to be used for establishing stage-discharge relationships in hydrometry.

Hydraulic characteristics in channel confluence affect the nitrogen dynamics through altering interactions among multi-trophic microbiota

Identifying the distribution of multi-trophic microbiota under the complicated hydrodynamic characteristics of channel confluences and evaluating the microbial contributions to biogeochemical processes are vital for river regulation and ecological function protection. However, relevant studies mainly focus on bacterial community distribution in confluence, neglecting the essential role of multi-trophic microbiota in the aquatic ecosystems and biogeochemical processes. To address this knowledge gap, this study investigated the distribution of multi-trophic microbiota and the underlying assembly process under the hydraulic characteristics in the confluence and described the direct and indirect effects of multi-trophic microbiota on the nitrogen dynamics. Results revealed that, in a river confluence, eukaryotic communities were governed by deterministic processes (52.4%) and bacterial communities were determined by stochastic processes (74.3%). The response of higher trophic levels to environmental factors was intensively higher than that of lower trophic microbiota, resulting in higher trophic microbiota were significantly different between regions with varied environmental conditions (P < 0.05). Flow velocity was the driving force controlling the assembly and composition of multi-trophic microbiota and interactions among multi-trophic levels, and further made a significant difference to nitrogen dynamics. In regions with lower flow velocity, interactions among multi-trophic levels were more complex. There were intense nitrate and nitrite reduction and anammox reactions via direct impacts of protozoan and metazoan and the top-down control (protozoan and metazoan prey on heterotrophic bacteria) among multi-trophic microbiota. Results and findings reveal the ecological effect on river nitrogen removal in a river confluence under complex hydraulic conditions and provide useful information for river management.

A novel methodology to quantify hydraulic conveyance through an ice-impacted lake-outlet system

River ice can pose considerable challenges to hydropower operations in cold regions. Relative to open-water conditions, the presence of ice in various forms contributes to lower hydraulic efficiency. At the outlet of Lake Winnipeg, maintaining winter conveyance through the channels of the Outlet Lakes Area (OLA) is of paramount importance for downstream energy production on the Nelson River. The complex hydraulic conditions of the OLA are attributed to various factors, including the influence of hydraulic system operation, flow routing through lakes and rivers with non-uniform attributes, and the presence of dynamic ice processes throughout winter. In this study, a methodology was designed to quantify the impacts of ice on the OLA hydraulics using a combination of numerical modelling and statistical techniques. This approach includes adaptation and configuration of a two-dimensional river ice model, selection of suitable performance metrics, and derivation of hydraulic datasets for model simulations using historical observations and statistical relationships. Numerical modelling simulations feature treatments for predominant ice processes in the OLA, including freeze-up jamming, thermal growth and decay of a stable ice cover, and under cover transport and deposition of brash ice. The methodology was evaluated using historical winters 1996–1997 to 2020–2021, with most results falling within an acceptable performance range, even in response to varying hydro-meteorological conditions. Instances of error exceeding accepted thresholds were attributed mainly to factors outside of the study, including uncertainty in discharge estimation and the effects of mid-winter forebay operation. Influence of Lake Winnipeg water levels on winter hydraulics was identified as significant, as higher upstream Lake Winnipeg water levels can mitigate ice impacts by providing more hydraulic head for conveyance. As expected, ice restriction severity also varies in accordance with heat fluxes. Targeted areas for improvement of the methodology and future work are discussed, including enhancing the simulation of the thawing (‘pre-breakup’) period and field verification of flow split quantities during winter. The methodology presented provides an estimate of ice-impacted hydraulic conveyance which serves to benefit hydropower operators, regional water resources studies, and further investigations of river ice impacts that can be attributed to future climate change.

Impacts of hydraulic conditions on microplastics biofilm development, shear stresses distribution, and microbial community structures in drinking water distribution pipes

Both microplastic and biofilm are contamination sources in drinking water, but their integrated impacts on water quality have been rarely studied, especially in drinking water distribution pipes with complex hydraulic conditions. This study explored the impacts of hydraulic conditions (0–2 m/s) on microplastic biofilm (MP-BM) development, shear stresses distribution, and microbial community structures. The research was conducted for two weeks using a pilot test device to simulate practical water pipes. The following were the primary conclusions: (1) According to morphology analysis, clusters (>5 μm) significantly increased in the plastisphere when the flow velocity ranged from 0.55 m/s to 0.95 m/s, and average size of clusters decreased when the flow velocity ranged from 1.14 m/s to 1.40 m/s (2) Characteristics of MP-BM impact shear stress on both plastisphere and pipe wall biofilm. Shear stresses were positively correlated with flow velocity, number of MP-BM, and size of MP-BM, while negatively correlated with diameters of pipes. (3) 31 genera changed strictly and monotonously with the fluid velocity, accounting for 15.42%. Opportunistic pathogens in MP-BM such as Sediminibacterium, Curvibacter, and Flavobacterium were more sensitive to hydraulic conditions. Moreover, microplastics (<100 μm) deserve more attention to avoid human ingestion and to prevent mechanical damage and bio-chemical risks.

Simulation Research on System Characteristics of Valve Opening Curve of Bidirectional Water Transfer System

Due to long pipelines, complex hydraulic conditions, and high flow rate, Bidirectional Water Transfer System of ship is prone to producing Water Hammer Effect when the valve opens and closes, which has a great impact on the pipeline system. In this paper, Flowmaster software is used to simulate the Bidirectional Water Transfer System to study the system characteristics under different valve opening curves. The simulation results show that when the valve opens and closes, Bidirectional Water Transfer System will have a large pressure mutation. But the pressure changes of the stepped and the stepped curve opening curves are smaller and smoother than that of the linear opening curve. But the stepped and the stepped curve opening curves can’t eliminate the pressure and flow rate mutation when the valve opens and closes; In addition, the stepped and the stepped curve opening curves can effectively improve the phenomenon of water flowing out of the reservior, and effectively avoid the phenomenon of gas flowing into the reservior.

Hydraulic conditions affect pollutant removal efficiency in distributed ditches and ponds in agricultural landscapes

Distributed ditches and ponds in agricultural landscapes can retain agricultural pollutants (such as nutrients and pesticides) like wetlands while facilitating crop field drainage. Their complex hydraulic conditions affect pollutant transport and degradation processes, but the existing lump-sum method for estimating pollutant removal treats the total area simply as one unit without considering their specific hydraulic conditions (HCs). In this paper we proposed an analytical method for evaluating pollutant removal efficiencies of distributed ditches and ponds by considering their different HCs explicitly. A realization factor (RF) was used to compare pollutant removal rates with and without considering specific HCs. Application of the method was demonstrated with a case study based on field investigations in an intensively farmed area in southeastern China. The total area of ditches and ponds accounts for 15% of drained crop fields; and the calculated RFs were 0.70–0.84% for various removal rate constants. The difference was mainly caused by the uneven distribution of ditches and ponds along different drainage paths. For pollutants with small values of removal rate constants, the calculated concentration reductions along different flow paths were proportional to their wetland sizes, making the pollutant removal as area limited. For pollutants with larger values of removal rate constant, however, the calculated pollutant removal became concentration limited when the wetland to farmland area ratio was high. Large ponds and ditches were major contributors (85–94%) of pollutant removal in the whole system, while the field ditches contributed to less than 10% of the total removal due to their small dimension and shallow water depth. The distributed nature of ditches and ponds poses some inherent limitations to their water quality functions due to variable hydraulic conditions; understanding such underlying constraints may help guide proper evaluation and conservation of the existing ditches and ponds in agricultural landscapes.

Seepage simulation of high concrete-faced rockfill dams based on generalized equivalent continuum model

This research focused on the three-dimensional (3D) seepage field simulation of a high concrete-faced rockfill dam (CFRD) under complex hydraulic conditions. A generalized equivalent continuum model of fractured rock mass was used for equivalent continuous seepage field analysis based on the improved node virtual flow method. Using a high CFRD as an example, the generalized equivalent continuum range was determined, and a finite element model was established based on the terrain and geological conditions, as well as structural face characteristics of the dam area. The equivalent seepage coefficients of different material zones or positions in the dam foundation were calculated with the Snow model or inverse analysis. Then, the 3D seepage field in the dam area was calculated under the normal water storage conditions, and the corresponding water head distribution, seepage flow, seepage gradient, and seepage characteristics in the dam area were analyzed. The results show that the generalized equivalent continuum model can effectively simulate overall seepage patterns of the CFRD under complex hydraulic conditions and provide a reference for seepage analysis of similar CFRDs.

Discussion on Operation Mode of Long Distances Gravity-Fed Pressure Diversion Project

The characteristics of long distance gravity-fed pressure water-conveying projects are long pipe length, huge changes in rise and down of pipeline arrangement, and complex hydraulic conditions. It is the water hammer that mainly influences the safe operation of such projects. Based on a real long distance gravity-fed pressure water conveying pipeline system, fluid transients processes under different operation modes were analyzed by using the method of characteristics. The pipeline longitudinal arrangement is high in two ends and low in the middle part. The research puts forward that for such pipeline arrangement using valve set in the midway of the pipeline to control the system is evidently better than that of valve at the downstream end of pipeline. In this way, pipeline working pressure can be effectively reduced, in turn, the pipe pressure grade can be decreased and the investment of the project can be reduced.

Experimental quantification of the swimming performance and behaviour of spawning run river lamprey Lampetra fluviatilis and European eel Anguilla anguilla

Using a large-scale open-channel flume, the swimming ability and behaviour of individual adult European eel Anguilla anguilla and river lamprey Lampetra fluviatilis, species that exhibit anguilliform locomotion, were quantified under complex hydraulic conditions created by a 0·2-0·3 m high under- or overshot weir during four discharge regimes. Fishes were allowed to approach the weirs from both up- and downstream. All fishes passed the undershot weir, independent of discharge and direction of movement, and under high flow (mean ±S.E. 194·63 ± 6·48 l s(-1)) moved upstream against velocities that ranged between 1·75 and 2·12 m s(-1), suggesting greater maximum swimming capability than previously reported. In comparison, passage efficiency during upstream movement was lower for the overshot weir for both L. fluviatilis and A. anguilla. Downstream moving A. anguilla took longer to pass the over- than undershot weir. This study describes a methodology to attain realistic measures of swimming ability and behavioural performance required to develop multispecies fish passage criteria.

Influence of position and type of Doppler flow meters on flow-rate measurement in sewers using computational fluid dynamic

The key to the successful management of sewer networks is the accurate understanding of flow quantity. Unfortunately, the measurement of flow-rate in sewers is often expensive, labor intensive, and the performance limitations of the available technology may lead to inaccurate results. Computational Fluid Dynamics (CFD) can be a useful tool for making the measurement more representative. A new flow measurement approach, based on the use of CFD software, was developed to allow accurate measurement of flow rates in open channels and pipes, even under complex hydraulic conditions. This paper presents an application of CFD to calculate the corrective coefficient, which must be applied to the measured value of velocity to obtain the mean velocity for different acoustic Doppler sensors. The variation of the corrective coefficient for maximum measured velocity ( K U max ) was less according to the height of water level and position of sensors compared to the corrective coefficient for mean measured velocity ( K U mean ). The flow measurement obtained by a sensor with a large cone volume was independent of the position for high water levels, while it was slightly dependent on the position at low water levels due to a large scanned volume. The bottom and free surface positions are found to be optimal to obtain a velocity close to that of the central zone, where it is not disturbed by the walls. The main idea is to obtain a reliable methodology by the combined use of an instrument and a measuring section, in order to improve the reliability and the accuracy of the measured values.

Energetic costs of migration through the Fraser River Canyon, British Columbia, in adult pink (Oncorhynchus gorbuscha) and sockeye (Oncorhynchus nerka) salmon as assessed by EMG telemetry

Adult Pacific salmon (Oncorhynchus spp.) depend on energy reserves to complete their upriver spawning migration. Little is known about how flow patterns and bank characteristics affect energetics or how species differ in reach-specific energy use. In 1999, electromyogram (EMG) radiotelemetry was used to describe activity levels and estimate energy use of 12 adult pink salmon (Oncorhynchus gorbuscha) during their upstream migration in a 7-km section of the Fraser River Canyon. Data collected previously on sockeye salmon (Oncorhynchus nerka) in the same study area provided a species comparison. We could not identify any strong differences in energetics between species. Although sex had some influence, reach characteristics were the primary factors affecting migration activity and energetics. Fish increased their activity levels when they migrated through reaches constricted by islands or gravel bars compared with nonconstricted reaches. The former contained higher velocity currents and more complex hydraulic conditions than the latter. Two behavioural responses, with similar energetic consequences, occurred in constricted reaches. Either fish swam slowly and took more time, presumably searching for lower velocity areas for migration thus increasing passage time, or they swam quickly through higher velocity flow fields.

Optimal Nonlinear Predictive Control for Canal Operations

The predictive canal operation method (PCOM) provides optimal real-time control of irrigation canals with incorporation of current and forecasted demands. PCOM utilizes an efficient, nonlinear, optimal control algorithm interacting with a fully dynamic, unsteady-flow hydraulic model. Optimal predictive controls are determined for all check structures and demand points along the canal, as well as the intake pump station, if one is present. Optimal control is performed with consideration of hydraulic conditions along the entire canal, as modeled by a Preissman-type implicit scheme for the complete St. Venant equations. The algorithm generates predictive control policies (anticipatory control) and system-wide feedback control under complex hydraulic conditions, including zero flow and closed gates. Equable distribution of shortages is achieved in cases of water supply deficiencies. PCOM is applied to Main Canal 3 of the Formoso H project, Bahia, Brazil, as a case study, and performs well under severe operational constraints. The computational efficiency of the algorithm allows implementation on microcomputer controllers for real-time use.

Near‐substrate hydraulic conditions under artificial floods from peaking hydropower operation: A preliminary analysis of disturbance intensity and duration

AbstractFST hemispheres of identical size but varying density were used to evaluate the intensity and duration of near‐bottom shear stresses during peaking hydropower floods of various magnitudes (maximum 345 m3 s−1; baseflow 2.75 m3 s−1). The FST values at single points were recorded at rapid intervals along previously surveyed transects during the rising limb of flood events at various distances from the hydropower facility. Whole transect evaluations were ‐accomplished after the ‘flood’ level had stabilized.Measurements of over 1300 FST values were significantly correlated with mean water column velocity and complex hydraulic conditions such as turbulence, shear velocity and viscous sublayer. FST hemispheres are a rapid means of characterizing hydraulic conditions in medium order rivers. Changes in near‐substrate hydraulic conditions were patchy and could be classified in terms of risk to fauna of either dislodgement or physical damage. Low risk (class 1) changes occurred when FST values increased rapidly but returned to initial values after a short period of time (&lt; 90 minutes) from the arrival of the peaking wave. Medium risk (class 2) changes occurred when FST values increased rapidly and decreased after a short period of time, but remained at levels higher than before the arrival of the flood wave. High risk (class 3) changes occurred when FST values increased rapidly and remained at high levels during the entire flood event.It is suggested that floods that do not initiate significant bed movement create a mosaic of patches of variable disturbance risk to benthic fauna. Rapid evaluation by FST hemispheres could be used to characterize the overall disturbance potential for the channel by the construction of a weighted index based on the frequency of the various risk classes occurring in the reach being evaluated. A more appropriate analysis of impacts of peaking hydropower and other flood events must include the existence of hydraulic refugia and the movement patterns of both benthic species and those species that occupy the water column.