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In this work, surface/interface effects for pull-in voltage and viscous fluid velocity effects on the dimensionless natural frequency of fluid-conveying multiwalled piezoelectric nanosensors (FC-MWPENSs) based on cylindrical nanoshells is investigated using the Gurtin–Murdoch surface/interface theory. The nanosensor is embedded in a viscoelastic foundation and subjected to nonlinear van der Waals and electrostatic forces. Hamilton’s principle is used to derive the governing and boundary conditions and is also the assumed mode method used for changing the partial differential equations into ordinary differential equations. The influences of the surface/interface effect, such as Lame’s constants, residual stress, piezoelectric constants and mass density, are considered for analysis of the dimensionless natural frequency with respect to the viscous fluid velocity and pull-in voltage of the FC-MWPENSs.

Grass swales, originally used for erosion control in agricultural settings, are now widely employed in urban environments as an effective best management practice for controlling pollutants in stormwater runoff. In particular, vegetated swales are quite successful in removing heavy metal concentrations when the depth of flow is small relative to grass height. However, guidance materials currently available for design of vegetated channels focus on larger depths of flow (large flow conveyance/erosion control), and for such conditions the hydraulic resistance exerted by the vegetation can be significantly different than that observed when the depth of flow is small (remediation). Utilizing a series of laboratory channels, small-flow retardance curves have been developed in the present work for Bluegrass, Centipede, and Zoysia grass species. These 'small-flow' curves extend the well-known Stillwater n versus VR diagram by approximately 1 order of magnitude, to smaller values of VR. Experimental results should provide valuable design guidance to those faced with the need to hydraulically design a swale intended for shallow depths of flow. CE Database subject headings: Best management practice; Grasses; Channel flow; Swales; Flow resistance; Roughness coefficient; Environmental engineering.

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ABSTRACT: Hydropower with a small elevation change from inlet to outlet, known as “low-head” hydropower, is a relatively untapped resource for reliable green power generation. One major barrier to entry is the cost of the components needed to generate the power. Each installation site is unique, with various head levels, flow rates, and other unique site characteristics that drive up the cost of development and installation. As a result, custom-made components are necessary because the sites are intrinsically inefficient. However, customized parts are generally more expensive to manufacture than ready-made parts. Often times, the cost of custom-made components is so high that the low-head hydropower installation becomes non-viable. Additive manufacturing offers the ability to make custom components, ideal for one-off applications, at low costs that are well suited for the needs of low-head hydropower. Indirect additive manufacturing, such as making tools or dies rather than end use components, can also be used to make low-cost composite tooling as needed for these custom applications. This paper explores the use of additive manufacturing, both directly and indirectly, to produce the components of a turbine system for a low-head hydropower site. The parts were designed to form a unique modular system, which saves time for future designs and iterations. The system has operated for more than three years without failure at a test site in Wisconsin, USA. This work serves as a basis for future application of AM to low-head systems, in which the modular components can be customized for each unique hydropower installation.

As it is known, vegetation is an important component of aquatic ecosystems. Because of the variety of species and, thus, of the characteristics of the vegetation elements (form, size, stiffness, etc.), it is difficult to develop a widely applicable method to predict mean flow and flow resistance. Despite the intense activity research, much work has to be done in understanding hydrodynamics in vegetated channels. This is important to analyse many physical processes involved in the ecosystem at different spatial and time scales. In this paper, attention is restricted to flexible vegetation. After a brief description of results obtained in previous experimental works conducted in a rectangular laboratory flume at the Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale, dei Materiali – University of Palermo (Italy), the data are used to investigate how stems' concentration and flow submergence affect the mean flow and flow conveyance characteristics in vegetated channels. The results indicate that both these parameters affect the flow profile and flow conveyance characteristics, but flow submergence especially influences the dominant mechanism of momentum exchange between the vegetation layer and the layer above it. [ABSTRACT FROM PUBLISHER]

Two generalized dynamic reliability models (integrating both hydrologic and hydraulic uncertainties) based on binomial and Poisson distributions are developed for evaluating flow conveyance reliability of hydraulic structures. The two generalized models correct the deficiencies of dynamic reliability models developed previously. Relative performance of the generalized models and two conventional reliability models were examined. It is found that the total risk is significantly underestimated by the conventional approaches when hydraulic uncertainty is moderate or large. [ABSTRACT FROM AUTHOR]

The article discusses a study which explored changes in high water occurrence in the Sava River near Zagreb, Croatia. The series of maximum annual Sava River stages and discharges measured at the Zagreb gauging station from 1926 to 2004 were analysed. It examined long-term stages and linear trends in discharges using a technique which converted stages to actual river channel morphology conditions. The study found that the construction of embankments near the riverbed and the exclusion of upstream flooplains caused an increase of high water levels.

The presence of macroroughness elements directly affects the flow velocity in mountain headwater streams. Hydraulic roughness is the dominant resistance to flow caused by objects protruding into the water, but it is not measurable in the field. This study quantified the reach-average hydraulic roughness based on the channel morphology in two mountain streams. The average flow velocities of the reaches were measured using the dye-tracing method. The magnitude of the hydraulic roughness was derived from the grain size of the streambed materials (D50 and D84) and the cross-sectional/longitudinal bed roughness. The observations for low flows (0.04–0.43 m2/s discharge per unit width) indicated that the longitudinal 90% inter-percentile range ( I P R 90 L ) seemed to have considerable merit in examining the influences of large roughness elements on flow conveyance. A dimensionless hydraulic geometry relation that can reflect the field measurements over a limited range of hydraulic characteristics was also developed for estimating the reach-average flow velocity in steep and rough streams. Thus, the research framework used appears to provide a reliable method of quantifying reach-average hydraulic roughness from local data in mountain headwater streams. [ABSTRACT FROM AUTHOR]

The process of icing involves the freezing of overflow layers, on ground or within streams, and results in ice bodies called "aufeis" that are common in most northern landscapes. Knowledge about aufeis is still limited despite the cold region engineering challenge they represent. Understanding the causes of overflow events leading to aufeis development represents a key for the prediction, mitigation, and management of this geohazard and can also support the planning and design of infrastructure in the North. This paper introduces a practical classification for the diverse range of overflow processes that generate aufeis, including under-represented processes, such as the instability of winter streamflow. Importantly, it distinguishes flow conveyance from water supply overflow processes and describes the temporal aspect of icing intensity. Finally, research topics are proposed to improve our understanding of aufeis, including their predictability, the impact of climate change on their occurrence and extent, and stream morphology–aufeis interaction. [ABSTRACT FROM AUTHOR]

A paramount determinant in the selection of irrigation canal overflow configurations resides in their flow conveyance capacity. This overflow capacity is contingent upon the effective length and geometric characteristics of the weir. In the present investigation, the hydraulic performance and discharge coefficient (Cd) of circular-crested weir were scrutinized through the utilization of FLUENT software. Specifically, the study delved into the impact of geometric parameters, namely the radius and height of the crest, on these hydraulic aspects. Following the execution of calibration and validation procedures using FLUENT in conjunction with laboratory-derived data, the outcomes of the simulation revealed that augmenting the radius of the crest led to a corresponding escalation of 144.28% in the maximum pressure exerted on the crest and a 6.84% increase in flow depth. Conversely, the maximum velocity and Cd experienced reductions of 6.84% and 7.82%, respectively. The elevation of the weir height exhibited negligible influence on the maximum pressure magnitude at the crest. Contrastingly, a reduction in weir height constricted the range of pressure variations on the crest, indicating a more limited domain of pressure changes. Elevating the weir height induces a notable augmentation in the maximum flow velocity at the crest by 44.36%, concomitant with a reduction in both the depth and Cd by 52.66% and 68.96%, respectively. [ABSTRACT FROM AUTHOR]

Grass-lined spillways are flow conveyance structures with environmental benefits. The stability of such spillways has been typically assessed considering soil erosion, but the design of grass-lined spillways based on hydraulic considerations has rarely been conducted. While subcritical flows in channels with grass have been studied extensively, studies of velocities and flow resistance in supercritical flows in spillways are limited. Herein, this experimental study investigated the application of a multilayer velocity model for supercritical self-aerated flows on a spillway with submerged artificial grass. Velocities were measured with a pitot tube and dual-tip air–water flow conductivity probe, providing the most systematic assessment of velocities and flow resistance in supercritical vegetated flows to date. The velocity distributions were well described with a multilayer velocity model previously developed for subcritical flow conditions, and a constant interfacial velocity supplemented the observed supercritical aerated free-surface layer. Based on this velocity model, explicit expressions for the mean flow velocity and the friction factor were developed for grass-lined spillways, which were also applicable for subcritical flow conditions with comparable vegetation cover. The flow resistance model provides a theoretically developed design option for grass-lined spillways that is solely based on vegetation properties and hydraulic boundary conditions. [ABSTRACT FROM AUTHOR]

Vegetation notably influences transport and mixing processes and can thus be used for controlling the fate of substances in the hydro‐environment. Whilst most work covers fully vegetated conditions, the novelty of this paper is to focus on flows with real‐scale flexible willow patches. We aimed to investigate how longitudinal dispersion varies according to the spatial distribution, density and coverage of the patches and to evaluate the explanatory power of predictors that consider the hydraulics, vegetation and channel geometry. Salt tracer experiments were performed in a trapezoidal channel where we established 3–4 m long and 1–1.6 m wide patches of artificial foliated willows that reproduced the shapes and plant densities observed on woody‐vegetated floodplains. We examined sparsely distributed patches with low areal/volumetric coverage of 6–11%, and non‐vegetated conditions for reference. Flow depths and surface widths were 0.7–0.9 and 6–7 m, respectively, and the mean flow velocities ranged at 0.3–0.6 m/s. The emergent patches generated from a negligible to over a four‐fold increase in the longitudinal dispersion when compared with non‐vegetated conditions. The patches with a preferential location in low‐velocity areas, such as near banks, or with a high plant density and a blockage of the cross‐sectional flow area ⪆0.4, led to the largest dispersion and residence times. Patches under such configurations enhanced the normalized differential velocity defined as the difference between the highest (90th percentile) and lowest (10th percentile) cross‐sectional flow velocities divided by the mean velocity, thus increasing shear dispersion. As existing analytical predictors failed to estimate the effect of different patch configurations, we proposed the change in the normalized differential velocity between vegetated and corresponding non‐vegetated conditions as a basic predictor of the reach‐scale longitudinal dispersion coefficient under patchy vegetation. In contrast, we observed no clear relationship between flow resistance and dispersion. Thus, our findings indicated that bankside vegetation may allow for reduced peak concentrations and lengthened residence times, supporting pollutant management, while ensuring good flow conveyance. Such rare field‐scale analyses improve the estimation of solute transport in real vegetated flows. [ABSTRACT FROM AUTHOR]

In drainage and sewerage systems, vertical dropshafts are commonly used to convey water flow from high to low elevations. When the underground tunnel is surcharged, the lower part of the shaft is submerged. The impact of falling water on the free surface in the dropshaft entrains a vast amount of air, leading to the transport or entrapment of air in the tunnel, causing undesirable effects such as the reduction in flow conveyance capacity or air blowback. In this study, a comprehensive series of experiments was performed to study the influence of flow variables on the flow regimes in a submerged dropshaft connected to a horizontal tunnel. The air-water flow in the dropshaft was recorded using high-speed imaging, with air concentration and high-frequency pressure measurements. The experiments showed that the flow in the dropshaft-tunnel system can be classified into four regimes: (I) bubbly column flow, (II) rising slugs, (III) instability and surging, and (IV) net air transport in the tunnel, based on the dropshaft Froude number and the ratio of dropshaft diameter to tunnel diameter. [ABSTRACT FROM AUTHOR]

Flow control programs on regulated rivers can improve winter flow conveyance for hydropower operations. On the Upper Nelson River, station flows at Jenpeg Generating Station are reduced during freeze-up to promote formation of a smooth ice cover in often turbulent upstream areas. This ice cover reduces the risk of frazil generation, which could otherwise result in blockages and subsequent energy losses. In this study, a characterization of freeze-up conditions for the Upper Nelson River is presented through 15 years of historical observations, supplemented by a short-term detailed monitoring program (2015–2018). Observations of rapid leading edge celerity are associated with increased ice production under dampened hydraulic conditions. Analysis of ice cores and drone footage highlights the role of skim ice runs in early cover formation, while predictions of skim ice formation show agreement with ice floe taxonomy from the literature. Establishing a baseline of freeze-up conditions for the region will assist in the development of predictive tools, such as numerical models, to optimize flow control decisions for this significant hydropower system. [ABSTRACT FROM AUTHOR]

Hydropower infrastructure systems are complex, high consequence structures which must be operated safely to avoid catastrophic impacts to human life, the environment, and the economy. Dam safety practitioners must have an in-depth understanding of how these systems function under various operating conditions in order to ensure the appropriate measures are taken to reduce system vulnerability. Simulation of system operating conditions allows modelers to investigate system performance from the beginning of an undesirable event to full system recovery. System dynamics simulation facilitates the modeling of dynamic interactions among complex arrangements of system components, providing outputs of system performance that can be used to quantify safety. This paper presents the framework for a modeling approach that can be used to simulate a range of potential operating conditions for a hydropower infrastructure system. Details of the generic hydropower infrastructure system simulation model are provided. A case study is used to evaluate system outcomes in response to a particular earthquake scenario, with two system safety performance measures shown. Results indicate that the simulation model is able to estimate potential measures of system safety which relate to flow conveyance and flow retention. A comparison of operational and upgrade strategies is shown to demonstrate the utility of the model for comparing various operational response strategies, capital upgrade alternatives, and maintenance regimes. Results show that seismic upgrades to the spillway gates provide the largest improvement in system performance for the system and scenario of interest. [ABSTRACT FROM AUTHOR]

Global climate change is expected to impact hydrodynamic conditions in stream ecosystems. There is limited understanding of how stream ecosystems interact and possibly adapt to novel hydrodynamic conditions. Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions. The interplay of vegetation growth and hydrodynamics results in a spatial separation of the stream into densely vegetated, low-flow zones divided by unvegetated channels of higher flow velocities. This self-organization process decouples both local flow velocities and water levels from the forcing effect of changing stream discharge. Field data from two lowland, baseflow-dominated streams support model predictions and highlight two important stream-level emergent properties: vegetation controls flow conveyance in fast-flowing channels throughout the annual growth cycle, and this buffering of discharge variations maintains water depths and wetted habitat for the stream community. Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity. [ABSTRACT FROM AUTHOR]

Vegetation growth along rivers may have effects on water resistance and velocity distribution. Roughness evaluation is crucial in constructing river stage-discharge curves, due to its great importance in river management and risk assessment. Usually, land managers mechanically remove vegetation to increase flow conveyance and reduce flooding risk, with negative effects on the riverine ecosystem and hydraulic risk downstream. The study aims to implement a useful methodology for management planning along vegetated riparian zones through the development evaluation of both unmanaged and anthropically disturbed riparian ecosystems, using tree stands quantitative parameters required to estimate roughness caused by riparian vegetation. For each watercourse, it was also possible to evaluate the equivalent roughness dependent on river morphology and the effective flow resistance over time. The outputs of vegetation parameters analysis also may provide practical support in gentle maintenance interventions of Tuscan watercourses planning, to ensure positive effects both on water flow and on riverine ecosystem. [ABSTRACT FROM AUTHOR]

The United States National Flood Insurance Program (NFIP) relies on floodway and encroachment line standards to regulate floodplain development and minimize flood damage while ensuring public safety. A regulatory floodway includes a watercourse's main channel and adjacent floodplain areas critical for safely conveying a specified flood flow (the base flood discharge) without raising water surface elevations beyond permitted levels. The flood fringe, the remaining floodplain area inundated by the regulatory flood, can be developed under specific conditions. This paper introduces an optimization-based method to set encroachment limits while minimizing the value-weighted land area within the regulatory floodway, thereby maximizing the developable land in the flood fringe. The procedure organizes the complex decision process into a series of individual choices made at each cross section of a stream reach. These choices affect water surface elevations while meeting specific criteria, focusing primarily on limiting water level increases. Furthermore, floodplain encroachments are required to reduce a specified cross-section property on both sides of the floodplain equally. Two cross-section properties are considered in this study: conveyance and flow area. The NFIP's required approach is equal conveyance reduction. However, the cross-section flow area is more equitable for defining regulatory boundaries with long-lasting consequences. The computational method utilizes dynamic programming to minimize the value-weighted land area within the floodway. Additionally, it reduces the occurrence of irregular floodway boundaries and the need for discretionary modifications to encroachment limits, potentially eliminating such adjustments. [ABSTRACT FROM AUTHOR]

As the demand for transcontinental commerce has increased over the past century, navigation channels have been maintained at increasingly greater depths to continue access of deep draft vessels to inland ports. Over time, these deep navigation channels require routine dredging to counteract the gradual processes of sedimentary accumulation, known as shoaling, that can enter the channel from terrestrial or oceanic sources through natural (e.g., tides, streamflow, runoff) or anthropogenic (e.g., vessel wake) processes. To limit the cost of moving the dredged material to upland or offshore storage facilities and to prevent long-term sediment loss from the system, the material can instead be reused locally to build marsh or island habitats. While the various environmental impacts of keeping and reusing the material within the sourcing embayment have been investigated at length, the hydrodynamic impacts of large-scale within-embayment placements have previously been understudied, particularly regarding potential changes to navigation channel shoaling. In this work, we use numerical models to investigate how channel-parallel linear island features may modify sediment transport mechanisms and pathways, and discuss long-term shoaling implications. Based on the various tested channel and embayment geometries, taken from nautical charts detailing the evolving topobathymetric history of Lake Calcasieu and the Calcasieu Shipping Channel (Louisiana, USA), linear and near-continuous islands are shown to have the potential to increase sedimentation in the channel by altering both local hydrodynamics around the islands and estuarine-scale tidal dynamics. However, the degree to which the islands are continuous (i.e., number and size of gaps between islands) and the dominant forcing factors (i.e., tidally driven versus wind-driven circulation) are shown to limit the increase in shoaling likelihood by island presence. [ABSTRACT FROM AUTHOR]

Shallow mixing layers developed in partially-distributed canopy flows (PCFs) are important for water conveyance, sediment transport and solute dispersion. In this paper, we address the response of shallow mixing layers in PCFs to several influential factors associated with bed friction, water shallowness and canopy denseness using depth-averaged Large Eddy Simulation (DA-LES). The results show that under certain canopy denseness, shallow mixing layers in PCFs display asymptotic behaviour for the variation of bed friction and water shallowness, consistent with classic shallow mixing layers. The canopy drag encourages the asymmetric growth of the inner and outer parts of the mixing layer, and this effect decreases when bed friction and water shallowness become pronounced. Characteristic velocity and length scales show similarity well delineated by exponential decay function regarding a stabilization efficiency parameter. The exception happens for the inner length scale of the mixing layer when only changing canopy density. We conclude that changing the canopy denseness can encourage the overall shift of mixing layer scaling regarding a broad range of bed friction and water shallowness. Furthermore, the bed friction parameter thresholding triggering flow instability of mixing layers in PCFs is found about 0.03, lower than 0.09 for splitter-plate induced mixing layers. [ABSTRACT FROM AUTHOR]

In this study an urban stream network with earthen and concreted sections were studied for different seasons (wet and dry) to investigate the macroinvertebrate composition and the governing factors. The factors considered were water quality (nitrogen species, soluble reactive phosphorus etc.) and stream eco-hydraulics (velocity, wetted depth and width, vegetative indicators, number of mesoscale physical habitats, etc.). In contrast to common perception, results showed that concrete lined sites are not ecologically dead. Even though low, concrete line section had viable populations of macroinvertebrates and importantly a few native species. Interestingly, some macroinvertebrate indices of the concrete lined sites did not show a significant difference with the earthen sites. About 60% of the macroinvertebrates were grazers and filterers, and these two group populations always showed an inverse relationship. Earthen and concrete lined sites had similar diversities, but for different reasons. In general earthen sites diversity and pollution tolerance index of macroinvertebrates (PTI) was positively correlated, but no uniform correlation was observed in concrete lined sites. Some concrete lined sites with high diversity showed low PTIs (i.e. high diversity as a result of many types of pollution tolerant species) whereas in some the high diversity associated with high PTIs. Macroinvertebrate composition and the influencing factors were to a greater degree section dependent and to a lesser extent were dependent on the season. Physical heterogeneity played an important role in the macroinvertebrate responses in earthen sites. Water quality and flow rate explained comprehensively, the variations in the concrete lined sites. Results proved that nutrient levels need to be limited and instream heterogeneity needs to be improved to enhance diversity and populations of pollution intolerant species. Also, controlled vegetation harvesting is recommended in contrast to the current practice of complete removal for flow conveyance. [ABSTRACT FROM AUTHOR]

Due to climate change, the frequency and intensity of torrential rainfall in urban areas are increasing, leading to more frequent flood damage. Consequently, there is a need for a rapid and accurate analysis of urban flood response capabilities. The dual-drainage model has been widely used for accurate flood analysis, with minimum time step synchronization being commonly adopted. However, this method has limitations in terms of speed. This study applied the hyper-connected solution for an urban flood (HC-SURF) model with fixed-time step flow synchronization, validated its accuracy using laboratory observation data, and tested its effectiveness in real urban watersheds with various synchronization times. Excellent performance was achieved in simulating real phenomena. In actual urban watersheds, as the synchronization time increased, the errors in surcharge and discharge also increased due to the inability to accurately reflect water level changes within the synchronization time; however, overall, they remained minimal. Therefore, the HC-SURF model is demonstrated as a useful tool for urban flood management that can be used to advantage in real-time flood forecasting and decision-making. [ABSTRACT FROM AUTHOR]

Irrigation and drainage engineering encompasses the human-made supply of water as well as the artificial drainage of excess water. A basic feature of many historical and modern irrigation and drainage systems has been the integrated use of hydraulic structures, most often low-head structures. These structures play a key role in water storage, conveyance, flow control and measurement, and energy dissipation. Yet, most systems are often designed assuming relatively simplistic design flow conditions. In this contribution, a number of relevant key challenges for hydraulic structures used in irrigation and drainage systems are discussed, using the operation of minimum energy loss weirs, the nonlinear behaviors of circular-crested weirs and the instabilities in fish-friendly box culverts equipped with sidewall baffles as examples. Altogether, the design approach of many hydraulic structures needs a rethink, far beyond the naive optimization for simplistic design flow conditions, with a greater focus on the safe and efficient operation across a broad range of less-than-design discharges, to be embedded in the design optimization approach. [ABSTRACT FROM AUTHOR]

Hydraulic modelling of natural floodplain vegetation using leaf area index (LAI) has been applied successfully for non-submerged conditions whereas its suitability for submerged conditions requires further development. This study investigates the vegetative flow resistance at low relative submergences and extends existing LAI-based approaches building upon new flume data and prior experiences from field-scale applications. We provide advanced LAI-based formulas for modelling the flow resistance from emergent to submerged conditions, with water depth up to three times higher than the vegetation height. Such low relative submergences are highly relevant in hydraulic analyses of riverbank and floodplain flows but not adequately represented in existing formulas. The use of the deflected vegetation height as the characteristic height provided the most accurate modelling results, whereas the use of undeflected height resulted in significant errors. As a new development for submerged conditions, we proposed von Kármán scaling factor for improved model predictions. Overall, the results proved that LAI-based modelling is suitable also at low relative submergences for a wide range of vegetation densities (LAI = 1–5) and mean flow velocities (0.05–1.2 m s−1). For both emergent and slightly overtopped vegetation the JAR and VAS approaches outperformed the BAPmod-LAI approach that does not account for reconfiguration. For modellers, we provide a workflow and guidance on the use of the newly developed LAI-based formulas in 1D/2D hydrodynamic models for both emergent and submerged conditions. [ABSTRACT FROM AUTHOR]

Rapid urbanization has an accelerated impact on catchment hydrology and geomorphology due to land use and land cover changes as a result of anthropogenic development activities in river catchment areas that cause increased surface runoff and higher sediment yield. The present study investigates the channel changes and sediment transport phenomena, including bed material movement from the upstream to the estuaries of the Pahang River Basin, Peninsula Malaysia. The river geometry survey associated with the spatial variation in sediment transport has confirmed that changes in river bed profile occur due to the erosion and sediment deposition along the Pahang River. The sediment size distribution for the Pahang River was very coarse sand and gravel after the December 2014 flood. The river geometry survey showed a gentle slope that can induce lower discharge typical of alluvial rivers relating to flood events. Quantitative assessment of sediment load is, therefore, of critical importance for future river basin management. [ABSTRACT FROM AUTHOR]

Here we investigate fluid flow in 90-degree bends with and without orifice-like constrictions. The results of flow in non-constricted bends were compared with experimental results for similar Reynolds numbers and found to be in good agreement. Calculations were then carried out for various Reynolds numbers in the laminar and turbulent regimes. In addition, constrictions up to a 60% blockage were incorporated. The present study shows that the Reynolds number and the presence of an orifice-like constriction affects the velocity profile and the pressure distribution. The results indicate that if a sudden contraction is encountered, the peak velocity is larger and the flow is more predisposed to the outer wall than it otherwise would be. In addition, a sudden contraction increases the pressure loss compared to the constant-area bend and it affects the pressure distribution throughout the entire bend. This paper provides a means to predict pressure losses (similar to minor loss coefficients) in rounded bends in the presence or absence of constrictions. Such information is important to practicing engineers for designing fluid-flow conveyance systems. The behavior of the fluid is shown to be connected to the constriction and is also affected by the Reynolds number. [ABSTRACT FROM AUTHOR]

Weird horizontal shapes of branches, in large branching estuaries, often cause significant flood risks and environment-related problems. People usually resort to engineering methods to improve the horizontal shape of the weird branches and solve related issues. The responses of the riverbed evolution of a branching estuary to anthropogenic activity are complicated because of complex estuarine hydrodynamics and sediment transports, especially when the project locates specially (e.g., at estuary outlets). The North Branch of the Yangtze Estuary has a narrow upper reach which is almost orthogonal to the South Branch and has a trumpet-shaped lower reach with a wide outlet. The weird horizontal shape of the North Branch brings significant flood risks to cities along this branch, the shrinkage of its entrance, and other problems. In this study, a regulation of the North Branch, which is launched at Guyuan Sand (GYS) just outside the exit of the North Branch, is taken as an example. The GYS regulation aims to improve the weird horizontal shape of the North Branch by building new layouts of outlets, by which people decrease the flood risk of the surrounding cities. The GYS regulation is studied using a 2D numerical model. The riverbed evolution of the Yangtze Estuary in a typical hydrological year is simulated, while the water/sediment fluxes at cross-sections of branches in the estuary during a spring/neap tide are quantitatively calculated. It is found that the regulation changes the rotational flows near the shore, and further reshapes the estuarine circulations of mass inside the outlets, especially exchanges of water/sediment between different branches. The regulation directly changes the riverbed evolution at the outlet of the North Branch, and meanwhile has significant indirect influences on the riverbed evolution of the entrance of the North Branch. The varying riverbed evolution at the entrance of the North Branch and the varying water/sediment fluxes, under different designs of regulations, are related and analyzed. An essential improvement for the weird horizontal shape of the North Branch by an engineering method is shown to be possible, while the regulation mechanism of the engineering method and the response of estuarine riverbed evolution to the regulation are clarified. This study provides a new insight for improving estuarine branches with weird horizontal shapes, by reshaping the tidal processes and the accompanying sediment transports in a branching estuary. [ABSTRACT FROM AUTHOR]

Silt removal is crucial for maintaining navigable waterways in harbors. Jet pumps, without moving parts, are highly suitable for underwater operations such as channel dredging in port environments. Despite their structural advantages in slurry handling, the prolonged transport of solid–liquid two-phase flows can lead to wear on the wall materials, resulting in decreased efficiency and potential pump failure. The wear characteristics of the jet pump walls due to sand particles of varying grain sizes were experimentally investigated. The characteristic of the sands having a higher distribution above the axis as they enter the jet pump was captured by a high-speed camera. The experiment recorded the variations in mass loss at different sections of the jet pump over a period of 120 h, identifying that backflow within the throat region is a significant contributor to wall wear. Scanning electron microscopy was employed to examine the microstructure of the abraded pump surfaces. It was found that there are noticeable differences in the surface wear microstructure across various pump areas, and that particles of different grain sizes result in distinct wear patterns on the pump surfaces. The underlying causes of this phenomenon were discussed from the perspective of particle motion. [ABSTRACT FROM AUTHOR]

The piano key weir has been successfully used to address discharge deficiencies and site limitations for run-of-river structures and new and existing spillways, serving as an economical alternative to traditional weirs. In addition to upstream sedimentation, weirs may also be exposed to floating driftwood mobilized by hydrologic events. Driftwood accumulation immediately upstream of or on a weir crest can decrease hydraulic performance, potentially increasing upstream flooding and altering hydrodynamic forces on the weir that may cause structural or foundational concerns. It is unclear if floating driftwood accumulation might also influence the sediment self-cleaning characteristics of piano key weirs. Thus, this study used physical experiments to systematically investigate the sediment self-cleaning ability of a Type A piano key weir with driftwood accumulation in a run-of-river setting. The simulated substrate was an alluvial sand bed and the driftwood was naturally shaped. Experiments included combinations of discharge and different driftwood volumes. Results indicate that driftwood accumulations can have a significant influence on the flow field upstream of a piano key weir and positively affect the self-cleaning of sediment. For the conditions considered herein, the cleaning capacity was a function of driftwood volume, accumulation surface area or its extent in the upstream reach, and discharge. Higher flow rates and increased driftwood volume increased and extended upstream scour, resulting in higher sediment transport and self-cleaning without causing a significant backwater or increase in upstream water elevation. With sufficient flow depths at the piano key weir, driftwood would also be anticipated to pass downstream. Based on the results, driftwood accumulation can positively affect the ability of a piano key weir to remove adjacent upstream noncohesive sediment deposits. [ABSTRACT FROM AUTHOR]

This study focused on the effect of the transversal bed slope on scouring at bridge piers. Twenty-four experiments were conducted, half of them being on a horizontal bed and the other half on inclined beds. Three inclination angles, three flow intensities, and three pier diameters were combined within the degrees of freedom of the available experimental setup. Velocity measurements were performed to characterize the velocity field at triangular cross sections. Contrary to intuition, it was concluded that the equilibrium scour depth around cylindrical piers inserted in an erodible inclined bed decreases with the inclination angle for angles between approximately 11° and 25°, which suggests that practitioners can safely use scour depth predictors derived for horizontal beds to calculate the scour depth at inclined beds, provided that they properly assess the approach flow velocity and the critical velocity for the beginning of sediment motion on inclines. Within the range of nondimensional values covered by this study, practitioners can also use a new scour depth predictor. [ABSTRACT FROM AUTHOR]