Vegetation in watercourses is increasingly recognized as a vital Nature-Based Solution (NBS) for ecosystem preservation. However, from a hydraulic perspective, rigid emergent vegetation also increases flow resistance, which can lead to higher water levels if not properly managed. To calculate the water surface profiles, it is essential to assess the drag coefficient values. Numerous formulas have been proposed in the literature for staggered and random arrangements, while relatively fewer ones have been suggested for linear configurations. Generally, these formulas were derived under uniform flow conditions, and it remains uncertain whether they are relevant for steady-flow conditions, which are more commonly encountered in natural settings. Consequently, the reliability of the estimated drag coefficients is often questionable. In this study, four formulas from the literature, derived for linear arrangements, and one formula for staggered and random arrangements, were employed to simulate thirty-six water surface profiles from two experimental series. These profiles span a broad range of vegetation densities, from 0.008 to 0.42. The profiles belong to accelerated subcritical flow (M2 type), and the standard step method was applied for their simulations. A comparison between the experimental and computed profiles was performed using several statistical parameters, particularly the Taylor diagram. One of the equations analyzed was applied over the aforementioned range of vegetation density, and the computed profiles exhibited a root mean square relative error of approximately 6% compared to the experimental data. The best-performing equation is dependent solely on vegetation density and is likely applicable to higher Reynolds numbers than those encountered in the experimental conditions. Finally, providing a reliable tool for estimating flow resistance is crucial for the successful implementation of vegetative NBSs, allowing engineers to perfectly balance flood discharge capacity with environmental sustainability.

In this paper, the temporal tendencies of monthly, seasonal, and annual temperature data were analyzed in Friuli-Venezia Giulia (northeastern Italy) by applying two non-parametric tests for trend detection to 34 temperature series in 62 years (1940–2011), for which data are freely available online. As a result, an overall increase in the temperatures in both the minimum and the maximum values has been detected. In particular, regarding the maximum seasonal temperature data, a marked positive trend has been identified in all the seasons, except autumn, and especially in summer, with more than 80

This study examines the scaling behavior and structural nature of bed roughness structures observed in controlled laboratory experiments conducted by Penna et al. (J Hydraul Res 59(3):420–436, 2021), utilizing the analytical framework of Taylor’s variate Power Law (TPL) as extended by Rizzello et al. (Phys Rev E 109(3):034306, 2024). The results reveal a marked contrast in the scaling regimes as a function of the reorganization of the bed surface induced by hydraulic forcing. Specifically, unworked bed surfaces, i.e., those not subjected to water flow, exhibit predominantly multi-scaling behavior, indicative of underlying multi-fractal organization. On the contrary, water-worked beds are characterized by a simpler, simple-scaling regime, consistent with mono-fractal surface structuring. This suggests that flow-induced reorganization acts as a homogenizing mechanism, suppressing heterogeneity and reducing the complexity of bed surface patterns, with important implications for sediment transport dynamics, hydraulic resistance, and morphodynamic modeling.

Understanding the interaction of flow and vegetation in open canals has a great impact on better implementation of environmental projects and hydraulic engineering. The purpose of this research is to apply spatiotemporal (spatial and temporal) averaging method in concrete canals in the presence of vegetation patches. Therefore, in this research, four reaches of irrigation canals with vegetation patches were investigated in Iran. The measured data includes flow velocity and reaches surveying. The results of spatiotemporal velocity profiles showed that the log-law fits nicely the measured velocity data near the bed with vegetation patches. The local values of velocity and shear velocity were compared with the unit value extracted from the double-averaged velocity profile. The results of this comparison showed that the percentage difference between the local values resulting from each flow velocity profile and the unit value of the spatiotemporal velocity is not significant in most cases. Thus, the spatiotemporal velocity method is able to reflect the characteristics of the entire flow conditions in concrete canals in the presence of vegetation patches.

The turbulent jet produced by a ship propeller may impact the seabed even for distances of the order of tens of times the diameter of the propeller itself. The result is the formation of a scour hole close to the propeller and a deposition mound. The present work aims at investigating, for the first time, the scaling behavior of the high-order structure functions for this turbulent jet, by discussing the experimental results in light of monofractal or multifractal models. This latter would explain the possible existence of intermittency. To this end, an experimental test was performed in a laboratory flume in still water condition, simulating the case of a ship in a harbour basin. The propulsion system was constituted by an electric motor turning a propeller (8.2 cm in diameter) with four blades. The flow field induced by the propeller rotation was measured with an Acoustic Doppler Velocimeter (ADV). Specifically, the longitudinal structure functions were studied in this work using Taylor’s hypothesis.

In this paper, the local flow and turbulence characteristics of rigid submerged vegetated flow are studied using the double-averaging methodology. Experimental results indicate that the double-averaged streamwise velocity profile above the canopy follows a logarithmic law, while the canopy-induced drag significantly reduces the velocity through the vegetation elements. At the canopy top, an inflection occurs in the velocity profile, implying the existence of the Kelvin–Helmholtz (K–H) instability. The faster-moving fluid above the canopy interacts with the slower-moving fluid within the canopy, creating a strong shear at the canopy top. This induces the Reynolds shear stress, which peaks at the canopy top. The localized accelerated and decelerated flow regions occurring within the canopy produce dispersive shear stress that enhances fluid mixing and momentum transport. The second-order correlation shows the presence of coherent structures at the canopy top due to the K–H instability. The third-order correlation and the quadrant analysis demonstrate that the sweep events dominate the flow in the canopy layer, and the ejection events prevail in the main-flow layer. The turbulent kinetic energy (TKE) fluxes also confirm these findings. The negative streamwise dispersive kinetic energy flux within the canopy suggests that local interactions transport the TKE upstream. The TKE production rate peaks near the canopy top, while the TKE dissipation rate continuously increases within the canopy down to the bed. Higher streamwise spatial fluctuations downstream of the vegetation elements result from the effect of the canopy on the flow.

Orifice jet through a small opening or orifice into a surrounding fluid exhibits intricate fluid dynamics, encompassing the interaction of the jet with the fluid. Although the dynamics of simple jets has been extensively studied, there are still unresolved issues that need to be addressed. In this study, we experimentally investigated the characteristics of non-buoyant jets emerging from a sharp-edged orifice located in the wall of a pipe with a constant flow rate. Specifically, we examined how the ratio between the variable jet flow rate to the constant pipe flow rate upstream of the orifice influences not only the jet trajectory but (for the first time to the authors' knowledge) also the jet velocity-related features. Particle image velocimetry measurements were performed to explore the velocity fields in the near and intermediate regions of the jet and data were analyzed in terms of fields of time-averaged velocity components, turbulent intensities, Reynolds shear stresses, vorticity, and Q-criterion. The transversal velocity profiles were shown and their Gaussianity investigated via skewness and kurtosis. Thus, second-order statistics of turbulence of the velocity fluctuations were carried out. Moreover, a spectral analysis was performed after the Taylor hypothesis verification was proved and a net scale separation was guaranteed to develop the inertial sub-range. The influence of variable jet flow rate and the constant pipe flow rate on the jet behavior is shown and, in particular, how, as this parameter decreases, the jet moves away from the typical axisymmetric features of a round simple jet. In addition, the spectra analysis is used to identify the jet potential core and the large-scale organization zones, highlighting the effect of variable jet flow rate and the constant pipe flow rate on the extension of the potential core region and on the mixing layer.

In open-channel water transfer projects, hydrodynamic modeling has been one of the tools commonly used by the scheduling staff to perceive the changes in the water condition of the channel. The reliability of the flow monitoring data has not been guaranteed due to restrictions in the flow monitoring method. Flow monitoring errors directly reduce the accuracy of hydrodynamic modeling calculations, making it impossible to accurately grasp the real-time changes in the internal water conditions of the channel. In this paper, by utilizing the characteristics of the hydrodynamic model itself, which can be solved discretely with multiple boundary conditions, the method of correcting the boundary anomaly data is proposed by changing the combination of hydrodynamic boundaries. This solves the problem of the inaccuracy of hydrodynamic model calculations due to errors in the monitoring data and improves the accuracy of the hydrodynamic model calculations. In the actual operation process, it is found that the method proposed in this paper solves the problem of hydrodynamic model misalignment caused by flow observation errors by correcting the flow during the flow adjustment period, which greatly improves the calculation accuracy of the hydrodynamic model. Secondly, for a stable flow period, the method proposed in this paper can quickly capture and correct the local monitoring of abnormal data and improve the overall hydrodynamic simulation accuracy.

This paper presents a hydrodynamic optimisation of hull shapes achievable through the implementation and integration of cascading computational tools, targeting reduction of energy consumption. Parametric modelling was applied to a hull by non-uniform rational spline (NURBS) using the Rhinoceros plug-in Grasshopper. Hull shape optimisation was performed by using IMPROVEit® software, which constitutes the interface between Grasshopper and OpenFOAM. The optimiser can use various methods such as radial basis functions, krigging, gradient methods, neural networks, genetic algorithms, evolutionary and stochastic algorithms. The main software idea is to identify an analytical function that acceptably reproduces the unknown real objective function. This principle, used to calculate the hydrodynamic forces, was appropriately validated using Wigley’s hull with experimental data from the literature. Validation was carried out on four Froude numbers, respectively, 0.250, 0.316, 0.350, and 0.408. Drag coefficient has shown a maximum relative error of –15.71

Helical structures are a hallmark of hydrodynamic turbulence, and they play a key role in determining the transport and diffusion properties of the flow. Helicity, defined by the linking of velocity and vorticity, is, thus, of primary significance, particularly in systems such as propelled jet wakes. In this paper, we present a novel approach for determining helicity in turbulence, based on one-dimensional filtering methods. First, we test our new technique using analytical solutions and numerical simulations and find that the model can identify high-helicity patterns qualitatively well. Then, we employ the technique in experiments with propelled, helical turbulent flows. The model reliance on single-point velocity measurement may be especially advantageous for measurements with limited acquisition dimensionality.

Although vegetation in watercourses has an important ecological function, from a hydraulic point of view, it increases flow resistance, determinates higher water levels and generates a greater risk of flooding. In engineering practice, to determine water levels, the drag coefficient must be known, whose experimental values, in literature, are provided for uniform or quasi-uniform flow. In this paper, the expression of a drag coefficient, previously proposed by the authors for the case of emergent rigid vegetation arranged in a linear manner, was used to simulate experimental water surface profiles, employing the effective width for the first time. The formula was validated by simulating 26 experimental profiles observed at the University of Calabria, over 1100 points in total, plus 8 published in literature. In some of these applications, the vegetation density was much higher than that for which the drag coefficient expression was derived. For this reason, it is possible to consider a new, wider field of validity for it. The proposed equation is independent of the Reynolds stem number, so that it can be used in natural streams and rivers, provided that viscosity effects can be considered negligible. Finally, some comments are offered on the application of a new formula proposed in literature regarding the computation of the profile when downstream depth is taken as a boundary condition.

This paper presents a comparison of two turbulence models implemented in two different frameworks (Eulerian and Lagrangian) in order to simulate the motion in calm water of a displacement hull. The hydrodynamic resistance is calculated using two open-source Computational Fluid Dynamics (CFD) software packages: OpenFOAM and DualSPHysics. These two packages are employed with two different numerical treatments to introduce turbulence closure effects. The methodology includes rigorous validation using a Wigley hull with experimental data taken from the literature. Then, the validated frameworks are applied to model a ship hull with a 30 m length overall (LOA), and their results discussed, outlining the advantages and disadvantages of the two turbulence treatments. In conclusion, the resistance calculated with OpenFOAM offers the best compactness of results and a shorter simulation time, whereas DualSPHysics can better capture the free-surface deformations, preserving similar accuracy.

Building flood reduction dams for territory protection is very often necessary as it allows the reduction of peak flows during flood events by creating a storage in upstream areas. An online structure with such characteristics is outlined, presenting one or more openings in order to allow normal and moderate flows to pass downstream. A stilling basin is provided downstream of the openings and, on one side of the flooded area, a spillway weir is set. For low river flows, the openings will act as free-surface weirs. The openings are equipped with a sill in such a way to let the discharge independent of the downstream flow conditions. For moderate flood flows, the water level upstream of the dam will rise, and the openings will become submerged, effectively behaving as an orifice arrangement. For large flood flows, the crest of the flood spillway weir is reached and they will be discharged via both the orifice structure and the flood spillway structure. The silled openings and the stilling basin are one only hydraulic complex. Since no examples exist of their behavior as a whole, the aim of this paper is to give the designers the opportunity to size them given the basic requirement of the flood reduction dam, i.e. the max discharge allowed downstream. For this reason, the paper will focus on the opening discharge coefficients, the stilling basin energy dissipation and water level. Both the orifices and the stilling basins were studied starting from the hydraulic models of three dams that were built in Calabria (Italy). The structures of the stilling basins are original. The results appear in dimensionless form and offer useful guidance for similar hydraulic cases, with the exception of specific terrain related issues. Finally, an example of a preliminary design of orifices and stilling basin is presented.

Most of the existing works on vegetated flows are based on experimental tests in smooth channel beds with staggered-arranged rigid/flexible vegetation stems. Actually, a riverbed is characterized by other roughness elements, i.e., sediments, which have important implications on the development of the turbulence structures, especially in the near-bed flow zone. Thus, the aim of this experimental study was to explore for the first time the turbulence anisotropy of flows through emergent rigid vegetation on rough beds, using the so-called anisotropy invariant maps (AIMs). Toward this end, an experimental investigation, based on Acoustic Doppler Velocimeter (ADV) measures, was performed in a laboratory flume and consisted of three runs with different bed sediment size. In order to comprehend the mean flow conditions, the present study firstly analyzed and discussed the time-averaged velocity, the Reynolds shear stresses, the viscous stresses, and the vorticity fields in the free stream region. The analysis of the AIMs showed that the combined effect of vegetation and bed roughness causes the evolution of the turbulence from the quasi-three-dimensional isotropy to axisymmetric anisotropy approaching the bed surface. This confirms that, as the effects of the bed roughness diminish, the turbulence tends to an isotropic state. This behavior is more evident for the run with the lowest bed sediment diameter. Furthermore, it was revealed that also the topographical configuration of the bed surface has a strong impact on the turbulent characteristics of the flow.

Investigating the interaction between flow intensity and a ship propeller jet scouring process is paramount to predict scour dimensions in mooring sites in navigation channels, for instance. While the condition of still water is typical in protected mooring sites, in other real-world conditions, like docking in waterways, the presence of an additional flow approaching a rotating propeller can induce changes in the propeller jet hydrodynamics and in turn in the scouring process. Note that, although ship-hull and rudders influence the jet propagation and the flow field, the present research project aimed at studying the propeller-inducing effects only. Literature studies that have relied on this assumption are rarely found, with only a few examining the impact of the intensity of the flow on the propeller jet scour. This study presents an experimental campaign aimed at assessing the effects of flow intensity on propeller jets in confined conditions. Specifically, three different flow intensities and three propeller distances from a vertical quay-wall were tested. The findings are presented through profiles of the scoured bed, and bathymetries at the equilibrium condition and empirical formulas for calculating the principal dimensions of the scour holes are given. To explore the intricate hydrodynamics and understand how the intensity of the flow affects the scour hole development, and to investigate boundary effects on the flow field, we performed Reynolds-Averaged Navier- Stokes (RANS) simulations. These simulations were applied to the three-dimensional scoured bathymetry in a state of equilibrium. The satisfactory match between numerical results and sampled velocities at the equilibrium stage ensures the reliability of the simulations. To the authors' knowledge, these configurations had not been previously simulated, owing to the complexities involved in computing a moving mesh in presence of a bathymetry and a confining vertical wall. The results offer the first numerical demonstration of boundary effects on the characteristics of propeller jets both in the presence and in the absence of an additional channel flow.

The densimetric Froude number, F0, which depends on the propeller rotational speed, n, and on the median diameter of bed sediments, d50, is the main parameter considered by researchers for analysing the propeller -induced scouring process. Common literature equations for evaluating the three-dimensional (3D) geometric characteristics of the scour hole and deposition mound are functions of F0. In this paper, the agreements among the data and these literature equations are critically discussed, demonstrating that the use of other two dimensionless parameters (the propeller Froude number, F0p, and d50/Dp where Dp is the propeller diameter), which are separately dependent on n and d50, returns more satisfying results than using F0 solely.Also, the influence of the water depth, h, on the scour hole and the deposition mound is here analysed. Re-searchers commonly neglected the effects of h, because the ratio between it and Dp was large enough. This is reasonably true when h/Dp is considerably high, but no clear cut-off value was found in the literature. For the first time, by investigating a larger range of h, the present study underlines that the effects of h on the scour hole and the deposition mound are negligible for h/Dp >= 2.44.

<p>Alpine mountainous regions of northern Italy, constituting one of the major mountain areas in Europe, have been identified among the main vulnerable areas to climate change of the continent. In fact, over the last century, global warming has caused all Alpine glaciers in Europe to recede as well as triggered changes in rain and snowfall patterns shortening snow seasons and causing glaciers to recede. Within this context, in this study, the spatiotemporal variability of temperatures in Friuli-Venezia Giulia (north-eastern Italy) has been evaluated by means of 34 monthly series for the period 1940-2011, for which data are freely available online. Indeed this region is characterized by a mountainous northern part, belonging to the Southern Alps, and a southern side touched by the Adriatic Sea. In particular, a trend analysis, at annual, seasonal and monthly scales, was performed on the minimum and maximum values through the Mann-Kendall test. Moreover, the application of the Theil-Sen estimator allowed us to quantify the magnitude of the increase/decrease in the temperature values. The results evidenced an overall increase of the temperatures in both the minimum and the maximum values, mainly detected in the summer months, even though in some stations located in the alpine and pre-alpine areas an opposite trend has been identified.</p>

Vegetation present in the water streams, on the banks and in the floodplain areas largely affects the river hydraulics. Indeed, river vegetation significantly influences hydrodynamics, sediment transport, bedforms, and pollutant transport. Environmental management of rivers requires an understanding of the various processes and predictive capabilities of models. In the past, many studies were conducted, especially in laboratory settings, in order to quantify flow resistance due to vegetation. It is only recently that the effects of vegetation on sediment transport came to the attention of researchers. In particular, both suspended and bedload transport were considered. This paper reviews recent works conducted on the effect of vegetation on incipient sediment motion and bedload transport. With regard to the incipient sediment motion, methods based on critical velocity, turbulence, vegetation drag, and velocity in the bed roughness boundary layer have been discussed. For bedload transport, methods based on bed shear stress, turbulent kinetic energy, a revisiting of classical formulas for estimating bedload transport in non-vegetated channels, and estimation from erosion around a single vegetation stem are analyzed. Finally, indications on further research and new development are provided.

Bed roughness influences the hydrodynamic behaviour of the river, for example, elevating water levels for a constant flow discharge. In most hydrodynamic river models, the roughness is assumed as a function of the grain size. However, natural riverbeds are characterized by a wide variety of bedforms at different scales, from the small- to the large-scale bedforms. Hence, bed roughness should be considered as a complex expression of topographical variability of a bed surface at multiple scales rather than being simply related to the grain size. Neglecting these important aspects may lead to high errors in the river water level results, inducing dramatic consequences on the flood risk and land use planning. To explore the bed roughness, an in-depth statistical analysis is applied, in this study, to three different surfaces simulated in an experimental laboratory flume. In fact, if the description of bed roughness structures is limited to second-order statistics, then some important information may remain unidentified. Higher-order structure functions are computed to provide information on the bed roughness structures and on their orientation and multifractal characteristics.