Downstream Water Depth Research Articles

Numerical study of impact pressure and force of cascading dam-break floods on the downstream dam

Cascading dam-break floods are among the most catastrophic natural disasters, causing significant casualties worldwide. Currently, research on cascading dam-break scenarios primarily focuses on the gradual dam-breaching and flood evolution processes. However, the research on the impact of cascading dam-break flood on downstream dam surface is rarely reported. Therefore, this study addresses this gap by establishing a shallow water hydrodynamic model based on the finite volume method. We conduct a numerical investigation into the effects of various parameters, including dam spacing, channel bed slope, initial water depths in upstream, middle and downstream reservoirs, and different cascading dam-break processes (two-stage and three-stage), on the impact on the downstream dam surface. The following conclusion can be drawn: factors such as dam spacing, bed slope and water depth have a significant impact on the impact pressure and force of downstream dam surface. All other conditions remain unchanged, the larger the dam spacing, the higher the peak and average values of downstream impact pressure, and the later the arrival time of dam-break floods on the downstream dam. The greater the bed slope, the higher the impact pressure, and the earlier the arrival time of the dam-break floods. The deeper the upstream or middle water depth, the greater the peak value and occurrence time of the impact pressure. The smaller the downstream water depth, the lower the impact pressure. The impact time of the three-stage dam-break floods is slightly later than that of the two-stage dam-break floods, but its peak and average impact pressure are higher. This study offers valuable scientific guidance and technical support for disaster prevention and mitigation strategies concerning cascading dam-break floods.

Simulation of flow characteristics in open channels with inflatable dam

Abstract Inflatable dams are structure cylindrical inflatable and deflated bile structures made of rubberized material placed on top of a rigid base and inflatable by air, water, or a combination of both. The present paper aims to measure the water surface elevation, and depth of flow in Shatt Al Ibrahim and comparison with design depth and study the flow state according to design discharge and also according to scarce discharge. The study effect of the height of the dam filled with water on upstream and downstream water depth and analyzed numerically by using HEC-RAS program one–one-dimensional flow in two states, steady flow and unsteady flow under different variables such as changing of discharge. Good results were obtained in two flow states. The results show that the proper solution for maintaining the required water levels is to construct inflatable dams, due to lower construction and maintenance costs, easy and simple of operation, simple and easy to inflate and deflate quickly to prevent upstream flooding. The results of the current study indicated an increase in the water surface height (WS) and water depth (Wd) across the channel after the implementation of inflatable dams compared to natural conditions. Specifically, the data indicate a significant increase in (WS) and (Wd) at “station 52”, where (WS) increased by 0.45 m with a 0.5 m dam and 1.43 m with a 1.5 m dam compared to the basic scenario. This confirms the adaptability of inflatable dams in adapting water levels to real-time requirements, underscoring their potential as a cost-effective solution to mitigate upstream floods and improve water resource management practices.

Experimental study on the influence of water depth and bed slope variations on dam-break flood wave propagation

Damage to dam structures frequently results in catastrophic consequences. Consequently, understanding of the characteristics of the movement of dam-break flow along the sloping wet bed can assist in the issuance of timely flood warnings and risk mitigation. In this study, a series of large-scale flume experiments was conducted with the objective of investigating the effects of upstream and downstream water depth and bed slope on the propagation of dam-break waves. The water level is measured and processed to calculate the wavefront velocity. Results show that the wave propagation behavior can be classified as bore and undular waves through the global Froude numbers (Frx) and local Froude numbers (Frl). When Frx < 1.225 or Frl < 1.475, the dam-break wave propagates as the undular wave. In the undular wave state, the wavefront velocity (U) decreases with increasing water depth ratio α. Additionally, the U with Frx shows a similar trend, where the experimental value surpasses the analytical solution. The dimensionless maximum wave height (ΔHmax) increases with Frx and then decreases. The deviation from the analytical solution ranges between 67.22% and 127.38%. When Frx > 1.225 or Frl > 1.475, the dam-break wave propagates as the bore wave. In the bore wave state, the U increases slightly with the water depth ratio α, while the change rule of U with Frx is similar to it. The dimensionless maximum wave height (ΔHmax) remains relatively constant as Frx increases, showing a high degree of consistency with the analytical solution. The presence of bed slope results in increased wavefront velocity and wave heights, while an increase in α results in the emergence of more pronounced undular wave phenomena. Furthermore, the experimental results are compared with existing analytical solutions, and the validity of the analytical solutions and their limitations are discussed.

Experimental investigations of propagation characteristics and wave energy of dam-break waves on wet bed

Understanding the characteristics of dam-break flows that move along a sloping wet bed is essential for timely flood warnings and risk mitigation. This study conducts laboratory experiments in a sizable flume, encompassing various upstream and downstream water depths and bed slopes. It examines the effects of the ratio between upstream and downstream water depths and the slope of the flume on the dam-break wave height and the velocity of the wavefront. The findings revealed that the average relative error between theoretical and experimental values initially decreases and increases as the slope rises. The dam-break waveform is characterized by introducing a global Froude number Frx and a local Froude number Frl, with critical values of Frx=1.225 and Frl=1.475. In addition, a model for predicting the dam-break wave height is developed by linearly fitting the values between dimensionless wave height and the local Froude number, and it is validated by comparison to experimental data. Based on experimental data and the Stoker equation, an attenuation function for the dam-break wave height at a downstream location is proposed for the undular wave. Finally, a theoretical analysis is conducted to predict the energy of the first dam-break wave.

Bed configurations downstream combined V-Notch-sharped edged Weir with inverted V-Shaped gate

ABSTRACT Weirs and gates are hydraulic structures installed in canals, mainly for controlling the discharge. Because of their existence, unfavorable influences regarding the downstream bed configurations were recorded. This study experimentally explores the combined effect of simultaneous flow through a hydraulic device consisting of a V-notch sharped weir with an inverted V-shaped gate, aiming to minimize the downstream bed scour. Eighty-one runs were carried out using nine weir-gate models with three different vertex angles. The tests were executed considering three upstream and three downstream water depths. A V-notch weir with an angle of 120º was tested under similar hydraulic conditions and was used for comparison. The results revealed that the length of backflow was increased by the decrease in weir angle under a fixed 120° gate angle. The bed configurations were sensitive to gate angle. The combined device showed a significant decrease in bed disturbances regardless of the angles used compared to the traditional V-notch weir. Simple formulas were developed to predict the scour parameters.

Analysis of the hydraulic interference between the baffles and the composite hydraulic structure

The purpose of the present study is to examine the influence of baffles presence at downstream system on weir gate hydraulic response. Two baffles configuration (triangle and angle shapes) are installed in bed flume. Two different spacing are used between the baffles and two different directions for baffles are also adopted. The study tries to investigate the variation in upstream Froude number, downstream Froude number, Reynolds number, actual discharge, discharge coefficient, downstream average water depth and the hydraulic system efficiency which is expressed as function of downstream water depth. It has been shown that the number of baffles has a direct and significant impact on flow hydraulic characteristics of weir-gate structure regardless of the spacing between baffles and the direction of baffles related to flow. Baffles number and spacing have essential impact on the water flow velocity of system and this impact leads to increase the flow resistance. The results clarify that the upstream Froude number, downstream Froude number, Reynolds number, actual discharge and discharge coefficient are decreased with the increase in baffles number except the average downstream water depth which increases with increase in baffles number. The efficiency of hydraulic system gives a good indicator for using baffles with weir-gate structure. At the end this paper shows a fruitful result of efficiency. This experiment run condense on the baffle’s numbers and directions with respect to the water flow direction at the downstream regime. So, the rises in the water level relies on the numbers and directions of the baffles as compare to the case without using baffles at the flume downstream region. The actual discharge and weir-gate discharge coefficient are more sensitive to the increase in the baffles’ numbers and the baffles direction with respect to the water flow direction

Effect of Perforated Sills on Maximum Scour Depth Downstream From a Sluice Gate

Aims: Experiments were conducted to study the effect of using a perforated sill on maximum scour depth downstream from a sluice gate. Background: Previous studies have shown that screens may be utilized efficiently for dissipating the energy of water downstream of a hydraulic structure. Objective: For the present study, a series of experiments was conducted to investigate the effect of using a perforated screen sill on the maximum scour depth downstream of a hydraulic structure. Methods: In the present study, a single perforated sill with varying porosity (10.3%, 18.3%, 28.5%, and 41.1%) and an inclination angle of 90° were used. Perforated sill with different shapes of holes (circular, rectangular, and square holes) was used during the study. The major parameters for the present study are the porosity of the perforated sill, different shapes of holes, downstream water depth, and the Gate Froude number (FG) for a range covering from 2.15 to 4.7. The gate opening simulating a hydraulic structure is adjusted at heights of 4 cm, 5 cm, and 6 cm during the experiments work. Result: The results revealed that an increase in the sill porosity (Ao/As) increases the screen effect to reduce the max scour depth. In addition, the results showed that the sill with square holes is better than the sill with circular and rectangular holes in reducing the maximum scour depth. Conclusion: The perforated sill with a square porosity of 41.1% reduces the maximum scour depth downstream of a sluice gate by 60%.

Momentum and mass transport and flow structure characteristics for the unsteady flow in compound channel

In recent decades, the study of steady flow in the compound channel has received much attention, while the flow characteristics of flood in the compound channel are rarely reported. In this paper, the characteristics of the flood propagation under different initial main channel depths are studied using the laboratory experiments and numerical simulation. Results show that the overflowing water from the main channel soon forms the reverse flow after hitting the floodplain sidewall. This reverse flow influences the subsequent overflowing process and significantly enhances the bed shear stress on the floodplain. However, this effect gradually decreases with the flood evolution distance and the increase of the initial downstream water depth. Unsteady transverse transport during flooding inhibits the formation of coherent eddies at the interface between the main channel and floodplain, while the high shear region will extend to the internal of the main channel or floodplain. Complex multi-vortex structures are found on the floodplain due to transverse interaction behavior. The main transverse mass transport takes place in the first half of the period after the flood arrival. It is found that the weir flow equations used in the previous studies are unable to accurately describe the transverse mass transfer between the main channel and floodplain. Secondary currents have a little contribution to the unsteady transverse momentum transport, while the transverse currents and transverse Reynolds stresses have a significant effect. The time when the peak transverse current arrives is later than that when the peak transverse Reynolds stresses does in the current study.

A momentum-based prediction model of backwater rise within and downstream of an emergent canopy in nonuniform flow

Vegetation is widely used to restore waterways and wetland ecosystems. However, emergent canopies create a nonuniform water surface, and predicting the backwater rise is necessary to evaluate the flood hazard. This paper investigates the water surface elevation from downstream to upstream of an emergent canopy in a steady nonuniform flow and predicts the upstream backwater rise. Laboratory flume experiments are conducted on rigid vegetation with varying coverage exposed to different flow rates. The backwater rise and the nonuniformity of vegetated flow are explored based on a momentum equation, and a general formula for backwater rise within and downstream of an emergent canopy is proposed for nonuniform flow. The results reveal that a unified phase diagram of backwater rise can be derived from the momentum model, which presents the variation of both the upstream and downstream water surface elevations and acquires a threshold to identify strong or weak nonuniformity in vegetated flow. The upstream water depth H1 exhibits a nonmonotonic variation, first decreasing and then increasing with water depth H2 at the trailing edge of the emergent canopy. Two partitions of subcritical flow and supercritical flow for the downstream water depth H3 are quantified by the experimental data. The proposed model can be used to accurately predict the backwater rise based on a dimensionless vegetated parameter Cveg and unit discharge q, as demonstrated by both the present and previous experimental results. This work improves the understanding and predictability of the nonuniformity and backwater rise generated by emergent canopies in natural or ecology-restored rivers.

Formation conditions of wave-type flows at stilling basins with a drop

The formation conditions of maximum- and minimum-wave jumps were experimentally investigated. A total of 110 wave-type jump experiments were carried out for several discharges, supercritical upstream and subcritical downstream water depths and drop heights. The experimental results revealed that the influential parameters on wave-type jumps are the upstream Froude number and the relative drop height. As the classical hydraulic jump equation is not sufficient to define conjugate depths of wave-type flow, empirical equations were developed for defining the conjugate depths of maximum-wave jumps and minimum-wave jumps (for which insufficient experimental data are available in the literature). The agreement between calculated and measured conjugate depths was good. It was also found that the value of the lower limit for the upstream Froude number is not constant for the formation of a maximum-wave jump – it depends on the relative drop height. Furthermore, the experimental results showed that the energy-dissipation ratios of maximum- and minimum-wave jumps are equal to or larger than those of classical hydraulic jumps. For this reason, wave-type jumps may be preferred at stilling basins with drops along with A-jumps.

Mesh-free simulation of height and energy transfer of landslide-induced tsunami waves

The landslide-induced tsunami wave poses a threat to human society and the living environment by causing disasters such as run-up of water surfaces and overtopping of dams. In this paper, we systematically investigated the relationship between landslide properties and induced tsunami wave characteristics as well as the energy transfer between the landslide and waves. A meshless smoothed particle hydrodynamics (SPH) framework was presented and validated with four experiments of different landslide types. The validations indicate that the SPH model is capable of reproducing the complex processes of tsunami wave generation induced by both rigid and deformable landslides. Then we perform numerical simulations of 162 landslide-induced waves scenarios with varying landslide deformability, relative initial positions, densities, landslide size, and downstream water depths using the validated SPH model. The results show that the effect of density and initial water depth on the maximum wave height can be disregarded, while the effective landslide volume has a significant effect. The analysis of the kinetic and potential energy of the induced waves reveals that energy transfer occurs rapidly, which mainly increases the potential energy of the water downstream. We also find an exponential relationship between landslide potential energy reduction and maximum wave height. These findings provide valuable insights into the landslide-induced tsunami waves and enhance risk assessment and mitigation efforts.

MPS-based simulation of dam-break wave propagation over wet beds with a sediment layer

In this study, a two-phase mesh-free method is employed to simulate the dam-break wave propagation along different wet bed conditions in the presence of sediment. The method is based on the mixture theory and volume fraction is incorporated for both water and sediments. The pressure Poisson equation is explicitly solved to obtain the pressure field for the water and the pressure field for the sediment is calculated by using the rheology model. The method is validated by simulating submerged granular column collapse and dam-break flow over a sediment layer. The method can reproduce the interface variation between water and sediment. The validated model is then used to simulate the dam-break wave propagation in the presence of both downstream water and sediment. Different dam-break waves induced by the upstream water depths are simulated and it is found that the dam-break wave can make the sediment move violently. The larger downstream water depth can slow down the sediment movements while the sediment movements are violent for shallower water downstream.

Numerical simulation of transient pipe flow with entrapped air and wet bed effects

In this study, the evolution of transient pipe flow along the wet bed is numerically investigated. In the investigation, the shear stress transport k-ω model is used and the volume of fluid method is employed to track the surface of air and water. Two key parameters in the flow as upstream head H and initial water depth h in the pipe are examined. It is found that the bottom stress is significantly affected by the two parameters. The upstream head H determines the magnitude of the shear force, and the downstream water depth in the pipe affects the stability of the shear force. The boundary layer separation and flow pattern are the essential causes of shear instability. By analyzing the simulation results, an empirical equation with the average flow velocity is obtained to estimate the overflow capacity of the pipe by just the upstream water level and the depth of the wet bed.

Experimental study on failure mode and failure mechanism of multi-box girder bridge under attack of tsunami

Comprehensive and intensive understanding to the failure process and failure mechanism of girder bridges is extremely crucial for anti-tsunami design of coastal bridges. The scaled down model of the multi-box girder bridge was manufactured and physical experiments were conducted in the dam-break flume to investigate the failure mode and failure mechanism. Results show that the superstructure can fail in three modes: HM (horizontal movement), HMR (horizontal movement with rotation) and HMRD (horizontal movement with rotation and dropping). And the two variables, namely the exceedance duration and the exceedance impulse, are proposed to analyze the possible failure mode and failure mechanism of the superstructure. The analysis conclusions obtained by the proposed method agree with the failure modes observed in the physical experiments. It is found that transverse horizontal movement of the superstructure always takes precedence over rotation and flow upward. With the increase of incoming tsunami bore height, the risk of failure increases; with the increase of the initial downstream water depth, the exceedance duration and exceedance impulse of horizontal force decreases firstly and then increases, the exceedance duration and exceedance impulse of vertical force and overturning moment increase.

Response of Fish Habitat Quality to Weir Distribution Change in Mountainous River Based on the Two-Dimensional Habitat Suitability Model

Weirs are often constructed on mountainous rivers because of their low construction costs and their ability to provide irrigation and facilitate landscaping, yet there is little research on how fish habitat quality in mountainous rivers responds to weir distribution. This study categorized the distribution characteristics of weirs on typical reaches according to their sinuosity and calculated the corresponding habitat suitability index (HSI) and weighted usable area (WUA) under various discharge conditions using a coupled MIKE21 and habitat suitability model. Then, the relationship between the distribution characteristics of weirs and the quality of fish habitats under different discharge conditions was analyzed. The results show that weirs in mountainous rivers can affect the habitat suitability of the rivers, but this effect is closely related to discharge conditions and layout mainly because the key hydraulic factors that determine habitat quality for different sinuous reaches vary under different discharge conditions. This study found that in high-sinuosity rivers with high discharge conditions, water depth is the key factor determining the quality of fish habitats, so weirs can improve habitat quality by improving the suitability of downstream water depth. However, in other conditions, velocity is the key factor determining habitat quality, in which case weirs cannot improve habitat quality and can even degrade it. Therefore, other methods of improving velocity are needed to enhance habitat quality. The results of this study provide a reference for the protection of fish habitats in mountainous river channels and the determination of suitable locations for weir construction.

Numerical Study on Tsunami Force on Coastal Bridge Decks with Superelevation

Many coastal bridges have been destroyed or damaged by tsunami waves. Some studies have been conducted to investigate wave impact on bridge decks, but there is little concerning the effect of bridge superelevation. A three-dimensional (3D) dam break wave model based on OpenFOAM was developed to study tsunami-like wave impacts on bridge decks with superelevation. The Reynolds-averaged Navier–Stokes equations and the k-ɛ turbulence model were used. The numerical model was satisfactorily checked against Stoker’s analytical solution and the published hydrodynamic experiment. The validated model was employed to carry out parametric analyses to investigate the effects of upstream and downstream water depths and the bridge deck’s superelevation. The results show that the tsunami force is proportional to the relative wave height. The dam break wave impact on the bridge deck can be identified as two distinct scenarios according to whether the wave height is higher than the bridge deck top. The trend of the tsunami force is also different in different scenarios. The superelevation will significantly influence the tsunami forces acting on the box girder, with some exceptions.

Experimental investigation and prediction of free fall jet scouring using machine learning models

The current study deals with the depth of scour at the location of impact between a free fall jet and a riverbed. The current study is based on extensive laboratory experiments that were designed to mimic full-scale behavior. The literature review shows that relations among hydraulic parameters for predicting the depth of scour are complex; therefore, six artificial intelligence techniques are used in the current study to capture these complex relation. A total of 120 observations are used for the analysis. Results from the experiments show that with increasing downstream water depth (h), the impinging jet causes increasingly turbulent currents and large vortices that increase the scouring of the riverbed. Increasing discharge per unit width (q) enhances the relative scour depth (D/H) while increasing the average diameter of the riverbed materials (d) decreases D/H, where D is maximum scour depth and H is the height of the falling jet. With increasing (particle Froude number Fr), the relative scour depth increases. In the current study the prediction accuracy of Gene Expression Programming (GEP), Multivariate Adaptive Regression Spline (MARS), M5P Tree, Random Forest (RF), Random Tree (RT), and Reduces Error Pruning Tree (REP Tree) techniques are evaluated using the relative scour depth (D/(H−h)). The performance evaluation indices and graphical methods suggest that the GEP based model is more accurate than other prediction methods for the relative scour depth with a coefficient of determination (R2) equal to 0.8330 and 0.8270, a mean absolute error (MAE) equal to 0.1125 and 0.0902, root mean square error (RMSE) values of 0.1463 and 0.1116, and Willmott's Index (WI) equal to 0.8998 and 0.9014, for the training and testing stages.

Investigation of flow characteristics in open channel with leaky barriers

• Backwater rise and flow characteristic of open channel with leaky barrier were experimentally investigated. • Theoretical equation of the water level upstream the leaky barrier was presented. • The equation was easy to use and agreed well with the experimental results. • Solid volume fraction of the leaky barrier was the primary factor affecting backwater rise. Traditional flood control projects, such as dams and gates, may disrupt river connectivity, resulting in the fragmentation of river habitats. Leaky barriers, as a new method of flood defense, are gradually used in flood management especially in small rivers due to functions of the engineering in ecological and connecting rivers and regulating floods. Understanding the hydraulic effects and especially the backwater rise caused by leaky barriers is necessary to assess its impact and optimize the design. This paper investigates the influence of the leaky barrier on hydrodynamics through a designed flume experiment. A formula that reveals the backwater effects of the barrier was obtained by solving the momentum and continuity equations. Comparing the predicted and measured values of upstream water depth, the difference was within a reasonable range. Based on the results, the factors affecting the backwater rise are the Froude number of the approaching flow, downstream water depth, and the longitudinal length, drag coefficient, the solid volume fraction of the leaky barriers. Among the characteristics of leaky barrier, the solid volume fraction is the main factor affecting the backwater effect. The findings are helpful to understand the hydraulic influence of leaky barriers and can provide references for practical project.

Evaluation of the hydraulic behavior of the composite hydraulic structure considering a bed flume with special obstacle

The experimental simulation between the composite hydraulic structure and the found obstacles in the downstream region is a challenging process due to the energy losses and kinematic dissipation. The current work focuses on a comparative analysis of free flow conditions that exist without obstacles and submerged flow conditions that occur due to obstacles. It indicates the evaluation of hydraulic variables and geometrical variables of composite hydraulic structure for both flow conditions. In addition, it includes an investigation of the interaction among these variables. The hydraulic variables include actual discharge, flow velocity, flow cross-sectional area that crosses the gate, downstream water depth, discharge coefficient, Reynolds number and, Froude number, while the vertical distance between the weir and gate represents the geometry variable. The interference between the weir discharge and gate discharge plays a significant role in the result fluctuation and variation for both flow conditions, while the form and size of the obstacles only have a major effect on the submerged flow. For both flow conditions, the water depth is investigated; there would be a drastic increase in water depth by using obstacles in the downstream area as compared with not using the obstacles. This study adopts different obstacles in shape and size, therefore, the variation of maximum and minimum water levels related to the location will occur.

Experimental investigation and one-dimensional (1D) dynamic modelling of steady flow through a levee breach

Accurate prediction of levee breach flow is crucial to the mitigation of floods, and for timely breach closure. In this work, flow in an idealized levee breach has been studied for the case of a trapezoidal embankment. Flow data including water depths, surface velocities, and flow discharges were obtained from 28 experiments considering different cases of breach width and main channel downstream water depth. Ultrasonic sensors were used to record the water depth in the channel and the breach. The water surface velocity was measured using a particle tracking velocity method. A one-dimensional dynamic model based on the conservation of mass and momentum in two control volumes was developed by drawing similarities between levee breach flows and diverging open channel junction flows. The proposed model shows satisfactory performance against two independent datasets.