Water Surface Profiles Research Articles

Discharge Calculation of Side Weirs with Several Weir Fields Considering the Undisturbed Normal Flow Depth in the Channel

Discharge behavior at side weirs is significantly influenced by the water surface profile along the weir crest. In the past century, different approaches were developed to describe this profile and the associated discharge coefficients. However, the application of these methods to practical problems poses a particular challenge, as a complex three-dimensional funnel is formed due to the discharge reduction, leading to significant uncertainties in determining the relevant flow depth. For this reason, a new approach for the determination of the discharge coefficient of side weirs was developed that refers to the undisturbed normal flow depth in the main channel. Based on a comprehensive parametric study utilizing 3D-numerical simulations, the influence of the weir and channel characteristics on the discharge behavior at the side weir was analyzed. A revised formula for estimating the discharge coefficient for side weirs with multiple weir fields was derived using multiple regression analyses. Validation of the numerical simulations was carried out by applying a physical scale model, showing good agreement between the results.

Estimating River Channel Bathymetry in Large Scale Flood Inundation Models

AbstractFlood inundation modeling across large data sparse areas has been increasing in recent years, driven by a desire to provide hazard information for a wider range of locations. The sophistication of these models has steadily advanced over the past decade due to improvements in remote sensing and modeling capability. There are now several global flood models (GFMs) that seek to simulate water surface dynamics across all rivers and floodplains regardless of data scarcity. However, flood models in data sparse areas lack river bathymetry because this cannot be observed remotely, meaning that a variety of methods for approximating river bathymetry have been developed from uniform flow or downstream hydraulic geometry theory. We argue that bathymetry estimation in these models should follow gradually varying flow theory to account for both uniform and nonuniform flows. We demonstrate that existing methods for bathymetry estimation in GFMs are only accurate for kinematic water surface profiles and are unable to simulate unbiased water surface profiles for reaches with diffusive or shallow water wave properties. The use of gradually varied flow theory to estimate bathymetry in a GFM reduced model error compared to a target water surface profile by 66% and eliminated bias due to backwater effects. For a large‐scale test case in Mozambique this reduced flood extents by 40% and floodplain storage by 79% at the 5 years return period. The wet bias associated with uniform flow derived channels could have significant implications for modeling the role floodplains play in attenuating river discharges, potentially overstating their role.

Simulation research on hydraulic characteristics of conical X-shaped flaring gate piers in lock chamber based on CLSVOF method

3-D numerical simulation was carried out for flood discharge and energy dissipation process of conical X-shaped flaring gate piers in a hydropower project by using coupled Level Set and VOF method and RNG k-ε turbulent model. The change laws of flow pattern, water surface profile, velocities and pressures distributions in lock chamber of conical X-shaped flaring gate piers were gained. The results of numerical simulation were compared with the model test data and good agreement was found. The numerical results show that, there are differences on both of water surface profiles in lock chamber. With the increase of discharge, water surface profiles falls at the longitudinal axis and vertical diffusion of ski-jump flows are large on the downstream of flaring gate piers.

Characteristics of Water Surface Profile over Rectangular Side Weir for Supercritical Flows

AbstractThe supercritical flow over a side weir is a type of spatially varied flow with decreasing discharge. Most studies of side weir flows are limited to the estimation of the discharge coeffici...

SPH Open Boundary Simulation of Free-Surface Flow Over Ogee-crested Spillway

This study was conducted to compare water surface profiles with standard ogee-crested spillways. Different methods were used, such as (experimental models, numerical models, and design nomographs for the United States Army Corps of Engineers, USACE). In accordance with the USACE specifications, three different models were constructed from rigid foam and then installed in a testing flume. The water surface profile has been recorded for these models with different design heads. For modeling the experimental model configurations, a numerical model based on the smoothed particle hydrodynamics (SPH) technique was used and is developed to simulate the water surface profile of the flow over the ogee-crested spillway. A 2D SPHysics open-source software has been used in this study, using the SPH formulation to model fluid flow, developing the SPH boundary procedure to handle open-boundary simulations, and modifying the open-source SPHysics code for this purpose. The maximum absolute difference between the measured and computed results of the water surface profile for all head ratios of (H/Hd), does not exceed 4.63% at the crest region, the numerical results for the water surface profile showed good agreement with the physical model results. The results obtained experimentally and numerically by SPH are compared with the CFD results in order to be more reassuring from the results. Additional comparisons were made using interpolated data from USACE, Waterways Experiment Station (WES), and design nomographs. The SPH technique is considered very promising and effective for free surface flow applications.

Simulation of flow around a permeable dike using physical and 3D-CFD models

ABSTRACT In this research, complementary numerical and experimental physical models were conducted to investigate flow parameters around an isolated permeable spur dike using ANSYS FLUENT ver. 16.1 software. The volume of fluid method VOF with the help of CFD technique and the turbulence model was used to simulate the complex free-surface flow by applying a geometric reconstruction scheme. Two different mediums with different porosities were used, namely, gravel and glass beads. It was found that, for low flow rate values, there are no significant changes in the water profiles in both longitudinal and lateral directions for both media. Although for high flow rate values, the differences tend to be clearer. Results showed that there is a slight effect of the medium's properties if the dike width is less than 1/3 of width of the channel, in particular with low flow rate values. Good agreement was observed between the computational and the measured results for the water surface profiles. Also, there is an exact match between the lateral velocity distribution of gravels and glass beads. Downstream the dike, the lateral velocity profiles exhibit an S shape curve due to high velocity in the free flow and small flow velocity behind the porous dike. The results show good agreement between the CFD results and the experimental observations of the water surface profiles and velocity distribution according to the statistical analysis using some standard indexes error.

FEM analysis of water surface profile using VOF Method

The prediction of water surface elevation in open channels is important for evaluation and determination of the heights of side wall of structures in open channel systems. At present empirical equations are basically used for the purpose. In the early half of the 19th century experimental approach was mainly used but it had the drawbacks of laborious data collection and instrument operation limitation. The 3D flow behavior or some complex turbulent structure which is the nature of any open channel flow, cannot be effectively captured through experiments, so in these circumstances, computational approach can be adopted to overcome these obstacles. In comparison to experimental studies computational approach is repeatable, can simulate at full scale, can generate the flow taking all the data points into consideration. The motive of the present work is to use the simple geometry of the rectangular broad crested weir to test the commercial CFD software ANSYS-CFX in order to test its feasibility for implementation in more complex open channel flows. The experimental results of Hager & Schwalt’s are validated and then the analysis has been done for weirs with different slopes.

Assessment of Artificial Intelligence Models for Estimating Lengths of Gradually Varied Flow Profiles

The study of water surface profiles is beneficial to various applications in water resources management. In this study, two artificial intelligence (AI) models named the artificial neural network (ANN) and genetic programming (GP) were employed to estimate the length of six steady GVF profiles for the first time. The AI models were trained using a database consisting of 5154 dimensionless cases. A comparison was carried out to assess the performances of the AI techniques for estimating lengths of 330 GVF profiles in both mild and steep slopes in trapezoidal channels. The corresponding GVF lengths were also calculated by 1-step, 3-step, and 5-step direct step methods for comparison purposes. Based on six metrics used for the comparative analysis, GP and the ANN improve five out of six metrics computed by the 1-step direct step method for both mild and steep slopes. Moreover, GP enhanced GVF lengths estimated by the 3-step direct step method based on three out of six accuracy indices when the channel slope is higher and lower than the critical slope. Additionally, the performances of the AI techniques were also investigated depending on comparing the water depth of each case and the corresponding normal and critical grade lines. Furthermore, the results show that the more the number of subreaches considered in the direct method, the better the results will be achieved with the compensation of much more computational efforts. The achieved improvements can be used in further studies to improve modeling water surface profiles in channel networks and hydraulic structure designs.

Experimental investigation of flood energy reduction through vegetation at various angles

AbstractThe efficiency of flow energy reduction past emergent vegetation has been typically studied assuming a right angle of the vegetated corridor to the flow direction. However, in many real‐world cases the riparian zones of natural, restored, or engineered rivers and waterways, are found at an oblique angle to the flood flow direction. In the current study, the effect of vegetation angle with respect to the flow direction is investigated experimentally in an open channel rectangular flume. The experiments are conducted under a range of subcritical steady flow conditions, with varying Froude number (Fro). The vegetation cover is placed at various angles to the flow direction (90°, 45°, and 30°), for a sparse and intermediate vegetation density, defined from the ratio of spacing of each vegetation element in the cross stream direction (B), and the diameter of vegetation element (d) (B/d = 2.13 and 1.09, respectively). Detailed water surface profiles are obtained for all those cases, demonstrating a considerable backwater rise, increasing with increasing vegetation density, Froude number, and flow approach angle. The energy reduction decreased by increasing the Froude number for the perpendicular (90°) and increased for oblique vegetation (45° and 30°). For the perpendicular vegetation, the average energy reduction rate for sparse (90VS) and intermediate (90VI) vegetation densities are 25.44% and 31.44%, respectively. The range of average energy reduction for sparse vegetation at 45° (45VS) and at 30° (30VS) are 18.3–19.8% and 18.7–19.7%, respectively. Similarly, range of average energy reduction for intermediate vegetation at 45° (45VI) and at 30° (30VI) are 21.4–22% and 18.8–22%, respectively.

Modelling of flow pattern in an open channel with sidewall obstruction

To predict flow pattern of shallow obstructed open channel flows, laboratory experiments of flow around a vertical emergent sidewall abutment (lateral constriction) in an open channel flow is simulated numerically and results of water surface and vertical profile of velocity are compared with the numerical results. The turbulence kinetic energy at the separation zone and bed shear stresses are also investigated. A computational fluid dynamic (CFD) numerical tool and volume of fluid (VOF) were used to predict water surface profiles. Results showed a very good agreement between the numerical and the experimental results of the water surface profiles. The numerical findings highlighted an increase in the velocity around the structure of two times the average flow velocity. The maximum pressure was observed in front of the constriction increases with increasing discharges. The vertical velocity profiles upstream the sidewall abutment at the three selected locations showed reasonable results. The maximum turbulence kinetic energy is shown at the zone of separation when the flow passes around the nose with high velocity. In this research, numerically it was found that the estimated bed shear stresses are 2-3 times the mean bed-shear stress of incoming flow. While, previous researchers finding showed a maximum value of bed shear stress near the leading edge 3.63 to 5 times the bed shear stress of the incoming flow. Because of the wide rang variation in calculating bed shear stresses by the previous researchers, so our research aims to calculate it using CFD and compare it with others. Also, dynamics of the flow around the obstacle was considered in this research under uniform flow conditions for an aspect ratio ranged 5 to 10.

Numerical study on hydraulic characteristics of improved X-shaped FGP

The three dimensional numerical simulation was carried out for flood discharge and energy dissipation process of five improved X-shaped FGPs in hydropower project by using coupled Level set and VOF model and RNG k-ε turbulent model. The change laws of flow pattern, water surface profile and velocity distribution of X-shaped FGP and lock chamber were gained. The results of numerical simulation were compared with the model test data and good agreement was found. It validated the numerical simulation method is reliable, It can provide strong references for the design of energy dissipation and shape optimization of practical project, the results from computation can be supplement for experiment.

Numerical Study of Discharge-Head Relationship of Piano Key Weirs for Low Heads

Piano Key Weirs (PKW) is a free-flowing weir, and an improvement over the labyrinth weir family. PKW has higher discharge for the same head as compared to other types of weirs. They tend to reduce the upstream submergence in reservoirs or other flow systems and can be effectively used for flood risk mitigation. CFD studies have been carried out earlier but mostly for H/P (Total head to height ratio) greater than 0.1. The present paper investigates the use and validation of Computational Fluid Dynamics (CFD) for modeling Open Channel flows over common hydraulic structures such as PKW for small discharges with the entire range of head to height ratio h/P from 0.035 to 0.1, where h is not the total head upstream of PKW but the head measured at the crest of PKW. The numerical results have been validated with experimental results. Since the discharge is minimal surface tension force has been incorporated in the numerical model. The numerical model is a half PKW unit model with the same geometrical parameters as the experimental setup from Literature. The results show that CFD simulations can reproduce flow depths near PKW with reasonably good accuracy. The present paper compares the head obtained from CFD with that of empirical formula in the Literature but with head measured at the crest of PKW. Investigation of water surface profile and velocity profile near the upstream of PKW has also been carried out.

A Methodical Assessment of Floodplains in Mixed Land Covers Encompassing Bridges in Alabama State: Implications of Spatial Land Cover Characteristics on Flood Vulnerability

The mixed land covers encompassing bridges (MLB) are integral indicator of the socio-economic hydrological system, and their progressions are vital for flood risk assessment. However, most of the previous studies have neglected a thorough evaluation of MLBs (e.g., types, areas, and depths) on impacting flood vulnerability. This paper addresses this research gap by methodically assessing the spatial characteristics of MLBs in floodplains and their divergent impacts on flood vulnerability using four case studies of Alabama State in the USA. The hydrological and bridge data were synthesized from United States Geological Survey and National Bridge Inventory, respectively. A union of Hydrologic Engineering Center's-River Analysis System (HEC-RAS), Geographic Information System, and Surface Difference Model were employed to retrieve water surface profiles and floodplain assessments in MLBs. The results highlighted that the occurrence of floodplains was more correlated to flood depths compared to flood areas in the MLBs of Alabama. The spatial contribution of the diverse MLBs in producing deep (19%) and shallow (30%) flood depths in the bridges of Alabama were 49%, while medium flood depths were impacted only on 4% of the MLBs. The highest and lowest flood areas were noticed in the MLBs of pastures and mixed forests, respectively. Overall, the findings implied that the contribution of the individual MLBs in floodplains is multifaceted in the bridges of Alabama with spatially varying land cover distribution. Further, it is recommended that for assessing flood vulnerability, the stakeholders should focus not only on the MLBs but also on its spatially dynamic characteristics.

A Study on the accuracy of finite volume numerical models with non-rectangular mesh

During numerical simulation of complex geometries and flow depth variations, non-rectangular computational cells are to be generated. However, application of this kind of mesh cause numerical errors. A 3-D model, which was verified and validated before, was used to illustrate the problem in a simple open channel flow. A zigzag computational mesh was used to study the effect of non-rectangular cells on the accuracy of the model. Results showed that water surface and velocity profiles oscillated around the correct answer. Investigating the reason for this oscillation showed that assuming constant velocity at non-rectangular computational cell surfaces, which is a usual practice in all numerical schemes, cause this error. Variation of velocity at mesh surfaces was then added to the computation model and as a result, the oscillations in velocity profiles and water surface were eliminated. Further analysis showed that this is a general problem in any finite volume model with non-rectangular mesh.

Numerical Modeling of Venturi Flume

In order to measure flow rate in open channels, including irrigation channels, hydraulic structures are used with a relatively high degree of reliance. Venturi flumes are among the most common and efficient type, and they can measure discharge using only the water level at a specific point within the converging section and an empirical discharge relationship. There have been a limited number of attempts to simulate a venturi flume using computational fluid dynamics (CFD) tools to improve the accuracy of the readings and empirical formula. In this study, simulations on different flumes were carried out using a total of seven different models, including the standard k–ε, RNG k–ε, realizable k–ε, k–ω, and k–ω SST models. Furthermore, large-eddy simulation (LES) and detached eddy simulation (DES) were performed. Comparison of the simulated results with physical test data shows that among the turbulence models, the k–ε model provides the most accurate results, followed by the dynamic k LES model when compared to the physical experimental data. The overall margin of error was around 2–3%, meaning that the simulation model can be reliably used to estimate the discharge in the channel. In different cross-sections within the flume, the k–ε model provides the lowest percentage of error, i.e., 1.93%. This shows that the water surface data are well calculated by the model, as the water surface profiles also follow the same vertical curvilinear path as the experimental data.

Analysis of the water surface profiles of spatially varied flow with increasing discharge using the method of singular points

Spatially varied flows with increasing discharge can be encountered in several hydraulic systems. The analysis of water surface profiles in such flow conditions is useful for the verification and design of these systems. In this paper, a comprehensive analysis of the possible flow profiles in non-prismatic trapezoidal channels is performed using the method of singular points, by taking into account bed slope and friction. Different cases are identified depending on whether singular points occur or not along the collecting channel. It is verified that a singular point can be of the saddle, nodal, or spiral type, and that two singular points may occur in special circumstances. Furthermore, water depth profiles may be non-monotonic, showing a minimum or a maximum. The method is applied to both a theoretical example and three experimental tests taken from the literature, and to a real-field case concerning the side spillway channel of a dam.

Infrastructure Study for Solving Connectivity Problems Through the Nile River

Fiber optics cables present various benefits over regular cables when used as a data transportation medium in today’s communication networks. It is noted that there are significant challenges in the connectivity of inner cities that are located far inland away from the coastal areas. Most of the networks developed in Africa, especially in Egypt, are connected via submarine cables flowing across coastal areas. Very few connections are constructed to connect inner cities by crossing the Nile. The Nile River is characterized by a wide area, offering a natural path for underwater cables’ laying areas. In this study, the analysis and evaluation of the laying of these cables along the bed of the Nile River in Egypt, rather than crossing it, is investigated. There are many issues with laying fiber optic cables across the Nile River. Some of these are the requirement of using more than one node over fiber optic cable for each. When the number of nodes increases, the cost of installation and drilling effort increases with each node. The fiber optic cable path along the Nile River is simulated with a numerical model (Delft-3D). Two different scenarios for laying cables were applied and analyzed to evaluate the effect of the predicted water surface and sediment profiles on the fiber optic cable path. Based on the results obtained, the fiber-optic network infrastructure is proposed to solve connectivity problems by laying fiber optic cables along the Nile River.

Sensitivity Analysis of Rock-Fill Dam Break Flood on Different Dam Break Durations

The dam break pattern of rock-fill dams is normally gradual failure. This kind of dam failure is caused by seepage piping or overtopping, in which dam crest overflow is more common. The dam breach expansion process shall depend comprehensively on the structure pattern, material property of dam, and damsite cross sectional topography. And the break duration has a significant impact on the magnitude of break flood and the counter-measures for excess-standard flood. Take the Karot Hydropower Project constructed on the Jhelum River in Pakistan as an example, the dam break mathematical model is set up to analyze the sensitivity of damsite discharge process, downstream highest flood water surface profile and flood peak appearance time to dam break duration. The results show that: with the increase of dam break duration, damsite peak discharge is decreased sharply, flood peak appearance time extends, on-way highest water levels below Karot dam are lowered significantly, and some settlement places below Karot dam can avoid being inundated until the break duration reaches a critical value. If encountering probable maximum flood, the dam break occurs when the reservoir water level reaches dam top EL, some measures can be taken to extend the break duration, so as to effectively reduce the loss of downstream flood. The research results will help to understand the relationship mechanism between rock-fill dam break flood and break duration and provide a scientific basis or some solutions for optimization design of dam and counter-measures of dam break flood.

The Effect of Geometric Parameters of the Antivortex on a Triangular Labyrinth Side Weir

Side weirs are important structural measures extensively used, for instance, for regulating water levels in rivers and canals. If the length of the opening is limited, the amount of water diverted out of the channel and the effective length can be increased by applying a labyrinth side weir. The present study deals with numerical simulations regarding the hydraulic performance of a labyrinth side weir with a triangular plan in single-cycle mode. Specifically, six different types of antivortexes embedded inside it and in various hydraulic conditions at different Froude numbers are analyzed. The antivortexes are studied using two groups, permeable and impermeable, with three different heights: 0.5 P, 0.75 P, and 1 P (P: Weir height). The comparison of the simulated water surface profiles with laboratory results shows that the numerical model is able to capture the flow characteristics on the labyrinth side weir. The use of an antivortex in a triangular labyrinth side weir reduces the secondary flows due to the interaction with the transverse vortexes of the vertical axis and increases the discharge capacity by 11%. Antivortexes in a permeable state outperform those in an impermeable state; the discharge coefficient in the permeable state increases up to 3% with respect to the impermeable state. Finally, based on an examination of the best type of antivortex, taking into account shape, permeability, and height, the discharge coefficient increases to 13.4% compared to a conventional labyrinth side weir.

FLOOD INUNDATION MODELLING FOR TUNGABHADRA BASIN USING HEC-RAS: A CASE STUDY OF HARALAHALLI DISCHARGE SITE

The Hydrologic Engineering Center’s River Analysis System (HEC-RAS) can model flood events and produce water surface profiles over the length of the modeled stream. Flood Inundation Modelling is important for engineers, planners, and government agencies used for municipal and urban growth planning, emergency action plans, flood insurance rates, and ecological studies. This paper describes the application of the HEC-RAS model for the development of floodplain maps for the part of Tungabhadra River, Haralahalli discharge site that lies in Haveri district of Karnataka. Since most of the flood plain area/area vulnerable to flooding is currently used for agriculture. By understanding the extent of flooding and floodwater inundation, we can decide how to best allocate resources to prepare for emergencies. Keywords: Flood; Inundation; HEC-RAS Modelling