Water Surface Profiles Research Articles

Combined statistical and hydrodynamic modelling of compound flooding in coastal areas - Methodology and application

This paper presents a robust cost-effective framework for assessment of coastal-fluvial flooding due to compound action of multivariate dependent drivers. The methodology is an 8-step process that links statistical and hydrodynamic models to determine probabilities of multiple-driver flood events and associated hazards. The method involves individual and combined extreme value analysis, assessment of dependencies and interactions between flood drivers, multivariate joint probability determination accounting for dependencies, high-resolution hydrodynamic modelling of flood scenarios derived from multivariate statistical analysis, and ultimately mapping of inundation.Using Cork City, on the south coast of Ireland, as a study case, the research shows that the interactions and dependencies between tides, surges and river flows affect flood severity when they occur jointly. Tide-surge interactions have a damping effect on the total water level, while dependence between the surge residual and river flow amplifies the risk of flooding. The multivariate joint exceedance probability occurrence of high discharges and water levels represents a more realistic representation of the spatially variable water surface profiles then the combined univariate marginal scenarios. Multivariate analysis allows also considering multiple combinations of joint probability solutions along RP iso-curves. The results show that the quantification of compound flood impacts must be performed along the entire RP probability curve. This is because the physical/hydrological impacts of multiple-driver same-RP flood events can be very different leading to substantially different characteristics of flooding. The multi-scale nested flood model (MSN_Flood) was used to simulate flood wave propagation over urban floodplains for an ensemble of statistically derived flood scenarios. The hydrodynamic runs provide inundation maps that can be used to draw inferences about flood mechanisms and impacts.

ANALISIS DEBIT BANJIR RANCANGAN UNTUK NORMALISASI SALURAN DRAINASE DAN DESAIN DINDING PENAHAN TANAH DI DAERAH SEKITAR SUNGAI EPHEMERAL

Rehabilitation of buildings around the area around the river is considered by the owner of the activity because during high rainfall it will cause flooding. Flooding will result in delays in the building rehabilitation process because river water overflows into the activity location. One of the areas around a river in Bali, namely Tukad Bangin located in Pecatu Badung, is an ephemeral river, namely a river whose water only exists during the rainy season and often floods due to abnormal drainage channels and the absence of retaining walls. In the environment around Tukad Bangin there are buildings which during the rainy season cause frequent flooding, so a plan for building rehabilitation is carried out by making drainage channels and senders, then the results of calculating the design flood discharge in the Tukad Bangin Pecatu Badung area are carried out. The method used in this study is a quantitative method, namely measuring from direct observation at Tukad Bangin and then calculating the design flood discharge for various return periods for planning the design of drainage channels and shores. The results of the design flood discharge analysis with Q1 year are 15.47 m3/sec, Q2 year is 49.74 m3/sec and Q5 year is 65.89 m3/sec. From the simulation results of the water surface profile, the extreme depth values for discharge at 2-year return period are 1.54 m, 5-year return periods are 1.80 m, 10-year return periods are 1.93 m, 25-year return periods are 2.06 m and a 50-year return period of 2.04 m, so that with the HEC-RAS modeling it can control the height of the flood protection embankment and the design of the planned drainage channels and canals can be carried out.

Study of the Instantaneous Water Level Measurement Method on Unsteady Flow Based on Single Camera and Fixed Scale Compensation in the Tunnel Model

The shape of instantaneous water surface profiles for the unsteady flow in the tunnel model can be determined by measuring the instantaneous water levels at multiple points synchronously. However, the measurement accuracy of the ultrasonic method is affected greatly because of the complex state of the water surface when water level changes rapidly. Using an optical method, multicamera synchronous measurement is difficult to control, and the cost is high. For single camera measurement, the reading of the steel ruler in the image cannot be clearly seen when the distance between the measuring point and single camera is far. When the distance is short, all steel rulers cannot be captured at the same time. Hence, in this paper, a single camera and fixed scale compensation method for instantaneous water level observation in unsteady flow is proposed. A series of fixed scales is placed with the same height and width near the water surface to be measured. In order to capture dynamic images of all fixed scales with a clear water surface, a single camera is set at a far position to continuously record the water level change process within the model range. According to the height of the fixed scale, the image accuracy is compensated and the effect of the wide-angle image distortion is automatically avoided. The water level elevation is obtained according to the relationship between the fixed scale and the water surface. In this paper, the unsteady flow model measuring test is applied to the Southern Main Tunnel and the Water Distribution Pool of the Huangchigou Water Diversion Project. The accuracy of this method in measuring the dynamic water level is 1–2 mm, which meets the accuracy requirement and greatly reduces the observation cost of the model test. The proposed method may also be suitable for measuring the instantaneous water level of the unsteady flow in other similar hydraulic model tests.

Study on Hydraulic Characteristic of Unsteady Flow at Huangchigou Water Distribution Hub by Observing Instantaneous Water Level Based on Single-Camera and Fixed-Scale Compensation Method

The Huangchigou Water Distribution Hub is the core water distribution structure in the Hanjiang-to-Weihe Valley Water Diversion Project. It plays a decisive role in ensuring the safety of downstream water transport, allocating water reasonably and reducing the waste of abandoned water. The study on its unsteady-flow hydraulic characteristics is of key significance in the formulation for the opening and closing rules of the hub gates. The shape of the instantaneous water surface profile is an important factor for the hydraulic characteristics of the unsteady flow in the hub. The effect of the traditional instantaneous water level measurement method is not ideal. A single-camera and fixed-scale compensation method is proposed for an instantaneous water level observation. The proposed method meets the requirement of measurement accuracy and reduces the observation cost of the model test. The unsteady-flow test of the hydraulic model in the Southern Main Tunnel of the Huangchigou Water Distribution Hub was carried out under two operating conditions when the model flow is 0.0246 m3/s. Precise data such as wave front propagation velocity and hydraulic oscillation recovery time of unsteady flows in the Southern Main Tunnel was obtained. It has an important reference value for the research and design of water transfer dispatching and gate-opening and gate-closing rules for the Huangchigou Water Distribution Hub.

Research on the Influence of Siltation Height of Check Dams the on Discharge Coefficient of Broad-Crested Weirs

With the continuous operation of check dams, the silting elevation of the whole dam gradually increases. When the silting height is close to the elevation of the broad-crested weir, it will result in a large change in the hydraulic characteristics of the original flow pattern. For subsequent reinforcement work, it is necessary to know how excessive sediment deposition affects the overflow from the broad-crested weir into the spillway. However, few studies about discharge coefficients are available in the case of spillways with sediment. In this paper, the hydraulic characteristics and discharge coefficient of a broad-crested weir whose width is 270 mm are investigated with physical experiments under different siltation heights and discharges. The research shows that: (1) With the increase in siltation height, the water level on the weir decreases and the drop of the flow becomes smaller. The overall flow pattern tends to the open-channel flow pattern. (2) In the same siltation height condition, the water surface profile along the broad-crested weir rises with the increase in discharge, and the surface velocity of the water in front of the weir increases with the increase in discharge. However, in the same discharge condition, the water surface profile along the broad-crested weir decreases with the increase in siltation height, and the surface velocity of the water in front of the weir gradually increases, which reflects that the increase in siltation height improves the overflow capacity of the broad-crested weir. (3) The present empirical formulas for the discharge coefficient have large errors when there is sediment accumulation. Therefore, a new formula for the discharge coefficient with sediment deposition is obtained using experimental data and its maximum relative error is 4.02%, which can provide a theoretical basis for risk elimination and reinforcement work on check dams in the Loess Plateau.

Investigation of flow characteristics in gabion stepped weirs

Abstract Weirs are used to control and regulate the flow in open channels. In gabion structures, the flow conditions are more complex due to the complexity of flow through the porous body of a gabion. The present study aims to investigate the water surface profile, the overflow velocity profile, and both the through-flow and overflow ratios. Six physical models of the three downstream slopes (V:H 1:1, 1:2, and 1:3) and two types of rockfill (crushed stone and rounded gravel) were investigated. Results show that for the same discharge, the milder slope model (1:3) shows higher water surface and higher velocity than the steeper slope (1:1) with about 9 and 8% on average respectively. The water surface was 60% higher on the lower steps than on the upper steps at the nappe flow regime. Moreover, the low porosity models show a slightly higher velocity and flow depth than higher porosity models for all sections. Furthermore, increasing the porosity from 0.38 to 0.42 led to about a 27% increment in the through-flow ratio. Finally, four relationships were developed to estimate the through-flow and overflow ratios at the upstream and inner sections of the gabion weir. The suggested relationships can be considered novel relationships.

Hydrodynamic considerations for improving the design/evaluation of over-topped bridge decks during extreme floods

Flow over an Iranian bridge deck is studied under an actual extreme flood event happening similarly nowadays in many countries due to climate change. Rigorous transient fluid-structure interaction analyses using the realizable k-ε turbulence model and the VOF Method are conducted. Geotechnical and abutments damages are neglected. Water surface profiles, velocity vectors, and hydrodynamic coefficients are determined. Based on the latest hydrological regime, particularly in supercritical flows, the results are partially compared against the latest advanced design codes, to evaluate the performance of their hydrodynamic and hydraulic provisions in similar incidents. It was acknowledged that the flood loads recommended by the Federal Highway Administration (FHWA) are fairly acceptable, Eurocode-1 predicts them rather accurately but not in extreme cases, and the Australian Standard (AS-5100.2) is less effective due to over-estimation of the hydrodynamic loads. Instead, the latter offers comprehensive user-defined hydraulic conditions. Furthermore, upon gradual rise of the water level to thrice the deck height, bridge stability is found to be at risk due to highly turbulent states. It is recommended that due to such threats, re-evaluation of flood regime, as well as its distinct hydrodynamic properties have to be accounted for, when evaluating existing bridges or designing new ones.

Assessment of the Hydraulic Geometry of the Upper Meghna River in Bangladesh

The Meghna is one of the major rivers in Bangladesh. Frequent changes in flow and water level is a regular phenomenon due to the high seasonal rainfall variation. Such variations are exaggerated with cliamte change induced effects. Hence, it is crucial to figure out how climate change will affect the Meghna river's hydraulic properties. This study assesses water surface profile of a specific 120 km long reach of the Meghna river. A model was set up to run unsteady flow analysis for the years 2018, 2019, and 2020. The result matches well with the actual observation after calibration and validation. The study finds maximum water level during August, which mostly correlates with the high rainfall during this month of the monsoon season. The model has also been used to run a steady flow analysis for the return period of 2.33 years, 5 years, and 20 years. The result is useful for the sustainable design of bridges and other hydraulic structures. Journal of Engineering Science 13(2), 2022, 1-10

MATLAB‐based program for computation of open‐channel flow profiles

AbstractIn engineering practice, open channel water surface profile data frequently serve as the scientific foundation for engineering design, flood forecasting, reservoir scheduling, and the calculation of dam‐break flood evolution. Water surface profiles in open channels (WSPOC), Matrix Laboratory (MATLAB)‐based software was developed to help students better learn and improve their interest in surface line theory. According to the flow characteristics, the program is divided into two modules: steady flow and unsteady flow. The steady flow module guides students to master the judgment methods of various gradually varying flow types and can program independently to explore the solution process of the water surface profiles. The unsteady flow module is designed to help students learn finite difference methods in computational fluid dynamics (CFD), and allow students to interact with software in engineering cases to achieve the purpose of effectively integrating theory and practice. This software employs MATLAB graphical user interface(GUI) visualization technology to embed students' autonomous programming in crucial phases and transforms abstract concepts and theories into vivid animation demonstrations using CFD simulation tools. Furthermore, the transformation from theory to practice has been realized by providing a large number of practical engineering examples, which may improve students' ability to solve complex engineering problems. Based on the survey results, the user experience and application effect of the software are satisfactory, and the software's design objective has been achieved.

Effect of anti-vortex structures installed on stepped labyrinth side weirs on discharge capacity

Side weirs are essential structural elements commonly used to control water levels in rivers and canals. If the length of the opening is limited, a labyrinth side weir can be used to increase the amount of water diverted out of the channel and the effective length. This research studied the influence of installing an antivortex structure in stepped labyrinth side weirs on discharge capacity. It has four types of antivortex installed in different hydraulic conditions at different Froude numbers, dimensionless crest height, dimensionless weir opening length, step number, and head angle. Using data from 168 experimental runs without antivortex to allow comparison and 672 experimental runs to determine the best performance of antivortex structures that improved discharge capacity, and 528 runs measured velocity to investigate the intensity of secondary currents generated by lateral flow and other hydraulic conditions, including water surface profiles. According to the research results, installing antivortices regulated the flow, significantly improved the efficiency of the single-cycle stepped labyrinth side weir, and lowered secondary flows caused by interaction with the vertical axis. Finally, the discharge coefficient improves to 18% after analyzing the best type of antivortex, considering shape and height.

Ecogeomorphological Condition and Hydrological Indicators of the Self-Purification Capacity of Rivers: A Case Study of Siminehrood River in Northwestern Iran

Aims: The steady development of human communities and the spread of industrial activities are major contributors to environmental pollution, especially the contamination of water resources. Population growth and thus the acceleration of municipal, industrial, and agricultural wastewater release have adversely affected these inestimable resources and restricted their accessibility. This work attempts to identify the ecogeomorphological condition of rivers in drainage basins emphasizing the Siminehrood River in Northwestern Iran. The purpose is to study all nonpoint source (PS) and PS pollutions and circumstances that weaken and intensify the pollution rate and self-purification capacity of rivers, especially in the Siminehrood River. Materials and Methods: All data and statistics were collected and their seasonal average was calculated. Maps and variables associated with the physical properties of drainage basins were then extracted through ArcGIS. The Schuler diagram was plotted through Chemistry software for all stations and each season to assess the type and chemical quality of the river's drinking water. HEC-RAS model, HEC-GEORAS extension, and ArcGIS were employed for simulation of river flow and calculation and determination of water surface profiles and other hydraulic characteristics of flow including water depth, water flow rate, stream shear stress, and stream power. Results: According to the analyses and results, the improper ecogeomorphological condition of rivers and their low self-purification capacity are directly correlated with the mean river water depth, water flow rate, slope of the river basin, and environmental differences. Conclusions: Within the study area, the highest environmental instability and the least self-purification capacity were observed downstream of the sub-basin in which the mean and maximum depth of water were, respectively, 3.10 m and 8.803 m. Insignificant water flow rate (0.86 m/s on average) and slope of <4% in the area have stagnated water flow in most areas and consequently declined the content of dissolved oxygen and the quality of water. Conclusively, this sub-basin can be reported as a region with an improper ecogeomorphological condition.

Statistical approach of contemporary hydrogeomorphological channel changes of the middle Allier River, France: morphostructural controls, human impacts and flow regime

The Allier River, France, known for its very dynamic river sections in its lower course, was nevertheless subjected to human impacts. The present study aims to better explain the recent hydrogeomorphological channel changes of the middle Allier River considering morphostructural constraints, human impacts and flow regime since the second half of the 20th century. Channel changes are analyzed from six historical aerial photographs (1954, 1974, 1992, 2000, 2010 and 2016) and four longitudinal water surface profiles (1934/35, 1999, 2005 and 2020), based on descriptive statistical analyses and a Principal Component Analysis followed by a Hierarchical Cluster Analysis. The influence of morphostructural controls and human impacts are tested using a Correspondence Factor Analysis, whereas temporal trends of the flow regime are analyzed using Mann Kendall and Pettitt tests. Overall, results show that during the last sixty to eighty years the channel bed incised by 0.86 m, narrowed by 25% and that lateral mobility decreased by 68%. Four morphological evolutionary trajectories were identified for the alluvial plain sections, laterally more mobile than the naturally confined section. These evolutionary trajectories were caracterized by a more or less important presence of human impacts on the channel, such as gravel mining activities and, more locally, in-channel engineering works. Moreover, hydrological changes recorded at the end of the 20th century, characterized by a decrease of the frequency, the duration and the intensity of floods, has led to a general increase of annual abandoned surfaces and, conversely, to a decrease of annual eroded surfaces. In conclusion, future river management schemes will have to consider past and present human impacts on channel morphodynamics as well as current climate change and its consequences on the flow regime.

Assessment of water surface profile in nonprismatic compound channels using machine learning techniques

Abstract Accurate prediction of water surface profile in an open channel is the key to solving numerous critical engineering problems. The goal of the current research is to predict the water surface profile of a compound channel with converging floodplains using machine learning approaches, including gene expression programming (GEP), artificial neural networks (ANNs), and support vector machines (SVMs), in terms of both geometric and flow variables, as past studies were more focused on geometric variables. A novel equation was also proposed using gene expression programming to predict the water surface profile. In order to evaluate the performance and efficacy of these models, statistical indices are used to validate the produced models for the experimental analysis. The findings demonstrate that the suggested ANN model accurately predicted the water surface profile, with coefficient of determination (R2) of 0.999, root mean square error (RMSE) of 0.003, and mean absolute percentage error (MAPE) of 0.107%, respectively, when compared with GEP, SVM, and previously developed methods. The study confirms the application of machine learning approaches in the field of river hydraulics, and forecasting water surface profile of nonprismatic compound channels using a proposed novel equation by gene expression programming made this study unique.

Theoretical investigation of dam-break waves in frictional channels with power-law sections

Both the hydraulic resistance and the channel cross-sectional geometry have significant effect on the propagation of the dam-break waves. Analytical models including either of them have been available. However, it is not feasible to assess the comprehensive influence using the existing solutions. The present study considers a resistance-dominated wave tip region followed by an ideal fluid flow region in a dry horizontal channel whose cross-sectional shape is controlled by a power-law index n. Laboratory experiments and numerical simulations are conducted to measure/predict the water surface profiles of the dam-break flows in five types of flumes. The water depth, location and celerities of the wave front predicted by the analytical model agree well with the experimental and numerical results. The quantitative effects of the bottom resistance and the channel cross-sectional shape on the wave properties are investigated. Results show that the spatio-temporal variation in the wave feature of the dam-break flows strongly depends on the channel cross-sectional geometry; while the retardation effect of the bottom resistance becomes more significant as n increases. Furthermore, the derived analytic solution as well as the experimental data can be used for evaluating numerical solutions considering the hydraulic resistance and cross-sectional geometry.

Analysis of steady flow in radial porous media

Abstract The outflow depth from the radial porous media (inflow to the well) is very useful as the downstream boundary condition and the starting point for water surface profile calculations. Based on the studies, unlike the Stephenson's hypothesis (the outflow depth is equal to the critical depth), the outflow depth from the rockfill media is a coefficient (Γ) of the critical depth. In the present study, using several (large scale and almost real) experimental data in the radial non-Darcy flow condition, dimensional analysis and the particle swarm optimization (PSO) algorithm, an equation was presented to calculate the mentioned coefficient based on upstream water depth (h) and distance between the well center and the upstream (R). Then, using the calculated outflow depth and the 1D flow analysis equations, the water surface profile in the radial non-Darcy condition was calculated for the first time. The results showed that considering an outflow depth equal to the critical depth and using the proposed solution in the present study, the mean relative error (MRE) values of 83.43% and 3.53% were obtained, respectively. In addition, using the proposed solution for different experimental conditions, an average MRE of 2.58% was calculated for the water surface profile.

Dissolved Oxygen Variation on the Steps with a Quarter Circle End Sill for Flows over the Stepped Spillways

Determining the aeration efficiency of the stepped spillways is important because the Dissolved Oxygen (DO) concentration helps indicate the water quality. This study investigated the effects of varying step shape and chute slope on the aeration efficiency for stepped spillways. The measured parameters were DO, the inception point of the free surface, and the water surface profile above the crest to evaluate the geometry variation impacts. Several experiments were conducted on a six-step configuration over a stepped spillway with chute angle (θ = 26.6°, 21.8°, and 8.9°). The discharges up to 0.055 m3/s. The step configurations were including flat step, normal end sill, and quarter circle end sill. The results showed when the chute angle changed from 26.6° to 8.9°, the aeration efficiency of E20 improved with 11.51% at the lowest discharge and 6.05% at the highest discharge for the flat step model with 10 steps. Also, E20 improved 11.39% at the lowest discharge and 6.50% at the highest discharge for the flat step model with 6 steps. The performance of the steps with the quarter circle end sill model in terms of aeration efficiency increased by 10%.

Investigation of effect of logjam series for varying channel and barrier physical properties using a sparse input data 1D network model

Targeted design and placement of natural flood management leaky barriers, or engineered logjams, and accurate representation of logjams in hydraulic models across different scales is necessary to generate desired water storage and flood peak attenuation for effective river restoration and natural flood management projects. We systematically assess the effect of varying logjam spacing, extent of logjam-generated change in water surface profile, vertical height of lower gap, overflow to local floodplain, and varying channel slope, representing a series of logjams in a sparse input data 1D network model including the jam-generated backwater, which depends on loss of momentum within the jam. To guide catchment-scale representation, best-fit increased channel resistance was found to increase with number of jams, approaching an analytically determined maximum for close inter-jam spacing, useful for setting an upper envelope for efficacy.

Flow characteristics on the leeside of a geotextile mattress with floating plate

The Geotextile Mattress with Floating Plate (GMFP) is a novel scour prevention structure. This paper provides an insight into the effects on the flow pattern near the GMFP to better understand the GMFP working mechanism. The GMFP design parameters were emphasized, including the sloping angle, the height of the floating plate, and the opening ratio. In most cases, the bottom vortex is located immediately downstream to the GMFP. The near bottom velocity downstream to the bottom vortex is remarkably lower than the undisturbed value. The location variation of the bottom vortex reattachment point with the GMFP design parameters was studied. Within the range of hydrodynamic parameters tested, the reattachment point moves upstream when the opening ratio increases over 0.231, which agrees with previous studies. With the increase of the obstruction height of the floating plate, the reattachment point tends to move downstream when the relative obstruction height is below 0.2, and then retreats to the upstream side, which may be attributed to the variation in the water surface profile and the enhanced flow through the sand-pass gap due to the intensified blockage effect. An equation was proposed to predict the location of the reattachment based on the GMFP obstruction height.

Implementation of heuristic search algorithms in the calibration of a river hydraulic model

In this contribution, two heuristic search algorithms, (1) particle swarm optimization (PSO) and (2) genetic algorithm (GA) are used to calibrate the iRIC, a two-dimensional hydraulic model for a test case on the Green River in Utah. The goal of the search algorithms was to find the combination of roughness values that minimized model error compared to the measured water surface elevation. An artificial neural network (ANN), which was trained based on the simulated water surface profiles obtained from iRIC, was used to measure the fitness of each solution. Implementation of PSO and GA both improved the accuracy of the calibration by 34 and 30 percent respectively relative to the trial and error. This research demonstrates that the implementation of heuristic search models provides an objective methodology for the calibration of hydraulic models with improved performance when compared to models calibrated via trial and error.

Hydrodynamic forces on emergent cylinders in non-uniform flow

The main objective of conducting numerical simulations of flows in rivers with vegetation is to investigate the complex flow dynamics involved in non-equilibrium conditions. In such cases, it is inappropriate to apply the drag coefficient CD, which is typically derived based on uniform flows involving groups of infinitely long cylinders. This paper presents a method for evaluating the drag forces acting on emergent obstacles for non-uniform open-channel flows. This method is devised based on two sets of experiments: on flows with small-diameter cylinders, focusing on the water surface profiles through the group; and on flows with large-diameter cylinders, focusing on the local pressure distribution and local water surface profile around a target cylinder. In addition to the conventional drag force expression that includes CD, two new terms are proposed to account for the effects of water surface variation and pressure gradient in non-uniform open-channel flow on the drag. The first of these terms, which introduces the use of the Froude number to account for the effect of water surface variation, is derived theoretically and evaluated against past and present experimental results under uniform-flow conditions. On the other hand, the second of these terms, which includes the representative length of the separation zone to evaluate the effect of pressure gradient, is confirmed to be a necessity through numerical calculation of the longitudinal water surface profile in emergent cylinders. The incorporation of these two terms using a simple unified expression can help improve the accuracy of numerical simulations for practical problems of flows with emergent obstacles.