The Coefficient of Broad-Crested Weir in Natural Channels

2018 ◽  
Vol 1 (01) ◽  
Author(s):  
Ahmed Said
Keyword(s):  
Cross Section ◽  
Water Surface ◽  
Discharge Coefficient ◽  
Surface Profile ◽  
Digital Terrain Model ◽  
Channel Cross Section ◽  
Water Drainage ◽  
Section Data ◽  
Cross Section Area ◽  
Surface Profiles

Weirs have been designed and used extensively in hydraulic structures to control the flow depth and discharge. To estimate the discharge over the weir, a weir coefficient is required. The discharge coefficient can be obtained experimentally as a function of the dimensionless total head of the approaching flow or as a function of various parameters. However, a universally acceptable discharge coefficient does not exist. Beside the man-made weirs that have been constructed by hydraulic engineers, some natural channel characteristics and slopes can be simulated as broad-crested weirs that are clearly noticeable in examining water surface profiles. The study area is Centralia watershed in Central Florida, which contains several cascades of step like waterfalls that can be selected for transecting. Cross-section data from 5 transects and detailed hydraulic data was obtained using the Digital terrain model (DTM) and the Triangular Irregular Network (TIN). The Hydrologic Engineering Center-River Analysis System (HEC-RAS) stepbackwater technique was used to calculate water surface profiles for natural channels that are likely used for storm water drainage. The results show that these channels have chains of steps that dissipate the momentum of falling water in steep areas and maintain a steady rate of flow. The weir coefficients were determined by comparing the steady state discharges to the equivalent weir discharges. The results indicate that the weir coefficient can be expressed as a function of weir height and channel cross-section area. The relationship between this function and the weir coefficient showed a high correlation with R2 = 0.991. The results of this study can be used to estimate the discharge in similar reaches in any water surface profile.

scholarly journals PENGARUH BENDUNG TERHADAP PROFIL MUKA AIR SUNGAI BATANG GADIS

2014 ◽  
Vol 8 (1) ◽  
pp. 1
Author(s):  
Sudarmanto ,
Keyword(s):  
Numerical Integration ◽  
Cross Section ◽  
Water Surface ◽  
Surface Profile ◽  
Uniform Flow ◽  
Flood Discharge ◽  
Before And After ◽  
Numerical Integration Methods ◽  
The Village ◽  
River Cross Section

Placement of the weir in the river Batang Gadis will cause population anxiety in the village Pulungan which located upstream weir as far as 3 km, due to a weir can cause water surface profile of the river getting higher and ultimately to increase the pool of flooding in residential areas.Assuming modeling of river a uniform flow, river cross-section has a rectangular shape with width 50 m and 40 m, the roughness Manning 0.0025, the profile of water flow floods that occurred in 2 yaears, 25 years, and 100 years before and after the existing weir can be calculated by numerical integration methods.  From the calculation, the length of the water behind the weir is 1.4 km upstream towards the weir, which means that the depth of the water level rises to as far as 1.4 km and after that the depth of water before and after there the weir is same. Because the village Pulungan located 3 km to the upstream, the weir did not affect the increase in the flood waters in the village Pulungan. At 2 years flood discharge does not cause inundation in the village Pulungan, but the flood discharge 25 years and 100 years has led to inundation in the village Pulungan with the depth of each pool 0.971 m and 1.675 m. Keywords: uniform flow, numerical integration, inundation, flood discharge.

scholarly journals Experimental study to estimate the discharge coefficient over inclined side spillway

2020 ◽  
Vol 7 (2) ◽  
pp. 44-54
Author(s):  
Ayat Mehdi kadhim ◽  
Faisal A. Majid
Keyword(s):  
Experimental Study ◽  
Froude Number ◽  
Water Surface ◽  
Discharge Coefficient ◽  
Flow Direction ◽  
Surface Profile ◽  
Side Weir ◽  
Discharge Water ◽  
Water Surface Profile ◽  
Crest Length

Abstract: Weir is usually used in different hydraulic purposes, mainly for head discharge-water relationship in channels. In this research, the flow has been carried out over the side of spillway using three cases of crest inclination by means of increasing one side of the weir a half centimeter each time with constant crest length equal to 15 cm. This means that the angle θ equals to (1.91˚, 3.82˚ and 5.71˚) respectively towards of the flow and is opposite to the flow with decreasing a half centimeter. Also in case of the breadth is horizontal (θ=0), seven cases have been tested. It is known that the greater amount of discharge occurs when the breadth is horizontal (θ=0). In case of the inclination of the weir is inclined opposite to the flow direction, the discharge is greater than that of which the weir inclined towards the flow direction for all cases of inclination. The greater discharge was obtained when decreasing the angle, which is opposite to the flow direction. The amount of discharge over the side of weir decreases by increasing the angle of the slope opposite to the direction of the flow and become more decreasing in case the inclination of side weir towards the flow. In case of increasing the angle of inclination in flow direction, the amount of discharge over side weir will be decreased. The effect of Froude number has also studied with the discharge coefficient and found that, they are proportionally related to each other. Also the water surface profile along the side spillway weir is studied and taken under consideration theoretically and experimentally in this research.

scholarly journals Flood Analysis with HEC-RAS: A Case Study of Tigris River

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Selman Ogras ◽  
Fevzi Onen
Keyword(s):  
Cross Sections ◽  
Water Surface ◽  
Flood Hazard ◽  
Surface Profile ◽  
Natural State ◽  
Human Beings ◽  
Residential Areas ◽  
Tigris River ◽  
Digital Elevation ◽  
Surface Profiles

Floods are seen in countries in tropical climatic zones, both in terms of quantity and harm. The non-tropical climate countries such as Turkey are also affected by the floods. The geographical structure of Turkey is extremely complex and varies even at short distance. Therefore, the shape and effects of the floods vary from region to region. Considering the peculiar state of nature, floods, which are the greatest disasters after the earthquake, are unlikely to occur. But floods are becoming more risky for human beings day by day because of the population growth, need of water and settlements, wrong zoning plan, and unplanned engineering practices. Regulation comes at the beginning of measures to be taken to minimize the damages that occur from the floods. To do these studies, it must be specified the changes which bridges on the rivers and hydraulics structures like regulator cause in cross sections and the effects of the changes to water surface profile due to the natural state of the land. In order to determine water surface profiles, many software packages have been developed for facilitating the analysis and calculation. HEC-RAS is one of them. In this study, the floodplain analysis was handled between Diyarbakır-Silvan Highway and historical Ten-Eyed Bridge. There are three bridges, and one of which are historical bridges, as well as fertile agricultural lands, facilities, and hospitals in the Dicle University campus, the Hevsel Gardens on the UNESCO World Cultural Heritage List, and some residential areas on the route under study. The aim of the study we have done in this much important route is to evaluate the flood areas and create a flood hazard map which can predict risky areas. And also contributing to the Tigris River Rehabilitation Project is one of the aims. About methodology, the 1/1000 maps of the study area were digitized using the AutoCAD Civil 3D program and cross sections were made by obtaining the digital elevation models of the region. The obtained cross sections were defined in the HEC-RAS software, and the hydraulic characteristics of the flood bed and the water surface profiles of the Q25, Q50, Q100, and Q500 flood recurring and one-dimensional floodplain analysis of the Tigris River were determined.

Interfacial Shear in Two-Phase Wavy Flow in Closed Horizontal Channels

1974 ◽  
Vol 96 (2) ◽  
pp. 97-102 ◽  
Author(s):  
E. Kordyban
Keyword(s):  
Shear Stress ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Cross Section ◽  
Water Surface ◽  
Interfacial Shear Stress ◽  
Interfacial Shear ◽  
Channel Cross Section ◽  
Two Phase ◽  
The Waves

The interfacial shear stress for air flowing over a wavy water surface was determined experimentally in a closed horizontal channel by measuring the pressure drop and the structure of the water surface. The wall shear stress was measured with the aid of a Preston gauge. The range of tests included the conditions where the waves were large in comparison to the channel cross section. The equivalent sand roughness determined from the resistance formula for rough walls in fully turbulent flow was found to be related to the rms wave height through ks = 32Δh.

scholarly journals Experimental Study on Flow Structure around Spur Dikes of Different Types

CONVERTER ◽  
2021 ◽  
pp. 778-788
Author(s):  
Tao Yu, Et al.
Keyword(s):  
Flow Structure ◽  
Cross Section ◽  
Water Surface ◽  
Circular Cross Section ◽  
Surface Profile ◽  
Spur Dike ◽  
Trapezoidal Cross Section ◽  
Variation Characteristics ◽  
Regulation Function ◽  
Water Surface Profile

As water damage phenomenon of spur dike exists generally, spur dike must be maintained in order to ensure its regulation function, but its structure changed in the process of maintenance.  In order to find out flow structure around the spur dike of different pattens, through generalized flume model tests, variation characteristics of water surface profile and flow velocity around the spur dike of five different pattens were analysed. The results show that the straight head had a greater influence than hook head spur dike on the water surface profile, circular cross-section had smaller effects than trapezoidal cross-section spur dike on the water surface profile; Velocity of Choke area and contraction order from large to small is trapezoidal cross-section and fan straight head dike, trapezoidal cross-section and arc straight head dike, arc section and arc straight head dam, trapezoidal cross-section and fan hook head dike, trapezoidal cross-section arc hook head dike; Cross section vertical velocity distribution from large to small is trapezoidal cross-section and fan hook head dam, trapezoidal cross-section and circular straight head dike, arc cross-section and circular straight head dam, trapezoidal cross-section and circular hook head dike.

scholarly journals Physically based model for gully simulation: application to the Brazilian semiarid region

2020 ◽  
Vol 24 (8) ◽  
pp. 4239-4255
Author(s):  
Pedro Henrique Lima Alencar ◽  
José Carlos de Araújo ◽  
Adunias dos Santos Teixeira
Keyword(s):  
Cross Section ◽  
Daily Rainfall ◽  
Threshold Value ◽  
Gully Erosion ◽  
Channel Cross Section ◽  
Semiarid Region ◽  
Economic Activities ◽  
Cross Section Area ◽  
Section Area ◽  
Physically Based

Abstract. Gullies lead to land degradation and desertification as well as increasing environmental and societal threats, especially in arid and semiarid regions. Despite this fact, there is a lack of related research initiatives. In an effort to better understand soil loss in these systems, we studied small permanent gullies, which are a recurrent problem in the Brazilian northeastern semiarid region. The increase in sediment connectivity and the reduction of soil moisture, among other deleterious consequences, endanger this desertification-prone region and reduce its capacity to support life and economic activities. Thus, we propose a model to simulate gully-erosion dynamics, which is derived from the existing physically based models of Foster and Lane (1983) and Sidorchuk (1999). The models were adapted so as to simulate long-term erosion. A threshold area shows the scale dependency of gully-erosion internal processes (bed scouring and wall erosion). To validate the model, we used three gullies that were over 6 decades old in an agricultural basin in the Brazilian state of Ceará. The geometry of the channels was assessed using an unmanned aerial vehicle and the structure from motion technique. Laboratory analyses were performed to obtain soil properties. Local and regional rainfall data were gauged to obtain sub-daily rainfall intensities. The threshold value (cross-section area of 2 m2) characterizes when erosion in the walls, due to loss of stability, becomes more significant than sediment detachment in the wet perimeter. The 30 min intensity can be used when no complete hydrographs from rainfall are available. Our model could satisfactorily simulate the gully-channel cross-section area growth over time, yielding a Nash–Sutcliffe efficiency of 0.85 and an R2 value of 0.94.

The Normal Depth and Critical Depth of Special Cross-Section

2012 ◽  
Vol 594-597 ◽  
pp. 2003-2008
Author(s):  
Bing Qian Wei ◽  
Zheng E Wang ◽  
Wen Qiang Meng ◽  
Yang Liu
Keyword(s):  
Cross Section ◽  
Water Surface ◽  
Circular Cross Section ◽  
Surface Profile ◽  
Water Diversion ◽  
Critical Depth ◽  
Water Delivery ◽  
Circular Shape ◽  
Water Surface Profile ◽  
Mathematical Derivation

In water diversion project and water delivery project, horseshoe cross-section and circular cross-section are commonly used. The hydraulic elements of nonstandard horseshoe shape and circular shape are difficult to calculate because of their complex section. This article gives the formulas of hydraulic elements and iterative formulas of normal depths and critical depths of horseshoe shape section composed of 6 arcs and 2 kinds of irregular circular shape section by mathematical derivation. And on the basis of the relation with depth, normal depth and critical depth, we can estimate the type of water surface profile. It can be applied in calculation of water surface profile 81.68 km Qinling tunnel of south water to north project. The formulas of normal depth and critical depth and hydraulic elements can be used in other similar water delivery project.

scholarly journals Effect of Flaring Gate Piers on Discharge Coefficient for Finite Crest-Length Weirs

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1349
Author(s):  
Zhong Tian ◽  
Wei Wang ◽  
Ruidi Bai ◽  
Nan Li
Keyword(s):  
Comparative Analysis ◽  
Water Surface ◽  
Discharge Coefficient ◽  
Discharge Coefficients ◽  
Water Head ◽  
Contraction Ratio ◽  
Plunging Jets ◽  
Surface Profiles ◽  
Crest Length ◽  
Contraction Angle

The use of flaring gate piers (FGPs) along with finite crest-length weirs changes the shape of plunging jets and increases the efficiency of energy dissipation in some projects; however, the FGPs may affect the discharge capacity. In this study, the flow pattern and discharge coefficient were experimentally investigated under different conditions by varying the weir lengths Lw, contraction ratio β, contraction angle θ, and water heads H. A comparative analysis of the weirs with and without FGPs was performed. For the finite crest-length weirs with FGPs, the water-surface profiles in the flow channel were backwater curves. Moreover, the plunging jets leaving the weir became narrower and then subsequently diffused largely in the transverse and longitudinal directions in air. The discharge coefficients of the weirs with FGPs were approximately equal for various weir lengths. Moreover, following the earlier studies on traditional finite crest-length weirs, a discharge-coefficient equation was developed for the weir with an FGP in this study. The results showed that in the weirs with FGPs, the discharge coefficients clearly increased with the increase in the contraction ratio and water head, but the changes in their values along with the contraction angle were neglected.

Effect of Relaxation on Drag Forces and Diffusivities of Particles Confined in Rectangular Channels

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Panadda Dechadilok ◽  
Chakrapong Intum ◽  
Sasipan Manaratha ◽  
Umnart Sathanon
Keyword(s):  
Particle Size ◽  
Cross Section ◽  
Charged Particles ◽  
Relaxation Effect ◽  
Channel Cross Section ◽  
Drag Forces ◽  
Cross Section Area ◽  
Section Area ◽  
Rectangular Channels ◽  
Charged Spheres

When a particle is moving inside a channel, its hydrodynamic interaction with channel walls increases its drag coefficient, causing a diffusivity reduction. For charged particles moving in an electrolytic solution, there is an additional drag due to the distortion of an electrical double layer caused by particle motion known as the relaxation effect. Effects of relaxation on drag forces on spheres confined in rectangular channels are computed employing perturbations involving particle Peclet number and surface charge densities. Results indicate that confinement amplifies electrokinetic retardation; increasing the relative particle size or decreasing the channel cross section area enhances the relaxation effect. With the relative particle size kept constant, the relaxation effect on the drag exerted on charged spheres in cylindrical pores with its smaller cross section area is stronger than that on charged spheres in rectangular channels and slit pores. However, for certain values of Debye length and particle size, the ratio between excess drag due to relaxation on confined charged spheres and hydrodynamic drag on uncharged spheres confined at the same location is higher for particles in rectangular channels, resulting in higher percentages of diffusivity reduction. Diffusivity reduction due to relaxation of charged particles in square ducts displays a maximum as a function of relative particle size, whereas that of charged particles in rectangular channels with higher cross section aspect ratio increases monotonically as particle size increases.

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