Physical Modeling of Spatial and Temporal Development of Local Scour at the Downstream of Bed Protection for Low Froude Number

Local scour at the downstream of the river bed protection is one of the most important parameters for the design criteria and sustainable management of the hydraulic structures. Previously, various researches on its process in the equilibrium state have been suggested with experimental and numerical approaches. In this study, relatively long-term laboratory experiments of local scouring at the downstream of fixed bed in an open channel were conducted with mono-granular sediment bed and analyzed about maximum scour depth and its temporal development. In particular, we conducted experiments with relatively low Froude number (less than 0.5) and their duration of tests was exceeded over 700 hours. We modified the relationship between the dimensionless time and length scales of the maximum scour depth of the local scour hole based on the turbulent shear layer thickness. A new functional relationship between dominant factors and the maximum scour depth in the equilibrium state were suggested and compared with previously suggested formula. Also, from the results by nonlinear regression, Froude number was founded as a dominant factor on the prediction of equilibrium maximum scour depth.

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Nose-Angle Bridge Piers as Alternative Countermeasures for Local Scour Reduction

The Baltic Journal of Road and Bridge Engineering ◽

10.7250/bjrbe.2018-13.405 ◽

2018 ◽

Vol 13 (2) ◽

pp. 110-120 ◽

Cited By ~ 2

Author(s):

Ibtesam Abudallah Habib ◽

Wan Hanna Melini Wan Mohtar ◽

Atef Elsaiad ◽

Ahmed El-Shafie

Keyword(s):

Froude Number ◽

Local Scour ◽

Bridge Piers ◽

Scour Depth ◽

Skew Angle ◽

Flow Angle ◽

Sediment Size ◽

Low Froude Number ◽

Skew Angles ◽

Depth Reduction

This study investigates the performance nose-angle piers as countermeasures for local scour reduction around piers. Four nose angles were studied, i.e., 90°, 70°, 60° and 45° and tested in a laboratory. The sediment size was fixed at 0.39 mm whereas the flow angle of attack (or skew angle) was varied at four angles, i.e., skew angles, i.e., 0°, 10°, 20° and 30°. Scour reduction was clear when decreasing nose angles and reached maximum when the nose angle is 45°. Increasing the flow velocity and skew angle was subsequently increasing the scour profile, both in vertical and transversal directions. However, the efficiency of nose angle piers was only high at low Froude number less than 0.40 where higher Froude number gives minimal changes in the maximum scour depth reduction. At a higher skew angle, although showed promising maximum scour depth reduction, the increasing pier projected width resulted in the increase of transversal lengths.

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Clear-water local scour at wide piers in shallow-water flow

Water Practice & Technology ◽

10.2166/wpt.2014.035 ◽

2014 ◽

Vol 9 (3) ◽

pp. 331-343 ◽

Cited By ~ 3

Author(s):

N. Ahmad ◽

T. Mohamed ◽

F. H. Ali ◽

B. Yusuf

Keyword(s):

Laboratory Data ◽

Local Scour ◽

The Other ◽

Scour Depth ◽

Temporal Development ◽

Clear Water ◽

Shallow Water Flow ◽

Equilibrium Time ◽

Sediment Size ◽

Flow Intensity

Laboratory data for local scour depth regarding the size of wide piers are presented. Clear water scour tests were performed for various pier widths (0.06, 0.076, 0.102, 0.14 and 0.165 m), two types of pier shapes (circular and rectangular) and two types of uniform cohesionless bed sediment (d50 = 0.23 and d50 = 0.80 mm). New data are presented and used to demonstrate the effects of pier width, pier shape and sediment size on scour depth. The influence of equilibrium time (te) on scouring processes is also discussed. Equilibrium scour depths were found to decrease with increasing values of b/d50. The temporal development of equilibrium local scour depth with new laboratory data is demonstrated for flow intensity V/Vc = 0.95. On the other hand, the results of scour mechanism have shown a significant relationship between normalized volume of scoured and deposited with pier width, b. The experimental data obtained in this study and data available from the literature for wide piers are used to evaluate predictions of existing methods.

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Investigation of Local Scour around L-Shape Submerged Groynes in Clearwater Conditions

Tikrit Journal of Engineering Sciences ◽

10.25130/tjes.28.3.12 ◽

2021 ◽

Vol 28 (3) ◽

pp. 159-169

Author(s):

Saleh Issa Khassaf ◽

Budoor Mohammed Rashak

Keyword(s):

Froude Number ◽

Local Scour ◽

Scour Depth ◽

Contour Lines ◽

Low Profile ◽

Scour Hole ◽

Number Flow ◽

Flow Intensity ◽

Good Determination ◽

New Formula

Submerged Groynes are low profile linear structures that are generally located on the outside bank to form Groynes fields and prevent the erosion of stream banks by redirecting high-velocity flow away from the bank. This research was studied in detail through two major stages. The first stage of the study is based on laboratory experiments to measure the development of local scour around L-shape submerged Groyne with the time, and special attention is given to the effects of different hydraulic and geometric parameters on local scour. Also; maps were drawn showing contour lines that represented the bed levels for maximum scour depth after reaching the equilibrium case. The result showed that a decrease in the scour depth ratio due to the increasing submerged ratio, and the number of Groynes. While the scour hole geometry will increase with the Froude number, flow intensity, and the spacing between Groynes, the decreasing percentage in the scour hole was measured to be about (4.3) % and (4.4) % for decreasing the spacing between Groynes from (2Lg) to (1.5Lg). Besides, it was range about (11.1) % and (14.0) % when reducing the spacing from (1.5Lg) to (Lg) under the same value of maximum Froude number. The second stage of the study is based on experimental results. A new formula was developed by using statistical analysis and it was found that a good determination coefficient.

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Numerical Simulation of the Influence of Spur Dikes Spacing on Local Scour and Flow

Applied Sciences ◽

10.3390/app9112306 ◽

2019 ◽

Vol 9 (11) ◽

pp. 2306

Author(s):

Jian Ning ◽

Guodong Li ◽

Shanshan Li

Keyword(s):

Shear Stress ◽

Pearson Correlation ◽

Fixed Bed ◽

Maximum Velocity ◽

Turbulent Energy ◽

Local Scour ◽

Shielding Effect ◽

Scour Depth ◽

Spur Dike ◽

Spur Dikes

The spacing of spur dikes is an important consideration for the layout of spur dike channels. This study focuses on the local scour morphology and flow field characteristics of spur dikes with different spacings. The results show that the maximum scour depth is generally found in the vicinity of the first spur dike head. With the increase of the spacing of spur dikes, the shielding effect of the first spur dike is weakened. The maximum velocity in the main flow zone is twice that of the approach flow velocity in the fixed bed. But it is approximately the same as the incoming velocity in equilibrium scouring. The maximum turbulent energy appears to be mainly located in the backflow area of the fourth spur dike in the fixed bed, while the maximum value appears at the second spur dike head in the movable bed. Further, the shear stress decreases as scouring develops. Pearson correlation analysis was carried out between scour depth and shear stress. The analysis results are significantly correlated, indicating that the bed shear stress plays a prominent role in the scouring process. These discoveries can serve as a guide to determine the most reasonable spacing of spur dikes.

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An experimental study into local scour in a channel caused by a 90° bend

Canadian Journal of Civil Engineering ◽

10.1139/l06-037 ◽

2006 ◽

Vol 33 (7) ◽

pp. 902-911 ◽

Cited By ~ 5

Author(s):

Jueyi Sui ◽

Daxian Fang ◽

Bryan W Karney

Keyword(s):

Froude Number ◽

Flow Direction ◽

Local Scour ◽

Scour Depth ◽

Factors Affecting ◽

Downstream Section ◽

Series Of Experiments ◽

Bed Material ◽

Hydraulic Variables

Based on a series of experiments, this paper explores the influence of a 90° change in flow direction on local scouring. The influence on local scour patterns due to hydraulic parameters such as the Froude number, the slope of the protection wall, the width of the protection apron along the outside wall of the downstream section, and the grain size of the channel bed material is examined. Protection-wall slopes ranging from 1:0.5 to 1:4 (vertical to horizontal) were investigated, as were different widths of the protection apron; the goal was to ascertain the role of these variables in local scour patterns in the vicinity of the bend. The factors affecting local scour depth are related through empirical equations to key hydraulic variables, the slope of the protection wall, and the width of the protection apron.Key words: bent flume, channel erosion, Froude number, scour depth, slope of protection wall (SPW), width of protection apron (WPA).

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Experimental study of local scour around T-shaped spur dike in a meandering channel

Water Science & Technology Water Supply ◽

10.2166/ws.2020.331 ◽

2020 ◽

Author(s):

Ravi Prakash Tripathi ◽

K. K. Pandey

Keyword(s):

Froude Number ◽

Research Work ◽

Local Scour ◽

Scour Depth ◽

Spur Dike ◽

Meandering Channel ◽

Work Related ◽

Channel Bend ◽

River Training ◽

Training Structure

Abstract A spur dike is mainly constructed as a river-training structure and is primarily used to prevent bank erosion. The restriction to flow caused by the construction of a spur dike promotes local scour around the structure. In the case of a dike placed in a channel bend, the scour becomes more aggressive. The literature review found that the research work related to local scour around a spur dike located in a meandering channel is very limited or minimal. Therefore, an experimental investigation was conducted to study the local scour process around a T-shaped spur dike placed at different locations along the outer bank (or concave) of a reverse-meandering channel. Non-dimensionalized empirical equations for temporal and maximum local scour depth were developed as the function of the Froude number of approach flow and spur dike location. It is observed that local scour around the dike increases with the increase in Froude number and location in the meander (measured from the entry to meander). The formulation for the maximum scour depth was further evaluated with the experimental data related to the 180° bend, from literature, and it was found that the proposed equation's application is very much limited.

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