Erosion of unconsolidated gravel beds

1985 ◽  
Vol 12 (3) ◽  
pp. 559-566 ◽  
Author(s):  
S. P. Chee ◽  
E. M. Yuen
Keyword(s):  
Analytical Study ◽  
Local Scour ◽  
Hydraulic Control ◽  
Control Structures ◽  
Gravel Beds ◽  
Water Jets ◽  
River Bed ◽  
Motion Condition ◽  
Scour Hole ◽  
Tail Water

In any riverbed degradation phenomenon, the vertical dimension of the deepest part of the scour hole is a pertinent parameter since all the other erosion parameters describing the configuration of the scour hole depend on its numerical value. Hence, it is necessary to be able to evaluate the maximum depth of the scour hole.For most practical situations, the impingement of submerged water jets on a granular riverbed occurs at an angle, and it is the object of this study to include the effects of obliqueness in the analysis. Some examples of the effects of impingement by water jets are the erosion problems caused by plunging water jets from hydraulic control structures as they discharge into the tail-water downstream.Basic to an understanding of the mechanism of local scour is the concept of "initiation of motion." Hence, the analytical study will use this concept to derive generalized relations that will link the incipient motion condition at the deepest point of the scour hole with the numerical value of the scoured depth. In addition, care was taken to ensure that only those hydraulic variables that are frequently used in hydraulic engineering design are included in the analysis in order to make the results useful to practicing engineers. Key words: local scour, maximum erosion, river bed, plunge basin, diving jets, energy dissipation, riverbed degradation.

scholarly journals Application of neuro-fuzzy model to estimate the characteristics of local scour downstream of stilling basins

2009 ◽  
Vol 12 (2) ◽  
pp. 201-211 ◽  
Author(s):  
J. Farhoudi ◽  
S. M. Hosseini ◽  
M. Sedghi-Asl
Keyword(s):  
Fuzzy Model ◽  
Local Scour ◽  
Bridge Piers ◽  
Type I ◽  
Effective Parameters ◽  
Promising Alternative ◽  
Neuro Fuzzy ◽  
Scour Hole ◽  
Stilling Basins ◽  
Tail Water

The local scour phenomenon in the vicinity of bridge piers and stilling basins has received considerable attraction from designers due to its consequences which may endanger these structures. Various factors govern the pattern of scour evolution which results in the complexity of this phenomenon. Many researchers indicated that the use of fuzzy logic in modeling this phenomenon could be a promising alternative to reflect the vagueness and ambiguity of effective parameters. The aim of this study is to investigate the performance of a neuro-fuzzy model based on Takagi and Sugeno's theory in estimating the maximum depths, pattern and time evolution of scour hole downstream of a stilling basin of U.S.B.R. type I. The investigation was conducted under various discharges, tail-water depths (low, balanced and high), different bed materials and model sizes. The characteristics of the equilibrium state of the scour phenomenon as well as the time to reach the maximum scour depth were considered. The results showed a significant conformity between estimated and experimental data which recommends an acceptable outcome using a neuro-fuzzy model to forecast the properties of scour hole downstream of stilling basins. This would contribute to predicting the design geometry of stilling pools and taking the appropriate precautions to protect the downstream channel bed.

scholarly journals Influence of Using Floor Jets on the Local Scour Downstream Fayoum Type Weir

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Gamal Elsaeed ◽  
Abdelazim M. Ali ◽  
Alaa Nabil El-Hazek ◽  
Ahmed Mahmoud Ibraheem
Keyword(s):  
Optimum Design ◽  
Local Scour ◽  
Hydraulic Structures ◽  
Base Case ◽  
Optimal Arrangement ◽  
Stilling Basin ◽  
Water Jets ◽  
Complete Failure ◽  
Tail Water ◽  
Water Depths

Local scour downstream hydraulic structures may cause damage or complete failure of these structures. In this paper, an experimental study was carried out to investigate using floor water jets as a mitigation measure to minimize the local scour downstream stilling basin and to clarify the best arrangement of these jets. Different cases were established during this study including different flow discharges, tail water depths and floor jet locations. A base case without using water jets was included to estimate the influence of using suggested water jets arrangements. Additional four cases for various jets arrangements were established and studied. Obtained results were analyzed and graphically presented. The optimum design was easy to be used for increasing the performance of stilling basin. The results indicated that the optimal arrangement of floor jets was the case (D), where the last three rows of floor jets were used. This optimum design results in a reduction in maximum scour depth ranged from 44.53 % to 76.15 % and reduction in scour length ranged from 25.00 % to 71.93 % compared to the base case.

scholarly journals Impact of Bed Material on the Local Scour Downstream Fayoum Type Weir with Various Designs of Floor Jets

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Ahmed Mahmoud Ibraheem
Keyword(s):  
Local Scour ◽  
Medium Sand ◽  
Stilling Basin ◽  
Water Jets ◽  
Materials By Design ◽  
Stilling Basins ◽  
Bed Materials ◽  
Tail Water ◽  
Bed Material ◽  
Fine Gravel

Local scour downstream hydraulic structures should be studied well to avoid damage or even failure of these structures. In this paper, an experimental model was conducted to study the influence of bed material size on the local scour downstream stilling basins of Fayoum type weir as a hydraulic structure. Two bed material were tested. The model included stilling basin and five rows of water jets. Forty-five test runs were carried out for each bed material. Different cases were implemented during this study including three flow discharges, three tail water depths and five various designs of floor jets. Based on the obtained results, it was found that the maximum and minimum scour depths for the two bed materials occurred by design A and design D. The maximum scour lengths happened for medium sand by design C and for fine gravel by both designs A and E, while the minimum scour lengths were recorded for medium sand by design D and for fine gravel by design A. The maximum scour volumes were found for the two bed materials by design A, while the minimum scour volumes occurred by both designs C and D for medium sand and by design E for fine gravel. Employing fine gravel instead of medium sand as a bed material achieved maximum reduction percentages of 86.8 %, 53.3 % and 89.8 % for scour depth, scour length and scour volume, respectively.

scholarly journals Enhancing scour protection in river bends: a novel slotted bank-attached vane

2020 ◽  
Vol 20 (6) ◽  
pp. 2175-2184
Author(s):  
Mohamad Azizipour ◽  
Farshid Amirsalari Meymani ◽  
Mohammad Mahmoodian Shooshtari
Keyword(s):  
Effective Area ◽  
Local Scour ◽  
Flume Experiments ◽  
Rectangular Slot ◽  
Outer Bank ◽  
Scour Hole ◽  
Submerged Vane ◽  
River Bends ◽  
Scour Protection ◽  
Control Erosion

Abstract One of the most effective approaches for bank control erosion is using bank-attached vanes. In spite of the superiority of the bank-attached vanes to spur dikes, the vanes' tips are still vulnerable to local scour caused by flow–structure interaction. In this study, slotted bank-attached vanes are proposed to reduce local scour at the tip of the triangular submerged vane. For this, a rectangular slot is created parallel to the chord of the vane with an area of ten percent of the effective area of the vane surface. Two types of conventional vanes and slotted vanes were installed at different angles of attack of 23, 30, 40 and 60 degrees in an arch flume. Experiments were carried out in clear water conditions with different flow regimes with Froude numbers of Fr = 0.287, 0.304 and 0.322. The results show that the slotted vane outperforms the conventional vane by reducing maximum scour depth by about 70, 20, 17 and 54 percent for different angles of attack of 23, 30, 40 and 60 degrees, respectively. The proposed slotted vane also resulted in reduction of scour hole volume around the vane and formed the scour hole away from the outer bank.

Development of a Three-Dimensional Iterative Methodology Using a Commercial CFD Code for Flow Scouring Around Bridge Piers

2012 ◽  
Author(s):  
Phani Ganesh Elapolu ◽  
Pradip Majumdar ◽  
Steven A. Lottes ◽  
Milivoje Kostic
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
Computational Domain ◽  
Time Step ◽  
Mesh Morphing ◽  
River Bed ◽  
Scour Hole ◽  
The Stability

One of the major concerns affecting the safety of bridges with foundation supports in river-beds is the scouring of river-bed material from bridge supports during floods. Scour is the engineering term for the erosion caused by water around bridge elements such as piers, monopiles, or abutments. Scour holes around a monopile can jeopardize the stability of the whole structure and will require deeper piling or local armoring of the river-bed. About 500,000 bridges in the National Bridge Registry are over waterways. Many of these are considered as vulnerable to scour, about five percent are classified as scour critical, and over the last 30 years bridge failures caused by foundation scour have averaged about one every two weeks. Therefore it is of great importance to predict the correct scour development for a given bridge and flood conditions. Apart from saving time and money, integrity of bridges are important in ensuring public safety. Recent advances in computing boundary motion in combination with mesh morphing to maintain mesh quality in computational fluid dynamic analysis can be applied to predict the scour hole development, analyze the local scour phenomenon, and predict the scour hole shape and size around a pier. The main objective of the present study was to develop and implement a three dimensional iterative procedure to predict the scour hole formation around a cylindrical pier using the mesh morphing capabilities in the STARCCM+ commercial CFD code. A computational methodology has been developed using Python and Java Macros and implemented using a Bash script on a LINUX high performance computer cluster. An implicit unsteady approach was used to obtain the bed shear stresses. The mesh was iteratively deformed towards the equilibrium scour position based on the excess shear stress above the critical shear stress (supercritical shear stress). The model solves the flow field using Reynolds Averaged Navier-Stokes (RANS) equations, and the standard k–ε turbulence model. The iterative process involves stretching (morphing) a meshed domain after every time step, away from the bottom where scouring flow parameters are supercritical, and remeshing the relevant computational domain after a certain number of time steps when the morphed mesh compromises the stability of further simulation. The simulation model was validated by comparing results with limited experimental data available in the literature.

Formula Type of Local Scour Depth on Spur Dike Nose

2014 ◽  
Vol 641-642 ◽  
pp. 271-274
Author(s):  
Qiang Ying
Keyword(s):  
Formation Process ◽  
Local Scour ◽  
Scour Depth ◽  
Calculation Methods ◽  
Spur Dike ◽  
Scour Hole ◽  
Main Factors ◽  
Formula Type ◽  
Suggested Formula

This passage introduces the formation process of scour hole, analyzes the main factors contributed to the local scour hole’s depth and classifies today’s calculation methods of scour depth into three categories. Then, given the conditions where those methods can be applied and drawbacks of those methods, this article also recommends some suggested formula in calculation.

Sign in / Sign up

Export Citation Format

Share Document