Effect of Concurrent Use of the Six-Legged Element and Rip-Rap for Scour Control with Economic Considerations

Document Type : Research Article


1 Ph.D Student- Hydraulic structures- Dep. of Civil Engineering- University of Sistan and Balouchestan- Zahedan

2 University of Sistan and Baluchestan

3 Prof. Faculty of Water Science Engineering, Shahid Chamran University of Ahvaz

4 Professor of Civil & Environmental Engineering, The University of the West Indies, St. Augustine Campus, Trinidad


The scour control downstream of the ski-jump spillways is one of the most important issues encountered by hydraulic engineers. In this paper, an experimental investigation was performed to evaluate the reduction in the maximum volume of the scour hole due to the concurrent use of the six-legged concrete elements (A-Jacks) and rip-rap materials in different hydraulic conditions. These elements were placed in the downstream of the ski-jump spillway. The experiments included a single size of concrete element and two sizes of rip-rap with five flow discharges and three tail-water depths. The change in tail-water depth resulted in the spillway having free, semi-submerged and submerged conditions. The results were showed that as scour depth increased, the scouring rate is significantly reduced. By simultaneous usage of concrete elements and rip-rap materials, the maximum scour volume decreased up to 100% in different hydraulic conditions as compared to the control tests. In addition, the results showed that the use of a rip-rap layer is about 80% cheaper than the coating with six-legged elements, which this difference is reduced by increasing the thickness of rip-rap layer.


Main Subjects

[1]N.A. Amanian, N., Scour Below a Flip Bucket Spillway, Ph.D. Dissertation Submitted to Utah State University at Logan, UT, (1993).
[2]M. Mehri, Simulation of hydraulic behavior of water flow on Balarood Dam spillway by using a small scale physical model, Thesis, University of Shahid Chamran, Ahvaz, (2007). (In Persian)
[3]M.R. Vesalian, M.H. Jahromi, M. Shafai Bajestan, Scouring caused by rectangular jets in downstream of Ski jump spillways with non-uniform materials, Journal of Agricultural Science and Natural Resources, (2009).
[4]P.J. Mason, K. Arumugam, Free jet scour below dams and flip buckets, Journal of Hydraulic Engineering, (2)111 235-220 (1985).
[5]S. Heng, T. Tingsanchali, T. Suetsugi, Prediction formulas of maximum scour depth and impact location of a local scour hole below a chute spillway with a flip bucket, WIT Transactions on Ecology and the Environment, (2013) 172 262-251.
[6]B. Dargahi, Scour development downstream of a spillway, Journal of hydraulic research (426-417 (2003) 4(41.
[7]H.M.D. Azmathulla, M.C. Deo, P.B. Deolalikar, Estimation of scour below spillways using  neural networks, Journal of Hydraulic Research, 1)44) (2006) 69-61.
[8]H.M.D Azmathulla, A.Ab. Ghani, and N.A. Zakaria, Prediction of Scour below Flip Bucket using Soft  Computing Techniques, The 2nd International Symposium and The 12t International  EPMESC Conference, (2010) 1593-1588.
[9]M.K. Ayoubloo, H.M.D. Azamathulla, Z. Ahmad, A.Ab. Ghani, J. Mahjoobi, A. Rasekh, Prediction of Scour Depth in Downstream of Ski-Jump Spillways Using Soft Computing  Techniques, International Journal of Computers and Applications. 1)33) (2011) 97-92.
[10]A.J. Peterka, Hydraulic Design of Stilling Basins and Energy Dissipators, Engineering Monograph, (7)25  125-91(1983).
[11]S. Dey, A. Sarkar, Characteristics of Submerged Jets in Evolving Scour Hole Downstream of an Apron, Journal of Engineering Mechanics 936-927 (2008) (11)134.
[12]J. M. Wang, X. G.Yang, H. W. Zhou, X. Lin, R. Jiang, E. Q. Lv, Bed Morphology around various solid and flexible grade control structures in an unstable gravel-bed river, Water.822 (2018) 10.
[13]M. Zolghadr, M. Shafaei Bajestan, M. Rezaeianzadeh, Investigating the Effect of Six-Legged Element Placement Density on Local Scour at Wing-Wall Bridge Abutments, World Environmental and Water Resources Congress, (36-28 (2016.
[14]S. Mohammadpour, M. Shafai Bajestan, Investigation of The Area of Around Bridge Abutment by A-Jacks to Protect Against Scour, Irrigation Sciences and Engineering, (1)40 35-25 (2017). (in Persian)
[15]L. Torfi Salehi, M. Shafai Bajestan, Hydraulic Jump Stilling Basins Downstream Scour Covered with SixLegs Elements under Reduction of Basin Length, Irrigation Sciences and Engineering, 124-109 (2018) (4)40. (in Persian)
[16] A.A. Hossein Reza, M. Shafai Bajestan, M. Ghomshi, M. Fathi Moghadam, Investigation the Joined Effect of Riprap and Six legged Elements (SLC) Installation on Scour Depth Mitigation at Vertical Wall Bridge Abutments, Irrigation Sciences and Engineering Journal, (2019). (in Persian)
[17]G.H. Akbari, M. Kavianpour, E.S. Samani, Experimental investigation of scouring downstream of ski jump spillway, Journal of Water Resources Engineering, (64-51 (2014.
[18]C.I. Thornton, S.R. Abt, C.C. Watson, Field Assessment of A-Jacks Installation, A Case Study of: Brush Creek, Kansas City, Missouri Powell Creek, Waukegan, Illinois. Proceedings of the Wetlands Engineering & River Restoration Conference, Reno, Nevada (2001).
[19]P.J. Mason, Practical guidelines for the design of flip buckets and plunge pools,Water and Dam Construction,10/9)45) (1993) 45-40.
[20]B.W. Melvillel, Pier and abutment scour: integrated approach, Journal of Hydraulic Engineering, 2)123) (1997) 136-125.
[21]W.C. Little, P.G. Mayer, Stability of Channel Beds by Armoring, Journal of Hydraulic Division, (1976).
[22]S. Pagliara, M. Palermo, Scour control and surface sediment distribution downstream of block ramps, Journal of Hydraulic Research. 343-334 (2008) (3)46.
[23]S.M. Scurlock, C.I. Thornton, S.R. Abt, Equilibrium scour downstream of three- dimensional grade-control structures, Journal of Hydraulic Engineering, (2)138 176-167 (2012).
[24]F. Bhuiyan, R.D. Hey, P.R. Wormleaton, Hydraulic evaluation of W-weir for restoration, Journal of Hydraulic Engineering, ASCE. 605-596 (2007) (6)133.
[25]S.Y. Lim, J. Nugroho, Observations on Flow Field around an Abutment in a Two-stage Channel. Proceedings of the 2nd International Conference on Scour and Erosion, Singapore 1, (2004) 164-156.