Journal of Hydraulic Structures

Journal of Hydraulic Structures

Local scour downstream of compound weirs under free and submerged flow conditions

Document Type : Research Paper

Authors
Mohamed Abdelrazek Zidan 1
Ahmed Abouelfetouh 2
Ahmed Shwaky 2
Tarek Hemdan 2
Fahmy Abdelhaleem 2
1 Department of Civil Engineering, MISR High Institute for Eng. & Tech., Mansoura, Egypt, (C. O.).
2 Department of Civil Engineering, Benha Faculty of Engineering, Benha University, Benha, Egypt.
10.22055/jhs.2026.51451.1373
Abstract
Scour downstream of compound weirs remains a complex hydraulic phenomenon with significant implications for channel stability. This natural process, driven by the erosive action of currents and waves, often compromises the structural integrity of hydraulic foundations, leading to substantial annual expenditures on maintenance and rehabilitation. In weir configurations, scour is primarily exacerbated by intense turbulence and the abrupt transition from supercritical to subcritical flow regimes. The extent of this erosion is governed by a multifaceted interplay between bed material characteristics (e.g., grain size, grading, and cohesion), hydrodynamic parameters, and the specific geometry of the weir structure.
This study systematically investigates the scour dynamics associated with various compound weir geometries under both free and submerged flow conditions. Utilizing a high-precision recirculating flume, an extensive experimental campaign was conducted, complemented by a theoretical framework based on dimensional analysis. This approach correlates key scour characteristics with dominant independent variables and flow regimes. The findings reveal that the geometric configuration of the compound weir significantly dictates the downstream scour depth, identifying an optimized profile that minimizes erosive impact. Finally, a robust empirical correlation was developed to accurately predict the maximum scour depth, providing a practical tool for hydraulic design and risk mitigation.
Keywords
Energy dissipation
Local scour
Compound weirs
Sharp-crested weirs
Apex angle
Subjects
  1. Raudkivi AJ, Ettema R. Clear-water scour at cylindrical piers. Journal of Hydraulic Engineering. 1983;109(3):338-50.
  2. Raudkivi AJ. Functional trends of scour at bridge piers. Journal of Hydraulic Engineering. 1986;112(1):1-13.
  3. Li J, Qi M. Local scour induced by upstream riverbed level lowering. Natural Hazards. 2015;77:1811-27.
  4. Azmi S, Zakwan M. Data Specific Pier Scour Predictors. In: Proc. 3rd Nat. Con. on Sustain. Water Resour. Dev. and Manag., Aurangabad. 2016. p. 326-9.
  5. Wu W, Xu Y, He S. Numerical Investigation of Bridge Pier Scour Processes under Steady Flow Conditions. Water Resources Management. 2020;34(14):3809-22.
  6. Sharafati A, Haghbin M, Haji Seyed Asadollah SB, Tiwari NK, Al-Ansari N, Yaseen ZM. Scouring depth assessment downstream of weirs using hybrid intelligence models. Applied Sciences. 2020;10(11):3714.
  7. Abdelhaleem F. Effect of semi-circular baffle blocks on local scour downstream clear-overfall weirs. Ain Shams Engineering Journal. 2013;4:675-84.
  8. Helal E. Minimizing scour downstream of hydraulic structures using single line of floor water jets. Ain Shams Engineering Journal. 2014;5:17-28.
  9. Ibrahim MM. Bed profile downstream compound sharp crested V-notch weir. Alexandria Engineering Journal. 2015;54:607-13.
  10. Amin A. Physical model study for mitigating local scour downstream of clear over-fall weirs. Ain Shams Engineering Journal. 2015;6:1143-50.
  11. Eltoukhy M, Ibrahim M. Velocity Distribution Downstream Compound Weirs. Aust. J. Basic & Appl. Sci. 2015;9(1):238-45.
  12. Omran HA, Khassaf SI, Hassan FA. The effect of flow conditions and geometric parameters on the scour value downstream composite structures of Weir and gate. Kufa J. Eng. 2016;7(1):115-28.
  13. Jüstrich S, Pfister M, Schleiss A. Mobile Riverbed Scour Downstream of a Piano Key Weir. Journal of Hydraulic Engineering. 2016;142:04016043.
  14. Guan D, Melville B, Friedrich H. Local scour at submerged weirs in sand-bed channels. Journal of Hydraulic Research. 2016;54:172-84.
  15. Khassaf S, Omran H, Abdulabbas F. The relationship between the coefficient of discharge and the scour hole depth generated due to the combined flow over weir and below gates. MATEC Web of Conferences. 2018;162:03010.
  16. Karthik R, Kumar U, Barbhuiya AK. Two-Dimensional Analysis of Flow Field and Associated Scour Parameters at Downstream of Weir with and without Sloping Apron. International Journal of Engineering and Advanced Technology (IJEAT). 2019.
  17. Guan D, Liu J, Chiew Y, Zhou Y. Scour Evolution Downstream of Submerged Weirs in Clear Water Scour Conditions. Water. 2019.
  18. Verdugo J, Torres B, Ayala M. Experimental Study of Scouring Downstream of Weirs. In: 38th IAHR World Congress - "Water: Connecting the World". 2019.
  19. Eltoukhy M, Abdelhaleem FS, Nasralla TH, Shaban S. Effect of Compound Weir and below Circular Gate Geometric Characteristics on its Discharge Coefficient. International Journal of Scientific & Engineering Research. 2020;11(10).
  20. Ibrahim M, Abdelhaleem F. Flow downstream sluice gate with orifice. KSCE J. Civ. Eng. 2020;24(12):3692-702.
  21. Suleiman S, Ismael A. Predicting the scour depth downstream single step broad crested weirs. Journal of Physics: Conference Series. 2021;1973.
  22. El-Mahdy ME. Experimental method to predict scour characteristics downstream of stepped spillway equipped with V-Notch end sill. Alex. Eng. J. 2021;60(5):4337-46.
  23. Kurdistani SM, Varaki ME, Larsari ZK. Scour downstream of stepped-baffle weirs in wide rivers. Sådhanå. 2022;47:178.
  24. Lantz W, Crookston B, Palermo M. Evolution of local scour downstream of Type APK weir in non-cohesive sediments. Journal of Hydrology and Hydromechanics. 2022;70:103-13.
  25. Elsaeed G, Ali AM, El-Hazek AN, Ibraheem MM. Influence of Using Floor Jets on the Local Scour Downstream Fayoum Type Weir. Asian Journal of Engineering and Technology. 2020;08(01).
  26. Namadian B, Asadi E. Investigation of temporal variations of scour depth in combined weir-gate structure using FLOW-3D numerical model. Iranian Journal of Irrigation & Drainage. 2022;16(2):432-45.
  27. Shehata, A. H., Youssef, T. F., Hamada, H. A., M, I. M., and Samy, A. (2024). Optimizing Trapezoidal Labyrinth Weir Design for Enhanced Scour Mitigation in Straight Channels. Water, 16(17), 2443
  28. Diwedar, A. I., Mamdouh, L., and Ibrahim, M. M. (2022). Hydraulics of combined triangular sharp crested weir with inverted V-shaped gate. Alexandria Engineering Journal, 61(10), 8249-8262.‏
  29. Mahdian Khalili, A., and Hamidi, M. (2023). Time evolution effect on the scour characteristics downstream of the sluice gate with the submerged hydraulic jump in a laboratory model. Journal of Hydraulic Structures, 9(2), 32-47.‏ ‏
  30. Bagherzadeh, M., Mohammadi, M., and Ghaderi, A. (2025). Experimental investigation of the effects of tailwater depth on scour cavity formation downstream grade control structures. Acta Geophysica, 73(6), 5991-6004.‏
  31. Mahdian Khalili, A., and Hamidi, M. (2026). Modified prediction equations for scour parameters downstream of sluice gates considering nonuniform sediment. Acta Geophysica, 74(1), 19.‏
  32. Sohrabzadeh Anzani, H., Kantoush, S. A., Mahdian Khalili, A., and Hamidi, M. (2024). Experimental investigation of slit weir discharge. ISH Journal of Hydraulic Engineering, 30(5), 645-654.‏