Journal of New Approaches in Water Engineering and Environment
Scientific Journal

Experimental and Numerical Investigation of Riprap Stability for Protection Downstream of the Spillway

Document Type : Original Article

Authors

Mehdi Saiahi 1
ali reza masjedi 2
Amin Bordbar 2
Mohammad Heidarnejad 1
Aslan Egdernezhad 2

1 Department of Water Science Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran

2 Department of Water Science Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz

https://doi.org/10.22034/nawee.2025.504263.1134
Abstract
Objective:  This research was conducted to investigate the stability of the riprap downstream of the flip bucket spillway. For this purpose, a flip bucket spillway model with four angles and four sill lengths was used. In clear water, riprap with four different diameters was used in experiments to measure flow depth.
Material and Methods: In all experiments, the flow strength was adjusted, and the water depth upstream of the spillway was measured immediately downstream after the flow passed through the spillway. The exit jet from the triangular launcher was then formed, followed by the formation of a hydraulic jump. In each step, the necessary variables were measured. The Froude Number in the unstable condition of the riprap, the relative diameter of the riprap in the unstable condition, and the stability number of the riprap were calculated.
Results and Discussion: This research showed that the most stability number, related to the spillway with a sill angle of 45 degrees and a relative length of 0.17, and the least stability number was observed in a spillway with a sill angle of 15 degrees and a relative length of 0.05. To this end, 8 experiments performed on the physical model were simulated in FLOW-3D, and the results were compared.
Conclusions: In the study of the physical model, an increase in the threshold length improved the energy dissipation performance of the structure. However, in the mathematical model, this increase deteriorated the performance at angles of 15° and 25° but enhanced the performance at angles of 35° and 45°. In the mathematical model, the flow projected from buckets at 35° and 45° caused a hydraulic jump further from the structure.

Keywords

Flip bucket spillway
Tailwater
Sill
Riprap
Flow 3D
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Journal of New Approaches in Water Engineering and Environment
Volume 4, Issue 2
Special Issue: Guest Editor: Prof. Ozgur Kisi
September 2025
Pages 20-37

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