Bed protection below culvert outlets

• Main Author: Ma, Yin
• Other Authors: Lim Siow Yong
• Format: Final Year Project
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Environmental engineering
• Online Access: http://hdl.handle.net/10356/39600
• Institution: Nanyang Technological University

Riprap continues to be the most widely used method for protection of erodible channel boundaries. In this report, an experimental study was conducted to understand the mechanisms and characteristics of scour without protection below culvert outlets, and thereby investigating a suitably sized riprap protection for the bed material to reduce the scouring effect of the jet flow. The basis of protection is by laying a blanket of riprap stones at culvert outlets to dissipate the highly erosive kinetic energy of the discharge. Two sets of experiments were done. The first set sought to understand the basic characteristics of scour without protection. Based on the experiments conducted, it was found the scour depth and geometry depends on the tailwater depth and Froude number. The second set investigated the effects of varying size and thickness of riprap blanket on the downstream condition at incipient flow velocities below the culvert outlets. The results were compared with the first set under the same test condition. It was found the riprap protection significantly minimizes the scour condition and the optimum thickness of the riprap layer was 2D50. The empirical relations between the size of stone with flow velocity and Froude number were proposed as well.