Erosion downstream of non-full flowing triangular culvert cutlets

• Main Author: Wong, Wan Ee.
• Other Authors: Lim Siow Yong
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Civil engineering::Water resources
• Online Access: http://hdl.handle.net/10356/15642
• Institution: Nanyang Technological University

In this project, observation and evaluation of erosion downstream of non-full flowing culvert outlets was conducted and presented. The main aim of this study is to identify the controlling parameters which affect local scouring of the sediment bed used, and to compare the present study with the previous works. The sediment consists of uniform, poorly graded coarse-grained sand. Experimental runs were conducted as a subcritical culvert flow outlet control, with a range of tailwater depth over brink depth ratio and flow rates represented as Densimetric Froude number, while keeping other variables constant. The duration of an experiment is approximately 48 hours, where the maximum extend of the scour has been reached. The scour hole characteristics, such as maximum equilibrium scour depth, maximum scour width, maximum scour length tailwater depth and volume of the scour hole, are analyzed with respect to the channel outflow. Froude number, Densimetric Froude number, Reynolds number and water channel profile are in relation to the tailwater depth. In general, the results show that the effect of the Densimetric Froude number is the one of the main parameters controlling maximum equilibrium depth, width, length and volume of the scour hole. Through analysis, the location of the maximum depth is not necessarily located along the centreline profile but may located elsewhere due to the Coanda effect, where the direction of the jet flow is influenced by the channel it is attached nearest to, in each experiment. The other main parameter affecting the scour hole sizes is the ratio of the tailwater to brink depth. In general, experimental run with the ratio of the tailwater to brink depth more than one will have a decrease of scour size with experimental run less than one. Another finding relating to Densimetric Froude number and is the variation of Densimetric Froude number does not affect much of the scour hole size under a constant value of tailwater to brink depth ratio. After the parameters are analyzed, a comparison of the present data with the previous studies has been made. It shows that the data for non-full flowing culverts follow the same trend, but are generally lower than scouring with full-flowing culverts. The triangular culvert outlet of total vertex angle of 90° is recommended as the best triangular hydraulic section to achieve most effect cross-section for the outflow. In recommendation of bed protection for this particular study, rock material such tested concrete cubes could be used, in obtaining compacted sediment bed protection, and an alternative in cutting down waste disposal and overall cost in bed protection.