3D culvert scour under non-full flowing condition

Sheau Maan Tan, Siow Yong Lim

Tuesday 30 june 2015

15:20 - 15:35h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 6A. Sediment - Erosion

This paper presents the results of 3D culvert scour under non-full flowing condition. The local scour under non-full flow culvert is different from the pressurized full-flowing jet in a conduit. The results from 62 non-full flowing culvert scour experiments conducted in Nanyang Technological University (NTU) are presented. The experiments consist of water issued from rectangular channels of different widths, ranging from 0.05 m to 0.16 m. The experiments used non-cohesive sediments with median diameter (d50) ranging from 1.6 mm to 3.8 mm and the geometric standard deviation (_g) from 1.13 to 3.56. The flowrates and tailwater depths were varied systematically, and the experiments were run for sufficient time to ensure equilibrium scour state was achieved. The characteristic length scales of scour hole at equilibrium state are the maximum scour depth (dse), length (Lse), width (Wse), and volume of scour (Vse). The densimetric Froude number (Fo), based on d50 and mean flow velocity (Uo), was found to be the dominant parameter to study the effects of varying d50 and Uo on the scour hole dimensions. Generally, non-uniform sand produced smaller scour hole compared to uniform sand under similar experimental conditions. Equilibrium scour hole dimension prediction equations based on dimensionless analysis are proposed. The relative importance of other variables such as relative tailwater depth and channel width differs among the different scour hole dimensions.