Effect of Deposition Thickness on the Incipient Motion of Sediments

Charles Hin Joo Bong, Tze Liang Lau, Aminuddin Ab. Ghani

Tuesday 30 june 2015

9:30 - 9:45h at Mississippi (level 1)

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

Parallel session: 4A. Sediment - Erosion

The current literature on incipient motion are largely for loose boundary channel with unlimited depth of sediment as compares to rigid boundary channel with limited sediment depth. A few existing literature for rigid boundary channel suggested that the incipient motion value is substantially lower than for loose boundary channels for any particle size. Some existing literature also shown that the current available equations for incipient motion in rigid boundary channel become less accurate as the sediment deposition thickness increased. Nevertheless, the understanding on how the deposition thickness could affect the incipient motion of sediment is still lacking in the literature and need further study. The current study highlights the effect of sediment deposition thickness on incipient motion using data from experimental work from rigid rectangular flume with widths 0.3 m and 0.6 m. Results revealed that the Shields stress and particle Froude number increased but at diminishing rate as the relative sediment deposition thickness increased. New equations for both the critical shear stress approach and critical velocity approach were proposed by incorporating the effect of sediment deposition thickness. The applicability of existing equations in the literature to predict critical shear stress and critical velocity has also been verified and compared with the new equations. The new equation for critical shear stress performed better than the existing equations while the new equation for critical velocity offered just slight improvement from the existing equations. The new equations could be used for self-cleansing design of sewers and storm drains where the sediment deposition thickness is limited.