Erosion Rate Equations for Coarse- Grained Materials Using a Small Flume Testing

Erosion rate of soils during a levee or dam overtopping event is a major component in risk assessment evaluation of breach time and consequently in determining the downstream consequences. There is uncertainty in estimation of the erosion rate especially for coarsegrained materials that comprise the outer shell layer of dams as well as homogenous levees that are constructed of such materials. In this paper, erosion rate results are presented on three soil mixes that share the same median grain size D50 of 2 mm, the fines content varies between zero and 20%, and the gravel content between zero and 30%. Each of the three mixes is compacted in the box at optimum or near optimum moisture content as determined from standard Proctor test. The box measures 0.3 m wide x 0.6 m long x 0.15 m deep. Each material is tested several times at varying hydraulic loading to determine the erosion rate after equal time intervals. The water depth, velocity are measured at each hydraulic loading and the acting bed shear is calculated. The validity of the excess shear stress equation is discussed as well as other bilinear and nonlinear models that could fit the erosion rate of such materials as it relates to the acting bed shear stress. The effect of fines content and level of acting shear stresses are presented in the paper.