Contribution of riprap to local turbulence at the downstream of a low-head sill

The objective of this study is to experimentally explore how riprap affects the relative turbulence intensity and local scour coefficient of riprap protection downstream of low-head sills. Flow depth and channel bed elevation measurements were repeated for five sill intervals to obtain the average readings. Velocity profile measurements were taken using two-dimensional electromagnetic current meter. They were taken when scour hole reached the equilibrium stage. Research results indicate that the relative turbulence intensity at the end of riprap protection gradually increases with the increases of protection length to flow depth ratio, similarly to the increases of relative roughness induced by riprap sizes. Long riprap length produces smaller Breusers relative turbulence intensity. Smaller Breusers relative turbulence intensity gets, smoother the hydraulic surface becomes. Our findings also suggest that finer the riprap that bed protection constitutes of, higher the local scour coefficient and erosion capacity that flow possesses.