Erosion and riprap design for hydraulic structures’ protection

Studying the effect of flow on stability of riprap particles downstream the hydraulic structures is very important. This study presents a series of experimental investigations on the effect of subcritical as well as supercritical flow on the riprapprotection downstream of hydraulic structures. The stability of riprap protection downstream the apron in the case of subcritical flow was studied using different sizes of riprap with different layer thicknesses. These experiments were conductedusing different water depths over riprap layer, varying bed slopes and discharges for Froude numbers range from 0.45 to 0.95. The results led to non-dimensional equations to estimate the mean diameter of riprap for subcritical flow. Regardingthe supercritical flow, the effect of time on the scour hole characteristics for flat floor case was tested using different time increments. The effect of different types of stilling basins on the scour hole characteristics were studied. These stillingbasins contains (a) continuous sill of different slopes and heights at varyinglocation from the sluice gate; (b) one row of baffle piers with end sill of different heights and (c) two staggered rows of baffle piers with end sill of constant height.The experimental work were conducted under different flow conditions withFroude number ranges from 2.0 to about 7.0. The analysis of the experimentaldata shows the effect of layer thickness and particle size on riprap stability. The effect of time on scour process was shown. Comparison between the scour hole parameters for each developed stilling basin was made. The characteristics of the stilling basin which minimizes the scour hole downstream the apron was specified.The results led to non-dimensional equations to estimate the relative scour depth as a function the mean diameter of riprap and flow parameters for supercritical flow.