Channel protection: Turbulence downstream of structures

An experimental study, funded by the Department of the Environment, was made of the stability of riprap and concrete blocks for channel protection in highly turbulent environment. An extensive literature review on riprap sizing formulas is presented in this report as well as some general background on turbulence generated downstream of hydraulic structures. It was found that the existing guidelines do not apply to highly turbulent flows and that the nominal stone size given by the different equations can vary as much as four times. The second part of the study was concerned with the stability of concrete blocks on a flat bed and on sloped of 1:2.5 and 1:2 as an alternative material to riprap. It was found that the same type of equation proposed for the design of riprap can be applied to concrete blocks on a flat bed and on slopes of 1:2.5 (or flatter).