Developing Riprap Stability Criteria Downstream of Rectangular Impinging Jet

One of the common ways of dissipating the excess kinetic energy downstream of dam spillways is the use of flip-bucket. Usually a scour hole is created on the river bed at the point of jet impingement which may cause damage to the structures. Riprap can be used to stabilize the river bed. It is the main purpose of this study to develop design criteria for riprap size. To reach such a goal, first general relations were developed at the point of the incipient motion and failure condition for riprap. These relations were developed based on the stability criteria of riprap particles using dimensional analysis. Then extensive experimental tests were conducted in a physical flume. Five different sizes of riprap materials were tested under different flow conditions. Analyzing many linear and none-linear equations, the best fit relations were developed and presented. Other tests also were conducted to establish the filter criteria which must be placed beneath the riprap materials to prevent escaping of the fine materials.