| The purpose of riprap is to prevent erosion of underlying materials. A generalized riprap design equation results when equating the Manning, Strickler, and Shields (MSS) equations. Two experimental based factors, a correction factor and a stability coefficient, applied to the MSS equation result in a highly calibrated generalized riprap design equation. An understanding of the mechanics is necessary for correct application of the equations and experimental based factors.;The second hypothesis regards a characteristic size fraction. Reasoning, based on Shields parameter, leads to the hypothesis that a single size fraction cannot represent the entire riprap mixture. Indeed, flume data show that there is no single particle fraction size that is characteristic of the entire riprap mixture. Two riprap mixtures, a poorly graded and well-graded mixture, with the same median rock size, exhibit differing degrees of stability. The poorly graded mixture withstands a greater unit discharge at failure than the well-graded mixture. Flume data from this investigation and Abt lead to an expression relating a uniformity coefficient to unit discharge. The coefficient of stability, ;The combination of the Manning and Strickler equations, and the limiting point of critical shear stress defined by the Shields parameter, leads to a generalized riprap design equation. The derived equation differs from an empirical based equation, the Abt equation. The generalized equation and the Abt equation define the median rock size as a function of the slope and unit discharge. The third hypothesis states that the difference between the two equations is due to the overestimation of the hydraulic radius in aerated flow. Comparison of the two equations leads to an expression that compensates for the overestimation of the hydraulic radius. The expression for the aeration coefficient, ;Three hypotheses give definition to the mechanics of riprap in overtopping flow. The first hypothesis regards the Shields parameter in low submergence flows, a flow regime common to riprap in overtopping conditions. Fractional analysis leads to the hypothesis that the Shields parameter is constant in the region of the Shields diagram where the boundary Reynolds number is greater than 10... |
