Model Study of Low Drop Grade Control Structures

A generalized model study was conducted on low drop, grade control structures. A low drop was defined from this study as an hydraulic drop with a difference in elevation between the upstream and downstream channel beds, H; a discharge, Q; and a corresponding critical depth, Y_c, such that the relative drop height, H/Y_c, is equal to or less than 1.0. Conversely a high drop is defined as one with a relative drop height, H/Y_c, greater than 1.0. Tentative design criteria, in the form of dimensionless equations, are given to proportion and hydraulically design the stilling basin for low drops with energy dissipation devices. A method is given to determine the size and placement of a baffle pier or baffle plate to achieve optimum flow conditions in the downstream channel.