LOW-DROP GRADE-CONTROL STRUCTURE

This study was conducted to develop design criteria for a structural l aw-drop (drop height/critical depth of h/d(c) less than or equal to 1. 0) grade-control structure that will have good performance characteris tics and have general acceptance by the engineering community involved with stabilization of degrading channels. The structure has a 2:1 (ho rizontal:vertical) sloping floor at the entrance, 0.5d(c) high floor b lock with 1:2 upstream sloping face, and a 0.25d(c) high end sill with a 3:1 sloping upstream face. Criteria are presented to design the str ucture given the channel width, critical depth, drop height, and tail water elevation and to determine the size and placement of riprap down stream of the structure to ensure the integrity of the structure. A mi nimum tail water elevation is required for acceptable performance of t he structure.