Flow over a "killer" weir design project

Flow over a sharp-crested weir can create dangerous countercurrents downstr eam under high tailwater conditions. A comprehensive experimental design pr oject in open-channel hydraulics used in a senior/graduate course and in a freshman exploratory experience is illustrated. This applied problem allows the instructor to demonstrate hydraulic jumps, aerated versus nonaerated n appes, similitude and modeling, and the need for experimentation in hydraul ics. A series of experiments requires students to compare their predictions of several parameters to those measured, and asks them to design a supplem ental structure for the weir to reduce the power of the frontal vortex such that people are ejected and carried downstream to calmer water. The studen t designs are then tested in the flume during class. During the course of t he project, spontaneous discussions occur about the extent to which enginee rs should be held liable for designs that may increase the likelihood of de ath. The experiments have been well received and have even saved the life o f one student who was swept over a dam and caught in the roller downstream.