ABSTRACT
Drop structures are used to dissipate energy in locations where the downstream channel is not deep enough to cause a hydraulic jump. The flow approaches an almost horizontal impact bottom instead of a stilling basin with a tangential approach flow. This chapter introduces some concepts for the design of drops used in smaller hydraulic structures. It is in part a complement to the trajectory bucket. It focuses on the scour action of impact jets on an erodable basin bottom for free and submerged jets. Impact structures receive a falling jet and deflect the almost vertical flow into a horizontal current, thereby dissipating excess energy by jet diffusion. Two basic configurations can occur: either the tailwater submergence is small, and the jet is not allowed to scour, or a plunge pool is allowed to form as a result of scour action.
