Author(s): A. Jacob Odgaard; Troy C. Lyons; Andrew J. Craig; Anthony Margevicius; David Servidio
Keywords: Drop structure; Baffle drop; Cascading flow; Storm water conveyance; Urban flooding
Abstract: A baffle-drop structure is a flow conveyance structure that can be used for transport of urban storm water down to underground storage tunnels. The water cascades down the structure from baffle to baffle and plunges into a pool at the bottom from where it is conveyed to the tunnel via an adit. The structure has been used successfully in a number of urban drainage schemes for design discharges up to about 4. 2 m3/s (150 ft3/s). Using a series of laboratory experiments, an analysis has been tested and validated that may be used for design of structures for larger design discharges. The analysis provides a dimensionless relationship between key variables, including design discharge, shaft diameter, baffle spacing, and position of a vertical wall that divides the shaft into dry and wet portions. The laboratory studies showed that by using this relationship the shaft can be designed to maintain atmospheric pressure throughout its height with little or no air being entrained into the tunnel. The laboratory results are compared with performance data from the (limited number of) structures already in service.