Hydraulic Design of Stilling Basins and Energy Dissipators

Although hundreds of stilling basins and energydissipating devices have been designed in conjunction with spillways, outlet works, and canal structures, it is often necessary to make model studies of individual structures to be certain that these will operate as anticipated. The reason for these repetitive tests is that a factor of uncertainty exists regarding the overall performance characteristics of energy dissipators. The many laboratory studies made on individual structures over a period of years have been made by different personnel, for different groups of designers, each structure having different allowable design limitations. Since no two structures were exactly alike, attempts to generalize the assembled data resulted in sketchy and, at times, inconsistent results having only vague connecting links. Extensive library research into the works of others revealed the fact that the necessary correlation factors are nonexistent. To fill the need for up-to-date hydraulic design information on stilling basins and energy dissipators, a research program on this general subject was begun with a study of the hydraulic jump, observing all phases as it occurs in open channel flow. With a broader understanding of this phenomenon it was then possible to proceed to the more practical aspects of stilling basin design. This monograph generalizes the design of stilling basins, energy dissipators of several kinds and associated appurtenances. General design rules are presented so that the necessary dimensions for a particular structure may be easily and quickly determined, and the selected values checked by others without the need for exceptional judgment or extensive previous experience. Proper use of the material in this monograph will eliminate the need for hydraulic model tests on many individual structures, particularly the smaller ones. Designs of structures obtained by following the recommendations presented here will be conservative in that they will provide a desirable factor of safety. However, model studies will still prove beneficial to reduce structure sizes further, to account for nonsymmetrical conditions of approach or getaway, or to evaluate other unusual conditions not described herein.