Hydraulic Design of Energy Dissipators for Culverts and Channels

This aid to selecting and designing an energy dissipator wihch will meet the requirements indicated by an erosion hazard assessment, details the design concept, and the erosion hazards, and discusses such aspects as culvert outlet velocity, velocity modification, flow transitions and the erosion of culvert outlets. Forced hydraulic jump and increased resistance, and details of impact basins, drop structures, stilling wells and riprap are also discussed. Preliminary energy dissipator selection is made by comparing the input constraints or design criteria flow regime, debris problems, location, channel characteristics, allowable scour, etc., with the attributes of the various energy distributiors. The attributes of individual dissipators include: Froude number (Fr) range for best performance; discharge velocity or other limitations; possible maintenance; operational or location problems; maximum size; and limiting features such as culvert slope or shape. Dissipator designs fall into 2 general groups: those with Fr less than 3 (most designs are in this group), and those with Fr greater than 3. The designs are treated as illustrated by the conceptual models, and are related to actual situations through example problems.