Correcting spillway design deficiencies

Underestimation of channel roughness or constructed conveyance capacity downstream of critical water control structures can lead to serious energy dissipation problems. The energy dissipation deficiencies may create an inability to pass design flows necessary to provide desired levels of flood protection. A case study downstream of Lake Istokpoga in the South Florida Everglades illustrates the design problem. Tail-water weirs using a modified CIT Drop Structure design were successfully used downstream of the control structures to dissipate the energy developed during high flow conditions. Performance was verified using very large flows through two of the structures modified in this manner.