Simulation of Coastal Water Control Structure Operations in South Florida Using HEC-RAS

The South Florida Water Management District (SFWMD) complex network of man-made canals and water control structures provides flood control in south Florida. Most of the canals ultimately discharge into the ocean through gated spillways. These facilities were designed by the U.S. Army Corps of Engineers (1950s and 1960s) assuming static hydraulic head conditions. Coastal structures are operated to maintain canal stages within pre-determined ranges (USACE Water Control Manuals), where gates are opened when the canal head water stage rises above its upper limit and closes when the head water stage drops below its lower limit. Gates are also closed to prevent reverse flow of salt water into the canal during high tide. The SFWMD is determining the current level of service (LOS) for flood control, which is to be established under dynamic rainfall conditions, regular and extreme (tropical storm) tidal conditions, different sea-level rise projections and different return frequencies. Transient hydraulic models are required to simulate stages and flows within a basin under these conditions. The first LOS pilot study was applied to the C-4 watershed located in Miami-Dade County. The HEC-RAS computer model (USACE) was selected for this purpose. This paper describes the process used to incorporate real-time structure operations into the model, along with customized structure flow rating equations developed by the SFWMD. Examples of modeling techniques for the operation of coastal spillways and pump stations are presented along with descriptions of the problems encountered, the solutions implemented and any unresolved issues.