Optimization of Frequency Distribution of Storm-Water Discharges for Coastal Ecosystem Restoration

Many coastal ecosystems have been adversely impacted by increased storm-water drainage due to expanding urbanization. The ecosystem of the St. Lucie Estuary (SLE), located on the east coast of south Florida, has been greatly influenced by development of an intricate network of storm-water drainage canals in the tributary watershed. A suite of models dealing with watershed hydrology, reservoir optimization, and estuary salinity and ecology are applied for optimal sizing and operation of storm-water reservoirs. The multipurpose storm-water control facilities provide for hydrologic restoration to predrained or natural hydrologic conditions for recovery of salinity-sensitive biota in the SLE, as well as supplemental irrigation water and pollution control through connected storm-water treatment areas. The optimization is challenging since the ecological goal is for mean monthly storm-water discharges to the SLE to coincide with the desired natural frequency distribution, rather than simply attempting to control individual extreme events. The OPTI6 optimization model applies a genetic algorithm, coupled with a daily simulation model of the storm-water drainage network, to optimize the sizing and fuzzy operating rules of reservoirs for controlling storm-water discharges to the SLE. Results indicate that the desired frequency distribution is closely matched and the level of service for the supplemental irrigation demand is met under reduced storage requirements.