Hydraulic Analyses of Stormwater Treatment Areas in South Florida

Constructed wetlands are an important component of plans to treat stormwater runoff from agricultural areas in South Florida. Several large wetlands are being constructed as part of a plan set forth by the Everglades Forever Act (EFA). Interim goals for these facilities include reduction of long-term total phosphorus concentrations to 50 ppb and restoration of the area's natural hydropatterns. To meet these goals, six Stormwater Treatment Areas (STAs) are being constructed on 18,210 ha of agricultural lands. STA 3/4, a 6,742 ha facility, is the largest of the stormwater treatment areas and the last to be constructed under the EFA mandates. STA 3/4 is being designed to serve the Miami Canal and the North New River Canal basins. It has a maximum design flow rate of 165 m³/s and a footprint that extends approximately 11 km from east to west and 6 km from north to south. To support the design of STA 3/4 models are being developed to simulate the hydraulic profiles and internal flow patterns within each treatment cell (STA 3/4 has five internal cells). Because of the large land area covered by the STA, use of a 2-dimensional (2-D) hydraulic model is necessary to simulate the performance of inflow and outflow control structures, spreader canals, collector canals, and variations in topography within the STA. The Federal Highway Administration's FESWMS-2DH software was selected for use in the design of STA 3/4. Models have been developed using topographic information collected from conventional and GPS surveys, a vegetation survey, and field data collected at other constructed wetlands. To date the models have been useful in demonstrating flow patterns resulting from the location of the control structures and how variations in structure spacing can impact flow patterns, thus reducing short-circuiting within the marsh areas.