HYDRODYNAMIC SIMULATIONS OF A CONSTRUCTED WETLAND IN SOUTH FLORIDA¹

Abstract

This paper describes the application of the SHEET2D model to the Florida's Everglades Nutrient Removal (ENR) Project. The ENR Project is a 3815 acre (1545 ha) pilot project, located in Palm Beach County. The operation of the treatment system will be used to demonstrate the performance of larger scale constructed wetland systems for removal of phosphorus from Everglades Agricultural Area (EAA) stormwater runoff. It is currently the largest stormwater wetland treatment system in the world. The SHEET2D model was used to analyze the performance of the ENR Project. SHEET2D is a two‐dimensional, depth‐averaged hydrodynamic model that is applicable to shallow water flow conditions. Subsequently, results from SHEET2D simulations were used to develop the ENEMOD model. ENRMOD is a lumped parameter box water quality model that can be used to analyze the long term performance of the ENR project with respect to hydrology and phosphorus uptake. Localized short‐circuiting in the agricultural ditches within the project area was analyzed by using the RBFVM‐2D model, which is a finite volume hydrodynamic model that is also applicable to shallow water flow conditions. The SHEET2D model was employed to simulate the hydraulics of the structures between cells and the hydrodynamics of the sheet‐flow moving across the buffer cell and treatment cells. Collection, distribution, and larger discharge canals within the project were simulated by means of the MultiBasin Routing (MBR) model features that are built into the SHEET2D model. Constant inflows (75 to 600 cfs [2.1 to 17 m3/s]) were used in all runs to simulate the discharge of the ENR Project based on the proposed operating schedule for the outflow pump station. The model simulated 30 days to reach steady state conditions. Under steady state conditions, the hydraulic retention times were computed for the project and the split of flow between the two treatment trains of the entire project from the common buffer cell. Additionally, design components such as height of the levees, capacity of the structures, and hydrographs at specified grids were obtained.

Drag, turbulence, and diffusion in flow through emergent vegetation

“…An increase in drag can also lead to an increase in water depth and thus residence time, further influencing species' fate and biological activity [Jadhav and Buchberger, 1995;Kadlec, 1990]. Several efforts have been made to model the additional drag using a modified Manning's equation [e.g., Guardo and Tomasello, 1995]. Although useful for its simplicity, this adaptation of Manning's equation reveals little information about the flow structure within and above the canopy and cannot represent regions of emergent vegetation or regions of creeping or transitional flow [Kadlec, 1990;Jadhav and Buchberger, 1995 In addition to affecting the mean velocity, vegetation also affects the turbulence intensity and the diffusion.…”

Large-scale constructed wetlands for nutrient removal from stormwater runoff: An everglades restoration project

“…Current operational plans call for a mean of 4.25 m:~/sec (150 cfs) to be diverted into the ENR project, which will resuh ira a HRT of approximately 14 days (Burns and McDonnell 1992). Based on hydrodynamic simulations (at steady state), a HRT of about 18 days is expected in the ENR project for the mean flow (Guardo and Tomasello 1995) at mean water depths slightly lower than 0.60 m (2.0 ft).…”

“…The simulation time was 30 days in order to reach steady state conditions for a constant intlows ranging from 2.12 to 17 m:~/sec (75-:600 cfs). To simulate waterbodies (e.g., canals) within Or adjacent to the grid network, the multibasin routing (MBR) model features that are buih into SHEET-2D were employed (Guardo and Tomasello 1995). The MBR basins can be connected to the SHEET-2D grid network by sheetflow or by structural or channel conveyances.…”

“…To generate estimates of mean flow velocities, water deplhs, and flow distribution expected within the ENR project, hydrodynamic simulations were performed using SHEET-2D (Guardo and Tomasello 1995), a twodimensional model. These results were useful fbr forecasting hydrologic conditions to which the levees, pumps, and wetland vegetation will be subjected.…”

Integrated Modeling of Groundwater and Surface Water Interactions in a Manmade Wetland

“…Regression models were used to estimate groundwater seepages in ENR and the whole ENR was treated as a single unit for water budget. Guardo and Tomasello (1995) simulated overland flow in ENR using a steady hydrodynamic model. Until recently, the hydraulic models applied to the design and management of constructed wetlands are quite limited in scope and detail.…”