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Development of Ecosystem Restoration and Sea-Level Rise Scenario Simulations for the Greater Everglades using the FTLOADDS code

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Project Investigators: Dorothy Sifuentes, Eric Swain

Project Personnel: Melinda Lohmann, Jeremy Decker, Michael Swain

Project Start Date: 2009 End Date: 2012

Recent Funding: (FY12) USGS GE PES


The changes in inundation hydroperiod, salinity in urban and natural areas, and aquifer salinity intrusion can all be simulated in the Flow and Transport in a Linked Overland/Aquifer Density-Dependent System (FTLOADDS) model.

One of the most apparent effects of climate-change is sea-level rise. Analyses of mean sea elevation and topography can produce maps of shoreline changes, but the climatic fluctuations and structural operations superimposed on the sea-level rise create dynamic and temporal effects. In order to study scenarios related to sea-level rise in south Florida, we propose the use of currently developed dynamic models of surface-water/ground-water flow to simulate varying levels of mean tidal-level increase with tidal and atmospheric fluctuations. The changes in inundation hydroperiod, salinity in urban and natural areas, and aquifer salinity intrusion can all be simulated in the Flow and Transport in a Linked Overland/Aquifer Density-Dependent System (FTLOADDS) model. Due to the model capability for simulating dynamic events for a multi-year timescale, the simulations will provide more information than map-based approaches.

FTLOADDS is a combination of two pre-existing codes, namely, the SWIFT2D two-dimensional hydrodynamic surface-water model code and the SEAWAT three-dimensional ground-water model code (Langevin and others, 2005). SWIFT2D computes vertically-integrated flow by solving the St. Venant equations in two dimensions. Additionally, SWIFT2D computes reactive constituent transport, density variations effects, drying and rewetting of periodically inundated areas, and hydraulic structures (Schaffranek 2004). SEAWAT is a combination of the commonly used ground-water model code MODFLOW and the solute-transport code MT3DMS (Guo and Langevin 2002). FTLOADDS therefore has the ability to simulate salinity transport in two dimensions for surface water and three dimensions for ground water. SWIFT2D and SEAWAT operate independently within FTLOADDS, with the exception of the leakage and salinity fluxes passed between the surface water and ground water. FTLOADDS has been enhanced to represent heat-transport in the surface water linked to evapotranspiration effects (Swain and Decker, 2008).

Applications of FTLOADDS to southern Florida coastal areas provide a comprehensive framework for predicting hydrologic changes (Swain and others, 2003). Applications in the area include: 1) The Tides and Inflows in the Mangrove Everglades (TIME) application in the Everglades National Park area (Wang and others, 2007); 2) The Ten-Thousand Islands (TTI) application between Everglades National Park and Naples; and 3) The Biscayne application from Biscayne Bay inland to the L-31N levee. The model-domain locations are shown in figure 1. The TIME application is used to evaluate CERP restoration scenarios by using output from the SFWMD regional 2x2 model and the TTI application yield information on manatee habitats. The TIME and Biscayne applications have been combined to produce the BIscayne/South-East Coastal Transport (BISECT) application. This tool has been used to develop a series of hindcast and futurecast simulations that can be used to examine landscape and topography changes, sea-level rise effects, precipitation changes, and ternperature changes.

The modeling application to the Ten Thousand Islands (TTI) area required a smaller-scale application to the Port of the Islands marina that can represent vertical stratification in salinity and temperature. The Environmental Fluid Dynamics Code (EFDC) was applied for this purpose and used boundary conditions from the TTI model to represent existing and restoration conditions.

The implementation of heat-transport in a wetland environment requires a number of heat-budget parameters that have not been well defined for the South Florida environment such as soil heat storage and albedo. Physical experiments are required to define these factors and improve the numerical model.

To achieve our goals, we are:

1: Refining model parameters and algorithms to better simulate water-levels, flows, salinity, and temperature in the hydrodynamic coastal area and underlying aquifer.

Based on ongoing testing of the FTLOADDS applications, advancements have been made in the following critical areas:

  1. The southern and western coastal boundaries are moved further offshore. The Gulf of Mexico boundaries are moved to approximately longitude 81° 24' west longitude and the Florida Bay boundary to latitude 25° 00' north latitude in order to delineate near-shore conditions.
  2. The discretization of the aquifer has been increased from 10 to 15 layers and newer aquifer characteristic data have been incorporated. The upper aquifer thickness has been reduced from 7 to 2.5 meters to improve the simulation of saltwater intrusion.
  3. The peat-layer representation for computing leakage will be given spatially-variable values based on recently developed peat maps.

2: Develop test simulation with the Sea Water Interface (SWI) package replacing the SEAWAT package to simulate ground-water flow and salinity.

SWI has a simpler representation of the interface as opposed to the full salinity transport capabilities of SEAWAT. The use of SWI represents a significant saving of computational effort and complexity, and the ability of SWI to represent the groundwater salinity interface is of great interest.

3: Develop simulations of sea-level rise and restoration scenarios.

The BISECT model using FTLOADDS has incorporating different scenarios of projected SLR and restoration options from CERP. These have been used to generate information on percent of time inundation and extent of salinity intrusion. Regional climate parameters downscaled from global models are used to define rainfall for future-scenario simulations. Comparisons of these scenarios yields information for coastal natural and urban areas.

4: Physical experimentation to delineate soil heat parameters for wetland and offshore heat-transport.

Physical experiments involve several circular tanks filled with soil and water to determine heat storage in the underlying soil and effects of bottom reflectance on the total heat budget. Thermocouples measure the temperature at various points in the soil and water, and instruments also measure solar radiation and humidity. The information is used to determine soil heat storage and albedo. Additional testing looks at different bottom types and their effect on the total heat budget.

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