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The USGS developed a coupled surface-water/ground-water numerical code known as the Flow and Transport in a Linked Overland/Aquifer Density-Dependent System (FTLOADDS) to represent the surface water and ground-water hydrologic conditions in south Florida, specifically in the Everglades. The FTLOADDS code combines the two-dimensional hydrodynamic surface-water model SWIFT2D to simulate variable density overland flow (Schaffranek, 2004; Swain, 2005), the three-dimensional ground-water model SEAWAT to simulate fully-saturated variable-density groundwater flow (Guo and Langevin, 2002), and accounts for leakage and salt flux between the surface water and ground water (Langevin and others, 2005). The code was then applied to two major testing regions: 1) the Southern Inland and Coastal Systems (SICS) model domain (Swain and others, 2004) and 2) the Tides and Inflows in the Mangroves of the Everglades (TIME) model domain. The first application used code versions 1.0 and 1.1 which only utilized the SWIFT2D surface-water code. Later applications in the SICS area used version 2.1 (Langevin and others, 2005) where SWIFT2D was coupled to the SEAWAT groundwater model code. The second domain, TIME (Wang and others, 2007), utilizes the enhanced version 2.2 code, which includes enhancements to the wetting and drying routines, changes to the frictional resistance terms applications, and calculations of evapotranspiration. In 2006, FTLOADDS was modified again to represent Biscayne Bay and surrounding areas.
This will provide one large sub-regional model that will give an integrated comprehensive assessment of how different scenarios will affect water flows in both Everglades National Park and Biscayne National Park. Once calibrated, additional simulations will be performed to estimate predevelopment hydrologic conditions and to predict hydrologic conditions under one or more of the proposed restoration alternatives, using inputs from the Natural Systems Model (NSM) (SFWMD, 1997A) and the South Florida Water Management Model (SFWMM) (MacVicar and others, 1984, SFWMD, 1997B).
Langevin, Christian D.
Swain, Eric D., Wolfert, Melinda A.
Wolfert, Melinda A.; Bales, Jerad D.; Goodwin, Carl R.
Langevin, C. D.; Jones, S. A.; Reich, C. D.; Wingard, G. L.; Kuffner, I. B.; Cunningham, K. J.
Swain, E. D.; Wolfert, M. A.; Langevin, C. D.; James, D. E.; Telis, P. A.
VanLent, T.; Castro, A.
The first steps to be taken are to replace the application-specific coding in the code with user-input options and implement methods to allow the model to be more user-friendly and portable. The code needs to be updated to accept the latest version of the SEAWAT and MODFLOW codes. This will require substantial changes because of recent changes in how SEAWAT stores and accesses variables. The existing interface code, for example, to calculate the leakage across the soil surface will be transferred to the new model and new code added to take advantage of the enhanced capabilities contained in the latest version of SEAWAT. Benchmark testing will be performed to insure the updated code is operational and reliable.
Recoding is 75% complete.
This task will merge the TIME and Biscayne Bay model discretizations and eliminate all interior boundary conditions, such as along the C-111 and L-31N Canals. Equations that can calculate leakage from the groundwater into the canals and from the canals to the groundwater will be added to the model. These equations will use simulated stage or the canal leakage that is provided by the SFWMM model simulations. This is necessary as the TIME model uses canals as hydrologic boundaries, but when the models are linked these canals will become interior features and a process to calculate their effects is needed. Currently, the TIME model uses 10 vertical layers; it needs to be modified to conform to the 20 layer-Biscayne Bay model. Extensive testing of the full model will be performed and calibrated using stage, flow, and salinity observations. Model performance will be evaluated by comparing simulations to those obtained with the two smaller models.
An approach similar to methods used to link the SICS model to the SFWMM (Wolfert, 2004) will be applied to link the models. Boundary input locations in the TIME/Biscayne Bay model are correlated with the SFWMM cell values. Boundary data of the models will be acquired from the SFWMM model for the simulation period of 1990-2000. This period was chosen with the TIME application to represent a series of consecutive years of varied hydrologic conditions useful to evaluate ecosystem and biological performance measures in ENP. Since most of the input data have already been assembled for this period, it is more cost efficient to run Biscayne Bay and the full ENP/BNP model simulations for the same period.
Several modifications are required to link the TIME/Biscayne Bay model with the NSM model. Land use and land surface elevations will be modified to match predevelopment conditions. Man-made features, such as roads and canals, will be removed. Surface water model cells located within former wetland areas that are now represented as developed areas of the Biscayne model domain will be activated. Model boundary data will be acquired from the NSM and interfaced in a parallel approach to that used with SFWMM model. The coupled TIME/Biscayne Bay model will be used to simulate likely predevelopment scenarios.
A report will be prepared to document methods, processes, and datasets used in development of the model to facilitate the ability of others to update the model or incorporate new or more efficient techniques or data as it becomes available. A USGS Scientific Investigations Report or journal article will be prepared that describes model development and calibration processes.
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