Geology topics

Melinda A. Wolfert

Publications and source records attributed to Melinda A. Wolfert.

3 recordsLinked to original sources

USGS2007

Application of FTLOADDS to Simulate Flow, Salinity, and Surface-Water Stage in the Southern Everglades, Florida

The Comprehensive Everglades Restoration Plan requires numerical modeling to achieve a sufficient understanding of coastal freshwater flows, nutrient sources, and the evaluation of management alternatives to restore the ecosystem of southern Florida. Numerical models include a regional water-management model to represent restoration changes to the hydrology of southern Florida and a hydrodynamic model to represent the southern and western offshore waters. The coastal interface between these two systems, however, has complex surface-water/ground-water and freshwater/saltwater interactions and requires a specialized modeling effort. The Flow and Transport in a Linked Overland/Aquifer Density Dependent System (FTLOADDS) code was developed to represent connected surface- and ground-water systems with variable-density flow. The first use of FTLOADDS is the Southern Inland and Coastal Systems (SICS) application to the southeastern part of the Everglades/Florida Bay coastal region. The need to (1) expand the domain of the numerical modeling into most of Everglades National Park and the western coastal area, and (2) better represent the effect of water-delivery control structures, led to the application of the FTLOADDS code to the Tides and Inflows in the Mangroves of the Everglades (TIME) domain. This application allows the model to address a broader range of hydrologic issues and incorporate new code modifications. The surface-water hydrology is of primary interest to water managers, and is the main focus of this study. The coupling to ground water, however, was necessary to accurately represent leakage exchange between the surface water and ground water, which transfers substantial volumes of water and salt. Initial calibration and analysis of the TIME application produced simulated results that compare well statistically with field-measured values. A comparison of TIME simulation results to previous SICS results shows improved capabilities, particularly in the representation of coastal flows. This improvement most likely is due to a more stable numerical representation of the coastal creek outlets. Sensitivity analyses were performed by varying frictional resistance, leakage, barriers to flow, and topography. Changing frictional resistance values in inland areas was shown to improve water-level representation locally, but to have a negligible effect on area-wide values. These changes have only local effects and are not physically based (as are the unchanged values), and thus have limited validity. Sensitivity tests indicate that the overall accuracy of the simulation is diminished if leakage between surface water and ground water is not simulated. The inclusion of a major road as a complete barrier to surface-water flow influenced the local distribution and timing of flow; however, the changes in total flow and individual creekflows were negligible. The model land-surface altitude was lowered by 0.1 meter to determine the sensitivity to topographic variation. This topographic sensitivity test produced mixed results in matching field data. Overall, the representation of stage did not improve definitively. A final calibration utilized the results of the sensitivity analysis to refine the TIME application. To accomplish this calibration, the friction coefficient was reduced at the northern boundary inflow and increased in the southwestern corner of the model, the evapotranspiration function was varied, additional data were used for the ground-water head boundary along the southeast, and the frictional resistance of the primary coastal creek outlet was increased. The calibration improved the match between measured and simulated total flows to Florida Bay and coastal salinities. Agreement also was improved at most of the water-level sites throughout the model domain.

Scientific Investigations Report↗

USGS2004

Assigning boundary conditions to the Southern Inland and Coastal Systems (SICS) model using results from the South Florida Water Management Model (SFWMM)

The Comprehensive Everglades Restoration Plan (CERP) requires the testing and evaluation of different water-management scenarios for southern Florida. As part of CERP, the South Florida Water Management District is using its regional hydrologic model, the South Florida Water Management Model (SFWMM), to evaluate different hydrologic scenarios. The SFWMM was designed specifically for the inland freshwater areas in southern Florida, and extends only slightly into Florida Bay. Thus, the U.S. Geological Survey developed the Southern Inland and Coastal Systems (SICS) model, which is an integrated surface-water and ground-water model designed to simulate flows, stages, and salinities in the southern Everglades and Florida Bay. Modifications to the SICS boundary conditions allow the local-scale SICS model to be linked to the regional-scale SFWMM. The linked model will be used to quantify the effects of restoration alternatives on flows, stages, and salinities in the SICS area. This report describes the procedure for linking the SICS model with the SFWMM. The linkage is shown to work by comparing the results of a linked 5-year simulation with the results from a simulation in which the model boundaries are assigned using field data. The surface-water module of the SICS model is driven by areal influences and lateral boundaries. The areal influences (wind, rainfall, and evapotranspiration) remain the same when the SICS model is modified to link to the SFWMM. Four types of lateral boundaries (discharge, water level, no flow, and salinity) are used in the SICS model. Two of three discharge boundaries (at Taylor Slough Bridge and C-111 Canal) in the current SICS model domain are converted to water-level boundaries to increase accuracy. The only change to the third discharge boundary (at Levee 31W) is that the flow data are derived from SFWMM model output instead of using measured field data flows. Three water-level boundaries are modified only by receiving their data from SFWMM model output data. Additionally, two marine water-level boundaries remain the same because the SFWMM does not include Florida Bay and, therefore, this model cannot provide input data for these boundaries. The SICS no-flow boundaries remain intact because no additional data, provided by the SFWMM, suggest that any significant flow occurs along these boundaries. The Florida Bay salinity boundary is not modified because the SFWMM does not contain any salinity data that can be used to modify the model. The ground-water module of the SICS model contains a general-head boundary and a no-flow boundary. The general-head boundary, which extends along the edges of the wetland part of the SICS model domain, is modified by acquiring stage values from SFWMM cells that correspond in location to the SICS model cells. Values from the SFWMM cells are bilinearly interpolated and assigned to the appropriate SICS general-head boundary cells in all layers of the ground-water model. The ground-water no-flow boundary in Florida Bay is unaltered because the SFWMM does not include this area. A 5-year simulation was developed to test the linkage of the SICS model with the SFWMM. Results from the linked model are similar to those obtained from the original SICS model in which boundaries are assigned using field data. The simulated discharges at the coastal creeks along Florida Bay are about 5 percent lower than the field data simulation; water levels in the wetlands are about 4 percent lower, and salinities at the various coastal creeks are slightly higher.

Florida↗

USGS2004

Two-dimensional hydrodynamic simulation of surface-water flow and transport to Florida Bay through the Southern Inland and Coastal Systems (SICS)

Successful restoration of the southern Florida ecosystem requires extensive knowledge of the physical characteristics and hydrologic processes controlling water flow and transport of constituents through extremely low-gradient freshwater marshes, shallow mangrove-fringed coastal creeks and tidal embayments, and near-shore marine waters. A sound, physically based numerical model can provide simulations of the differing hydrologic conditions that might result from various ecosystem restoration scenarios. Because hydrology and ecology are closely linked in southern Florida, hydrologic model results also can be used by ecologists to evaluate the degree of ecosystem restoration that could be achieved for various hydrologic conditions. A robust proven model, SWIFT2D, (Surface-Water Integrated Flow and Transport in Two Dimensions), was modified to simulate Southern Inland and Coastal Systems (SICS) hydrodynamics and transport conditions. Modifications include improvements to evapotranspiration and rainfall calculation and to the algorithms that describe flow through coastal creeks. Techniques used in this model should be applicable to other similar low-gradient marsh settings in southern Florida and elsewhere. Numerous investigations were conducted within the SICS area of southeastern Everglades National Park and northeastern Florida Bay to provide data and parameter values for model development and testing. The U.S. Geological Survey and the National Park Service supported investigations for quantification of evapotranspiration, vegetative resistance to flow, wind-induced flow, land elevations, vegetation classifications, salinity conditions, exchange of ground and surface waters, and flow and transport in coastal creeks and embayments. The good agreement that was achieved between measured and simulated water levels, flows, and salinities through minimal adjustment of empirical coefficients indicates that hydrologic processes within the SICS area are represented properly in the SWIFT2D model, and that the spatial and temporal resolution of these processes in the model is adequate. Sensitivity analyses were conducted to determine the effect of changes in boundary conditions and parameter values on simulation results, which aided in identifying areas of greatest uncertainty in the model. The parameter having the most uncertainty (most in need of further field study) was the flow coefficient for coastal creeks. Smaller uncertainties existed for wetlands frictional resistance and wind. Evapotranspiration and boundary inflows indicated the least uncertainty as determined by varying parameters used in their formulation and definition. Model results indicated that wind was important in reversing coastal creek flows. At Trout Creek (the major tributary connecting Taylor Slough wetlands with Florida Bay), flow in the landward direction was not simulated properly unless wind forcing was included in the simulation. Simulations also provided insight into the major influence that wind has on salinity mixing along the coast, the varying distribution of wetland flows at differing water levels, and the importance of topography in controlling flows to the coast. Slight topographic variations were shown to highly influence the routing of water. A multiple regression analysis was performed to relate inflows at the northern boundary of Taylor Slough bridge to a major pump station (S-332) north of the SICS model area. This analysis allows Taylor Slough bridge boundary conditions to be defined for the model from operating scenarios at S-332, which should facilitate use of the SICS model as an operational tool.

Florida↗