South Florida Water Management Model Research Articles

Projecting changes in Everglades soil biogeochemistry for carbon and other key elements, to possible 2060 climate and hydrologic scenarios.

Based on previously published studies of elemental cycling in Everglades soils, we projected how soil biogeochemistry, specifically carbon, nitrogen, phosphorus, sulfur, and mercury might respond to climate change scenarios projected for 2060 by the South Florida Water Management Model. Water budgets and stage hydrographs from this model with future scenarios of a 10% increased or decreased rainfall, a 1.5 °C rise in temperature and associated increase in evapotranspiration (ET) and a 0.5 m rise in sea level were used to predict resulting effects on soil biogeochemistry. Precipitation is a much stronger driver of soil biogeochemical processes than temperature, because of links among water cover, redox conditions, and organic carbon accumulation in soils. Under the 10% reduced rainfall scenario, large portions of the Everglades will experience dry down, organic soil oxidation, and shifts in soil redox that may dramatically alter biogeochemical processes. Lowering organic soil surface elevation may make portions of the Everglades more vulnerable to sea level rise. The 10% increased rainfall scenario, while potentially increasing phosphorus, sulfur, and mercury loading to the ecosystem, would maintain organic soil integrity and redox conditions conducive to normal wetland biogeochemical element cycling. Effects of increased ET will be similar to those of decreased precipitation. Temperature increases would have the effect of increasing microbial processes driving biogeochemical element cycling, but the effect would be much less than that of precipitation. The combined effects of decreased rainfall and increased ET suggest catastrophic losses in carbon- and organic-associated elements throughout the peat-based Everglades.

Ecological Responses of a Large Shallow Lake (Okeechobee, Florida) to Climate Change and Potential Future Hydrologic Regimes

We considered how Lake Okeechobee, a large shallow lake in Florida, USA, might respond to altered hydrology associated with climate change scenarios in 2060. Water budgets and stage hydrographs were provided from the South Florida Water Management Model, a regional hydrologic model used to develop plans for Everglades restoration. Future scenarios include a 10% increase or decrease in rainfall (RF) and a calculated increase in evapotranspiration (ET), which is based on a 1.5 °C rise in temperature. Increasing RF and ET had counter-balancing effects on the water budget and when changing concurrently did not affect hydrology. In contrast, when RF decreased while ET increased, this resulted in a large change in hydrology. The surface elevation of the lake dropped by more than 2 m under this scenario compared to a future base condition, and extreme low elevation persisted for multiple years. In this declining RF/increasing ET scenario, the littoral and near-shore zones, areas that support emergent and submerged plants, were dry 55% of the time compared to less than 4% of the time in the future base run. There also were times when elevation increased as much as 3 m after intense RF events. Overall, these changes in hydrologic conditions would dramatically alter ecosystem services. Uncertainty about responses is highest at the pelagic-littoral interface, in regard to whether an extremely shallow lake could support submerged vascular plants, which are critical to the recreational fishery and for migratory birds. Along with improved regional climate modeling, research in that interface zone is needed to guide the adaptive process of Everglades restoration.

Landscape analysis of tree island head vegetation in water conservation area 3, Florida Everglades

ABSTRACT Tree islands, forested islands in an herbaceous freshwater wetland landscape, are a major landscape feature in the Florida Everglades. The vegetation communities on the heads of 31 tree islands, including eight islands with recreational camp structures, were assessed throughout Water Conservation Area 3 to determine their composition, structure, and distribution across the landscape. The islands were a sample of the most elevated islands in the local landscape. Measures of forest canopy (> 3 m) and sub-canopy (1–3 m) structure and composition, including cover, species richness, number of exotics, and total canopy basal area were ordinated onto six hydrologic variables estimated from the South Florida Water Management Model (v5.5) simulation from 1984 to 1997, and history of recent fire. Ordination allowed identification of four island groups: Group A, higher islands, most with camp structures, low or no canopy structure, high level of fire history, driest hydrology, and largest number of exotic s...

SOUTH FLORIDA: THE REALITY OF CHANGE AND THE PROSPECTS FOR SUSTAINABILITY: The design of ecological landscape models for Everglades restoration

Restoration of the Everglades is a multi-objective, multi-scale, multi-agency program that requires numerous computer models to test alternatives, understand ecosystem processes, and evaluate restoration performance. Landscape models used for Everglades restoration include hydrologic models, transition probability models, gradient models, distributional mosaic models, and individual-based models. As tools for restoration feasibility and as the backbone of the policies that will drive Everglades restoration for the next 20 years, it is critical that a wide audience evaluate the strengths and weaknesses of six landscape models. Simulations of historic hydropatterns and current hydropatterns, based mostly upon sheet-flow equations and canal-flow equations, respectively, have been the realm of the Natural Systems Model (NSM) and the South Florida Water Management Model (SFWMM). Despite a lack of biology in these two models, a comparison of their spatial output became the basis for the Comprehensive Everglades Restoration Plan (CERP) approved by the US Congress in October, 2000. SAWCAT, a transitional probability model, was based upon an analysis of the patchiness of cattail (Typha) and sawgrass (Cladium) cells in association with levees, water depth, and phosphorus. This statistical approach was used to predict the amount of sawgrass that would be converted to less desirable cattail, if phosphorus runoff patterns to the Everglades remained constant. The Everglades Water Quality Model (EWQM), a mass-balance gradient approach used to track phosphorus according to a simple net phosphorus removal coefficient, was used to design Storm Water Treatment Areas (STA) and to evaluate where and when phosphorus ‘thresholds’ would be exceeded under various hydrologic restoration plans. The Everglades landscape Model (ELM), a complex distributional mosaic model, used site-specific biogeochemical mechanisms and mass-balance to control energy and material flows, and to predict changes in carbon and phosphorus structure of the soil, water, and plant communities as a result of modified water deliveries to the Everglades. The Across Trophic Level Spatial Simulation (ATLSS), also a distributional mosaic modeling approach, used individual-based rules of behavior to predict animal movement and abundance in relation to hydrologic restoration plans. When these landscape models are combined, they effectively contribute to water management and policy for Everglades restoration. To insure their effectiveness, an applied science strategy provides the framework for their integration into the restoration process.

Numerical errors in groundwater and overland flow models

Numerical error estimates are useful to evaluate the applicability of overland and groundwater flow models and verify the validity of their results. In this paper, methods of estimating numerical errors are developed and then applied to evaluate the numerical accuracy of the South Florida Water Management Model. Analytical expressions for errors generated during the propagation of disturbances due to well pumping, boundary water level changes, and rainfall are obtained for steady and transient conditions using Fourier analysis of the linearized governing equations. Different situations under which truncation errors are introduced into models and their variation with the spatial and temporal discretization are discussed. Numerical experiments are carried out with the three‐dimensional groundwater flow model MODFLOW and a number of implicit and explicit models to verify the results. Dimensionless parameters are used in the expressions so that the results can be used to determine discretization errors in any existing or new finite difference model of regional or local scale.

Performance Comparison of Overland Flow Algorithms

Two regional models, the South Florida Water Management Model (SFWMM) and the Natural System Model (NSM), are applied to analyze and predict water conditions in the Everglades and South Florida. Both of these models use an alternating direction explicit (ADE) type method to solve diffusion flow. In this paper, three finite-difference algorithms based on explicit, alternating direction implicit (ADI) and successive over relaxation (SOR) methods are examined as possible replacements for the ADE method. Various model solutions are verified using an axisymmetric test problem that is solved using an axisymmetric test model. A comparison of run time versus error plots proved that the ADI method has the best overall performance. The study includes a description of the relationship between the accuracies and run times of different algorithms and their spatial and temporal discretizations in dimensionless form. Linear and spectral analyses are used to derive theoretical expressions for numerical error, run time, and stability. Comparisons indicate that theoretical estimates of numerical error and run times closely approximate the experimental values. Results of this study are valuable as methods to determine optimum space and time discretizations of future modeling applications when the maximum allowable numerical error and the dimensions of the flow features to be simulated are known. Results can also be used to understand the magnitudes of numerical errors in existing modeling applications.

SIMULATION OF INTEGRATED SURFACE WATER AND GROUND WATER SYSTEMS ‐ MODEL FORMULATION1

ABSTRACT: The unique characteristics of the hydrogeologic system of south Florida (flat topography, sandy soils, high water table, and highly developed canal system) cause significant interactions between ground water and surface water systems. Interaction processes involve infiltration, evapotranspiration (ET), runoff, and exchange of flow (seepage) between streams and aquifers. These interaction processes cannot be accurately simulated by either a surface water model or a ground water model alone because surface water models generally oversimplify ground water movement and ground water models generally oversimplify surface water movement. Estimates of the many components of flow between surface water and ground water (such as recharge and ET) made by the two types of models are often inconsistent. The inconsistencies are the result of differences in the calibration components and the model structures, and can affect the confidence level of the model application. In order to improve model results, a framework for developing a model which integrates a surface water model and a ground water model is presented. Dade County, Florida, is used as an example in developing the concepts of the integrated model. The conceptual model is based on the need to evaluate water supply management options involving the conjunctive use of surface water and groundwater, as well as the evaluation of the impacts of proposed wellfields. The mathematical structure of the integrated model is based on the South Florida Water Management Model (SFWMM) (MacVicar et al., 1984) and A Modular Three‐Dimensional Finite‐Difference Groundwater Flow Model (MODFLOW) (McDonald and Harbaugh, 1988).