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Interactions Between Surface Water and Ground Water and Effects on Mercury Transport in the North-central Everglades

By Judson W. Harvey, Steven L. Krupa, Cynthia Gefvert, Robert M. Mooney, Jungyill Choi, Susan A. King, and Jefferson B. Giddings

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Introduction
Hydrogeology of NC Everglades
>Quantifying recharge and discharge
- Approach
- Land-surface topograhy, SW slope, water-level flux
- Horizontal hydraulic gradients
- Horizontal GW flow velocities
- Vertical hydraulic gradients
- Peat hydraulic properties
- Measured vertical head gradients vs hydrogeologic model simulations
- Recharge and discharge estimates
- Water balance
Use of Geochemical Tracers
Effect of GW and SW Interactions
Summary
References
PDF Version

Quantifying Recharge and Discharge in the North-central Everglades and Identifying the Key Controlling Factors

A better understanding of how water-resources management has altered natural hydrologic patterns in the Everglades is required for successful restoration. Inseparable from natural patterns of surface-water flow and ground-water flow in the Everglades are the interactions between them. Those interactions affect water flow in both the wetlands and aquifer, and are, therefore, important to the overall water balance of the Everglades as well as the movement and fate of chemicals, including contaminants.

Interactions between surface water and ground water are well studied in certain areas of the Everglades. Most investigations were conducted in the immediate vicinity of levees and/ or canals (Klein and Sherwood, 1961; Miller, 1978; Chin, 1990; Sonenshein, 2001). Very few investigations have considered interactions between surface water and ground water in the expansive interior areas of the Everglades. Merritt (1996) combined surface- and ground-water flow models in Everglades National Park, showing the importance of wetland-ground water interactions. A drawback of Merritt’s approach was that the model was calibrated mostly on hydraulic heads, an approach known to produce non-unique solutions that could result in uncertainty in model fluxes. The best way to improve the accuracy of modeling is to acquire more detailed data sets or complementary data of a different type.

At a regional scale, the Hydrologic Systems Modeling Group of the South Florida Water Management District (SFWMD) has conducted the most comprehensive hydrologic modeling in the Everglades. An important accomplishment of that group was developing the South Florida Water Management Model (SFWMM), a coupled model of surface-water and ground-water flow for the present-day Everglades. A companion model, the Natural Systems Model (NSM), simulates hydrologic patterns across the pre-drainage Everglades topography using the same algorithms and input data. Both the SFWMM and NSM operate by computing water flow and storage in a network of 2-mi by 2-mi grid cells covering much of the eastern two-thirds of south Florida. The SFWMM and NSM models are most appropriate for regional-scale simulations of surface-water flow and often have not been tested against detailed measurements or models.

The purpose of the present project was to collect and analyze detailed hydrologic and geochemical data at indicator sites in the north-central Everglades in order to develop reliable estimates of recharge and discharge. Therefore, this study project complements the regional-based SFWMM and NSM models by providing site-specific data sets for comparison with those models. The ultimate goal is to improve the accuracy of local and regional hydrologic models that will be used for testing hypotheses about Everglades hydrology, or for testing future water-resources management scenarios.

The specific questions addressed in this section are:

  1. What are the dominant pathways of ground-water flow in the north-central Everglades? How have they changed from pre-drainage conditions? Are present-day flow directions persistent over seasons or years?
  2. What are the major factors controlling recharge and discharge in the wetlands and the spatial and temporal variability of those fluxes?
  3. Are recharge and discharge substantial in comparison to other water-balance fluxes? What is the relative importance of recharge and discharge in interior areas of wetlands? Are the important factors that control recharge and discharge near levees the same in the interior areas of the wetlands?

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