Geophysical Studies of the Southwest Florida Coast

Project Proposal for 2001

CONTINUING PROJECT WORK PLAN - FY 2001

Project Title: Geophysical Studies of the Southwest Florida Coast

Project Type: SIR
Project Status: 2-AO/TCS REVIEW
Project Number: 7380-04
Project start date: 10/01/1996
Project end date: 09/30/2003

Lead Project chief:
Fitterman, David V.
Email address: fitter@usgs.gov
Phone: (303)236-1382
Fax: (303)236-1425
Mail address: P.O. Box 25046, Denver, 80225

Associate Project chief:
BASIS Manager
Email address: gs-g_irg_basis@usgs.gov

Prospectus Goals/Objective, elements, activities, sub-activities: 5.3.4.5 Ecological and Geological Studies of Southwest Florida
Percentage: 100

BACKGROUND NARRATIVES

Type: Proposed
Project Summary:
The focus of this project is the use of ground, airborne, and borehole electromagnetic geophysical methods to map subsurface geology and hydrology along the southwest Florida coast in Everglades National Park from Flamingo to Everglades City. These data will be used to develop a ground-water flow model (TIME) which is bounded on the north by the Tamiami Trail, on the south by Florida Bay, on the east by the Atlantic coastal ridge, and on the west by the Gulf of Mexico. Subsurface information from this area is limited because of the difficult access, which constrains most drilling to established roads. Airborne geophysical methods can be used to surmount this obstacle and provide three-dimensional subsurface information essential to ground-water-flow model development.

Project Objectives and Strategy:
Completion of a combined ground and airborne geophysical study in the southern portion of Everglades National Park has shown the utility of these methods to map the extent of saltwater intrusion and provide geological information needed to develop ground-water flow models. The same approach should prove equally useful in the development of hydrologic models in the region to the west where little subsurface information exists.

The approach requires three components: ground-based, airborne, and borehole electrical geophysical measurements. In combination these measurements can provide detailed information on the location of geologic and hydrologic boundaries essential for ground-water model development. The approach to be used includes the following elements:

1. Inventory of existing geophysical data: Several data sets already exist in the study area. These include helicopter electromagnetic data of the southern portion of the study area, time-domain electromagnetic soundings along and south of the Tamiami Trail, and small loop, time-domain electromagnetic soundings north of the Tamiami Trail. These data will be located and assessed for utility to this project.
2. Interpretation and analysis of existing data: Interpretation (where necessary) and analysis of existing geophysical will be carried out. This information will be shared with hydrologic modelers to determine its usefulness in developing model geometry and constraints. Areas requiring additional information will be identified and an plan for acquiring these data will be established.
3. Planning and flying helicopter electromagnetic survey: Using the ground based geophysical results and our experience in the Taylor Slough region of Everglades National Park, an airborne survey will be planned to provide more detailed geophysical information of the Shark River Slough area. Acquiring the airborne electromagnetic data earlier (FY-2001), rather than later, in the project cycle is advisable as the results will be available for the modelers to incorporate into their effort. Data which gets to the hydrologic modelers too late in the modeling cycle if often can completely incorporated into the model.
4. Collection of additional surface geophysical: Additional ground-based geophysical data will be collected to reduce uncertainty in the interpretation of airborne geophysical survey. The use of time-domain electromagnetic and/or DC resistivity soundings is anticipated.
5. Geophysical logging of boreholes: As there is little subsurface information available from the west coast area, drilling of boreholes may be required. This function is not considered a direct part of this project, however, it needs to be a component of the program effort. Drilling can be done by conventional means from existing roads or using a drilling barge, such as the one operated by the Coastal and Marine Geology group in St. Petersburg, in rivers and streams. If holes are drilled, this project will undertake some basic geophysical logging that would be of value in interpreting the geophysical data.
6. Synthesis of geophysical, geological, and hydrological data: The final stage of this project is a synthesis of all of the geophysical data with the results of drilling and hydrologic modeling. This final step of integrating all data sets is essential as it points out problem areas in the various data sets and often leads to new, improved interpretations which resolve these differences.

Potential Impacts and Major Products:
The development of ground-water flow models for the southwest coast of Everglades National Park is an essential part of resource management in the area because of the critical importance of water on the ecosystem and the strong interaction of ground- and surface-water flows in the region. Flow models, which will be developed by other projects working on this program, are only as good as the data upon which they are based. Critical to their development is information on the location of geologic boundaries and salinity transitions. Due to the inaccessibility of much of this area and low density of drill holes, an alternative approach is needed to obtain this information. Geophysical data combined with information from any existing or future drill holes provides a way of filling this void and insuring the development of ground-water flow models that are a value in resource management.

Products anticipated from this project include a report on geophysical data interpretation, a map of saltwater intrusion, and a 3-D model of geophysically estimated water quality in the surficial aquifer. Following completion of these reports and maps, a synthesis of geophysical and hydrologic data will be carried out.

Collaborators:

Clients:
Department of Interior, National Park Service, Everglades National Park Department of Interior, National Park Service, Big Cypress National Preserve

Florida, County Agencies, South Florida Water Management District

Bibliographic Citation for Products Completed During the Life of the Project:
Deszcz-Pan, M., Fitterman, D.V., and Labson, V.F., 1998, Reduction of inversion errors in helicopter EM data using auxiliary information, Exploration Geophysics, v. 29, p. 142-146.

WORK PLAN

Task Summary and Objectives:
This task entails the use of ground and airborne geophysical methods to obtain subsurface information needed to construct hydrologic models. This information includes the location of geologic and hydrologic boundaries, such as geologic contacts which form permeability boundaries and saltwater intrusion corresponding to changes in water quality. Such boundaries are often mappable using electromagnetic geophysical techniques. Data will be collected in areas where information is not available from wells.

Work to be undertaken during the proposal year and a description of the methods and procedures:
The work will consist several phases. Initially an inventory of existing geophysical data will be compiled. These data will be assessed as to their utility to the project. Data that are of use will be interpreted and compared to what is know about the geologic framework on the near-surface environment. Additional ground-based geophysical measurements will be made to expand coverage as needed for hydrologic modeling purposes. These measurements will take the form of either time-domain electromagnetic soundings or DC resistivity soundings based upon the target depth and access constraints. The newly acquired data will be interpreted and compared with the existing data.

One of the purposes of the ground-based geophysical measurements is for planning a helicopter electromagnetic (HEM) survey of the area. The HEM survey will provided much higher spatial resolution (one datum every 10-15 meters along flight lines), whereas the TEM measurements will have a density of one per 25 sq. km. or less. The HEM data will be collected and inverted to obtain a three-dimensional resistivity-depth model.

The final phase of the geophysical interpretation will require wells in selected key areas. These will provide a means of obtaining water quality samples, as well as geophysical logs. The geophysical logs will be correlated with the water quality information. If a reasonable correlation is found, the inverted HEM data can be turned into three-dimensional estimates of water quality, useful in developing ground-water flow models incorporating solute transport.

Planned Outreach:
This project will provide outreach to other government agencies through collaboration and the sharing of data with staff members of Everglades National Park, Big Cypress National Preserve, and the Faksahatchee State Wildlife Refuge. Outreach to the public will take place a periodic program review meetings, as well as Web-based documents describing project work and data exchange.

Publications delivered/completed for this Task:
Fitterman, David V., and Deszcz-Pan, M., 1999, Geophysical mapping of saltwater intrusion in Everglades National Park, Proceedings 3rd International Symposium on Ecohydraulics, 12-16 July 1999, Salt Lake City, Utah, 18 p. including 7 figs. (on CD-ROM).

Fitterman, D.V., Deszcz-Pan, M., and Stoddard, C.E., 1999, Results of time-domain electromagnetic soundings in Everglades National Park, Florida, U.S. Geological Survey Open-File Report 99-426, 152 p., 3 plates (on CD-ROM).

Fitterman, D.V., and Deszcz-Pan, M., 1998, Helicopter EM mapping of saltwater intrusion in Everglades National Park, Florida, Exploration Geophysics, v. 29, p. 240-243.

Fitterman, D.V., 1998, Sources of calibration error in helicopter EM data, Exploration Geophysics, v. 29, p. 65-70.

Fitterman, D.V., 1997, Analysis of errors in HEM calibration data, U.S. Geological Survey Open-File Report 97-742, 28 p.

Fitterman, D.V, 1996, Geophysical mapping of the freshwater/saltwater interface in Everglades National Park, Florida, U.S. Geological Survey Fact Sheet FS-173-96.

Publications planned for this task, to be submitted for publication in current or future fiscal years:
Fitterman, D.V., and Deszcz-Pan, Maria, 2000, Interpretation of Helicopter Electromagnetic Survey to Map Saltwater Intrusion in Everglades National Park, Florida

Fitterman, D.V., Hittle, C.D., and Schmerge, D.L., 2001, Results of Time-Domain Electromagnetic Soundings along Tamiami Trail and Adjacent Areas, Everglades National Park and Big Cypress National Preserve, Florida

Geographic area of task:
United States, South Florida Ecosystem, FL

ACCOMPLISHMENTS

Current year nonpublication accomplishments and outcomes:
Through the course of this project, we have developed a strong, working relationship with the research staff of Everglades National Park. This has resulted in invaluable assistance by Park personnel with field operations and data analysis problems.

Highlights- summary of the most significant outcome:
One of the main technical accomplishments of this project has been the development of geophysical analysis techniques needed to remove errors in helicopter electromagnetic data introduced by calibration and other errors. Without this procedure we would not have been able to invert the HEM data to obtain the formation-resistivity-depth models.

New Directions or Major Changes for Proposal Year:
The use of combined geophysical methods to obtain information needed to construct hydrologic models will shifts its focus from the southern edge of Everglades National Park to the western region of the Park between the Shark River and Everglades City. This region is the focus of a new modeling effort that incorporates and expands on the Southern Inland and Coastal Systems (SICS) project. The new modeling project is called Tides and Inflows in the Mangroves of the Everglades (TIME).

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