Geophysical Studies of the Southwest Florida Coast

Project Proposal for 1999

Project number: 7310-37300
USGS Geologic Division
continuing Project Work Plan - FY 1999

IDENTIFYING INFORMATION
Project title: Geophysical Mapping of Freshwater/Saltwater Interface
Geographic area: Everglades National Park, Florida
Project start date: April 1994
Project end date: September 1999

Project chief: David V. Fitterman
Region/Division/Team/Section: Central/GD/MRP
Email: fitter@musette.cr.usgs.gov
Phone: 303-236-1382
Fax: 303-236-1409
Mail address: Box 25046 MS 964, Denver, CO 80225

Program(s) (list all programs to which this work plan is being submitted):
Integrated Natural Resource Science

Program element(s)/task(s) (show percent distribution if more than one element/task). If submitting to more than one program, include element(s)/tasks from each program here:
South Florida: Element 1 (Synthesis), Task 1.1 (South Dade SICS) Element 2 (South Dade SICS), Task 2.8 (geophysical mapping)
 

BACKGROUND NARRATIVES
Project summary: This project focuses on the use of airborne, ground, and borehole geophysical measurements to map the freshwater/saltwater interface in Everglades National Park (ENP) and to monitor changes in this interface over time. In addition, these data provide information for hydrologic modelers studying possible ground-water seepage into Florida Bay and the influence of the Buttonwood Embankment on these flows.

Project objectives and strategy: Water quality in coastal areas of South Florida such as the Everglades National Park (ENP) and the discharge of fresh water into Florida Bay are closely tied to water use and water management policies. Determination and monitoring of water quality is essential to restoration of the South Florida ecosystem (SFE). The flow of fresh water through the Everglades into Florida Bay is critical to the well being of the SFE. Increased domestic use of water, drainage of land to allow farming, increased farming and subsequent nutrient loading of runoff, and changes in water management practices over the years have had a profound effect on the SFE. Monitoring of these effects is made difficult by the inaccessibility of much of this area. Airborne geophysical methods provide a means of rapidly and economically monitoring large areas where access is difficult.

This project relies upon the fact that changes in water salinity produce changes in specific conductance (SC) or water resistivity. Changes in SC produce changes in the bulk resistivity of geologic materials.

We utilize several electromagnetic geophysical techniques to map ground resistivity, each having different depths of exploration and preferred targets. Our primary tool is helicopter electromagnetic (HEM) surveying which allows rapid mapping of large tracts of otherwise inaccessible terrain. HEM
surveying is accomplished by flying an instrument package, which is slung below the helicopter, along parallel flight lines spaced 400 meters apart which cover the survey area. These data provide information on how the resistivity of the ground varies with position and depth. We have developed procedures to convert these data into interpreted resistivity-depth models. Time-domain electromagnetic soundings are also being used in this process and to provide information about resistivity variations at greater depth (as much as 100 meters). Finally, we are using borehole geophysical measurements to obtain information on formation resistivity and fluid conductivity. By sampling from various locations and depths, we are developing a correlation between formation-resistivity and water-quality. This will allow the interpreted HEM maps to be converted into estimated water quality maps. This information can be used by hydrologic modelers developing solute transport models for the Everglades.

Potential impacts and major products: Describe expected outcomes, both
scientific and management/policy-related. What scientific questions and land-management and policy issues does this project help answer? Why is it important to Program priorities? What products will you produce to contribute to the desired outcomes?
In addition to being valuable to hydrologic modelers, the results of this project provide a baseline for monitoring changes in the freshwater/saltwater interface caused by modifications of water deliveries to the Everglades planned as part of restoration activity. Future surveys in five or ten years can be compared to the results of this project to see if there has been any significant changes in the interface location.

Collaborators, clients (Names, affiliation, and roles of internal and external users of information generated by project) :Within USGS there has been collaboration with WRD-Miami on mapping the FWSWI in the southern part Dade County. Roy Sonenshein and Clinton Hittle have provided equipment and field help, and I have provided geophysical expertise. Gene Shinn (GD-St. Petersburg) has drilled several monitoring wells, Bob Halley has been invaluable in discussing applications of our data to his studies of Florida Bay salinity. Collaboration with Eric Swain (WRD-Miami) will be increased as he develops his SICS hydrologic model.

There has been considerable extramural collaboration. I have worked closely with the members of the ENP hydrologic staff (Robert Fennema, Tom Van Lent, Freddy James, Bob Zepp). The Park has provided field support in the form of vehicles (truck, airboat, and helicopter) and personnel for logging operations. We have co-authored a paper on the results of helicopter electromagnetic mapping and a report on the influence of roadways on surface-water flow in ENP. ENP staff has provided information on and access to wells inside the ENP, as well as GIS information for incorporation into map products.

Aaron Higer has provided many valuable contacts with the SFWMD. Of greatest importance was the commitment of Keith Smith and Milt Switanek to drill seven monitoring wells for this project. Five of these wells are inside the ENP and two are on SFWMD right of ways. Robert Fennema obtained the necessary permits to drill inside ENP, and Switanek did the same for the other wells.

Richard Green and Ken Campbell (Florida Geological Survey) have provided geologic maps from the Homestead area for use by this project. I have provided them with HEM apparent resistivity maps which they have used to help locate push-core sites for their mapping in the western part of ENP.

Gwen Burzycki of DERM and Bob Kesler of Florida Power and Light have expressed interest in having an HEM survey flown in the area between U.S. 1 and Card Sound Road (immediately adjacent to the eastern border of our study area), but funding obstacles still remain.

I maintain contact with hydrologists from the U.S. Army Corps of Engineers who are formulating a hydrologic flow model for South Florida. This includes Jerry Linn of Vicksburg and Jim May from Jacksonville. I will be providing them with resistivity depth models this summer for incorporation into there hydrologic models.
 
 

WORK PLAN
Time line (FY 1999 to project end): List MAJOR tasks and deliverables by fiscal year and indicate key staff responsible for each.

FY 1999 activities: Statement of the work to be undertaken in FY 1999 and a description of the methods and procedures.

This fiscal year will devoted to completing data interpretation work and writing reports and summary papers synthesizing all of the work done to date on this project. As these results become available we will be spending time working with the hydrologic modelers who can directly benefit from these results.

FY 1999 deliverables/products: Describe in more detail the specific deliverables/products that will result from this work in FY 1999.

1. Open-file report describing the interpretation of the TEM data (publication FY-99). These data will also form the basis of a journal article.
2. Interpreted airborne resistivity map from December 1994 survey (publication FY-99).
3. Interpreted airborne resistivity map from November 1996 survey (publication FY-99).
4. Open-file Report describing the borehole geophysical data and their analysis (publication FY÷99). C,
5. Open-file report synthesizing all geophysical data from this study (publication FY-99)
 

FY 1999 outreach: Emphasizing FY 1999, describe plans to address client requirements, decisions, and deadlines.

Outreach activities will focus primarily on working with ground-water modelers with USGS/WRD, the U.S. Army Corps of Engineers, and Everglades National Park. Researchers in these groups are at the point where they can use the 3-D water salinity data from this project for their solute transport model studies.

New directions or major changes for FY 1999 (if applicable):

No new directions or major changes are anticipated for FY-99.

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH

FY 1998 accomplishments and outcomes, including outreach:
During the last fiscal year we completed analysis on the errors found in HEM data. This work allows us to develop a correction procedure which we applied to our data. As a result we were able to produce 3-D resistivity models which give true formation resistivity as a function of location and depth throughout our survey area. This represented a major step as it allowed us to provide answers to the nagging question of how deep are the features which had been seen on our apparent resistivity maps. Additional well logging and measurements of water conductivity have allowed us to obtain better calibration of our logging tools and improve the correlation between formation resistivity and water conductivity. As a result our apparent resistivity maps can be used as estimated water quality maps.

During the course of the year, a question had arisen as to whether or not our geophysical measurements could be used to confirm or refute the "River of Sandä hypothesis. The proponents of this idea claim that there is a coarse grained, sand zone which transports water from near Lake Okeechobee to Florida Bay. Examination of our data suggest that no such feature exists, though it would be possible to bury, thin resistive zones, which simulate fresh-water saturated sands, into the preferred inversion models. Such models could not be distinguished from the optimal model, nor could the parameters of these resistive zones be resolved. This means that such models are allowable, but neither required nor well defined. Accordingly we have concluded that such a scenario is geophysically unlikely. If these thin, resistive zones are real, and produce by thin, fresh-water saturated sands, they pose some serious questions for the hydrologist to answer, such as 1) How is this zone hydrologically separated from the saline saturated aquifers above and below it?, 2) How would such a zone outcrop into Florida Bay?, and 3) Why have no fresh-water seeps been observed in Florida Bay?

It should be noted, however, that we have noticed a high resistivity zone to the southeast of Taylor Slough in the transient electromagnetic data. This is a very thick zone buried about 20 m deep. The exact cause of these zone is not yet certain, but it does correspond to the southward protrusion of the HEM resistivity contours to the south. However, the TEM resistive zone is much deeper than can be measured by the HEM data. This feature is intriguing, probably related to geologic controls on the location of Taylor Slough, and not completed understood at this time.
 
Project personnel served on the organizing committee for AEM 98, the International Symposium on Airborne Electromagnetics in Sydney, Australia. USGS staff presented four papers at this conference. Three of the papers, based on the work from this project, focussed on the effects of calibration errors in HEM data, methods of removing these errors, and our survey results from the Everglades. These papers were very well received at the meeting, and set the stage for some very interesting discussions between HEM contractors and users. Our efforts have pointed out some of the shortcomings in industry practices, shown methods of improving these practices, and gotten contractors to take the lead in improving data collection procedures. It is not an exaggeration to say that our presentations were one of the high points of this meeting.

FY 1998 deliverables, products completed:

The following papers were written during FY-98

1. Fitterman, David V., 1997, Analysis of errors in HEM calibration data: U.S. Geological Survey Open-File-Report 97-742, 28 p.
2. Fitterman, D.V., 1998, Sources of calibration error in helicopter EM data: Geophysical Exploration, in press.
3. Fitterman, D.V., and Deszcz-Pan, Maryla, 1998, Helicopter EM mapping of saltwater intrusion in Everglades National Park, Florida: Geophysical Exploration, in press.
4. Deszcz-Pan, Maryla, Fitterman, D.V., and Labson, V.F., 1998, Reduction of inversion errors in helicopter EM data using auxiliary information: Geophysical Exploration, in press.
 

The following abstracts were written during FY-98

1. Fitterman, D. V., and Deszcz-Pan, Maryla, 1997, Geophysical mapping of the freshwater/saltwater interface in Everglades National Park [abstract], in Gerould, S., ed., U.S. Geological Survey Open-File Report 97-385, U.S. Geological Survey Program on the South Florida Ecosystem-Proceedings of the Technical Symposium in Ft. Lauderdale, Florida, August 25÷28, 1997, p. 13-14.
2. Fitterman, David V., 1997, Sources of calibration error in helicopter EM data [abstract]: Proceedings of the International Conference on Airborne Electromagnetics, Sydney, Australia, 23-25 February 1998.
3. Fitterman, David V., and Deszcz-Pan, Maryla, 1997, Helicopter EM mapping of saltwater intrusion in Everglades National Park, Florida [abstract]:
Proceedings of the International Conference on Airborne Electromagnetics, Sydney, Australia, 23-25 February 1998.
4. Deszcz-Pan, Maryla, Fitterman, David V., and Labson, Victor F., 1997, Reduction of inversion errors in helicopter EM data using auxiliary information (abstract]: Proceedings of the International Conference on Airborne Electromagnetics, Sydney, Australia, 23-25 February 1998.
5. Fitterman, D. V., and Deszcz-Pan, M., 1998, Geophysical constraints on fresh ground-water flows to Florida Bay (abstract]: Proceedings of the 1998 Florida Bay Science Conference, May 12-14, 1998, Miami, Florida.
6. Fitterman, D.V., and Deszcz-Pan, Maryla, 1998, Airborne geophysical estimation of water quality in Everglades National Park: Proceedings of American Geophysical Union Spring Meeting, May 26-29, 1998, Boston, Massachusetts.
 

The following posters were presented during FY-98

1. Fitterman, D.V., and Deszcz-Pan, Maryla, 1997, Geophysical mapping of the freshwater/saltwater interface in Everglades National Park: U.S. Geological Survey Technical Symposium on the South Florida Ecosystem, Ft. Lauderdale, Florida, August 25-28, 1997
2. Deszcz-Pan, Maryla, Fitterman, D.V., and Labson, V.F., 1998, Reduction of inversion errors in helicopter EM data using auxiliary information: AEM 98 International Conference on Airborne Electromagnetics, Sydney, Australia, 23-25 February 1998.
3. Fitterman, D.V. and Deszcz-Pan, Maryla, 1998: Geophysical constraints on fresh ground-water flows to Florida Bay: 1998 Florida Bay Science Conference, May 12-14, 1998, Miami, Florida.
4. Fitterman, D.V., and Deszcz-Pan, Maryla, 1998: Airborne geophysical estimation of water quality in Everglades National Park: Special Session on ãHydrology and Water Quality in and Near the Everglades," American Geophysical Union Spring Meeting, May 26-29, 1998, Boston, Massachusetts.
 

Work continues on the following products and should be completed in FY-98:

1. Open-file report describing the interpretation of the TEM data. These data will also form the basis of a journal article to be completed in FY-99.
2. Interpreted airborne resistivity map from December 1994 survey.

PROJECT SUPPORT REQUIREMENTS
Names and expertise (e.g. carbonate petrology) of key project staff (list by fiscal year for duration of project):
David V. Fitterman electromagnetic geophysicist
Maryla Deszcz-Pan electromagnetic geophysicist
Barbara Ramsey publication specialist
Joyce Kibler well log processor

Other required expertise for which no individual has been identified (list by
fiscal year for duration of project)

Major equipment/facility needs (list by fiscal year for duration of project):
 

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