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Project Work Plan
Greater Everglades Science Program: Place-Based Studies
Project Work Plan FY 2003
A. GENERAL INFORMATION:
Project Title: Geophysical Studies of the Southwest Florida Coast
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 Big Cypress National Preserve and Everglades National Park from Flamingo to Everglades City. These data will be used to develop a ground-water flow model 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 data 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 a plan for acquiring these data will be established.
3. Collection of additional geophysical: Additional geophysical data will be collected including airborne and ground data.
4. Planning of airborne electromagnetic survey: Using the existing ground based geophysical results and airborne results from other regions of Everglades National Park, an airborne survey will be planned to provide more detailed geophysical information. This activity will take place in FY-2001.
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 in rivers and streams using a drilling barge, such as the one operated by the Coastal and Marine Geology group in St. Petersburg. 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 and Big Cypress National Preserve 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 in 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 of 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 aquifer. Following completion of these reports and maps, a synthesis of geophysical and hydrologic data will be carried out.
Collaborators: Department of Interior, National Park Service, Big Cypress National Preserve
Clients: Department of Interior, National Park Service, Everglades National Park
B. WORK PLANTitle of Task 1:Geophysical Mapping of Saltwater Intrusion
Task Funding: Place Based Studies
Task Leaders: David Fitterman
Task Status (proposed or active): active
Task priority: 1
Task personnel requested for FY-2003 are as follows:
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 to assist in construction of hydrologic models of the area.
Our objective is to develop a three-dimensional resistivity model of the ground that can be related to hydrologic conditions in the subsurface, such as aquifer geometry and water quality. This model will then be used by hydrologists in the development of flow models incorporating density variations.
Work to be undertaken during the proposal year and a description of the methods and procedures:
During FY-2003 work will continue on data set interpretation. This effort will be divided between two goals: 1) refining the geophysical (resistivity-depth) model, 2) obtaining a relationship to transform the geophysical model into a physical parameter useful in developing hydrologic models. The second goal requires the collection of data necessary to develop a relationship between formation resistivity and water quality, as well as, developing guidelines for interpreting the various resistivity ranges in terms of hydrologic units.
The results of this project will be related informally to colleagues inside and outside the USGS by direct communications over the phone, via e-mail, and in person. Formal presentation of results will be made at USGS sponsored workshops and public meetings, at technical meeting, and in USGS and technical-journal publications.
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