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geophysical mapping of saltwater intrusion in everglades national park
Geophysical Mapping of Saltwater Intrusion in Everglades National ParkDavid V. Fitterman and Maria Deszcz-Pan
Abstract
The mapping of saltwater intrusion in coastal aquifers has traditionally relied
upon observation wells and collection of water samples. This approach may miss
important hydrologic features related to saltwater intrusion in areas where access is
difficult and wells are widely spaced, such as the Everglades. To map saltwater
intrusion in Everglades National Park, a different approach has been used. We have
relied heavily on helicopter electromagnetic (HEM) measurements to map lateral
variations of electrical resistivity, which are directly related to water quality. The HEM
data are inverted to provide a three-dimensional resistivity model of the subsurface.
Borehole geophysical and water quality measurements made in a selected set of
observations wells are used to determine the relation between formation resistivity
and specific conductance of pore water. Applying this relation to the 3-D HEM
resistivity model produces an estimated water-quality model. This model provides
constraints for variable density, ground-water models of the area. Time-domain
electromagnetic (TEM) soundings have also be used to map saltwater intrusion.
Because of the high density of HEM sampling (a measurement point every 10 meters
along flight lines) models with a cell size of 100 meters on a side are possible,
revealing features which could not be recognized from either the TEM or the
observation wells alone. The very detailed resistivity maps show the extent of
saltwater intrusion and the effect of former and present canals and roadbeds. The
HEM survey provides a means of quickly obtaining a synoptic picture of saltwater
intrusion, which also serves as a baseline for monitoring the effects of Everglades
restoration activities.
This Paper: Fitterman, D.V., and Deszcz-Pan, M., 1999, Geophysical mapping of saltwater intrusion in Everglades National Park (on CD-ROM), in 3rd International Symposium on Ecohydraulics, Salt Lake City, Utah, 12-16 July 1999, p. 18 (on CD-ROM). Related information:
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U.S. Department of the Interior, U.S. Geological Survey
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