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Geophysical investigation of sentinel lakes in Lake, Seminole, Orange, and Volusia Counties, Florida

Open-File Report 2012-1201

Prepared in cooperation with the St. Johns River Water Management District
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Abstract

This study was initiated in cooperation with the St. Johns River Water Management District (SJRWMD) to investigate groundwater and surface-water interaction in designated sentinel lakes in central Florida. Sentinel lakes are a SJRWMD established set of priority water bodies (lakes) for which minimum flows and levels (MFLs) are determined. Understanding both the structure and lithology beneath these lakes can ultimately lead to a better understanding of the MFLs and why water levels fluctuate in certain lakes more so than in other lakes. These sentinel lakes have become important water bodies to use as water-fluctuation indicators in the SJRWMD Minimum Flows and Levels program and will be used to define long-term hydrologic and ecologic performance measures. Geologic control on lake hydrology remains poorly understood in this study area. Therefore, the U.S. Geological Survey investigated 16 of the 21 water bodies on the SJRWMD priority list. Geologic information was obtained by the tandem use of high-resolution seismic profiling (HRSP) and direct-current (DC) resistivity profiling to isolate both the geologic framework (structure) and composition (lithology). Previous HRSP surveys from various lakes in the study area have been successful in identifying karst features, such as subsidence sinkholes. However, by using this method only, it is difficult to image highly irregular or chaotic surfaces, such as collapse sinkholes. Resistivity profiling was used to complement HRSP by detecting porosity change within fractured or collapsed structures and increase the ability to fully characterize the subsurface. Lake Saunders (Lake County) is an example of a lake composed of a series of north-south-trending sinkholes that have joined to form one lake body. HRSP shows surface depressions and deformation in the substrate. Resistivity data likewise show areas in the southern part of the lake where resistivity shifts abruptly from approximately 400 ohm meters (ohm-m) along the edges to approximately 12 ohm-m in the center. These well-defined areas may indicate a "ravel" zone of increased porosity or clay content. Within Lake Helen (Volusia County), a parallel set of seismic reflectors within a host of chaotic reflectors may represent fill within a large sinkhole. The feature extends to more than 50 meters (m) deep and contains very steep pinnacles within the center. Seismic data in Lake Helen are supported by high resistivity values from adjacent continuous resistivity profiles that show possible center collapse within the lake and infilling of sandy material. When used together, HRSP and DC resistivity techniques provide a composite image of structure and lithology to detect potential conduits for fluid flow.

Geospatial Extents

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Geophysical investigation of sentinel lakes in Lake, Seminole, Orange, and Volusia Counties, Florida
Series title:
Open-File Report
Series number:
2012-1201
Year Published:
2012
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
St. Petersburg Coastal and Marine Science Center
Description:
viii; 58 p.; PDF Appendix
Number of Pages:
68
Country:
United States
State:
Florida
County:
Lake County;Marion County;Orange County;Seminole County;Sumter County;Volusia County
Other Geospatial:
Cherry Lake;Lake Louisa;Johns Lake;Lake Avalon;Lake Hiawassee;Crooked Lake;Prevatt Lake;Lake Saunders;Sylvan Lake;Trout Lake;Big Lake;Lake Colby;Lake Helen
Online Only (Y/N):
Y
Additional Online Files(Y/N):
Y