Characterizing the diverse hydrogeology underlying rivers and estuaries using new floating transient electromagnetic methodology
The hydrogeology below large surface water features such as rivers and estuaries is universally under-informed at the long reach to basin scales (tens of km+). This challenge inhibits the accurate modeling of fresh/saline groundwater interfaces and groundwater/surface water exchange patterns at management-relevant spatial extents. Here we introduce a towed, floating transient electromagnetic (TEM) system (i.e. FloaTEM) for rapid (up to 15 km/h) high resolution electrical mapping of the subsurface below large water bodies to depths often a factor of 10 greater than other towed instruments. The novel FloaTEM system is demonstrated at a range of diverse 4th through 6th-order riverine settings across the United States including 1) the Farmington River, near Hartford, Connecticut; 2) the Upper Delaware River near Barryville, New York; 3) the Tallahatchie River near Shellmound, Mississippi; and, 4) the Eel River estuary, on Cape Cod, near Falmouth, Massachusetts. Airborne frequency-domain electromagnetic and land-based towed TEM data are also compared at the Tallahatchie River site, and streambed geologic scenarios are explored with forward modeling. A range of geologic structures and pore water salinity interfaces were identified. Process-based interpretation of the case study data indicated FloaTEM can resolve varied sediment-water interface materials, such as the accumulation of fines at the bottom of a reservoir and permeable sand/gravel riverbed sediments that focus groundwater discharge. Bedrock layers were mapped at several sites, and aquifer confining units were defined at comparable resolution to airborne methods. Terrestrial fresh groundwater discharge with flowpaths extending hundreds of meters from shore was also imaged below the Eel River estuary, improving on previous hydrogeological characterizations of that nutrient-rich coastal exchange zone. In summary, the novel FloaTEM system fills a critical gap in our ability to characterize the hydrogeology below surface water features and will support more accurate prediction of groundwater/surface water exchange dynamics and fresh-saline groundwater interfaces.
Citation Information
| Publication Year | 2020 |
|---|---|
| Title | Characterizing the diverse hydrogeology underlying rivers and estuaries using new floating transient electromagnetic methodology |
| DOI | 10.1016/j.scitotenv.2020.140074 |
| Authors | John W. Lane, Martin A. Briggs, PK Maurya, Eric A. White, JB Pedersen, Esben Auken, Neil Terry, Burke J. Minsley, Wade Kress, Denis R. LeBlanc, Ryan F. Adams, Carole D. Johnson |
| Publication Type | Article |
| Publication Subtype | Journal Article |
| Series Title | Science of the Total Environment |
| Index ID | 70220212 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | New England Water Science Center; Lower Mississippi-Gulf Water Science Center; Geology, Geophysics, and Geochemistry Science Center; WMA - Earth System Processes Division |
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Floating and Towed Transient Electromagnetic Surveys used to Characterize Hydrogeology underlying Rivers and Estuaries: March - December 2018
John W Lane, Jr., Ph.D.
Senior Advisor for Water/International
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Martin A. Briggs
Research Hydrologist
Burke Minsley
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Denis R LeBlanc (Former Employee)
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Floating and Towed Transient Electromagnetic Surveys used to Characterize Hydrogeology underlying Rivers and Estuaries: March - December 2018
Surface and water-borne geophysical methods can provide information for the characterization of the subsurface structure of the earth for aquifer investigations. Floating and towed transient electromagnetic (FloaTEM and tTEM) surveys provide resistivity soundings of the subsurface, which can be related to lithology and hydrogeology. In the TEM method, a primary electrical current is cycled through - Connect
John W Lane, Jr., Ph.D.
Senior Advisor for Water/InternationalSenior Advisor for Water/InternationalEmailPhoneMartin A. Briggs
Research HydrologistEmailBurke Minsley
Research GeophysicistEmailPhoneWade Kress
Assistant Director, Hydrologic Decision ScienceEmailPhoneDenis R LeBlanc (Former Employee)
Research Hydrologist