Airborne Electromagnetics in the Marina Area Marina Coast Water District Ian Gottschalk and Rosemary Knight, Stanford University Aqua Geo Frameworks, Mitchell, NE 1
SkyTEM 2
Saltwater Intrusion cross section map view N Water Table Freshwater Sealevel Saltwater r o o l f a e a’ S a Saltwater Freshwater a a’ Tom Szenher 3
How do we learn about what lies underneath? ? 4
How do we learn about what lies underneath? ? 5
How do we learn about what lies underneath? ? 6
How do we learn about what lies underneath? Complex scenarios can be difficult to decipher, even with many wells drilled ? 7
Geophysics as a method to learn about the subsurface Goebel et al., 2017 8
Geophysics as a method to learn about the subsurface Goebel et al., 2017 9
Airborne Electromagnetics ? 10
Airborne Electromagnetics 30 m (100 ft) above the ground 80 km/hr (50 mph) ? 200-300m (650-1000ft) 250-350 km (150-220 miles) flown in a day 11
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Current flows around transmitter loop 13
Current flows around transmitter loop Primary magnetic field generated 14
Current flows around transmitter loop Primary magnetic field depth depends on electrical conductivity generated Eddy currents induced in the ground 15
Current flows around transmitter loop Secondary magnetic field Primary magnetic field detected by receiver coils generated Eddy currents induced in the ground 16
Resistivity profiles Elevation (m) 17
Resistivity profiles Fresh Saline Elevation (m) Saline Fresh 18
Resistivity measurements in wells A B Marina Salinas River Ocean Saline Fresh 19
Resistivity measurements in wells A B Marina Salinas River Ocean Data recorded in 2015 Saline Fresh 20
Resistivity measurements in wells A Saline B Marina Salinas River Ocean Fresh Saline Fresh 21
AEM data expands our knowledge A B Marina Salinas River Ocean Saline Fresh 22
AEM data expands our knowledge A B Marina Salinas River Ocean =Saline =Fresh 23
AEM data expands our knowledge A B Marina Salinas River Ocean =Saline =Fresh 24
A AEM data expands our knowledge B Salinas River Marina Saline Fresh 25
A AEM data expands our knowledge B Salinas River Marina Saline Fresh 26
A AEM data expands our knowledge B Salinas River Marina Saline Fresh 27
A AEM data expands our knowledge B Salinas River Marina Saline Fresh =Saline =Fresh 28
A AEM data expands our knowledge B Salinas River Marina Saline Fresh =Saline =Fresh 29
The data in action (video clip) 30
Moving forward geophysical properties that we measure 31
Moving forward geophysical properties that we measure hydrogeologic information that we want -water quality -hydraulic conductivity 32
Thank You 33
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