Hydrogeophysics: Applications of Geophysical Techniques in Hydrogeological Investigations

Transcription

1 Hydrogeophysics: Applications of Geophysical Techniques in Hydrogeological Investigations Lanbo Liu ( 刘澜波 ) Civil & Environmental Engineering University of Connecticut (Lanbo.Liu@UConn.edu) Tsinghua University, July 12, 2014

2 Outline Introduction Advantages for using hydrogeophysics A case example

3 Geophysics and Hydrogeophysics Geophysics enables us to "see" into the subsurface by interpreting the contrast in physical properties of earth materials. The physical properties of concern measured include: density, elastic modulus, electrical conductivity, dielectric permittivity, magnetic susceptibility, natural radioactivity, and thermal conductivity etc. The non-invasive investigation of subsurface (from directly below the surface to the depths of 100's of meters) material properties and conditions pertinent to surface water/groundwater studies through measuring, analyzing and interpreting physical fields at the surface.

4 Geophysics is the useful tool to characterize near-surface material properties at field scale Observation: characterizing and monitoring the environment Process understanding and modeling Management strategies and decision support

5 We need accurate and reliable 3D models of subsurface properties for: Motivation Prediction of contaminant migration Design and operation of remediation systems Evaluation and management of water resources Basic understanding of hydrologic and hydrogeologic processes?

6 We need accurate and reliable 3D models of subsurface properties for: Prediction of contaminant migration Design and operation of remediation systems Evaluation and management of water resources Basic understanding of hydrologic and hydrogeologic processes Motivation

7 Motivation Hydrologic Data: Sparse and local Require boreholes Expensive Non-unique interpretation How do we fill in the gaps???? Geostatistics, Geophysics

8 Electrical resistivity Chargeability (IP) Dielectric permittivity Radar attenuation Seismic velocity Seismic attenuation Etc. Motivation Need methods to capitalize on densely sample geophysical data

9 Advantages of using hydrogeophysics Geophysics offers advantages over conventional sampling to the hydrologist because of: High data sampling density Larger measurement volume more consistent with modeling needs Relative lower cost of measurements may avoid use of boreholes and/or allow quicker sampling Minimally invasive may allow investigations without affecting the hydrology of the system

10 from Geotimes, May x200 50x50 20x20 10x10 5x5 Noise free 10% Gaussian noise added

11 Detection of saltwater intrusion along the Noyo River

12 Electrode locations for DC resistivity Surveys East Lot of Building W3 W2 AGI 4 Personnel Gate N Wells from previous extraction system Hydraulic Test Wells Proposed electrode location Utility Pole 20 Vehicle Gate 20 Vehicle Gate 60 (Inject) W1 Water Storage Tanks Utility Shed Note: Layout displayed with 10 x 10 grid

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17 Findings The maximum groundwater flow occurs in the lower aquifer (~15 ft); The time-lapse resistivity tomography results suggest an average flow rate of ~ 0.3 ft/day to WNW. The hydraulic gradient is quite low (~0.1m/10m) so that the permeability is about 3x10-4 m/s. The horizontal diffusivity is about 0.09 cm 2 /sec.

18 Summary Geophysical technology should and can play an important role in hydrologic investigation. Successfulness of hydrogeophysical application depends on choosing the right tools and right combination of different techniques

19 Thank you and questions please.

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21 Geophysical techniques Seismic refraction/reflection, tomography Electric resistivity tomography (ERT) Spontaneous potential (SP) Induced Polarization (IP) Geomagnetic survey Electromagnetic Induction (EMI) Ground penetrating radar (GPR) Nuclear magnetic resonance (NMR) Geophysical well logging