111-9 Subsurface Characterization of the Goodwin Creek Experimental Watershed Coupling Geophysical and Geotechnical Methods.

Session: Using Near Surface Geophysics to Investigate Geological Problems (Posters)

Poster Booth No.: 232

Presenting Author:

Md Samiul Alim

Authors:

Alim, Md Samiul¹, Holt, Robert M.², O’Reilly, Andrew M.³, Wodajo, Leti T.⁴, Mamud, Md Lal⁵, Rossell, William B.⁶, Hickey, Craig J.⁷, Lawal, Abdullateef⁸

Abstract:

The Goodwin Creek Experimental Watershed (GCEW), a headwater stream in north-central Mississippi, experiences significant surficial and internal soil erosion. This erosion, primarily driven by surface runoff and subsurface seepage within its riparian zone, leads to soil pipe collapses and gully formation, adversely impacting adjacent agricultural and pastoral lands. Furthermore, bed load transport from the stream channel and its margins contributes to localized slope instability. A critical knowledge gap exists regarding the geotechnical properties, specifically soil density and strength, of the region's surficial and subsurface strata. To address these characterization deficiencies, a research initiative was undertaken employing an integrated approach utilizing Electrical Resistivity Tomography (ERT) and the Standard Penetration Test (SPT). The 501-meter ERT survey successfully delineated a continuous aquifer system extending from the creek beneath both cropland and pasture. This aquifer transitions from an unconfined or thinly confined state (~1 m depth) over a brief pasture segment (<30 m) to a more confined condition (3-7 m depth) on either side of this outcrop. Investigation of the SPT data from five boreholes revealed that clay layers in agricultural land exhibited N-values exceeding 30, which were higher than those found in pastured areas. Despite this, the corrected N₆₀ value in the same clay strata was also found to be greater than 30 in most boreholes, except for the outcrop location. A decline in N-value was progressively noted in cropland upon reaching the aquifer, which differed from the uniform N-value behavior characteristic of sandy formation within the pastureland aquifer. A comparative assessment demonstrated a consistent trend between inverted ERT resistivity values and SPT N-values across most boreholes, with the outcrop zone being an exception. Notably, ERT values exhibited a strong correlation with core samples obtained from all five borehole locations, with resistivity generally exceeding 200 ohm-m for N-values over 30.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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