Three-dimensional Characterization of the Permeability Field of Heterogeneous Modern Streambed Deposits

M. B. R. Cardenas
University of Nebraska- Lincoln, Dept. of Geosciences, Lincoln, NE

The transport of fluids in geologic deposits is dominantly controlled by the spatial distribution of the media’s physical properties. Knowledge about these distributions has numerous applications in different fields of earth science. Information about these distributions is best acquired through understanding the active processes that form these heterogeneous deposits. To partially address the current lack of information, geoscientists mapped the two-dimensional distribution of properties of ancient outcrops. However, three-dimensional data on modern examples is severely lacking.

This study aims to address the lack of knowledge about the hydraulic properties of modern streambed deposits. The main goal of this research is to characterize the heterogeneity of a modern streambed, and to differentiate the streambed from underlying older alluvial deposits.

The study area is located on a bend of Prairie Creek in Nebraska. Hydraulic conductivity was measured at 456 test points in a 45 m x 20m x 1.2m portion of the streambed using a modified constanthead injection test (CHIT). Slug tests, in conjunction with CHIT’s, were conducted on the same test hole for comparison. Grain-size analyses of the cores taken around this point verify the sensitivity of both hydraulic tests.

Initial analyses show that the three-dimensional permeability pattern of the streambed can be used to delineate it from older underlying alluvial deposits. The depth of this interface will be verified further through ground-penetrating radar (GPR) surveys. Computations for the maximum depth of scour in the test site will also serve as a proxy for the depth of the interface.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid