Characteristics of Fluvial Bed Material in and adjacent to Instream Aggregate Extraction Pits along the Bouie River in Hattiesburg, Mississippi

Joseph Grimball¹ and Franklin T. Heitmuller²
¹Department of Geology, University of Louisiana at Lafayette, P.O. Box 44530, Lafayette, Louisiana 70504
²Department of Geography and Geology, University of Southern Mississippi, Hattiesburg, Mississippi 39406

A characterization of channel-bed and bottom sediments adjacent to and along a 3.6 mi (5.8 km) reach of inundated aggregate extraction pits along the Bouie River in Hattiesburg, Mississippi, was made to infer compositional differences upstream and downstream of the disturbed reach. Sedimentary data reveal the following: (i) organic carbon content of fine-grained pit bottom sediments systematically increases with depth and, thus, exhibits an inverse relationship with particle size; (ii) maximum organic carbon content of pit bottom sediments approaches 6.0%; (iii) particle size distributions of gravel and sand channel-bed deposits upstream and downstream of the extraction pit reach are quite similar, with median values mostly ranging from 10 to 20 mm for gravelly sites and 0.38 to 0.40 mm for sandy sites; (iv) pit bottom sediments display a general downstream-fining sequence from medium to coarse sands near channel inflows to finegrained muds near pit outflows; and (v) variability in particle-size trends of pit bottom sediments is attributed to a subaqueous delta slope and relatively narrow zones that exhibit greater flow velocities during infrequent floods. The results indicate that welldocumented channel changes downstream of the extraction pit reach are not necessarily contingent on changes to bed material composition, but are attributed to the overall decrease in sediment load. Furthermore, downstream sediment loads will not be fully restored to pre-disturbance conditions until the extraction pits are completely infilled with basal muds, overlying delta slope sands, and sand and gravel channel bars.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012