29 Apr 2020

PUBLICATION NOTICE: Lake Providence to Old River Geomorphology Assessment

Abstract: This report integrates information from previous geomorphic studies coupled with new analysis to provide a comprehensive geomorphic characterization of the Lake Providence (River Mile [RM] 487.2 Above Head of Passes [AHP]) to Old River Control Complex, (RM 317 AHP) reach from the early-1800s to present. Individual components of this study included the following: historical geomorphic studies, development of an events timeline, specific gage records, stage and flow duration trends, trends in water surface slopes, bed material studies, suspended sediment data, channel geometry data, and effects of channel improvement features (cutoffs, dike, revetment, and dredging). These individual assessments were consolidated to develop an overall assessment of how the study reach has evolved since the early-1800s.

20 Apr 2020

PUBLICATION NOTICE: Application of Chirp Acoustic Sub-Bottom Data in Riverine Environments: Identification of Underlying Rocky Hazards at Cape Girardeau, Missouri, and Thebes, Illinois

ABSTRACT: Shallow acoustic reflection (chirp) data have been utilized to map the elevation of underlying stratigraphy in a wide range of aqueous environments. Of particular concern in riverine regions is the elevation of near-surface underlying rock that, if exposed during normal migration of sedimentary bedforms, can cause grounding and damage to vessels transiting the region during periods of low water. Given the ephemeral nature of the rock’s exposure, traditional surveying methods are insufficient to map rock when it is covered by a thin veneer of sediment, increasing the potential hazard. Accordingly, the US Army Corps of Engineers, St. Louis District, (MVS) explored the use of chirp sub-bottom surveys to identify buried rock within the Mississippi River in the vicinity of Cape Girardeau, MO, and Thebes, IL. Hazard maps showing the distribution of buried rock were generated, and the base of the mobile sediment layer was identified where possible. These data will allow MVS to accurately identify potentially hazardous regions during periods of low water. Although the study did not result in the complete mapping of all near-surface geologic hazards, regions that warrant further study are identified, and modifications to the original survey plan are provided to improve the accuracy of future data collection efforts.