10 Sep 2025

Geology, Geomorphology, and River Engineering in the Memphis-to-Rosedale Reach, Lower Mississippi River

Abstract: This study examines the geology and geomorphology of the Mississippi River between Memphis, Tennessee, and Rosedale, Mississippi, with a focus on the Tertiary (65 to 2 million years) surface and how the present-day river has impacted this surface. Previous mapping efforts involving the Tertiary surface by the US Army Corps of Engineers are reviewed. Relevant maps are included as plates herein to facilitate wider dissemination. Today’s channel has deepened through time due to river engineering, which includes oxbow cutoffs and hardening of river banks with revetment and training dikes to prevent uncontrolled bank caving and channel migration. The course of the river was fixed in place by 1962. The thalweg of the river intersects the Tertiary surface at Helena, Arkansas, at the Hardin oxbow cutoff, and near the vicinity of Memphis, Tennessee. At these three locations, the Tertiary surface occurs at shallow elevations and in close proximity to where Tertiary sediments outcrop. A deeply buried alluvial valley is present in the Tertiary surface. Erosion of Jackson Group sediments in this valley exposes the underlying Claiborne Group sediments. Jackson and Sunflower oxbow cutoffs occur in the deepest parts of the alluvial fill.

30 Apr 2024

Evaluating Soil Conditions to Inform Upper Mississippi River Floodplain Restoration Projects

Abstract: The US Army Corps of Engineers (USACE) has designed and constructed thousands of acres of ecosystem restoration features within the Upper Mississippi River System. Many of these projects incorporate island construction to restore geomorphic diversity and habitat, including floodplain forests. Soils are the foundation of the ecological function and successful establishment of floodplain forests as they are the basis through which plants obtain water and nutrients and provide critical ecosystem services. To improve floodplain forest island restoration outcomes, three natural and four recently (<10 years) constructed restoration sites were studied to compare soil physical, chemical, microbial, and fungal characteristics. Constructed islands had lower soil organic matter and dissolved organic carbon and differed in nutrient concentrations, bacterial assemblages, and fungal communities compared to reference sites. However, soil enzyme activity and some microbial community characteristics were functionally similar between the natural and created sites. Results align with previously established restoration trajectory theories where hydrological and basic microbial ecosystem functions are restored almost immediately, but complex biologically mediated and habitat functions require more time to establish. Data from this and future studies will help increase the long-term success of USACE floodplain forest restoration, improve island design, and help develop region-specific restoration trajectory curves to better anticipate the outcomes of floodplain forest creation projects.

6 Jan 2022

Vertical and Horizontal Datums Used in the Lower Mississippi Valley for US Army Corps of Engineers Projects

Abstract: Six geodetic datums have been used by the US Army Corps of Engineers (USACE), Mississippi River Commission (MRC), for river surveys in the Lower Mississippi Valley (LMV). These legacy elevation datums are the Cairo datum, the Memphis datum, the Mean Gulf Level (MGL), the Mean Sea Level (MSL), the National Geodetic Vertical Datum (NGVD) 1929, and the North American Vertical Datum 1988 (NAVD88). The official geodetic datum currently prescribed by the USACE is NAVD88 (USACE 2010). In addition to these different geodetic datums, hydraulic datums are in use by the USACE for rivers, lakes, and reservoir systems. Hydrographic surveys from the Mississippi River are typically based on a low water pool or discharge reference, such as a low water reference plane (LWRP), an average low water plane (ALWP), or a low water (LW) plane. The following technical note is intended to provide background information about legacy datums used in the LMV to permit comparison of historic maps, charts, and surveys pertaining to the Mississippi River in the LMV. The purpose of this report is to provide background information and history of different published horizontal and vertical datums used for presentation of hydrographic survey data from the Mississippi River. The goal is to facilitate understanding of differences with comparison to other historic surveys for change-detection studies along the river. Conversion values are identified herein for the earlier surveys where appropriate, and methods are presented here to evaluate the differences between earlier and later charts and maps. This report is solely intended to address the LMV area and historic surveys made there. This note is not applicable to areas outside of the LMV. Throughout this technical note, historic hydrographic surveys and data from the Memphis, TN, to Rosedale, MS, reach will be used as examples of features of interest for discussion purposes. Selected historic hydrographic survey sheets at Helena, AR, are included as Plates 1 to 3 (Appendix C) of this document and will be used as examples for discussion purposes.