Vertical and horizontal datums used in the Lower Mississippi Valley for US Army Corps of Engineers projects

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.

Personal Empires: Mapping, Local Networks, and the Control of Land in the Lower Mississippi Valley

The Louisiana and Florida territories sat at the intersection of empires in the late eighteenth century. Between 1750 and 1820 the area was controlled by the French and Spanish empires, the emerging United States of America, as well as the Choctaw, Creek, and Seminole nations. While political surveys produced images of the moving borders between sovereign powers, cadastral surveys show the constancy of local landowners. Landowners superseded national distinction and were a constant in an area in the midst of great change. As control of the region shifted, landowning families continued their way of life. The continued circulation of Spanish cadastral surveys after the transfer of the region to the United States of America shows how Spanish spatial representations of property ownership shaped the image of the Lower Mississippi Valley.

The Carolinas Campaign

This chapter examines the destructive Carolinas Campaign of 1864–1865 as a strategic culmination of the war by means of the transferal to the eastern theater of hard-war tactics that had long characterized the American Civil War’s western theaters. Infliction of property damage and psychological warfare expanded to wholesale destruction of towns and cities, widespread targeting of White civilians, male and female, summary punishment for irregular warfare, and the liberation of slaves in South Carolina as retribution for that state’s overwhelming and initial decision to secede. Federal commanders and soldiers alike, most from the West, were eager to implement this harder form of warfare in a theater known for a more traditional, limited mode of war making. The use of Black troops was most fully employed in the eastern theater in the Carolinas, much as it had been in the West in the Lower Mississippi Valley. As the war neared its end, the desperate Confederate commander in North Carolina, Gen. Joseph E. Johnston, unsuccessfully sought to prevent Maj. Gen. William T. Sherman’s troops from accomplishing destructive warfare, and thus victory, there. Sherman’s conciliatory surrender terms for Johnston’s army, which occurred days after Pres. Abraham Lincoln’s assassination, were rebuffed by angry Republicans in the cabinet, the War Department, and Congress, for whom leniency was now furthest from their minds.

Airborne geophysical surveys of the lower Mississippi Valley demonstrate system-scale mapping of subsurface architecture

The Mississippi Alluvial Plain hosts one of the most prolific shallow aquifer systems in the United States but is experiencing chronic groundwater decline. The Reelfoot rift and New Madrid seismic zone underlie the region and represent an important and poorly understood seismic hazard. Despite its societal and economic importance, the shallow subsurface architecture has not been mapped with the spatial resolution needed for effective management. Here, we present airborne electromagnetic, magnetic, and radiometric observations, measured over more than 43,000 flight-line-kilometers, which collectively provide a system-scale snapshot of the entire region. We develop detailed maps of aquifer connectivity and shallow geologic structure, infer relationships between structure and groundwater age, and identify previously unseen paleochannels and shallow fault structures. This dataset demonstrates how regional-scale airborne geophysics can close a scale gap in Earth observation by providing observational data at suitable scales and resolutions to improve our understanding of subsurface structures.

Automated characterization of ridge-swale patterns along the Mississippi River

The orientation of constructed levee embankments relative to alluvial swales is a useful measure for identifying regions susceptible to backward erosion piping (BEP). This research was conducted to create an automated, efficient process to classify patterns and orientations of swales within the Lower Mississippi Valley (LMV) to support levee risk assessments. Two machine learning algorithms are used to train the classification models: a convolutional neural network and a U-net. The resulting workflow can identify linear topographic features but is unable to reliably differentiate swales from other features, such as the levee structure and riverbanks. Further tuning of training data or manual identification of regions of interest could yield significantly better results. The workflow also provides an orientation to each linear feature to support subsequent analyses of position relative to levee alignments. While the individual models fall short of immediate applicability, the procedure provides a feasible, automated scheme to assist in swale classification and characterization within mature alluvial valley systems similar to LMV.

The Impact of Small Regional Economic Development Commissions: Is There Any Bang After Just a Few Bucks?

Despite substantial funding going to regional economic development programs, little is known about the benefits of some of the smaller, place-based programs. The authors extend the literature on regional commissions by analyzing the economic gains to the Delta Regional Authority (DRA). The DRA was founded in 2000 to provide enhanced development aid to 252 lower Mississippi Valley counties. Using data from 1997 to 2016, the authors assess the DRA’s impact on employment, income, migration, and poverty. One-to-one propensity score matching is used to generate counterfactual counties. Because of the endogenous nature of the treatment, the authors instrument for counties being included in the DRA using a dummy for whether the county is within the lower Mississippi watershed. The ensuing results reflect an estimation of the intent-to-treat benefits of the DRA. The authors find that the DRA is associated with income gains and decreases in unemployment; however, it has no impact on poverty or migration.

Predicting backward erosion piping hazard, Lower Mississippi Valley, USA

Backward erosion piping (BEP) is a form of internal erosion and common failure mode along levees. Despite over a century of study, predicting where BEP will initiate is still a considerable challenge. This study proposes a new model for predicting BEP initiation focused on the widest range of applicability. A logit model is trained using data from 15 sites along the Lower Mississippi Valley. The included parameters are independent of geography or geological regime and exhibit recorded or suspected correlations to BEP. Three significant factors (95% confidence interval) are retained for the final model: cumulative clay thickness within the blanket (odds ratio (OR) 0.520), critical gradient (OR 0.001) and exit gradient (OR 63.15). Receiver operating characteristics analysis indicates an area under the curve of 0.823. The model demonstrates 71% classification accuracy, a dramatic 10% increase over previous logit model attempts. Model results are most applicable within 150 m of the levee toe to predict new incidents of BEP initiation. The final model is a useful tool for BEP assessment and mitigation efforts.