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.

Application of an Optimization/Simulation Model for the Real-Time Flood Operation of River-Reservoir Systems with One- and Two-Dimensional Unsteady Flow Modeling

An application is presented of a new methodology for the real-time operations of river-reservoir systems. The methodology is based upon an optimization/simulation modeling approach that interfaces optimization with a one and/or two-dimensional unsteady flow simulation model (U.S. Army Corps of Engineers HEC-RAS). The approach also includes a model for short-term rainfall forecasting, and the U.S. Army Corps of Engineers HEC-HMS model for rainfall-runoff modeling. Both short-term forecasted rainfall in addition to gaged streamflow data and/or NEXRAD (Next-Generation Radar) can be implemented in the modeling approach. The optimization solution methodology is based upon a genetic algorithm implemented through MATLAB. The application is based upon the May 2010 flood event on the Cumberland River system in the USA, during which releases from Old Hickory dam caused major flooding in the downstream area of Nashville, TN, USA, and allowed the dam to be placed in an emergency operational situation. One of the major features of the modeling effort and the application presented was to investigate the use of different unsteady flow modeling approaches available in the HEC-RAS, including one-dimensional (1D), two-dimensional (2D), and the combined (1D/2D) approach. One of the major results of the application was to investigate the use the different unsteady flow approaches in the modeling approach. The 2D unsteady flow modeling, based upon the diffusion wave approach, was found to be superior for the application to the Cumberland River system. The model application successfully determined real-time operations that would have maintained the flood water surface elevations at the downstream control point in Nashville below the 100-year return period river water surface and maintaining the gate openings at the Old Hickory Dam from reaching an emergency operational situation, which could have caused major losses at the dam.

Field Jet Erosion Tests on Benbrook Dam, Texas

This report summarizes the results of eight field Jet Erosion Tests (JETs) performed on Benbrook Dam, TX. The results from these tests will be used by the U.S. Army Corps of Engineers, Fort Worth District, in assessments of the erosion resistance of the Benbrook Dam with regards to possible overtopping by extreme flooding. The JETs were performed at four different locations, i.e., two locations at the lowest crest elevation and two locations at the mid-slope face of the downstream embankment. Variations in estimated critical hydraulic shear stress and erosion rate values may have been caused by differences in soil composition, i.e., when the material changed from silt/sand to clay. The resulting values of the Erodibility Coefficient, Kd, and Critical Stress, τc, are very useful information in assessing the stability of Benbrook Dam during an overtopping event. Because of the observed natural variability of the materials, combining the erosion parameters presented in this report with the drilling logs and local geology will be imperative for assessing erosion-related failure modes of Benbrook Dam.

Predictions of the Climate Change-Driven Exodus of the Town of Tangier, the Last Offshore Island Fishing Community in Virginia's Chesapeake Bay

Sea-level rise (SLR) has been confirmed to be accelerating globally due to human-influence driven climate change. Multiple studies suggest many coastal communities will soon be inundated by SLR. Prior to inundation, habitable uplands above the high tide line first convert to uninhabitable wetlands, forcing human exodus. Habitability, not the land's presence above the low tide line, drives exodus. We determined the time left for uplands of the Town of Tangier of VA, USA to be converted to wetlands, analyzed local sea level rise data to determine the best local SLR scenario (low, mid, or high) fit, then compared upland conversion rate to the rate of population decline. The upland landmass constituting the Town of Tangier declined from 32.8 to 12.5 ha (1967–2019), accelerating over time, with complete conversion to wetlands predicted by 2051. The US Army Corps of Engineers (USACE) high SLR curve is the best fit to the local tide gauge's raw data (1967–2020), indicating local sea level rise has rapidly accelerated in recent decades, concomitant with the rate of wetland conversion. The Town's population, in decline since the 1930s, accelerated rapidly after 1980 and trended downward in tandem with the conversion of the Town's uplands to wetlands. We also estimated costs to relocate the Town as well as for a conceptual plan to provide long-term stability to the Town and Island of Tangier.

Thin layer placement for marsh enhancement: Planning, design, construction, and monitoring considerations

Thin layer placement (TLP) is the purposeful placement of thin layers of sediment in an environmentally acceptable manner to achieve a target elevation or thickness. TLP is used for a variety of purposes, such as sediment management, beneficial use of dredged material (DM), and ecological enhancement. The term “thin” is used to distinguish TLP from other methods of sediment placement in which sediments are applied in layers on the order of several meters thick. In this paper, DM disposal refers to the deposition of sediment in a location and manner where no beneficial use is attained; with DM placement the sediment is used to benefit society and the environment. The application of thin layers of sediment has advantages over more traditional, thicker sediment applications in environments where these thicker layers pose potential challenges to natural resources, infrastructure, navigation, or other assets. Although TLP projects are most often conducted in wetlands, there are open-water applications as well. But because TLP is relatively early in its development, there is a dearth of design and construction information and guidance available to practitioners. This paper provides a high-level summary of pending national TLP guidance being developed by the authors on behalf of the U.S. Army Corps of Engineers’ Engineer Research and Development Center (USACE ERDC).

Building Information Modelling Usage in Federal Hydropower Design and Construction Management

The use of Building Information Modeling (BIM) is widespread within the engineering and construction industry, with huge strides in both usage and technological advances in the past two decades. The benefits of design collaboration, communication, visualization, and risk mitigation are untold. The U.S. Army Corps of Engineers foresaw the benefits of BIM and began to write policy for its mandatory use across the enterprise in the early 2000s. As BIM technology evolved, the U.S. Army Corps of Engineers has struggled to keep pace with the speed of industry but continue to make improvements to policy and more widespread usage across the enterprise. The MILCON program sees widespread use in the planning and design phases using BIM for visualization, communication, creation of 2D construction drawings, and rough estimating. BIM usage stops short in two major areas of the U.S. Army Corps of Engineers work: hydropower rehabilitation and construction management. Professionals from the U.S. Army Corps of Engineers in design management, hydropower engineering, and construction management all agreed that BIM, utilized and implemented properly, can have a very strong impact in each major field that would improve efficiencies, aid stakeholders in better understanding of complicated design concepts, and realize a more streamlined construction management process for complicated hydropower work. Through literature review and interviews with construction professionals, this research studied how BIM is being used within the U.S. Army Corps of Engineers, specifically within hydropower rehabilitation programs, for design and construction management. This research also focused on how private industry has been and is currently using BIM in construction management, and to correlate how processes used in private industry may be used on hydropower generation unit rehabilitation projects at USACE-owned facilities.

Misremembering risk in the age of hurricanes: The Rhode Island Coast in the 1930s–1950s

This paper explores the lost history of New England hurricanes and how the “return” of hurricanes challenged understandings of the vulnerabilities of coastal communities due to weather. A series of severe New England hurricanes from 1938 to 1954 forced Rhode Islanders to reassess coastal vulnerabilities and protection strategies. Before the hurricane of ‘38, Rhode Islanders lived with the vulnerability of seasonal erosion and winter storms but believed their state was, and would remain, safe from hurricanes. In a new era of the shore-at-risk, the U.S. Army Corps of Engineers re-wrote the forgotten history of coastal dangers. Dense development along Narragansett Bay and the economic incentives to safeguard Providence, Rhode Island’s largest city, led state and federal authorities to address the environmental vulnerabilities wrought by hurricanes. The result was the U.S. Army Corps of Engineers’ pathbreaking analysis of the tidal dynamics of Narragansett Bay. Investigating human responses to coastal environmental threats, this paper reveals the political and engineering histories that attempted to reconcile hurricanes, risk, and coastal vulnerability in the state at mid-century.

Mobile Harbor, Alabama navigation study : ship simulation report

Mobile Bay is a large estuary located in the southwest corner of Alabama, which connects to the Gulf of Mexico. Mobile Harbor contains the only port in the state that supports ocean-going vessels. Some of the larger vessels calling on the port experience transit delays and limited cargo capacity, so a study was conducted by the US Army Corps of Engineers, Mobile District (CESAM), and the Alabama State Port Authority to investigate channel improvements. In 2017, the US Army Engineer Research and Development Center (ERDC) assisted CESAM in screening proposed deepening and widening alternatives in Mobile Bay by completing a Feasibility Level Ship Simulation (FLSS) study using the ERDC Ship/Tow Simulator. These lower-resolution databases from the FLSS study were used as a foundation to complete a more robust navigation study in 2020 to test the proposed modifications to Mobile Harbor. During this study, three main areas were focused on: a bend easing, a passing lane, and a turning basin. Testing of the proposed design was evaluated over the course of 2 weeks with eight pilots. Assessment of the proposed modifications was accomplished through analysis of ship simulations completed by experienced local pilots, discussions, track plots, run sheets, and final pilot surveys.

Application of an Optimization/Simulation Model for the Real-time Flood Operation of River-Reservoir Systems with One and Two-Dimensional Unsteady Flow Modeling

An application is presented of a new methodology for the real-time operation of flood control reservoir gate control operations of river-reservoir systems to minimize flooding. The methodology is based upon an optimization/simulation modeling approach that interfaces optimization with a one and/or two-dimensional unsteady flow simulation model (U.S. Army Corps of Engineers HEC-RAS). The approach also includes a model for short-term rainfall forecasting and the U.S. Army Corps of Engineers HEC-HMS model for rainfall-runoff modeling. Both short term forecasted rainfall in addition to gaged streamflow data and/or NEXRAD (Next-Generation Radar) can be implemented in the modeling approach. The optimization solution methodology is based upon a genetic algorithm implemented through MATLAB. The application is based upon the May 2010 flood event on the Cumberland River system in the USA, during which releases from Old Hickory dam caused major flooding downstream area of Nashville, Tennessee area. One of the major features of the modeling effort and the application presented was to investigate the use of different unsteady flow modeling approaches available in the HEC-RAS) including one-dimensional (1D), two-dimensional (2D), and the combined (1D/2D) approach. One of the major results of the application was to investigate the use the different unsteady flow approaches in the modeling approach. The 2D unsteady flow modeling is based upon the diffusion wave approach was found to be superior for the application to the Cumberland River system

Water level management for enhanced fish and wildlife habitat production in Upper Mississippi River navigation pools : an Engineering with Nature® review of practice

There is a long history of fish and wildlife management associated with Upper Mississippi River navigation dams owned and operated by the US Army Corps of Engineers (USACE). Many operational changes have been made to improve aquatic habitat, with recent emphasis on pool-scale drawdowns to enhance wetland benefits without affecting navigation or other uses. This special report describes projects successfully incorporating Engineering With Nature® principles in a review of the physical setting and historical fish and wildlife habitat management efforts using Upper Mississippi River System navigation dams. We reviewed 80 years of adaptation and lessons learned about how to integrate navigation operations and wildlife management. Several experiments have revealed the capacity to produce thousands of hectares of emergent and submersed aquatic plants, restoring much-needed riparian habitat for a variety of aquatic, wetland, and avian species.