27 Sep 2022

Wave Attenuation of Coastal Mangroves at a Near-Prototype Scale

Abstract: A physical model study investigating the dissipation of wave energy by a 1:2.1 scale North American red mangrove forest was performed in a large-scale flume. The objectives were to measure the amount of wave attenuation afforded by mangroves, identify key hydrodynamic parameters influencing wave attenuation, and provide methodologies for application. Seventy-two hydrodynamic conditions, comprising irregular and regular waves, were tested. The analysis related the dissipation to three formulations that can provide estimates of wave attenuation for flood risk management projects considering mangroves: damping coefficient β, drag coefficient CD, and Manning’s roughness coefficient n. The attenuation of the incident wave height through the 15.12 m long, 1:2.1 scale mangrove forest was exponential in form and varied from 13%–77%. Water depth and incident wave height strongly influenced the amount of wave attenuation. Accounting for differences in water depth using the sub-merged volume fraction resulted in a common fit of the damping coefficient as a function of relative wave height and wave steepness. The drag coefficient demonstrated a stronger relationship with the Keulegan–Carpenter number than the Reynolds number. The linear relationship be-tween relative depth and Manning’s n was stronger than that between Manning’s n and either relative wave height or wave steep

11 Aug 2022

Realizing Multiple Benefits in a Southeast Louisiana Urban Flood Control Project through Application of Engineering With Nature® Principles

PURPOSE: The application of Engineering With Nature® (EWN®) principles in urban environments and watersheds within and outside the US Army Corps of Engineers (USACE) is increasing. Extreme rainfall events have triggered the need and development of more sustainable urban infrastructure in urban areas such as New Orleans, Louisiana. This technical note documents a USACE–New Orleans District (MVN) project that successfully applied EWN principles in an urban landscape to reduce flood risk while providing other environmental, social, economic, and engineering benefits to both the community and the environment.

4 Aug 2022

Engineering With Nature® Principles in Action: Islands

Abstract: The Engineering With Nature® (EWN) Program supports nature-based solutions that reduce coastal-storm and flood risks while providing environmental and socioeconomic benefits. Combining the beneficial use of dredged sediments with the restoration or creation of islands increases habitat and recreation, keeps sediment in the system, and reduces coastal-storm and flood impacts. Given the potential advantages of islands, EWN seeks to support science-based investigations of island performance, impacts, and benefits through collaborative multidisciplinary efforts. Using a series of case studies led by US Army Corps of Engineers (USACE) districts and others, this technical report highlights the role of islands in providing coastal resilience benefits in terms of reducing waves and erosion as well as other environmental and socioeconomic benefits to the communities and the ecosystems they reside in.

27 Jun 2022

Tar-Pamlico and Neuse River Basins, North Carolina, Geomorphic Summary Report

Abstract: The Tar-Pamlico and Neuse River Basins are neighboring basins in eastern North Carolina, both originating in the piedmont physiographic region, transitioning to coastal plains, and emptying into Pamlico Sound. The Pittsburgh District is responsible for the continued efforts to assist local sponsors with managing these basins and submitted a Water Operations Technical Support (WOTS) request. The WOTS program, funded by Headquarters, US Army Corps of Engineers, provides funding for the Coastal and Hydraulics Laboratory (CHL) to provide technical assistance to develop innovative solutions to water resource problems. The objectives of this study are to identify flood risk management alternatives to address the accumulation of woody debris in the channel systems. CHL compiled existing conditions information and researched current and potential new methods for managing woody debris to provide a comprehensive list of recommendations. The results and recommendations are provided in this document.

9 May 2022

Three-Dimensional Underseepage Evaluation for Profit Island Vicinity Levee, North of Baton Rouge, Louisiana

Abstract: This project developed a three-dimensional (3D) seepage model to evaluate efficiency of 84 relief wells and factors of safety (FoS) along the Profit Island vicinity levee (PIVL), north of Baton Rouge, Louisiana. The PIVL model was built based on US Geological Survey MODFLOW-USG. Moreover, a 3D seepage model of RocScience RS3 was also built for a specific study of relief well experiments conducted by the US Army Corps of Engineers in the 1930s and 1940s. The PIVL model was calibrated with measured piezometric head data and relief well flow rates in 1997. Six flood scenarios were conducted: the extreme flood (56 feet), design flood (52.4 feet), 1997 flood (50 feet), 2008 flood (49.22 feet), 2017 flood (45.55 feet), and 2018 flood (49.1 feet). The modeling results show that FoS are all above 1.5 given relief wells at the 1997 design condition. FoS calculated by the blanket theory are more conservative than those by the PIVL model because designed discharge rates were not observed in the field. In comparison with measured flow rates in 2008, the PIVL modeling result indicates potential clogging at many relief wells. New piezometric data and well discharge data are recommended to re-evaluate factors of safety.

7 Jan 2022

Hydrodynamics in the Morganza Floodway and Atchafalaya Basin, Report 3: Phase 3; A Report for the US Army Corps of Engineers, MRG&P

Abstract: The Morganza Floodway and the Atchafalaya Basin, located in Louisiana west of the Mississippi River, were evaluated using a two-dimensional Adaptive Hydraulics model. Prior to this study, Phase 1 and 2 model studies were performed that indicated that the existing floodway may not be able to pass the Project Design Flood discharge of 600,000 cubic feet per second due to levee overtopping. In this study, all elevations of exterior and interior levees were updated with current crest elevations. In addition, the Phase 3 effort evaluated the sensitivity of the floodway’s flow capacity to variations in tree/vegetation density conditions. These adjustments in roughness will improve the understanding of the role of land cover characteristics in the simulated water surfaces. This study also provides a number of inundation maps corresponding to certain flows through the Morganza Control Structure.

6 Dec 2021

Development of a Sand Boil Testing Laboratory and Preliminary Results

Purpose: To document the purpose, use, and preliminary results of a full-scale sand boil generator developed at the Geotechnical and Structures Laboratory.

29 Nov 2021

Engineering With Nature: The Role of Mangroves in Coastal Protection

Purpose: The purpose of this Engineering With Nature technical note (EWN TN) is to review previous studies of mangroves as a nature-based adaptation alternative for coastal protection and flood hazard mitigation.

13 Oct 2021

Engineering With Nature®: Supporting Mission Resilience and Infrastructure Value at Department of Defense Installations

Abstract: This book illustrates some of the current challenges and hazards experienced by military installations, and the content highlights activities at seven military installations to achieve increased resilience through natural infrastructure.

29 Sep 2021

Backward Erosion Testing: Magnolia Levee

Abstract: Using a confined flume device, an experimental study investigated the critical horizontal gradient of soils obtained from a site identified as potentially vulnerable to backward erosion piping (BEP). Tests were conducted on glacial outwash material obtained from a sand and gravel quarry in the vicinity of Magnolia Levee in the community of Magnolia, OH. The two bulk samples collected from the quarry had similar grain-size distributions, grain roundness, and depositional environments as the foundation materials beneath the levee. Samples were prepared at various densities and subjected to gradual increases of flow in a wooden flume with an acrylic top until BEP was observed. The critical average horizontal gradient ranged from 0.21 to 0.30 for a bulk sample with a coefficient of uniformity of 1.6, while tests conducted on a bulk sample with a coefficient of uniformity of 2.5 yielded critical average horizontal gradients of 0.31 to 0.36. The critical average gradients measured during these tests compared favorably to values in the literature after applying adjustments according to Schmertmann’s method.