25 Jul 2024

Regeneration Dynamics of Bottomland Hardwood Sites Following Prolonged Growing-Season Inundation

Abstract: The spring flood of the Mississippi River and backwater areas in 2019 resulted in large-scale flooding and was the longest-lasting flood event since the Great Flood of 1927. This flood event provided a rare opportunity to establish permanent plots in batture and backwater habitats to evaluate forest-stand dynamics following prolonged flooding. In this study, we evaluated postflooding conditions of forest overstory, midstory, and regeneration by establishing permanent plots at four locations subjected to varying amounts of flooding within the Mississippi River batture and the Yazoo–Mississippi Delta backwater region. Our results highlight oak regeneration success following the 2019 flood event as well as the utility and need to establish and monitor permanent plots to increase our understanding of floodplain forest dynamics in regions experiencing prolonged riverine flooding during the growing season.

17 May 2024

Rolling Prairie, Minnesota, Beneficial Use Area: A 100-Year Plan for Multiuse Land Management and Restoration Using Dredged Sediment

Purpose: Inland waterway dredged sediment management is challenged by a lack of capacity in existing dredged material confined disposal facilities (CDFs) and a lack of available land to place sediment near frequently dredged navigation channels. Navigation operation and maintenance (O&M) dredging, material management, and coordination costs are increasing, and alternative long-term solutions are required. In response, the US Army Corps of Engineers (USACE), St. Paul District has addressed the challenge by investigating regional sediment management and beneficial use of dredged material when updating navigation pool–specific dredged material management plans (DMMP). The recently completed Pool 5 DMMP planning identified a 950 acre (384 ha)[1] placement site consisting of several land parcels available from willing sellers that will accommodate a “100-year plan” for dredged material management (USACE 2019). This technical note describes the multiple-use site plan that creates sand prairie and wetland habitat, provides public access to sand stockpiles, and implements agriculture studies with the University of Minnesota to evaluate the benefits of dredged material (i.e., sand) amendments in alluvial cropland soils, which has not been widely investigated. The Rolling Prairie site will demonstrate benefits of “distributed DMMPs” in which thin-layer placement on agricultural land near dredging locations can supplement traditional disposal methods. It also shows the advantage of having a large placement site to achieve multiple objectives.

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.

15 Apr 2024

Development and Testing of the Sediment Distribution Pipe (SDP): A Pragmatic Tool for Wetland Nourishment

Abstract: Standard dredging operations during thin layer placement (TLP) projects are labor intensive as crews are necessary to periodically move the outfall location, which can have lasting adverse effects on the marsh surface. In an effort to increase efficiency during TLP, a novel Sediment Distribution Pipe (SDP) system was investigated. This system offers multiple discharge points along the pipeline to increase the sediment distribution while reducing pipeline movements. An SDP Modeling Application (SDPMA) was developed to assist in the design of SDP field applications by quickly assessing the pressure and velocity inside the discharge pipe and approximating the slurry throw distances. An SDP field proof of concept was performed during a two-phase TLP on Sturgeon Island, New Jersey, in 2020. The SDPMA was shown to be an accurate method of predicting performance of the SDP. The SDP was successful at distributing dredge material across the placement site; however, further research is warranted to better quantify performance metrics.

21 Mar 2024

A Beneficial Placement Decision Support Framework for Wetlands: Case Study for Mobile Harbor, USA

Abstract: The US Army Corps of Engineers, in the responsibility of maintaining navigational infrastructure, has a unique opportunity to improve coastal wetland resiliency and conserve coastal natural infrastructure through the beneficial use of dredged material for wetland restoration. Opportunities are widespread, and tools such as biophysical models can aid coastal managers in assessing habitat vulnerability and planning restoration. In this study, the Marsh Equilibrium Model was utilized in concert with observed data to predict future conditions and evaluate potential effects of beneficial use of dredged material to restore marshes in Mobile Harbor, Alabama. A range of site conditions and two restoration strategies were considered, and the subsequent impact to dredged material management area volumes evaluated. Results showed that wetland restoration via the thin-layer placement of dredged material can restore marsh elevation to combat sea level rise and conserve fill capacity at dredged material management areas. This approach is demonstrated for adoption nationwide by coastal managers.

28 Feb 2024

Ecological Model to Evaluate Borrow Areas in the Lower Mississippi River

Abstract: An aquatic analysis of constructing borrow areas adjacent to the main line levees in the Lower Mississippi River was conducted as part of an Environmental Impact Statement for upgrading the levee system. A Habitat Suitability Index (HSI) regression model based on field collections was developed to predict fish species richness as a function of the morphometry and water quality of borrow areas. The HSI score was multiplied by acres of borrow areas created during construction to obtain habitat units (HUs) for each alternative indicating a substantial gain of fishery habitat in the floodplain. Environmental features identified by the model to increase fish species richness and overall habitat heterogeneity include the shape of the pit (e.g., bowl-shaped with deep water rather than long rectangular with shallower water), the availability of littoral areas for fish spawning and rearing, using best management practices such as tree screens and bank stabilization to lower turbidity, adding islands, and creating sinuous shorelines. The project results in an overall gain in aquatic habitat by creating permanent or semi-permanent water bodies on the floodplain that our research indicates may be occupied by at least 75 species of fish contributing to the overall biodiversity of the lower Mississippi River.

18 Oct 2023

Guidelines for How to Approach Thin-Layer Placement Projects

Abstract: Historically, dredged material (DM) has been placed at the nearest available placement site. There has been an increasing trend of beneficial use projects recently, often using innovative methods. Thin-layer placement (TLP) involves one- to two-foot-thick DM placement, compared to traditional, thicker sediment placement applications, to restore coastal wetlands. The main idea of TLP is to promote the natural recolonization or reestablishment of habitat and benthic species. These guidelines present a roadmap of TLP’s evolution and offer easily digestible examples and considerations for TLP applications in wetlands and open-water environments. Offered as a tool to the practitioner, the eight chapters of these guidelines cover the history of TLP, characterization of the project area, setting goals and objectives, project design, construction considerations, monitoring and adaptive management, knowledge gaps, and future research needs. Several case studies are presented as examples of how such applications have been implemented and highlight lessons learned, particularly best-management practices. These guidelines offer consideration of TLP as a critical component in the project development phase, a tool for the sustainable management of DM, and a method that may create, maintain, enhance, or restore ecological function while supporting navigation channel infrastructure and providing flood risk management benefits.

10 Oct 2023

Proceedings from the Soft Substrate Island Design Workshop

Abstract: This report summarizes the activities of the Soft Substrate Design Workshop held virtually on 08 September 2021. The 28 participants from federal, state, local, and academic organizations discussed designing and constructing islands with soft sediments in inland waterways. They were introduced to the US Army Corps of Engineers’ (USACE) Engineering With Nature® (EWN®) initiative and the vision for Tri-County Planning Commission (Peoria, Illinois). An overview of collaborative projects using landscape architecture and EWN principles was provided. The focus of discussion was on two primary waterways, the Upper Mississippi River System, and Illinois River. Participants discussed their experience associated with designing and constructing islands with and on soft sediments prior to breakout sessions to discuss specific design and contracting elements. The groups were brought together to discuss design techniques that could be implemented in the Upper Mississippi River and Illinois River systems.

10 Oct 2023

Spatial Screening for Environmental Pool Management Opportunities

Abstract: US Army Corps of Engineers (USACE) reservoir projects significantly alter river ecosystem structure and function. Each project adheres to a defined set of operating rules to achieve primary objectives, which typically include flood risk management, hydropower, or navigation along with ancillary objectives for drinking water/irrigation, recreation, and natural resources management. Environmental flows (E-Flows) planning under the Sustainable Rivers Program has demonstrated new opportunities for environmental pool management (EPM; Theiling et al. 2021a, 2021b) that have no negative impact on other reservoir functions. In some locations, water level drivers can be managed to improve ecological outcomes, like wetlands, waterbirds, reptiles, and water quality, by altering the magnitude, timing, frequency, and duration of pool level changes that affect riparian and shoreline plant communities. Reservoirs with large delta areas may provide particularly important wetland or riparian habitat management along avian migratory pathways or in wildlife conservation regions (Johnson 2002). These large deltas can be identified and characterized using available satellite imagery, which along with water level habitat drivers available in hydrology databases, can be used to identify USACE reservoirs with good potential for EPM. A spatial analysis of USACE reservoirs capable to support EPM can be developed utilizing estimates of water occurrence, transition, and seasonality as well as surface elevation data derived from satellite imagery to assess geomorphology drivers. USACE water management records can be used to assess wetland drivers. Nationwide screening will be broken down into ecoregions to establish the anticipated geographic range of variation for wetland and riparian habitat drivers. Southwestern US reservoirs, for example, will have much different hydrology and fauna than Midwest and Eastern US reservoirs.

13 Sep 2023

Sensitivity of Sediment Transport Analyses in Dam Removal Applications

Abstract: Dam removal has become a widespread river management practice in the US for a variety of goals including ecosystem restoration, removing aging infrastructure, flood risk management, and recreation. The ability to forecast the sediment impacts of dam removal is critical to evaluating different management alternatives that can minimize adverse consequences for ecosystems and human communities. Tullos et al. (2016) identified seven Common Management Concerns (CMCs) associated with dam removal. Four of these CMCs; degree and rate of reservoir sediment erosion, excessive channel incision upstream of reservoirs, downstream sediment aggradation, and elevated downstream turbidity are associated with stored sediment release and changing fluvial hydraulics. There are a range of existing qualitative and quantitative tools developed to infer or quantify geomorphic implications of disturbances like these in river environments (McKay et al. 2019). This study investigated how a one-dimensional (1D) sediment transport model can inform these four CMCs, develop an approach for assessing sediment transport model sensitivity in the context of the Simkins Dam removal, and use sensitivity analyses to identify key uncertainties, which can inform data collection and model building for other dam removal projects. For the selected case study, model outputs including the mean effective invert change (MEIC) and eroded sediment volume from reservoir were highly sensitive to the variation of the reservoir sediment gradation and sorting method selection. These model outputs also showed some sensitivity to the selected transport functions. Erosion method sensitivity using the channel evolution method will vary depending on side slope and channel parameter selection.