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Tag: Sedimentation and deposition
  • 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.
  • Effects of Sedimentation on Three Hawaiian Coral Species under Laboratory Conditions

    Abstract: Sedimentation can occur near a dredge operation in pulses over days, and potentially impact coral reefs occurring in close proximity. To improve the ability to predict the effects of dredging on corals, the effects of sedimentation in two 18-day experiments were studied for three common coral species representing different morphologies. In a laboratory setting, coral fragments were exposed to four sedimentation concentrations dosed every four days ranging from 0 to 60 mg cm-2. Separate experiments were performed in series, once with fine grain sediment and repeated with a coarse grain sediment. A 30-day sediment free observation period followed each experiment. Coral responses were measured throughout the experiment and at the end of the 18-day exposure and 30-day sediment free observation period. Photosynthetic yield, lipid ratios, tissue color, tissue loss, growth, and sediment cover varied among the treatment groups. All coral species were minimally affected when sediment concentrations were at or below 6 mg cm-2. P. meandrina and P. lobata experienced the most sediment coverage and tissue loss when exposed to sediment concentrations >30 mg cm-2 for either sediment. M. capitata experienced no sediment coverage or tissue loss when exposed to either sediment, but a reduction in photosynthetic yield at 60 mg cm-2 fine grain sediment was observed. During the 30-day post-exposure sediment free observation period, P. meandrina tissue loss continued, P. lobata nearly completely regrew lost tissue, while M. capitata showed no lingering effects. This study improves the US Army Corps of Engineers (USACE) ability to estimate the impacts of dredging on coral reefs.
  • Houston Ship Channel Numerical Model Update and Validation

    Abstract: The Houston Ship Channel (HSC) is one of the busiest deep-draft navigation channels in the United States and must be able to accommodate increasing vessel sizes. The US Army Corps of Engineers, Galveston District (SWG), requested the US Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, update and revalidate a previously developed three-dimensional Adaptive Hydraulics (AdH) hydrodynamic and sediment model of the HSC, Galveston, and Trinity Bays. The model is necessary for analyzing potential impacts on salinity, sediment, and hydrodynamics due to alternatives designed to reduce shoaling in the HSC. SWG requested an updated validation of the previously developed AdH model of this area to calendar years 2010 and 2017, utilizing newly collected sediment data. Updated model inputs were supplied for riverine suspended sediment loads as well as for the ocean tidal boundary condition. The updated model shows good agreement to field data in most conditions but also indicates potential issues with freshwater flow inputs as well as the ocean salinity boundary condition.
  • Evaluation of Structural and Operational Alternatives to Optimize the Distribution of Water and Sediment in the Passes of the Mississippi River

    Abstract: Mississippi River shoaling and dredging processes in the vicinity of Head of Passes and in Southwest Pass were investigated. Existing rates of deposition and dredging were determined using near-daily eHydro bathymetric surveys, National Dredging Quality Management dredge operating data, and geospatial processing steps developed for this study. These surveys provide a means to characterize the highly dynamic and variable sedimentation patterns observed in the navigation channel. The HEC-6T one-dimensional numerical sedimentation model was used to evaluate possible modifications to the distribution of water and sediment in the Mississippi River near Head of Passes in an attempt to reduce shoaling in the navigation channel. The model was used to evaluate the effects of partial closures of several distributaries downstream from Venice and to evaluate the effects of channel widening and channel deepening adjacent to the Hopper Dredge Disposal Area at Head of Passes. In this study, various structural alternatives were compared to a base test that represented existing conditions. Sedimentation and dredging effects were projected 50 years into the future.
  • Geomorphic Assessment of the St. Francis River: Between Wappapello Lake and Lake City

    Abstract: The St. Francis River is a complex system that lies in the historic floodplain of the Mississippi and Ohio Rivers. The basin has undergone extensive anthropogenic modifications, including reservoir construction, large-scale channelization, and construction of leveed floodways. Several analyses of available gage data, lidar data, and historical research have provided a picture of geomorphic trends and an overall understanding of the river’s stability. The types of analysis used to determine trends included yearly low stage plots, stage-duration curves, specific gage analysis, water surface slopes, and stream power changes. The results from these analyses were synthesized to develop an overall assessment of the reach. Channel cutoffs resulted in a significant decrease in channel length and sinuosity and triggered geomorphic change throughout the river. Immediately following channelization, dramatic decreasing trends in stage were observed for Fisk and Dekyn’s Store, while St. Francis and Holly Island began to aggrade. Slopes and stream power were significantly increased for the upper portion of the study area and showed a decreasing trend for the lower reach.
  • Geomorphic Feature Extraction to Support the Great Lakes Restoration Initiative’s Sediment Budget and Geomorphic Vulnerability Index for Lake Michigan

    Purpose: This Coastal and Hydraulics Engineering technical note (CHETN) details a Geographic Information Systems (GIS) methodology to produce advanced lidar-derived datasets for use in a coastal erosion vulnerability analysis conducted by the US Army Corps of Engineers (USACE) and other federal partners for the Great Lakes Restoration Initiative (GLRI).
  • A Review of Tidal Embayment Shoaling Mechanisms in the Context of Future Wetland Placement

    Abstract: Wetland construction in tidally influenced embayments is a strategy for beneficial use of sediment dredged from nearby navigation channels. These projects have the potential to alter basin morphology, tidal hydrodynamics, and shoaling trends. This special report provides a broad review of the literature related to engineering-induced changes in tidal range, salinity, tidal prism, tidal asymmetry, and other known causes of shoaling. Each potential shoaling mechanism is then evaluated in the context of wetland placement to provide a foundation for future beneficial use research. Based on a compilation of worldwide examples, wetland placement may reduce tidal amplitude and enhance ebb current dominance, thus reducing shoaling rates in the channels. However, constructed wetlands could also reduce the embayment’s tidal prism and cause accelerated shoaling relative to the pre-engineered rate. Because constructed wetlands are often created in conjunction with navigation channel dredging, the system’s morphologic response to wetland construction is likely to be superimposed upon its response to channel deepening, and the net effect may vary depending on a variety of system- specific parameters. Planning for future wetland placements should include an evaluation of local hydrodynamic behavior considering these factors to predict site-specific response.
  • Sediment Mobility, Closure Depth, and the Littoral System – Oregon and Washington Coast

    Abstract: Forty years ago, the depth of closure concept was introduced to provide a systematic, process-based approach to evaluate seasonal changes in cross-shore profiles and sediment mobility in the nearshore. This study aims to extend that theory by directly considering wave-asymmetry in the nearshore environment. This technical note introduces a methodology to calculate wave induced dispersal of dredged material placed in nearshore sites and summarizes analyses validating the approach using data from the South Jetty Site at the Mouth of the Columbia River. This investigation highlights the notion of a cross-shore gradient in nearshore placement effectiveness of dredged material that can assist project managers plan and execute sustainable sediment management practices at coastal inlets.
  • Sediment Supply from Bank Caving on the Lower Mississippi River, 1765 to Present

    Abstract: Bank caving rates and associated total sediment supply were calculated along the Lower Mississippi River from Cairo, IL, to Baton Rouge, LA, using historical maps between 1765 and 1992. Comparison of these maps reveals that the added sediment loads from bank erosion have greatly declined through time. In the pre-1960s period, erosion rates generally ranged from approximately 300 million cubic yards (MCY) to 400 MCY, with the 1880–1930s period having the highest erosion rates of approximately 600 MCY. By the 1990s, the sediment supply from bank erosion was essentially eliminated, with significant erosion being observed at only a few locations, totaling approximately 40 MCY/year. This equates to approximately a 90% reduction in the amount of total sediment being supplied to the channel system from bank erosion.
  • Current State of Practice of Nearshore Nourishment by the United States Army Corps of Engineers

    Abstract: This US Army Corps of Engineers (USACE) special report prepared by the US Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, provides an overview of the current state of practice for nearshore nourishment with dredged sediment. This special report was completed with responses and input from professionals across the dredging and placement teams from each of the USACE Coastal and Great Lakes districts, providing comprehensive overviews of the decision trees these districts utilize in the placement of their dredged sediment. This report describes the general practice of nearshore nourishment, the impediments and concerns faced by nearshore nourishment projects, and the practical methods utilized by the Coastal and Great Lakes districts for their nearshore nourishment projects. Understanding the current state of practice, along with the general and specific impediments the districts face, enables further research in and development of best practices for use across the USACE and better communication of the practice to other stakeholders.