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Tag: Sedimentation and deposition
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  • Monitoring Geomorphology to Inform Ecological Outcomes Downstream of Reservoirs Affected by Sediment Release

    Abstract: Increasingly, reservoir managers are seeking techniques that improve sediment management while considering long-term sedimentation and reduced operational flexibility. These techniques, often termed sustainable sediment management, involve passing sediment through reservoirs and into downstream rivers. Conceptually, restoring sediment continuity can benefit ecosystem function by increasing floodplain connectivity, contributing to the heterogeneity of channel geomorphology, and supporting the continuity of nutrient cycling. However, when a change is made to operations, geomorphic changes may need to be monitored to document benefits and mitigate any unexpected effects of the change. This investigation develops a geomorphic monitoring plan for downstream reaches affected by sediment-release operations at reservoirs. The monitoring objectives are aligned with potential geomorphic change caused by changes to sediment supply and the associated effects on river function. A tiered approach is presented to explain the quality of information that can be assessed from increasing levels of data collection. A general conceptual model is described in which geomorphic data may be linked to physical habitat conditions and, therefore, ecological processes. The geomorphic monitoring plan for the Tuttle Creek Reservoir water injection dredging (WID) pilot project is presented as a case study. This technical note establishes a general framework for monitoring the design for sustainable sediment management in different ecological and geomorphic contexts.
  • Coastal Modeling System User’s Manual

    Abstract: The Coastal Modeling System (CMS) is a suite of coupled 2D numerical models for simulating nearshore waves, currents, water levels, sediment transport, morphology change, and salinity and temperature. Developed by the Coastal Inlets Research Program of the US Army Corps of Engineers, the CMS provides coastal engineers and scientists a PC-based, easy-to-use, accurate, and efficient tool for understanding of coastal processes and for designing and managing of coastal inlets research, navigation projects, and sediment exchange between inlets and adjacent beaches. The present technical report acts as a user guide for the CMS, which contains comprehensive information on model theory, model setup, and model features. The detailed descriptions include creation of a new project, configuration of model grid, various types of boundary conditions, representation of coastal structures, numerical methods, and coupled simulations of waves, hydrodynamics, and sediment transport. Pre- and postmodel data processing and CMS modeling procedures are also described through operation within a graphic user interface—the Surface Water Modeling System.
  • Use of Sediment Tracers to Evaluate Sediment Plume at Beaufort Inlet and Adjacent Beaches, North Carolina

    Abstract: This report documents a numerical modeling investigation on the transport of sediment material placed on designated disposal sites adjacent to Beaufort Inlet, North Carolina. Historical and newly collected wave and hydrodynamic data around the inlet are assembled and analyzed. The data sets are used to calibrate and validate a coastal wave, hydrodynamic and sediment transport model, the Coastal Modeling System. Model alternatives are developed corresponding to different material placement sites. Sediment transport and sediment plume distribution are evaluated within and around the immediate vicinity of the Beaufort Inlet estuarine system for a representative summer and winter month. Results of model simulations show that high flows occur along navigation channels and low flows occur outside the inlet in open ocean area. Sand materials placed in nearshore sites tend to be trapped in and move along navigation channels entering the inlet. In offshore placement sites the sediment plume shows slow spreading and no significant sand migration from its release locations. Simulations for the summer and winter month present similar distribution patterns of sediments originating from placement sites.
  • 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.
  • Proceedings from the Basin Sediment Management for Unique Island Topography Workshop, Mayagüez, Puerto Rico

    Abstract: This report summarizes the Basin Sediment Management for Unique Island Topography Workshop hosted in-person and virtually at the University of Puerto Rico Mayagüez (UPRM) Department of Civil Engineering and Surveying, Mayagüez, Puerto Rico on 11 March 2022. The workshop was attended by approximately 80 federal, state, local, and academic organizations participants. It focused on Engineering With Nature® (EWN®), green infrastructure (GI) and low impact development (LID) opportunities for unique tropical island topography and included seven presentations from subject matter experts, a discussion on limitations and problems with prior projects, and two concurrent breakout sessions. Preworkshop activities included a field trip to multiple sites in the Añasco watershed conducted 09 March 2022, which served as a base case for the workshop. The field trip provided participants a unique perspective of the island’s topography and post 2017 Hurricane María issues and impacts. During the breakout sessions, participants identified new project opportunities for EWN®-GI and LID at two selected sites from the field trip. Each group developed alternatives for their chosen site and identified concepts that could turn into great opportunities for the surrounding communities and significantly benefit the state of practice in Puerto Rico’s unique tropical island topography.
  • 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.