Education

Research Description

The Environmental Sediment Mechanics Research Group conduct studies in the area of environmental hydraulics and sediment transport. We study phenomena related to the dynamics of water and sediment in a range of aquatic environments that include streams, rivers, and estuaries. These environments are continuously adjusting their form in response to hydrological fluctuations (including extreme events), changes in the quantity and size of supplied sediment, and anthropogenic modifications. Our work focuses on characterizing the inherent variability that marks such adjustment in nature for advancing the formulation of physics-based models that underpin our predictive understanding. This is critical nowadays given the effects of climate change on aquatic environments, which have modified their capacity to resist and recover from change imposed by disturbances (i.e., their resilience). Building on advanced physics-based models, our work ultimately aims to create a paradigm shift toward the application of performance-based risk analyses that inform the next generation of resilience-oriented design, practice, and policy.

Publications

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Grants

Linking Scour Evaluation and Data from Geotechnical, Erodibility, and Hydraulic 4 Investigation-An Integrative Approach

NC Department of Transportation(8/01/23 - 7/31/25)

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Linking Scour Evaluation and Data from Geotechnical, Erodibility, and Hydraulic 4 Investigation-An Integrative Approach

Sponsor: NC Department of Transportation

Start Date: 8/01/23

End Date: 7/31/25

Abstract

Traditional practice of bridge local scour estimation relies upon the use of analytical models such as the one specified in Hydraulic Engineering Circulars, HEC-18 and HEC 20 (Arneson et al., 2012). Models such as HEC-18 were however developed based on data collected mainly from flume testing on sand. The data used for HEC-18 model development were mainly for narrow pier erosion in sand (scour depth/pier width>1.4) per Benedict and Knight (2017). Yet the model is applied in practice to intermediate and wide pier cases as well. In addition, the materials classified as “soils” include sand, and/or silt, and/or clay with a grain size distribution that can yield a bed soil behavior that may not be captured by a single parameter, such as D50. Approaches such as the HEC-18 model also lump the flow channel and bridge hydraulic and geometrical parameters with the bed erosion resistance parameters in one equation. While such an approach is simple to use, there is consensus in literature that it yields overly conservative scour estimates. On a fundamental level, the magnitude of erosion and scour can be assessed through knowledge of the flow-induced shear stress, the soil’s erodibility parameters, which include the critical shear stress (τc), co- efficient of erodibility (α'), and m, which is “an exponent defining the functional variation of the soil erosion rate with the flow-induced shear stress.” This approach is fundamentally implemented in the FHWA Hy- draulic Toolbox and adopted by the NextScour Program. In parallel, geotechnical site investigation by the North Carolina DOT commonly involves the performance of SPT, and the retrieval of soil samples for characterization of physical and engineering properties. As such, there is an opportunity to obtain the site- specific erodibility (τc, α', and m) through linking such parameters with the geotechnical data for a rational assessment of site-specific scour magnitude, accounting for variability of channel-bed soil layers with depth.

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Improved Understanding of Sediment Dynamics for the Rachel Carson Reserve, North Carolina

National Oceanic & Atmospheric Administration (NOAA)(10/01/22 - 9/30/23)

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Improved Understanding of Sediment Dynamics for the Rachel Carson Reserve, North Carolina

Sponsor: National Oceanic & Atmospheric Administration (NOAA)

Start Date: 10/01/22

End Date: 9/30/23

Abstract

The goal of this project is to generate an improved understanding of sediment dynamics at and around the Rachel Carson Reserve. Specifically, this project seeks to: quantify the magnitude and change in sediment loading rates and sources; determine the mechanisms through which the changing geomorphology of the Beaufort Inlet drives shoreline change and sediment dynamics; and examine the degree of geomorphological change caused by extreme storm events and its impacts on the habitat and infrastructure resiliency. The project team will collaborate with the N.C. Coastal Reserve and NERR to produce: a functional numerical model that can be used to simulate sediment dynamics at and around the Reserve; and maps that show the variability of vulnerability indexes within the Reserve to pronounced geomorphological change and its impact on sediment dynamics. It is envisioned that results of this project will generate: an improved understanding of how the interaction between extreme storm events, river systems, and coastal processes impact sediment dynamics at and around the Reserve; refined decision making and management for engineering practices at the Beaufort Inlet; and an improved understanding of the impact of sediment dynamics on the vulnerability of coastal habitats and infrastructure for informing effective resilience planning.

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Bank Erosion and Sediment Transport in Stream Restoration: A Process-Based Framework for the North Carolina Piedmont Region

NC Department of Environmental Quality (DEQ)(2/02/22 - 11/01/22)

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Bank Erosion and Sediment Transport in Stream Restoration: A Process-Based Framework for the North Carolina Piedmont Region

Sponsor: NC Department of Environmental Quality (DEQ)

Start Date: 2/02/22

End Date: 11/01/22

Abstract

The objective of the propose research is to develop, validate, and implement a process-based framework for evaluating and predicting bank erosion and sediment transport associated with stream restoration practices. The research will focus on streams located within the North Carolina Piedmont region. It will contribute towards enhancing our understanding of existing conditions in degraded streams, improving the design of restoration projects in sites with limited information, and defining realistic expectations to formulate performance criteria. Ultimately, the goal is to provide the scientific community, Federal and States agencies, practitioners, and decision makers with a rigorous, physically-based tool for estimating and predicting rates of bank erosion and sediment transport in stream restoration projects.

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Unraveling the effects of grain size and moisture content on the linearity of cohesive soil erosion: Implications for predicting streambank retreat (Alexis Swanson)

NCSU WRRI Storm Water Consortium (SWC)(3/01/21 - 5/31/22)

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Unraveling the effects of grain size and moisture content on the linearity of cohesive soil erosion: Implications for predicting streambank retreat (Alexis Swanson)

Sponsor: NCSU WRRI Storm Water Consortium (SWC)

Start Date: 3/01/21

End Date: 5/31/22

Abstract

This work will examine the effects of sediment grain size and moisture content on: (1) the linearity of the relationship between applied boundary shear stress and erosion rates; and (2) the prediction streambank retreat. (Draft)

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NRI: INT: Towards the Development of a Customizable Fleet of Autonomous Co-Robots for Advancing Aquaculture Production

National Science Foundation (NSF)(11/01/20 - 10/31/24)

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NRI: INT: Towards the Development of a Customizable Fleet of Autonomous Co-Robots for Advancing Aquaculture Production

Sponsor: National Science Foundation (NSF)

Start Date: 11/01/20

End Date: 10/31/24

Abstract

Aquaculture, the rearing and harvesting of organisms in water environments, is a rapidly expanding industry that now produces more seafood than all wild caught fisheries worldwide. This inevitable growth must be steered towards sustainable production practices, which requires intensive monitoring in areas that are difficult and potentially dangerous to access. The vision of this project is to improve the efficiency and sustainability of near-shore aquaculture production through integrating a flexible, customizable, multi-task vehicle fleet, consisting primarily of unmanned aerial vehicles (UAVs) and unmanned surface vehicles (USVs), with a biologically-relevant framework for accelerated prototyping. This project will use oyster production along the Eastern US shoreline as a case study and testbed.

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Evaluation of 2D Hydraulics Models to Improve Scour Predictions and Countermeasures

NC Department of Transportation(8/01/19 - 10/01/22)

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Evaluation of 2D Hydraulics Models to Improve Scour Predictions and Countermeasures

Sponsor: NC Department of Transportation

Start Date: 8/01/19

End Date: 10/01/22

Abstract

The goal of the proposed research is to examine the capabilities of two-dimensional (2D) hydro-morphodynamic numerical models for improving the prediction of scour depths at bridge foundations, as well as for enhancing the design of countermeasures for scour mitigation. Despite major advances in predicting the spatial and temporal scales of scour at bridge crossings, bridge failure due to hydraulically induced scour still represents a major technical, economical, and societal challenge. To address this challenge, the proposed research aims to: (1) identify the key capabilities and limitations of the 2D depth-averaged numerical models when simulating scour phenomena at bridge foundations; (2) compare the performance of 1D numerical models to that of 2D numerical models when simulating scour phenomena at bridge foundations; and (3) develop recommendations for predicting scour depths and for evaluating scour mitigation countermeasures at bridge foundations using 2D numerical models. Results from the proposed research will primarily contribute to achieve better predictions of the scour phenomena at bridge foundations, as well as to enhance the design of countermeasures for scour mitigation. Additionally, through the deployment of a novel fiber-optic scour monitoring station, this research will provide new insights on the dynamic development of the scour hole using field data. Such information will effectively enhance the development, and thereby the predictive capabilities of numerical models when use to examine the impact of unknown or extreme hydrologic events.

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Bank Erosion and Sediment Transport in Stream Restoration: A Process-Based Framework for the North Carolina Piedmont Region

NC Department of Environmental Quality (DEQ)(6/01/18 - 5/31/22)

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Bank Erosion and Sediment Transport in Stream Restoration: A Process-Based Framework for the North Carolina Piedmont Region

Sponsor: NC Department of Environmental Quality (DEQ)

Start Date: 6/01/18

End Date: 5/31/22

Abstract

The objective of the propose research is to develop, validate, and implement a process-based framework for evaluating and predicting bank erosion and sediment transport associated with stream restoration practices. The research will focus on streams located within the North Carolina Piedmont region. It will contribute towards enhancing our understanding of existing conditions in degraded streams, improving the design of restoration projects in sites with limited information, and defining realistic expectations to formulate performance criteria. Ultimately, the goal is to provide the scientific community, Federal and States agencies, practitioners, and decision makers with a rigorous, physically-based tool for estimating and predicting rates of bank erosion and sediment transport in stream restoration projects.

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Collaborative Research: Geotechnical Investigation of Bivalve-Sediment Interaction with regard to Bivalve Farms as a Self-sustained Scour Mitigation Method

National Science Foundation (NSF)(8/15/18 - 7/31/22)

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Collaborative Research: Geotechnical Investigation of Bivalve-Sediment Interaction with regard to Bivalve Farms as a Self-sustained Scour Mitigation Method

Sponsor: National Science Foundation (NSF)

Start Date: 8/15/18

End Date: 7/31/22

Abstract

Scour is the most common cause for bridge failures in the U.S. Previous studies have suggested that bivalve colonies reduce local erosion through different processes, and that bivalves feature a high resistivity to strong flow. With today’s advancements in bivalve aquaculture design and management, the PIs hypothesize that bivalve aquacultures are suitable as a self-sustained scour mitigation method, and are proposing to investigate the geotechnical aspects of this hypothesis. Specifically, the PIs are proposing to test the following working hypotheses: H1) The presence of bivalve colonies reduces local scour and erosion. H2) Bivalve colonies form morphologies applicable to scour protection design. H3) Bivalve adhesive protein increases sediment strength and decreases erodibility. H4) Bivalve dislodgement from soil surfaces occurs as “block failure” for single bivalves, but becomes irrelevant for erosion issues in the case of bivalve groups. These hypotheses will be tested through an interdisciplinary and multi-method approach featuring: (i) field investigations at two bivalve colonies in Virginia and North Carolina, (ii) an analytic comparison of bivalve colony morphology and flow resistivity to modern scour protection designs, and laboratory tests investigating (iii) the change of sediment strength and erodibility resulting from mixing bivalve adhesive protein with sediment and (iv) soil failure behavior during bivalve dislodgement. The research team is composed of experts in geotechnical and hydraulic engineering, as well as in aquaculture design and management. The PIs will be supported by international collaborators and experts in etho-hydraulics from the Technical University of Darmstadt who will contribute through a preliminary numerical simulation of the field sites to the project.

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