Relationships among Fine Sediment Settling and Suspension, Bed Erodibility, and Particle Type in the York River Estuary, Virginia

In order to understand the processes controlling the temporal variability in settling velocity (Ws) and bed erodibility (ε), in the middle reaches of the York River estuary, VA, the relationships between the hydrodynamics and particle types were investigated with a near-­‐bed Acoustic Doppler Velocimeter (ADV) and the York River 3-­‐D Hydrodynamic Cohesive Bed Model. ADV observations of the flow characteristics that occurred over a strong temporal transition period indicated that Ws and ε were characterized by two distinct regimes with contrasting sediment and water column characteristics: (i) a physically-­‐dominated regime (Regime 1) which was a period dominated by flocculated muds (flocs), and (ii) a biologically-­‐influenced regime (Regime 2) which was a period dominated by biologically formed pellets mixed with flocs. During Regime 1, Ws averaged about 0.5 mm/s, and ε averaged about 3 kg/m2/Pa. In contrast, during Regime 2 average Ws increased to 1.5 mm/s, and average ε dropped to 1 kg/m2/Pa. The change between these two regimes and the transition in Ws and ε were linked with the arrival and departure of a seasonal density front. Comparison between ADV observations and the results from the York River 3-­‐D Hydrodynamic Cohesive Bed Model suggested that the current model version was not conducive to examining the temporal variability in settling velocity associated with the transition of the distinct sediment regimes. The existing model version estimated realistic values for current speed and concentration and resolved the daily variation associated with in current speed, bed stress, concentration, and settling velocity. However, model estimates of bed stress, current speed, settling velocity, and erodibility did not suggest the presence of two distinct sediment regimes. The model did a poor job of predicting peak bed stresses and settling velocities. Both were over estimated by a factor of 2 throughout most of the study period. Possible modifications to create a version that is able to simulate the bed stresses and sediment properties (i.e. erodibility and settling velocity) during each regime with more accuracy are: (1) define finer sediment classes in the model that are more representative of the water column and not just the seabed, (2) use a consolidation time scale of 5 days rather than 24 hours to allow more sediment to be suspended at lower bed stresses, (3) further reduce hydraulic roughness, and (4) turn on sediment induced stratification

Suspended Particulate Matter Longitudinal Survey – Currituck Sound, NC; Oct 13-15, 2015, Cruise: CS151013-15, CHSD Stations: S5566-5587

Dataset consists of water column and bottom burst data, PICS, and light attenuation data collected as part of a 21 station longitudinal survey of the Currituck Sound, NC along a ~60 km transect northward from the Wright Memorial Bridge

Including fine-grained sediment processes within numerical representations of a partially-mixed estuary, the York River, Virginia

The Community Sediment Transport Modeling System (CSTMS) is being used to represent conditions in the York River, Virginia, a partially-mixed tidal tributary of Chesapeake Bay. Our modeling approach includes both an idealized two-dimensional longitudinal representation of the estuary, and a more realistic full three-dimensional model of the York River. Both have been implemented using versions of the Regional Ocean Modeling System (ROMS). Our modeling efforts have been motivated by a rich set of observation data from in-situ measurements made by acoustic Doppler velocimeters (ADVs), a pulse coherent acoustic Doppler profiler (PC-ADP), a laser in-situ scattering and transmissometry (LISST), and a particle imaging camera system (PICS). Additionally, water column and bed inventories of Beryllium-7 will be used to constrain the three-dimensional model parameters. Within the full three-dimensional model, hydrologic conditions, physical forcing, and sediment characteristics are being used to examine spatial and temporal changes in sediment dynamics in the York River estuary. This version of the CSTMS accounts for suspended transport, erosion, deposition and cohesive processes via consolidation and swelling of the sediment bed, which change the critical shear stress of the seafloor in response to sedimentation. Adjustments to the open boundary conditions for salinity and wind forcing produced model estimates for the summer 2007 that show good agreement with observed sediment concentration, bed stress and other hydrological parameters. We analyzed the sensitivity of calculations of the total eroded mass to the bed consolidation time scale and the critical shear stress for erosion. Further analysis showed model sensitivities to the swelling time scale and the user defined initial and equilibrium critical shear stress profiles. The idealized two-dimensional model is being developed within the Coupled OceanAtmosphere-Waves-Sediment Transport (COAWST) version of the ROMS model family. The idealized model represents a longitudinal section of a partially-mixed estuary, accounting for a freshwater source, tides, and estuarine circulation, but neglecting across-channel variations. The impact of sediment-induced stratification and the flocculation of cohesive sediments on depositional patterns will be evaluated through the addition of these two processes into the twodimensional model. This simplified model will be used as a platform for implementing code to account for sediment-induced stratification and flocculation processes within the CSTMS framework, including our three-dimensional CSTMS model of the York River estuar

The importance of organic content to fractal floc properties in estuarine surface waters, insights from video, LISST, and pump sampling: Supporting data

The linked folders and associated data files contain the observations utilized in Fall, K.A., Friedrichs, C.T., Massey, G.M., Bowers, D.G., and Smith, S.J. (2021). The importance of organic content to fractal floc properties in estuarine surface waters: Insights from video, LISST, and pump sampling. JGR Oceans. The file “Description of Data Files.pdf” outlines the content of the ten data folders, each of which is associated with a data set collected on an individual one-day cruise in the York River estuary

Cruise: YR130612, Stations: S5127- S5138, York River Estuary and Pamunkey River, Virginia, MUDBED Longitudinal Profiler Station Survey bracketing a Flood Tide.

Dataset consists of profile and water column burst Data collected as part of a longitudinal profiler station survey at approximately 20 km, 25 km, 35 km, 45 km, 56 km and 62 km upriver from the mouth of the York River Estuary

Collaborative Research: The Role of Wind in Estuarine Dynamics, Upper Chesapeake Bay, VIMS Instruments deployed in collaboration with UMCES and WHOI; March-May, 2012 deployment.

While the project is a collaborative effort involving several researchers from the Virginia Institute of Marine Science (VIMS), the University of Maryland Center for Environmental Science (UMCES) and the Woods Hole Oceanographic Institution (WHOI), the Data archive here is primarily from VIMS owned instrumentation deployed as part of the project. A series of instruments were deployed in three transects in Upper Chesapeake Bay, South of the Choptank River from March to May 2012. This Dataset was collected with autonomously deployed Acoustic Doppler Current Profilers (ADCP), Acoustic Doppler Velicometers (ADV), and Conductivity and Temperature Sensors (CT)

Model Behavior and Sensitivity in an Application of the Cohesive Bed Component of the Community Sediment Transport Modeling System for the York River Estuary, VA, USA

The Community Sediment Transport Modeling System (CSTMS) cohesive bed sub-model that accounts for erosion, deposition, consolidation, and swelling was implemented in a three-dimensional domain to represent the York River estuary, Virginia. The objectives of this paper are to (1) describe the application of the three-dimensional hydrodynamic York Cohesive Bed Model, (2) compare calculations to observations, and (3) investigate sensitivities of the cohesive bed sub-model to user-defined parameters. Model results for summer 2007 showed good agreement with tidal-phase averaged estimates of sediment concentration, bed stress, and current velocity derived from Acoustic Doppler Velocimeter (ADV) field measurements. An important step in implementing the cohesive bed model was specification of both the initial and equilibrium critical shear stress profiles, in addition to choosing other parameters like the consolidation and swelling timescales. This model promises to be a useful tool for investigating the fundamental controls on bed erodibility and settling velocity in the York River, a classical muddy estuary, provided that appropriate data exists to inform the choice of model parameters

Fractal floc properties in estuarine surface waters: insights from video settling, LISST, and pump sampling

The goal of this study is to gain insight into the fractal properties of flocs in estuarine surface waters under conditions of variable floc size, density, concentration, and organic content. The properties of flocculated particles in estuarine surface waters are especially important to the fate of incident light, with direct ramifications for primary production, water quality, and optical remote sensing. Observations of particle properties were collected using a profiling system that includes a Laser In-Situ Scattering and Transmissometry (LISST) 100X Type C instrument, a high-definition Particle Imaging Camera System (PICS) incorporating a video settling tube, and a high-speed pump sampler. Results reported here were collected at a total of 45 sampling stations on nine cruises conducted in the York River Estuary, Virginia, between September and December over the course three years, 2014-2016. Samples were collected in the fall and early winter to avoid phytoplankton blooms, which are most likely to occur during spring and summer in this system. An aim of this study is to examine properties of flocculated particles without observations being significantly confounded by the presence of relatively large, intact algal cells. Preliminary results suggest that settling velocity and excess density as determined by the PICS in surface waters of the York River Estuary are very strongly fractal, with a median fractal dimension of ~2.3. However, particles with high organic content tend to have a significantly lower fractal dimension than particles with low organic content. For a given floc size, high organic content leads to lower floc density. But particle suspensions with higher inorganic content (and higher mass concentration overall) tend to have a larger median floc size, which leads to a lower bulk density for inorganic particles when integrated across all floc sizes