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*Kelsey A. Fall 1 , Courtney K. Harris 1 , Carl T. Friedrichs 1 , and J. Paul Rinehimer 2

Controls on particle settling velocity and bed erodibilty in the presence of muddy flocs and biologically packaged pellets: Modeling study utilizing the York 3-D Hydrodynamic Cohesive Bed Model. *Kelsey A. Fall 1 , Courtney K. Harris 1 , Carl T. Friedrichs 1 , and J. Paul Rinehimer 2

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*Kelsey A. Fall 1 , Courtney K. Harris 1 , Carl T. Friedrichs 1 , and J. Paul Rinehimer 2

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  1. Controls on particle settling velocity and bed erodibilty in the presence of muddy flocs and biologically packaged pellets: Modeling study utilizing the York 3-D Hydrodynamic Cohesive Bed Model *Kelsey A. Fall1, Courtney K. Harris1, Carl T. Friedrichs1, and J. Paul Rinehimer2 1Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 2Department of Civil and Environmental Engineering, University of Washington, Seattle, WA

  2. Study Site: York River Estuary ,VA (MUDBED Long-term Observing System) -- NSF MUDBED project benthic ADV tripods (1) and monthly bed sampling cruises (2) provide long-term observations within a strong physical-biological gradient. Physical-biological gradient found along the York estuary : -- Upper York Physically Dominated Site: ETM --Lower York Biological site: No ETM --Mid York Intermediate site: Seasonal STM Schaffner et al., 2001

  3. Study Site: York River Estuary ,VA (MUDBED Long-term Observing System) ADV observed Settling Velocity (WsBULK) and Bed Erodibility (ε) • Spatial variability in WsBULK and bed εbetween Biological Site and Intermediate Site. • Little seasonal variability in WsBULK and ε at the Biological Site. • Two distinct regimes linked to seasonal variability in WsBULK and ε at the Intermediate Site. Fugate and Friedrichs ,2002; Friedrichs et al., 2009; Cartwright, et al. 2009 and Dickhudt et al., 2010

  4. Study Site: York River Estuary ,VA (MUDBED Long-term Observing System) ADV observed Settling Velocity (WsBULK) and Bed Erodibility (ε) Strong Observed Transition between Regime 1 and Regime 2: June-August 2007 Cartwright et al.,2009

  5. Velocity Tidal Phase Averaged Analysis (Current Speed (a), Bed Stress (b), and Concentration(c)) (a) Tidal Current Speed (cm/s) 45 Regime 1 30 Tidal Phase Average Analysis (Fall, 2012): Average ADV data (current speed, concentration, bed stress and settling velocity) over the tidal phases with the strongest bed stresses for each regime to obtain representative values of each parameter throughout a tidal phase. Regime 1: Flocs -High C at relatively low τb (trapping of fines) -Lower τb despite higher similar current speeds Regime 2 15 (c) Concentration (mg/L) 200 (b) Bed Stress (Pa) 0.25 Regime 2: Pellets+Flocs -Lower C at high τb (dispersal of fines, pellets suspended) 150 Regime 1 0.2 Regime 2 100 0.15 0.1 50 Regime 1 0.05 Regime 2 0.5 1 0 0.5 1 0 Tidal Velocity Phase (θ/π) Tidal Velocity Phase (θ/π) Decreasing U Increasing U Decreasing U Increasing U

  6. ADV Observations: Velocity Phase Averaged Analysis (WsBULK ) ADV observations suggest different particles in are suspended during Regime 1 than Regime 2. A. ADV estimated WsBULK Regime 2: Pellets+Flocs -Higher observed WsBULK at peak |u| and τb (~1.5 mm/s) -Influence of pellets on WsBULK Regime 1: Flocs+Fines -Lower observed WsBULK at peak |u| and τb (~0.8 mm/s) WsBULK= (c/(c-cwash))*Ws ) • (Note that Bulk Settling Velocity, wsBULK = <w’c’>/csetis considered reliable for mud only during accelerating half of tidal cycle.) 0.1 0.2 0.3 0.4 0.5 Tidal Velocity Phase (q/p) Increasing U and τb

  7. York River Conceptual Model (Dickhudt et al., 2009) • Observations suggest seasonal variability in WsBULK and ε at the Intermediate Siteattributed to presence of STM. Biological Site Intermediate Site Physical Site • Regime 1: (Low WsBULKand High ε) • Stratified • Trapping of fines and/or flocs (STM) • Suppressed bed stresses • Regime 2: (High WsBULK and Low ε) • Little or no stratification • Dispersal of fines and/or flocs • No STM • Bed stress no longer suppressed

  8. Overarching Goal: Use 3-D hydrodynamic cohesive bed model to explore the fundamental controls on WsBULK and ε in muddy estuary. • A Preliminary Study: Application of bed consolidation and swelling model (Sanford, 2008) in realistic 3-D domain. • Implement a three-dimensional, numerical model that includes bed consolidation and swelling in the York River Estuary (Rinehimer,2008). • Evaluate “standard” model behavior compared to ADV tidal phase observations during a transition from Regime 1 to Regime 2 at the Intermediate Site (June-August 2007). • Investigate sensitivities of the bed consolidation and swelling model • Cohesive bed swelling time (Ts) • τc equilibrium profile (τceq ) • Initial bed sediment bed τc (τcinit )

  9. Overarching Goal: Use 3-D hydrodynamic cohesive bed model to explore the fundamental controls on WsBULK and ε in muddy estuary. • A Preliminary Study: Application of bed consolidation and swelling model (Sanford, 2008) in realistic 3-D domain. • Implement a three-dimensional, numerical model that includes bed consolidation and swelling in the York River Estuary (Rinehimer,2008). • Evaluate “standard” model behavior compared to ADV tidal phase observations during a transition from Regime 1 to Regime 2 at the Intermediate Site (June-August 2007). • Investigate sensitivities of the bed consolidation and swelling model • Cohesive bed swelling time (Ts) • τc equilibrium profile (τceq ) • Initial bed sediment bed τc (τcinit )

  10. Community Sediment Transport Modeling System (CSTMS): York River 3-D Hydrodynamic Model (Rinehimer, 2008) 3-D ROMS model grid showing every 5th grid cell. Water Column Seabed Figure by C. Harris CSTMS description see Warner et al 2008

  11. Consolidation Model (Sanford,2008) (Cohesive Sediment Bed - τcr vary with depth) τc τc τceq Depositional Beds Consolidate: become less erodible with time. Erosional Beds Swell: become more erodible with time. τceq = Equilibrium critical stress profile; is function of depth (z). τc = Modeled critical stress profile; is function of depth (z), location (x,y) and time (t). Tc, Ts = timescales for consolidation (1 day) and swelling (10 days). τc τceq τc τmin Implementation in ROMS – CSTMS: see Rinehimer et al. 2008

  12. Sediment Bed Model Standard Set Up Model includes bed consolidation BUT neglects aggregation and disaggregation of particles.

  13. Bed Consolidation Model (Sanford, 2008) (Cohesive Sediment Bed - τcr vary with depth) τceq Profiles Obtained by Power Law Fit to Observations Sept τceq=1.0m0.62 April τceq=0.4m0.55 Less Erodible More Erodible (Rinehimer, 2008) Initial Sediment Bed τcProfiles= September τc Profile User Defined τceq Profile: τceq=0.4m0.55 (April)

  14. Overarching Goal: Use 3-D hydrodynamic cohesive bed model to explore the fundamental controls on WsBULK and ε in muddy estuary. • A Preliminary Study: Application of bed consolidation and swelling model (Sanford, 2008) in realistic 3-D domain. • Implement a three-dimensional, numerical model that includes bed consolidation and swelling in the York River Estuary (Rinehimer,2008). • Evaluate “standard” model behavior compared to ADV tidal phase observations during a transition from Regime 1 to Regime 2 at the Intermediate Site (June-August 2007). • Investigate sensitivities of the bed consolidation and swelling model • Cohesive bed swelling time (Ts) • τc equilibrium profile (τceq ) • Initial bed sediment bed τc (τcinit )

  15. Preliminary Standard Model Run June-August 2007 Timeline ( river discharge) Date Erodibility @ 0.2 Pa Near Bed Settling Velocity Bed Stress (color) Depth Int. Current (aroows) Near Bed SSC

  16. Preliminary Standard Model Run June-August 2007 Erodibility @ 0.2 Pa Near Bed Settling Velocity Bed Stress (color) Depth Int. Current (aroows) Near Bed SSC Movie goes here

  17. Regime 1(blue) vs. Regime 2 (green) Model vs. ADV : Velocity Phase Averaged Analysis Current Speed (cm/s) Concentration (mg/L) Bed Stress (Pa) ADV Observations Model • Resolves similar current speeds between regimes. • Resolves difference in concentration between regimes • Does not resolve difference in bed stress between regimes. Tidal Velocity Phase (θ/π) Tidal Velocity Phase (θ/π) Tidal Velocity Phase (θ/π) Increasing U Increasing U Increasing U Decreasing U Decreasing U Decreasing U

  18. Model vs. ADV : WsBULK Velocity Phase Averaged Analysis B. Model estimated WsBULK A. ADV estimated WsBULK Regime 2 Regime 1 WsDEP (mm/s) 0.1 0.2 0.3 0.4 0.5 Removing CWASH and solving for settling velocity of the depositing component (WsDEP = (c/(c-cwash))*WsBULK ) Tidal Velocity Phase (q/p) Increasing U and τb Increasing U and τb

  19. Overarching Goal: Use 3-D hydrodynamic cohesive bed model to explore the fundamental controls on WsBULK and ε in muddy estuary. • A Preliminary Study: Application of bed consolidation and swelling model (Sanford, 2008) in realistic 3-D domain. • Implement a three-dimensional, numerical model that includes bed consolidation and swelling in the York River Estuary (Rinehimer,2008). • Evaluate “standard” model behavior compared to ADV tidal phase observations during a transition from Regime 1 to Regime 2 at the Intermediate Site (June-August 2007). • Investigate sensitivities of the bed consolidation and swelling model • Cohesive bed swelling time (Ts) • τcequilibrium profile (τceq ) • Initial bed sediment bed τc (τcinit )

  20. Sensitivity to Cohesive bed swelling time (Ts) Calculated τc Profiles Cluster Around user defined equilibrium profile (τceq) and displaying initial bed profile (τcrinit) τcrinit τceq τcrinit τceq τcrinit τceq Note: τceq ≠ τcrinit Ts=2 Days Ts=25 Days Ts=50 Days Some adjustment from τcrinit to τceq. Min. adjustment from τcrinit to τceq. Rapid adjustment from τcrinit to τceq. Swelling Time= 25 days Bed adjusts. Short Swelling Time Bed quickly becomes more erodible. Long Swelling Time Bed is more consolidated (less erodible).

  21. Sensitivity to Cohesive bed swelling time (Ts) A. Calculated τc Profiles Cluster Around user defined equilibrium profile (τceq) and displaying initial bed profile (τcrinit) τcrinit τceq τcrinit τceq τcrinit τceq Note: τceq ≠ τcrinit Ts=25 Days Ts=50 Days Some adjustment from τcrinit to τceq. Min. adjustment from τcrinit to τceq. Rapid adjustment from τcrinit to τceq. B. Phase Averaged Concentration • Model estimated suspended sediment concentration is sensitive to Ts. • A Ts = 25 days may be a more reasonable estimate for Ts in this system than previously used 50. Regime 1 Regime 2 Tidal Velocity Phase (θ/π) Tidal Velocity Phase (θ/π) Increasing U Increasing U Decreasing U Decreasing U

  22. Sensitivity to Initial Bed Profile (τcrinit ) A. τceq profiles obtained by power law fit to Gust (Rinehimer,2008). B. Calculated τc Profiles Cluster Around τcinit (based on data) Note: τceq = τcrinit Sept April September (less erodible) April (more erodible) Ts=25 Days Ts=25 Days The current version of the model has a more difficult time nudging the bed τc profiles to the τceq profile when a more erodible τcrinit was used.

  23. Sensitivity to Initial Bed Profile (τcrinit ) A. τceq profiles obtained by power law fit to Gust (Rinehimer,2008). B. Calculated τc Profiles Cluster Around τcrinit (based on data) Note: τceq = τcrinit Sept April September (less erodible) April (more erodible) Ts=25 Days Ts=25 Days C. Phase Averaged Concentration • Model estimated suspended sediment concentration is sensitive to initial bed τcrprofile because the model run time is short when compared to Ts and Tc. • For this particular version of the model the estimated suspended sediment concentration is more sensitive to initial bed τcrprofile than Ts. Tidal Velocity Phase (θ/π) Tidal Velocity Phase (θ/π) Increasing U Increasing U Decreasing U Decreasing U

  24. Conclusions and Future Work • This study showed the application of the 3-D Hydrodynamic York River Model (Rinehimer, 2008), a three-dimensional numerical model that included bed consolidation and swelling, in the York River Estuary, Virginia. • A standard model simulation showed that the York River 3-D model could be a useful tool in investigating the fundamental controls on bed erodibility and settling velocity in a muddy estuary. • Simulated observed current speeds and concentrations over a tidal phase. • Resolved the difference in concentration and settling velocity between regimes over a tidal phase. • Simulate observed bed stresses during Regime 2. Future work will involve turning on sediment induced stratification in the model with aim to simulate realistic stresses for Regime 1. • The bed consolidation model (Sanford, 2008) was found to be sensitive to bed swelling time, τcr equilibrium profile and τcrinitial profile.

  25. Acknowledgements Justin Birchler Funding: Adam Miller Julia Moriarty 10/10

  26. Study Site: York River Estuary ,VA (MUDBED Long-term Observing System) (1) MUDBED Benthic Tripod ADV (2) MUDBED Sampling Cruises Physical-biological gradient found along the York estuary : -- In the middle to upper York River estuary, disturbance by sediment transport reduces macrobenthic activity, and sediment layering is often preserved. (e.g., Clay Bank – “Intermediate Site”) -- In the lower York and neighboring Chesapeake Bay, layering is often destroyed by bioturbation. (e.g., Gloucester Point – “Biological Site”) -- NSF MUDBEDproject benthic ADV tripods (1) and monthly bed sampling cruises (2) provide long-term observations within a strong physical-biological gradient. Schaffner et al., 2001

  27. ADV Observations: Velocity Phase Averaged Analysis (a) Tidal Current Speed (cm/s) 45 (b) Bed Stress (Pa) 0.25 Regime 1: Fines+Flocs -High freshwater discharge -High C at relatively low τb (trapping of fines) -Lower τb despite higher similar current speeds….Why?? Regime 1 30 0.2 Regime 2 Regime 2 0.15 15 0.1 Regime 1 0.05 (c) Drag Coefficient (d) Concentration (mg/L) 0.0016 200 Regime 2: Pellets+Flocs -Decreased freshwater discharge -Lower C at high τb (dispersal of fines, pellets suspended) 0.0012 150 Regime 2 Regime 1 0.00008 100 CWASH 0.00004 50 CWASH Regime 1 Regime 2 1 0 0.5 0.5 1 0 Tidal Velocity Phase (θ/π) Tidal Velocity Phase (θ/π) Decreasing IuI Increasing IuI Decreasing IuI Increasing IuI

  28. Bed Consolidation Model Initial Sediment Bed τc Profiles (red-x) and τceqProfiles for Sept. and April Sept τceq=1.0m0.62 April τceq=0.4m0.55 Initial Sediment Bed τcProfiles= September τc Profile User Defined τceq Profile: τceq=0.4m0.55 (more erodible April)

  29. “Standard” Model Simulation • Study Period: June-August 2007 • Strongest Observed Transition • Continuous ADV data available (MUDBED)

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