Numerical modeling in support of the characterization and remediation of impacted sediments can be a challenging task, particularly in environments where multiple physical processes influence sediment fate and transport. The interaction of various controls is particularly complex in estuarine settings, where riverine input, water levels, waves, and other coastal processes combine to create a seasonally dynamic environment. Modeling of such environments requires a comprehensive and integrated approach such that the effects of each process can be assessed individually, as these processes can be allowed to interact to reproduce the natural environment as faithfully as possible Approach and Activities This contribution describes the development and calibration of an integrated Delft3D numerical model that includes flow, sediment transport, wave processes, and vegetation. The model boundary conditions are based on data collected during a comprehensive field program. Field data were also used to calibrate various model input parameters (such as bed and vegetation roughness). The model was used to understand erosion and deposition during both low and high flow regimes, and thus to aid in understanding important controls on sedimentary dynamics during these predominant regimes. Results and Lessons Learned The integrated numerical model predictions capture important sedimentation, erosion, velocity, and water level patterns. Model predictions indicate that during periods of low riverine input, velocity patterns and sediment transport associated with periodic water level changes dominate. During riverine flood conditions flow and sedimentation patterns are controlled by the river itself. Integrated modeling of this setting, including calibration to field data provides a valuable tool for assessment of future conditions, and thus for remediating impacted sediments.

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Integrated Sediment Transport, Vegetation, and Wave
Modeling of a Great Lakes Freshwater Estuary
Tim Wagner and Ben Sheets
Barr Engineering
4 November 2014

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Acknowledgements
Barr:
Ben Sheets, Irv Mossberger, Jamie Bankston, Eric Hedblom,
Don Richard, Eric Dott, Brad Leick
Deltares:
Bas van Maren, Arnold van Rooijen, Luca Sittoni, Theo van der
Kaaij, Katherine Cronin, Han Winterwerp, Thijs van Kessel,
Johannes Smits, Jan van Beek, Dick Ver Ploeg

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Presentation Overview
The St. Louis River Freshwater Estuary
Spirit Lake and its industrial legacy
Project process from Data Collection through Modeling
Modeling
Calibration
Vegetation
Wave
Future Predictive Simulations
Questions

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St. Louis River Estuary
model area

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St. Louis River Freshwater Estuary
• St. Louis River enters western Lake Superior through the
Duluth/Superior Harbor
• Like a tidal estuary, the water level changes cyclically due to
Seiche activity
• Flow and Sediment Load are controlled by three upstream
dams
• USACE maintains a dredged channel to the project site

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Spirit Lake History
• Historically a shallow water
embayment ringed by natural
levees
• Isostatic rebound/subsidence has
contributed to increased water
depth, and drowning of wetland
areas
• Construction and operations of
an industrial facility began in the
early 20th century and changed
the littoral regions

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Spirit Lake Industrial History
1939 1981

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Modeling Project Goals
• Validate the Conceptual Site Model
– Define data gaps and collect data
– Develop a model to understand current conditions
Apply model to future predictive simulations to assess
potential remedial alternatives

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Conceptual Site Model
• What do we think is happening?
– Spirit Lake is sheltered from river flows
– Sediment load is small as significant bed change hasn’t been
observed
–Waves, while large, do not appear to significantly shape the
littoral areas
– Vegetation may play a role

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Data Collection
• Data collected over several field
periods
• Both sediment and hydrodynamic data
collected
– Wind
– Waves
– Upstream discharge
– Water level elevation
– Point flow velocities
– ADCP measurements
– Sediment characteristics
– Suspended sediment concentrations
• Two full bathymetric surveys collected

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Importance of Seiche (Storm induced water level change)
Water level w.r.t. mean water level [m]
Frequency analysis of water level

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Wind Waves

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Suspended Sediment Data
I
II
II
I
Grey area = non-cohesive
sand dominated
clay dominated
silt dominated
Bed Sediments Suspended Sediments

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June 2012 Flood Event
• 10 + inches of rain fell over a
large portion of St. Louis River
watershed
• Flood flows for the St. Louis River
peaked at 45,300 cfs which was
the largest recorded flood on
record and a greater than 500
year return period
• Large sediment load delivered to
river through overland flooding
and through failure of a dam

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Modeling Approach
• Model aims to predict bed stability and thus morphological change
and sediment transport patterns
• Model is:
- Delft3D-FLOW / Delft3D-WAVE (SWAN) / Sed-online / Vegetation
- Set up in 2D
- Calibrated on 2012 flood to mimic changes
- Verified on measured normal flow conditions
- Waves and vegetation effects are built in later

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Model Grid, Bathymetry, and Boundary Conditions
Hydrodynamic Boundary conditions:
• Water Level downstream
• River Discharge Upstream
• Wind

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Flood 2012 Bed Change

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June 2012 Flood Velocity Movie

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Vegetation Implementation
• Vegetation can have a significant
impact on flow velocity fields and
thus sediment
erosion/deposition
• Barr completed survey of
vegetation in August 2012
• Two other vegetation scenarios
were evaluated
– Aerial photography
– Water depth (<1m)

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Impact of adding Vegetation

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Wind Wave Data
• Wind-waves present a significant
threat to the stability of sediments
in the St. Louis River
• Recorded data indicated significant
wave heights on the order of 25cm
• Wind data recorded both onsite and
at a nearby airport. Airport data
was used because of completeness
of data
• Data used as boundary conditions
for Delft3D-WAVE simulations

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Wave Simulations
• Evaluated different wind
cases as well as coupling
between Delft3D-FLOW
and SWAN
• Numerical parameters
within SWAN were
modified for shallow
conditions
– Bottom friction coefficient
– Accuracy parameters

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Limitations of Wave
• Vegetation importance
– Field observations indicate that
wave energy is dissipated in areas
with large amounts of vegetation or
bottom debris
• Simulations are run with a
constant wind
• Storm events influence water
level through seiche which
impacts wave development

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Modeling Summary
• Delft3D was key to the project because it allowed for
integration of multiple processes (flow, sediment, vegetation,
and waves)
• Under non-flood conditions Seiche induced water level change
influences flow velocities and direction
• Sediment load is almost zero under non-flood conditions
• Vegetation plays an important role in sediment deposition
patterns

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Future Predictive Simulations
• Alternative solutions for
environmental improvement will
have many components including
dredging and capping
• Activities may impact bed
stability locally and globally
• Model will look at potential
impacts for various alternative
scenarios

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Questions
Thank you for time