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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
1981 1939
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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
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