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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