1 Numerical Modeling Case Studies in Support of ELJ Restoration Projects The Hoh River & South Fork Nooksack by Bob Elliot northwest hydraulic consultants Seattle, WA nhc Objectives of Presentation • Present examples of higher-end numerical hydraulic modeling in ELJ restoration projects. • Discuss their use in analyzing, designing, and presenting ELJ alternative. • Illustrate benefits of two-dimensional (2D) and 1D branch-flow (quasi-2D) modeling, where appropriate. • Two case-studies: Hoh River & South Fork Nooksack River.
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Numerical Modeling Case Studies in Support of ELJ ... · presenting ELJ alternative. • Illustrate benefits of two-dimensional (2D) and 1D branch-flow (quasi-2D) modeling, where
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Numerical Modeling Case Studies in Support of ELJ Restoration Projects
The Hoh River & South Fork Nooksack
byBob Elliot
northwest hydraulic consultantsSeattle, WA
nhc
Objectives of Presentation
• Present examples of higher-end numerical hydraulic modeling in ELJ restoration projects.
• Discuss their use in analyzing, designing, and presenting ELJ alternative.
• Illustrate benefits of two-dimensional (2D) and 1D branch-flow (quasi-2D) modeling, where appropriate.
• Two case-studies: Hoh River & South Fork Nooksack River.
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Eroding Bank 500 ft
Hoh River Erosion Project Site
US 1
01
US 101
Objectives of Hoh Project
• An emergency response to bank erosion and revetment failures along US 101, most recently from October 2003 flood.
• Provide longer-term solution for protecting the highway and minimizing frequency of repairs.
• Emulate natural conditions that deliver net benefit to aquatic and riparian habitat (e.g. increased bank roughness, cover, and channel complexity).
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General Approach to Modeling
• Build “far-field” HEC-RAS reach model, analyze preliminary scenarios under wide range of flows, & develop conceptual plan (Herrera).
• Use SMS to develop “near-field” FESWMS (Flo2DH) model as a more accurate tool to help refine and finalize design.
• Use 2D model results to estimate and simulate potential channel response to ELJs and future river planforms.
• Recognize fixed-bed limitations of models.
Approach to 2D Modeling
• Establish accurate baseline conditions of the complex hydraulics at the site (sharp bend, side channels, etc.), including inundation area, flow depths, velocities.
• Incorporate proposed project elements into model. • Analyze only select key flow conditions (100-yr, 2-
yr, and 1-yr). • Provide inputs for refined design: dynamic forces,