Presentation Abstract

The South Arm Jetty Tidal Marsh Project is proposed by the Vancouver Fraser Port Authority's Habitat Enhancement Program. The proposed project site is located along the southern edge of Sturgeon Bank in Richmond, B.C. The project would increase the size of the existing marsh immediately adjacent to the site by converting approximately 30-40 hectares of low-value sand flat into highly productive marsh habitat. One of the main challenges for development of the proposed marsh is the mobility of the substrate, due to wave energy exposure, primarily from northwest storms. To provide sheltering for the proposed marsh, a cobble berm was proposed. This study evaluated the amount of wave energy that the proposed marsh surface will be exposed to. Spectral wave simulations were conducted to determine the wave-induced bed shear stresses at the marsh area under existing and proposed project conditions. A one-year record, found to be the most representative of long term conditions was used to force the spectral wave simulations. The maximum bed shear stress during a wave period tmax, was computed according to Fredsøe and Deigaard (1992) for each time step of the simulation. Introduction of the cobble berm provides the marsh area shelter from waves propagating from the northwest to northeast directions. This results in a considerable drop in bed shear stresses for the majority of the proposed marsh area. tmax statistics were compared for 3 points in the lee of the cobble berm. Points A and B are representative of areas where a considerable reduction in bed shear stress is observed (tmax decreases around 30 percent), as a consequence of wave sheltering from the cobble berm. In contrast, point C does not exhibit such obvious reduction in tmax, since its location is farther away from the cobble berm and its area of influence. This area is more exposed and therefore most influenced by waves that approach from the south to south-southeast directions. Under high energy storm conditions, large shear stresses occur over the majority of the marsh area with and without the presence of the cobble berm. However, the structure will promote favorable conditions for development of the proposed marsh predominantly throughout the year.

Session Title

Habitat Restoration

Keywords

Advanced mitigation, Spectral wave modeling

Conference Track

SSE1: Habitat Restoration and Protection

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE1-354

Start Date

5-4-2018 10:15 AM

End Date

5-4-2018 10:30 AM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 5th, 10:15 AM Apr 5th, 10:30 AM

Assessing the influence of wave-induced bed shear stresses on tidal marsh colonization potential

The South Arm Jetty Tidal Marsh Project is proposed by the Vancouver Fraser Port Authority's Habitat Enhancement Program. The proposed project site is located along the southern edge of Sturgeon Bank in Richmond, B.C. The project would increase the size of the existing marsh immediately adjacent to the site by converting approximately 30-40 hectares of low-value sand flat into highly productive marsh habitat. One of the main challenges for development of the proposed marsh is the mobility of the substrate, due to wave energy exposure, primarily from northwest storms. To provide sheltering for the proposed marsh, a cobble berm was proposed. This study evaluated the amount of wave energy that the proposed marsh surface will be exposed to. Spectral wave simulations were conducted to determine the wave-induced bed shear stresses at the marsh area under existing and proposed project conditions. A one-year record, found to be the most representative of long term conditions was used to force the spectral wave simulations. The maximum bed shear stress during a wave period tmax, was computed according to Fredsøe and Deigaard (1992) for each time step of the simulation. Introduction of the cobble berm provides the marsh area shelter from waves propagating from the northwest to northeast directions. This results in a considerable drop in bed shear stresses for the majority of the proposed marsh area. tmax statistics were compared for 3 points in the lee of the cobble berm. Points A and B are representative of areas where a considerable reduction in bed shear stress is observed (tmax decreases around 30 percent), as a consequence of wave sheltering from the cobble berm. In contrast, point C does not exhibit such obvious reduction in tmax, since its location is farther away from the cobble berm and its area of influence. This area is more exposed and therefore most influenced by waves that approach from the south to south-southeast directions. Under high energy storm conditions, large shear stresses occur over the majority of the marsh area with and without the presence of the cobble berm. However, the structure will promote favorable conditions for development of the proposed marsh predominantly throughout the year.