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Puget Sound Georgia Basin Model

Restoration Feasibility for the Restoration of Leque Island and zis a ba, Washington (Phase 2)

Model grid for Leque Island, including Skagit Bay and Port Susan Bay.

Ducks Unlimited, April 2014 - January 2015

Two sites along the mouth of the Old Stillaguamish River were assessed for habitat restoration involving the removal or modification of existing perimeter dikes at both locations. Leque Island is a 253-acre site owned by the Washington Department of Fish and Wildlife and zis a ba (formerly Matterand) is a 90-acre site owned by the Stillaguamish Tribe. PNNL supported Ducks Unlimited Inc. (DU) with hydrodynamic modeling to evaluate the performance of several proposed restoration actions in terms of achieving habitat goals while assessing potential hydraulic and sediment transport impacts to the site and surrounding parcels of land.

A previously-existing grid was refined and validated to tides, currents, and salinity for the period of October 10-26, 2005. Eight proposed restoration alternatives were then compared with the baseline condition across both a typical flow condition and a bank full flow condition. A year-long simulation with 2003 historic conditions was also examined to assess stakeholder concerns including flood risk to neighboring lands, erosion control, and potential channel migration.


Project Highlights

Comparing high tide and low tide results between the Baseline and Full Restoration scenario.

  • Restoration of estuarine functions to the Leque Island and zis a ba sites appears to be feasible for all scenarios based on simulation results.
  • It was assessed how frequently salinity, inundation, and bed shear stress are within the desired levels on an annual basis.
  • The two projects do not appear to significantly impact one another, based on model results.
  • Results addressed a number of site-specific questions and concerns related to impacts of the proposed restoration on neighboring infrastructure such as dikes, outfalls, docks, and pipelines with respect to inundation, sedimentation, and erosion.

Contacts and Project Team

Study Reports and Publications

Whiting J and T Khangaonkar. 2015. Hydrodynamic Modeling Analysis for Leque Island and zis a ba Restoration Feasibility Study. PNNL-24023, prepared for Ducks Unlimited by Pacific Northwest National Laboratory, Seattle, WA.

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