Assessing tidal marsh vulnerability to sea-level rise in the Skagit Delta

Northwest Science
Environmental Protection Agency Science to Achieve Results (STAR); Office of Naval Research (Tidal Flat Dynamics Departmental Research Initiative)
By: , and 

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Abstract

Historical aerial photographs, from 1937 to the present, show Skagit Delta tidal marshes prograding into Skagit Bay for most of the record, but the progradation rates have been steadily declining and the marshes have begun to erode in recent decades despite the large suspended sediment load provided by the Skagit River. In an area of the delta isolated from direct riverine sediment supply by anthropogenic blockage of historical distributaries, 0.5-m tall marsh cliffs along with concave marsh profiles indicate wave erosion is contributing to marsh retreat. This is further supported by a “natural experiment” provided by rocky outcrops that shelter high marsh in their lee, while being bounded by 0.5-m lower eroded marsh to windward and on either side. Coastal wetlands with high sediment supply are thought to be resilient to sea level rise, but the case of the Skagit Delta shows this is not necessarily true. A combination of sea level rise and wave-generated erosion may overwhelm sediment supply. Additionally, anthropogenic obstruction of historical distributaries and levee construction along the remaining distributaries likely increase the jet momentum of river discharge, forcing much suspended sediment to bypass the tidal marshes and be exported from Skagit Bay. Adaptive response to the threat of climate change related sea level rise and increased wave frequency or intensity should consider the efficacy of restoring historical distributaries and managed retreat of constrictive river levees to maximize sediment delivery to delta marshes.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Assessing tidal marsh vulnerability to sea-level rise in the Skagit Delta
Series title Northwest Science
DOI 10.3955/046.090.0107
Volume 90
Issue 1
Year Published 2016
Language English
Publisher BioOne
Contributing office(s) Pacific Coastal and Marine Science Center
Description 15 p.
First page 79
Last page 93
Country United States
State Washington
Other Geospatial Skagit River Delta
Online Only (Y/N) N
Additional Online Files (Y/N) N