[Geoldept] North Fork Skagit River Avulsion

[Eric Grossman]

Hi All,

Just in time for the Holidays, the recent Eastern Pacific's atmospheric rivers have brought us an amazing geomorphic event on the N Fork Skagit River.


On Nov 29 (~90,000 cfs) and again the last 40,000 and 30,000 cfs flows at Mt Vernon, a new distributary that I have been monitoring since 2005 since it was a little baby abruptly widened to near 60 m and is actively carving a new deep channel out to Skagit Bay. We have measured the discharge through the channel relative to the N and S Forks and mainstem of the Skagit over time and whereas in 2007 it conveyed about 1-2% of the total flow of the Skagit, as of last Friday, it now conveys ~70% of the N fork flow (and presumably sediment) or ~33% of the entire Skagit flow and sediment load. The attached short Powerpoint briefing describes a few aspects of it that my team is working on, note the last air photo of 2013 precedes the last doubling of the channel width.


Anyone interested in helping to measure bathymetry, currents/circulation, suspended sediment transport, bed sediment, and eelgrass using sonars, sidescan, ADCPs and discrete sampling instruments please let me know. We will be conducting repeat surveys over the next few months in addition to measuring floods on the Nooksack, Skagit, Stillaguamish rivers and coastal storm surge and wave overwash when they occur around Whatcom, Skagit and Island Counties.


Happy Holidays.

Eric



Eric E. Grossman, PhD
Research Geologist, U.S. Geological Survey
USGS Western Fisheries Research Center, 6505 NE 65th St., Seattle, WA 98115; 206-526-6282x334<tel:206-526-6282x334> (office), 831-234-4674<tel:831-234-4674> (cell)
email: egrossman at usgs.gov<mailto:egrossman at usgs.gov>

Affiliate Researcher, Western Washington University
Dept. of Geology, 516 High St., MS 9080
Bellingham, WA, 98225; 360-650-4697<tel:831-234-4674> (office)
email: Eric.Grossman at wwu.edu<mailto:egrossman at usgs.gov>
http://puget.usgs.gov/
http://coralreefs.wr.usgs.gov/
http://www.usgs.gov/coastsalish
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