Friday, July 1, 2016

What is going on at Ediz Hook?

The view along the base of Ediz Hook, with Mt. Baker in the distance
I get asked all of the time about Ediz Hook, and whether we are seeing any Elwha sediment nourish the spit.  We wrapped up annual surveying of the Hook today, and based on those data I've got to say that the answer is still no.  Here are some profiles that combine my own survey data (collected in many cases with assistance from students from Peninsula College, the Huxley College on the Peninsulas, or the University of Washington - this year's data were collected by Jacob Carleson and Melissa O'Brien, both incoming Huxley students) with a lidar dataset collected in 2012:

This is my first transect and suggests little in the way of beach evolution since 2012.  This is where one might expect to first see an influence of the dam removal in the beach profile...and there is nothing really obvious going on.

Underneath the mill proper it appears that there is an on-going pattern of systematic erosion, at least since 2012.  Some of this may be erosion of the nourish material placed every few years on the Hook by the Army Corps - I think the last placement was in 2011, so the erosion between that 2012 lidar and the first survey data shown here may be the loss or displacement of that nourish material.

Continuing to the east we reach the first complete inside-to-outside profile, which suggests a pretty stable profile.  Here you can see, at the very crest of the Hook, some indication that perhaps the rip rap was augmented or raised here between 2012 and 2013.

Continuing west we get into an interesting area.  On the outside of the Hook we can see another area that the ACOE nourished in 2011, and which since that time has been systematically eroding.  On the harbor side of the spit there has been some really interesting evolution - the 2012 profile is eroded back by 2014 (this was due, if I recall correctly, to a winter storm in 2013??).  The in the fall/winter of 2015 the Lower Elwha Klallam Tribe nourished the upper profile as part of a shoreline restoration program.  That material was then naturally moved down the beach and has been building up the middle and lower beach.  Again, though, the Strait-side of the Hook is where we would expect to see a profile response from the dam removal...and as of yet its not evident in these profiles.  Where there is obvious evolution of the profiles on Ediz Hook its apparently due to nourishment activities.



Coming to the end of the Hook; this is the only bit of the Hook that is unarmored, and these profile data suggest that Ediz Hook has been getting longer since 2012 - about 10m over that time period for an average rate of growth of ~2m/yr.  Interestingly this growth rate exceeds the average growth rate for 1870-1917 (1.3 m/yr) previously reported by Galster and Schwartz in their 1990 paper on Ediz Hook, and is quite a bit higher than the average rate of growth they identify for the "modern" era (1948-1970; 0.6 m/yr).  Whats going on here?  Is this a dam removal thing?  I don't think so.  Here is the final profile:


Its a bit hard to see here since I am showing a profile that cuts across the entire distal bulb of the Hook, but the Strait side of this profile is just to the east of the end of the rip rap that covers most of the Strait-side of the Hook.  And what is clear from the aerial photo above is that there is end-cutting, or erosion, just to the west of the end of this rip rap...its hard to see in the profile, but I estimate that the shoreline has eroded about 6m since 2012.  Interestingly there has been no growth of the shoreline on the harbor side of the Hook...so in essence the Hook, at its tip, is getting skinnier, and my hunch is that the erosion of the the Strait side of the distal end of the Hook is supplying the sediment that is lengthening the spit.  So the distal end of Ediz Hook is getting longer, but since its also getting skinnier my conclusion is that this is NOT due to a sediment supply from the Elwha Dam removal.




1 comment:

World History said...
This comment has been removed by a blog administrator.