Wednesday, October 26, 2016

The coastal anatomy of an October storm

Looking down at the Elwha River mouth on Friday October 14th at about mid-day.
Its not too often that you are in the right place and right time to sample during an extreme event, and while the series of storms that hit the Washington Coast starting on the evening of Thursday October 14th turned out to be not quite as severe as expected, they still represented a reasonably strong wallop to the coast in general.  I happened to be working through that entire series of stormy days on the beach of the Elwha River delta, primarily supporting a group of students from a University of Washington course that I am co-teaching.  But the intensive field time gave me the the chance to observe and measure various aspects of the storm response of the beach to the storm. 

As a starting point lets look at some of the forcing:

Surface pressure and wind magnitude recorded at the Port Angeles tide station
The pressure record from the Port Angeles tide station clearly shows the passage of the two major low pressure systems that passed over Washington - the first on Thursday evening and into Friday, and the second in the afternoon of Saturday.  The wind largely tracks those two pressure systems, though the wind speeds associated with the Saturday storm were about twice as strong.

Particularly important relative to the coastal impacts of a storm is water level, and during this storm water level peaked on Sunday mid-day at 2.74 meters above MLLW, which is more or less the average annual extreme water level at this station, and no where near the record high of 3.2 meters set in 2003:

Predicted tidal water level (red) and measured water level (blue) from the Port Angeles tide station.
But these relatively unexciting water levels occurred in part because this storm happened to coincide with a neap tide period, when the astronomical tides were relatively low, because the non-tidal residual, or 'storm surge', were pretty healthy for our area:

Sea level pressure (red) and non-tidal residual (the difference between the predicted tidal water level and the actual measured water level) from the Port Angeles tide station
For the storm surge the peak occurred around 7pm on Saturday, and coincided nearly perfectly with the peak low pressure.  It also (thankfully) happened to co-occur with a relatively low tide at this site, which again helped to keep the peak coastal water levels associated with this series of storms relatively low.  Amongst other things, this is another clear demonstration that in our area coastal flooding/erosion and other storm impacts is often a game of chance. 

The other beautiful thing about this plot is the obvious tight relationship between pressure and storm surge - the changing pressure essentially influencing the sea surface.  Here is another perspective on that:

Relationship between pressure and non-tidal residual between 12 and 18 October 16 based on data collected at the Port Angeles tide station
In this case the linear trend here is equivalent to roughly 13 mm of water level change per mb of pressure change, which is roughly similar to the other trends I've seen estimated for this relationship.  What is interesting here though is the suggestion that there are essentially two relationships, one that I am guessing is associated with the approach of the storm (i.e pressure lowering), and the other that I am guessing is related to the passed storm (i.e. pressure going back up).

Lets get back to the beach, though, and look at some of the morphology changes that occurred during this series of storms along this same set of cross-shore transects that I've discussed previously:

and lets start over towards the east side of the delta and move west.  Here are the profiles from a subset of the transects above, moving from east to west, showing typically profiles from 12 Oct, 14 Oct and 16 Oct, plus in most cases a profile from my most recent pre-storm survey in September.  At the bottom of each panel is a time-series of shoreline position over the last 5 years.

 In general the theme during this event seems to be overwash of the recently formed backshore driving accretion at the very upper part of the intertidal profile.  Here, for example is a photo taken on Friday October 14th, taken near Line 198, of an approximately 20-30 cm thick overwash deposit.  Based on the differences between the 14 October and 16 October profiles in the figure above, this deposit continued to grow over the next two days.

Interestingly, at most locations the accretion on the upper beach seemed to occur without much in the way of erosion of the beach face (except at Line 198), suggesting that the sediment building the upper beach was derived either from lower down the intertidal, or elsewhere (i.e. alongshore).  Regardless, it also suggests that the Elwha beach is in a state of plentiful sediment supply at the moment...not a huge surprise.

The exceptions here are Line 180, which was erosional on the upper beach during this storm (there always has to be one), and Line 156 right near the river mouth, which surprisingly didn't change much, especially because during the peak of the storm on Friday it was almost fully overwashed:

Photo taken Friday October 14th at 1:40 pm looking west from approximately Line 164 towards the river mouth and Line 156

The other interesting thing to note here is that in general the accretion on the shoreline was occurring relatively high on the beach face, above 3.0 m relative to MLLW in most cases (I use NAVD88 in the plots above, which is ~0.12 m offset from MLLW here), and well above the measured tidal water levels.  Clearly the other big process at play during this storm event on the Elwha River delta were waves.  Here is a video of waves breaking on the delta taken on Friday October 14 around 2pm:

So I don't have local wave data available for the Elwha for this period (though we did have sensors in the water - excited to check that out), but here are the significant wave height time-series (in orange) and wind (in blue) from the Hein Bank buoy, out in the middle of the Strait:

So here, the tight coupling between wind and wave height suggest that these are primarily locally generated wind waves...and big ones at that - 1.8 m significant wave heights in the Strait are not unheard of, but not extraordinarily common.  Another way of looking at the role of local wind as the wave generating force is by partitioning the significant wave height into wind wave (in blue) and swell wave (in orange) components:

Clearly most of the wave energy we saw on the beach during this storm was comprised of locally generated wind waves.

What was also clear from working on the beach was that during this time period there were often waves coming from both directions (east and west), and while I didn't take the time to analyze the full wave spectra, just in looking at the mean wave directions supplied by NOAA its evident that there was quite a bit of switching between east and west over the time period.  In the plot below the orange line is the significant wave heights at Hein Bank buoy during this time period, and the blue dots are the mean wave direction (this is the direction from which waves are coming):

Its also clear that the largest wave sizes during this period were associated with waves propagating from east to west, not west to east as is the case under most "normal" conditions.

and while its not a perfect way of thinking about it we can try to integrate the measured water level with the wave time-series from Hein Bank to at least start to think about the potential total water level (including the tidal, non-tidal and wave-driven components of water level) by looking at the measured water level (in orange) and the significant wave height estimates (m):

There are a few periods that pop out here that were the time periods when large waves coincided with high(ish) tides, and likely drove shoreline change high up on the beach face, and into the back shore, including mid-day on Oct 13th and Oct 14th and again probably during the night early on the 16th.  The influence of waves on water level, especially mid day on the 13th and 14th, on the delta is apparent in this timelapse looking down at the river mouth from the east:

Friday, August 19, 2016

An update on the Elwha delta

The Elwha River delta and view to the west, photographed 23 July 2015

Its been a good while since I've posted about the goings-ons of the beach of the Elwha River delta, and there have been some exciting developments this summer.  In particular, the beaches on the east side of the delta really added some volume this spring and summer.  Lets take a look at a few profiles, referenced to the map below:

So lets start at the river mouth and move east.  Line 156 and Line 164 are right on the new part of the delta, and where there has been massive accretion in the ~4 years since late 2012.  That massive growth has largely stopped this year, and at Line 164 the profile data show fairly rapid erosion:

By the way, the way each of these profiles is configured is a top panel that shows a selection of profiles (in this case I chose one "winter" profile from February or January of 2016, and then a set of three from this summer (June, July and August).  The bottom panel on each figure is a time-series of the cross-shore position of the Mean High Water contour on the upward slope is accretion or seaward movement of the beach, and a downward slope represents erosion.  

Moving east things really changed this year.  Profiles on the east side of the new deposit near the river mouth showed nice even growth through this year after a period of very rapid accretion that occurred last summer.  Here is Line 174:

But it was to the east, at the very northern end of the delta, where things really heated up this summer.  Here is Line 190 and 198:

At these two sites a pattern of chronic erosion reversed in the summer of 2014, but it was something of an uneven and intermittent pattern of accretion until early this summer.  Moving around the northern tip of the delta, we were seeing slow but chronic erosion until early this spring.  Here is line 204 and 210:

One of the things I find interesting about this stretch of beach is the apparent movement of material from low on the beach towards the upper part of the profile.  Things east of here are a bit more complicated, largely because the shoreline had been highly modified by a long segment of old abandoned rip-rap that started over closer to Line 198, but connected to shore near Line 216.  Where it connected to shore it seemed to be acting as a groin, which I suspect is why profiles at Line 216, 222 and 229 really show very limited growth this summer.  However, as of last week a project led by Jamie Michel of the Coastal Watershed Institute removed nearly all of that old rip rap...and at Line 216 there was an immediate if subtle response:

 In this profile you can actually see the rip rap boulders that connected to shore.  Here is a photo of what this section of beach looked like prior to Jamie's shoreline restoration:

Line 216 cuts right through this picture above, up along the rip-rap near the line marking the annotation that starts, "Shore-connected...".  Here is what this same stretch of beach looked like on Thursday (albeit from a different perspective, looking alongshore towards the west...roughly from where the white arrow is in the photo above):

So if you look closely at the profiles for Line 216 you can see that between July and August two things happened...the rip rap came out (you can actually see that in the profile, by how smooth it is between about 1 and 3 meters), and the beach grew a bit there.  You might expect that this would take a while...after all the big machines used to remove the old boulders probably left some pretty substantial holes in the beach.  But Jamie reported that the area where they had pulled the boulders out was filled in, and actually grew a bit, just one day after those boulders were removed.  

Completing the trip around the delta, Lines 222 and 229 both show some late summer erosion, which is consistent with what I've seen in previous summers on the delta:

but with the "groin" out I will be very interested to see what the beach looks like next month...

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 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.

Monday, June 13, 2016

When pigs fly, cats and dogs consort together, and dolphins frolic in Port Angeles Harbor

Photos of Common Dolphins in Port Angeles Harbor.  Courtesy of the Island Adventures blog.

Today Island Adventures posted a blog describing sightings of common dolphins in Port Angeles Harbor, which was picked up and pushed back out on the Feiro Marine Life Center Facebook page. First off, were these really Common Dolphins (Delphinus delphis)?  I really have no idea, and I would presume and hope that the folks on the Island Adventures boat would know quite a better than I would.  There is apparently some confusion about this species on the west coast, with at least one source saying they don't occur on the west coast, but others saying that there is.  I suppose they also might be Pacific White-sided Dolphins, which would be rare but not unheard of, at least in this general area?   Regardless, I am going to assume that these were common the end it doesn't really matter for my purposes.

Common Dolphins are typically associated with slightly warmer water than we are accustomed to here, and so these photos caught my attention, since just last week I was discussing elevated seawater temperatures with my colleague Eric Grossman, who was mentioning how warm the water was up near his home in Bellingham Bay.  This led me to remember that a few years back, when I was working on a climate change impacts assessment for the Olympic Coast National Marine Sanctuary, I put together some Matlab scripts to automate the download and analysis of temperature data collected at NOAA tide stations.  So I decided to run my old scripts again.

The NOAA tide gauge in Port Townsend, WA.  Image courtesy of NOAA

So this script downloads the entire available record of hourly temperature measurements from a NOAA tide guage (see the photo above of the P.T. gauge, located on the ferry dock in Port Townsend).  In most cases temperature is recorded a few feet below the surface.  In some cases the record is incomplete or short, but for some of our stations in our area the record typically goes back to the mid-to-late 1990's and can be fairly complete (i.e. no major gaps).  Lets look at a selection of those, starting with Seattle:
First, Seattle (above).  So what you are seeing here is the average monthly seawater temperature in blue, and then in red the anomaly from the monthly average.  In this case I've specifically defined the anomaly as being the deviation from the monthly average for the period from 1999-2008, for consistency with the "Marine Water Condition Index" used in Puget Sound.  Focus on the red line.  What this tells us is that seawater temperatures have been hovering around 1C above average since late 2014 (when the "blob" came ashore), after you account for and remove our "usual" annual signal (i.e. warm in summer, cold in winter).  
And its not just a Seattle thing.  The record above is from Port Townsend, Washington, where you see much the same signal.  Note how very warm the last two winters were in particular!
The signal is quite a bit more muted in Port Angeles (above; i.e. the anomalies are as large, but not as unprecedented in the record) and on the outer coast (Toke Point, shown below).  My take is that this is a reflection of just a great degree of water temperature variability as you move out of the Strait to the outer coast:

The record above is from Toke Point, at the mouth of Willapa Bay.  Note as well that on the outer coast the average temperatures are much warmer in general than in the inland waters. Back to the point, though...and moving on to a different way of looking at these data:
Above is a different way of looking at these data, shown here for Port Angeles - every hourly measurement available plotted together on an annualized axis.  I've bolded the temps from this year to show where they sit in the "usual" pattern.  Last year is also highlighted with the heavier blue line...also very warm.  So whats clear here is that the last two years in Port Angeles have been pretty warm when you put the whole record into context.  The real winner, though, in looking at these water temperature data though is up in Cherry Point, near the Canadian border:

The anomalies suggested here are so huge as to be unbelievable.  Is this true?  It certainly is consistent with Eric saying that "its warm"...but this is quite something.  Below are this year and last year's hourly data plotted together...really gives you a sense for how dramatically warm it is compared to the last 20 years, at least during the non-summer months:

So, circling back.  Common Dolphins in Port Angeles Harbor?  Are these dolphins taking advantage of these warm conditions to move into new space in the Salish Sea?

Monday, May 16, 2016

Light and sediment in the coastal ocean

Our dive site F1, roughly 1km east of the Elwha River mouth, before (top; summer 2011) and during (bottom; summer 2013) dam removal
Included among the many things that the Elwha dam removal project is teaching us is how sediment can interact with the community of living things in the coastal environment. In particular we are interested in the role that turbidity, due to fine sediment held in suspension, played during the height of the dam removal period (2012-2014) in driving changes to the marine algae community in the Elwha nearshore. The video set above shows, for example, what we saw at many of our sites scattered around the delta - places that had coarse substrate suitable for algae to attach to...but suppressed algae growth during dam removal. The answers to these sorts of questions go beyond the Elwha in regards to their importance. Globally, humans are changing the movement of sediment from the land into the coastal oceans, ergo we may also be altering coastal ecology on a grand scale via this sediment mechanism.

What turbidity can do to light - a video shot in May 2012 at the same site as the videos at the top of this post. Dark!

To get a better handle on the movement of fine sediment from the Elwha River into the coastal zone Andrea Ogston (from UW's Sediment Dynamics Lab) and I proposed a project to Washington Sea Grant, which was funded (full disclosure: since I work for WSG I am not funded by the project, but do act as a co-PI). The project continues the Sediment Dynamics Group's long history of work in the Elwha nearshore tracking fine sediment dispersal, but builds on that by adding in to the mix better measurements of light in the shallow coastal area around the Elwha River mouth, and partnerships with the coastal ecologists working on the project (like Helen Berry and team from the Department of Natural Resources, and Steve Rubin, Melissa Foley and Nancy Elder from the US Geological Survey).

Emily Eidam from the UW's sediment dynamics group collects a sediment sample from the sea floor with a Shipek sampler.

Last week was the first in a series of cruises on the UW's R/V Clifford A Barnes in order to collect bottom samples (i.e. see the video above), sample the water column for turbidity and other parameters, and also deploy a series of moorings specifically designed to measure sea-floor light:

Emily with a custom made mount and light measurement cluster

Looking down at the light measurement cluster - three HOBO light intensity sensors, and two Odyssey PAR sensors (provide by Washington Department of Natural Resources) 

A few more photos from the cruise are below:

A juvenile bivalve (probably Clinocardium?) in fresh mud deposits

Sediment samples!  Ready to go...

The spacious lab on the Barnes

UW undergraduate Morgan Mackay hauling the CTD.  Bachelor Rock is in the background

Barnes, side view

Cruise plan and station map