Friday, March 24, 2017

Glass Beach

I'm going to take a page out of Hugh Shipman's book here and take a stab at profiling a section of shoreline I had the opportunity to explore last weekend.  If you wander west from Port Townsend along the Strait of Juan de Fuca you will find a few treasures.

First, just a stunning, active, classic eastern Strait of Juan de Fuca bluff backed shoreline.  This stretch is complete with perplexing and beautiful stratigraphy, plenty of signs of active erosion,  and also plenty of futile efforts to control that erosion:

Next, beach glass!  This is why we try to find a mythic glass beach that I had heard whispers of.  These sorts of places are scattered along the coast (including perhaps the most famous of them all in CA?), presumably related to old but poorly documented informal dump sites.  Beach-combing for glass is one of those things that everyone in our family seems to love, so it was a treat to try to make it to this well-known glass hunting beach:

As it turns out we didn't make it all the way to the best sites, but made it plenty far to scratch everyone's itch:

Friday, March 3, 2017

Anatomy of a Coastal Storm: March 10, 2016

Nuisance flooding in Freeland, Washington on Whidbey Island after the March 10 storm.  Unknown photographer, photo courtesy of Island County Department of Natural Resources.  
We are coming up on the one year anniversary of the 10 March, 2016 storm that really walloped many communities in northern Puget Sound (see this link as well) and on the Washington Coast.  It was an interesting storm for a variety of reasons and in particular it seemed to impact coastal areas in northern Puget Sound in ways that those communities were not accustomed to. Perhaps as a result I've heard people refer to the March 10th storm as a "100 year storm" from the standpoint of its coastal impacts.  As a result I wanted to use this blog to look in a bit more detail at some of the aspects of this event in in relationship to the coastal impacts associated with the event.

Overwash of sand, gravel and wood on to a road near Oak Harbor, Washington.  Photo courtesy of Lori Clark, Island County Department of Natural Resources
The photos above, and indeed many of the most significant impacts associated with this storm were focused in Island, Skagit and Whatcom Counties, but there is a distinct lack of tide gauge data up in those parts.  So I'm going to focus first on Port Townsend, where there is a tide gauge.  To be clear the storm was exciting there too.  The photo below shows a distinct debris line and nuisance flooding adjacent to the Jefferson Title Company building in Port Townsend on the morning of March 10:

photo courtesy of David Wilkinson
Here are the water level data collected between 5 March and 15 March, 2016 at the P.T. tide gauge, located just east of where this photo was taken:

When interpreting these data I am going to distinguish between three different water levels; first the "astronomical tidal water level", which I will also refer to as the predicted tide (shown in blue in these plots); next the non-tidal residual, which I will refer to as "storm surge", which is the difference between the predicted (or astronomical) tide and the measured water level (shown in purple in these plots); and finally the actual measured water level, or "still water level", which is the sum of the two (shown in green in these plots).

So in P.T. the total measured water level measured during this event WAS high - the peak measured on the morning of March 10 was 3.41 m relative to MLLW...but this is nowhere near a "100 year coastal flood water level" for P.T.  In fact since the current tide gauge was installed in 1972 that water level has been exceeded numerous times, with a maximum measured water level of 3.57 m relative to MLLW reached on 12/10/1993.  NOAA places the March 10, 2016 measured water level as having somewhere around a 1-in-5 year recurrence interval, or a roughly 20% chance of occurring in any given year.  Here is another way of looking at it:

These are histograms of hourly water level data dating back to 1972 in Port Townsend, with the metrics associated with March 10 in red.  At the top is the predicted or astronomical water level...and here the predicted tide on this day wasn't particularly high, but the NTR (the panel at the bottom) is pretty high, but again nowhere near the highest on record (that record was set on 1 Jan 1997 in Port Townsend when the non-tidal residual was roughly half a foot higher than the surge on March 10). So indeed, the "still water level", as measured at the tide gauge WAS indeed high, primarily because of some pretty good "storm surge", the peak of which more or less coincided with high tide...but nowhere near a 1-in-100 year event.

So what compelled us to look at March 10th as extreme?  Well, clearly wind, and wind-driven waves, played a major role in driving flooding during this event.  Here is another photo taken the morning of March 10, 2016, looking south from the south-facing shoreline of downtown Port Townsend:

Photo courtesy of David Wilkinson
There are no wind data available for that event from the P.T. tide gauge, so I turned instead to average wind data (these are averages over an 8 minute period) dating back to 2004 available from NOAA's Hein Bank buoy in the Strait of Juan de Fuca, and in particular wanted to look at winds blowing from the south, so trimmed those data to winds that were recorded as coming from between 120 and 210 degrees.  The histogram of those data suggest that extreme winds here would be those in the 18-20 kt range...

and on March 20 that buoy in the strait recorded peak average winds from the south on the order of 18 kts:

so pretty strong winds.  Again, not horribly strong from the standpoint of the available record dating back to 2004, but pretty strong.  So this leaves us with the notion that what MIGHT have been unique about this storm wasn't so much the relative magnitude of any of the individual processes at play (i.e. astronomical tides, storm surge, and wind) but rather the co-occurrence of these factors...i.e. what is the chance that you get a relatively high astronomical tide, coupled with a strong storm surge, coupled with pretty strong south winds that kick up relatively large wind waves (large by Puget Sound standards).  Taken together, maybe those things do amount to a pretty darn rare event, possibly even a 1-in-100 year event...but calculating that joint probability distribution will have to wait for a later date.

Tuesday, February 14, 2017

Nourishment in Washington State - A look at Ediz Hook

Looking west along Ediz Hook at nourish material place in January along the base of Ediz Hook.  Photo shot from a location immediately east of the paper mill at the base of the Hook (red circle in map below).
Shoreline nourishment, where sand and/or gravel is placed on the shoreline to change the profile or character of the beach, is a relatively infrequently used tool in Washington State, at least compared to other parts of the country.  In Western Carolina University's beach nourishment database, for example, Washington State ranks 4th to last in spending on shoreline nourishment, behind Maine, New Hampshire and Rhode Island.

Part of US Army Corps plans for nourishment on Ediz Hook that took place in January 2017.  This particular nourishment project was limited to the areas in the black box at the base of Ediz Hook.
Ediz Hook though, again based on WCU's nourishment database, is the most nourished shoreline in Washington's protected waters (i.e. in Puget Sound and the Strait of Juan de Fuca).  On Ediz Hook nourishment is primarily used, interestingly enough, to protect the large rip rap material that stabilizes Ediz Hook, and is placed every few years.  Just last month there was a placement of roughly (by my math based on the drawing above) 35,000 cy of sand and cobble to replenish the eroding beach at the base of the rip-rap on the west end of Ediz Hook.

Looking east from the location marked with a red dot in the map above.
 The last nourishment on Ediz Hook that I am aware of occurred at some point in late 2011.  I snapped this photo in January of 2012 from more or less the same location and perspective as the top photo in this post:

Ediz Hook, though, is nothing if not exceptional in its ability to erode material off of its steep shoreface, end even by early April (the photo below was shot on 8 April 2012) most of that material has been eroded off of the upper beach:

Pretty impressive. But certainly it did act to fortify the toe of that beach, as shown in this beach profile from that area that I post a few months ago:

The first profile above is from March 2012.  Of course over the subsequent years that section of beach has eroded chronically.

Monday, January 30, 2017

Shoreline morphology monitoring

Tera Dummitt, student at the Huxley College on the Peninsulas program, walking a beach transect line on Dungeness Spit
Whoa, three months since my last post...far too long.  Things have been too busy.  But in the depths of winter I'm remembering summer, and just wrapped up two reports documenting this year's efforts to measure shoreline morphology at beaches on the Olympic coast and on the Strait of Juan de Fuca. This is a tiny program, and one that I keep afloat largely by determination and donation, but I continue to believe that these types of data will provide us important perspectives in the future.

Ruby Beach with students from the University of Washington MeSSAGE program
Another special part of the program for me is the opportunity it provides to work with students.  This year in particular I had great support from the Huxley College Program on the Peninsulas, as well as the University of Washington MeSSAGE Program.

Along the way I also put together summaries on patterns or trends I find interesting.  A few recent examples are here and here.

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...