Thursday, May 17, 2018

When timelapse fails, go to stills

Sadly the old timelapse cameras that I've had staring at the Elwha River mouth are starting to give up the ghost, and I don't have replacements. I had to pull one last month to try to revive it, and hoped that the remaining camera would hold out on solo duty for the month. Alas, it did not. It collected exactly 8 photos over a span of 4 hours. However, the 8 photos that it did collect do suggest some interesting continued evolution of the Elwha River mouth. The photo above was one of the 8, taken nearest to low tide. The river in that view still has a sizable channel draining to the west (in the near field).
The photo above, which I took with my hand-held shows that near field mouth completely close off, and the mouth to the north (in the far field) widened, and possibly shifted to the west a bit. As an added bonus, videographer John Gussman was out there yesterday as well, and captured some cool drone footage of the river pumping a nice plume out of that northeastern oriented mouth. Check it out.

Thursday, May 10, 2018

Cool new tool for understanding shoreline change



Shorelines are constantly responding to forcing conditions associated with waves, tides, precipitation, wetting/drying, wind, sediment supply, large wood...the list goes on and on.  The video above was shot at Kalaloch, Washington during a winter storm event, and provides a visual sense of the forces that beaches and shorelines are frequently exposed to.

So this is all fine and good - we would expect shorelines to change in response to these forces, and it is of interest from a scientific perspective to understand the processes that drive shoreline change and recovery.  However, there is also a distinct, and hopefully obvious, societal interest in understanding patterns of change, and in particular erosion trends in shorelines.  That interest is, of course, because we have put a lot of things that we value in the way of eroding shorelines.



Measuring long-term trends in shorelines, though, is surprisingly difficult.  I employ my own approaches based on surveying methods, but they are field-based and time-consuming and therefore limited in the geographic scope that they can be applied to.  In general, prior to survey based methodologies shoreline change analyses made use of aerial photography...which is very useful because of the time-frame over which trends can be inferred, but generally limited by the limited temporal frequency and the varying quality of aerial photographs.

So this problem associated with developing long-term trends in shorelines over large spatial scales remains an on-going challenge.  A few years ago, as part of an AGU annual meeting workshop, I was invited to spend a day at the Google office that handles Google Earth and Google Earth Engine, and learned about Google's efforts to hoover up the full record of LandSat imagery dating back to the 1980's and build them into a cohesive global dataset with applications to a variety of problems and questions.

As a consequence of that workshop I started to use the Google Earth Engine timelapse tool (embedded above) to understand local shoreline dynamics, and also played around with (taking advantage primarily of the skills and efforts of my fiend Matt Lucas) using Google Earth Engine specifically to assess multi-decadal shoreline change.  Here, for example, is an NVDI (which attempts to use pixel characteristics to identify water and land) applied to the Elwha River delta in 1984:



and another view from 2015:


in which you can see the pattern of change associated with the Elwha dam removal near the river mouth.  So clearly this tool can pick up, at least in some way, these large changes in shoreline position.

When Matt showed me these results I thought to myself, "there is some power here to do some large-scale shoreline change analyses".  Well, sure enough, a group of researchers from Holland has done the work, and developed a fascinating web based data visualization tool to go with it.

Its not perfect.  If you look closely at some portions of our local shoreline, for example (like this screen grab showing Cape Flattery near Neah Bay below), you see a bunch of red bars, suggesting long-term erosion.  But this is a bedrock shoreline, and is unlikely to have eroded at relatively high rates over this time frame.


But it does pick up some of the known patterns of change on the sandy shorelines of SW Washington.  Here, for example, is a screen grab showing Grays Harbor and parts of Willapa Bay:


here we can see the rapid erosion rates plaguing areas around the mouth of Willapa Bay, as well as the area around Westport, Washington.  So that is encouraging.  And of course there is nothing else out there that provides a global perspective like this tool does.  This represents a big advance in terms of understanding patterns of shoreline change on a global scale.

Friday, March 23, 2018

A new sea level record set in Washington?

Every few weeks I fire up a few Matlab-based tools that I've assembled to check in on what is going on with coastal water levels in Washington.  And a few weeks ago I noted an interesting milestone, the annually averaged water level in Seattle (from the Seattle tide gauge) set a new record high last year:


Check out the top panel, which is the mean sea level from the 2017 calendar year.  The previous record mean sea level was 2.120 meters relative to local MLLW, set in 1983 during that year's extreme El Nino.  Last year, by my calculation, Seattle hit an average sea level of 2.122 meters.

The subsequent two panels break that average down by season.

If we drill down further we see some interesting distinctions between WHY the 2017 average was so high versus the previous record from 1983.  Below are the same data as above, except showing the monthly averages, expressed as anomalies from the long-term seasonally-corrected average:

Focus in particular on the bottom panel, which is the monthly mean sea level anomaly.   So the intriguing thing is that while the record for 1983 seems to have been set by having a few months early in the year with really high average sea level, the average in 2017 seems to have been set by having a lot of months of somewhat above average sea level.

So its clear from the trends on these plots that relative sea level is rising in Seattle, which isn't a surprise to anyone that has been paying attention to the tide gauge data.  Is this new record due to pure sea level rise, versus subsidence of the land that appears to be happening in Seattle?  I will leave the fuller exploration of that till a later date, but wanted to quickly show the same annual water level estimates from Friday Harbor, just for comparison.  Our preliminary analysis suggests little, if any, vertical land movement in Friday Harbor, whereas Seattle appear to be subsiding.  Here it is:


So here you still see a trend - again not a surprise given NOAA's own analysis, but here appears to be entirely due to water level actually rising (not land falling).  And you will also note that 2017's average water level wasn't the highest on record...1983 retains its record by a good bit.

Friday, January 19, 2018

Big Waves




Yesterday the Washington coast was hammered by an potent combination of extraordinarily large and powerful waves, which coincided with a reasonably high astronomical tide and some storm surge. You can see these processes coming together (high tide was at roughly 1pm) in the video above, compiled from a webcam mounted on Kalaloch Lodge on Washington's Central Coast. This webcam is looking straight out the mouth of Kalaloch Creek, a small coastal creek, towards the ocean.  In the video you can see waves pulsing into Kalaloch Creek, mobilizing and transporting the massive jams of wood that line the beach and creek mouth there.  This storm led to at least one death, and a raft of incredible videos, photos and stories from along the coast.

How extreme were these waves? Pretty darn extreme. The Cape Elizabeth Buoy has been measuring waves just offshore of the Washington Coast since 1987, providing hourly estimates of significant wave height and other wave and weather parameters. To date the bouy has accumulated over 200,000 wave observations going back almost 20 years. The bouy estimated a peak significant wave height for this event of 9.9 m at 12:50 pm. There are only 14 larger wave observations on record, all associated with the "Great Coastal Gale" of December 3-5 2007.  I've plotted significant wave heights from Cape Elizabeth below, as a time series (top), and a histogram (bottom).




Friday, December 22, 2017

The Elwha Delta gets hammered



A couple of days ago John Gussman sent out some beautiful pictures of the Elwha River delta, most shot from his drone.  One of the things that really struck me was how much the morphology had evolved from the sort of classic crescent shape that has characterized the delta since the dam removal period, which is nicely illustrated in this 2015 aerial photo:

An aerial image of the Elwha delta taken 23 September 2015 by Andy Ritchie's PlaneCam

By contrast, in John's photo the bar to the east side of the river mouth is set quite a bit landward relative to the west side bar, giving the delta a somewhat lop-sided look.

So given this odd morphology I was stoked to find that my old creaky time-lapse cameras looking down at the river mouth had managed to shoot photos through December, capturing in particular the series of storms that hammered the delta around Thanksgiving (which included some river flooding).  Indeed, those cameras revealed that the eastern bar had been pushed landward quite rapidly between roughly December 1st and December 4th (check out the video above, or here).

The video below (and also here) is a time-lapse of the raw 30 minute photos (not averaged for the day), and suggest a few days of elevated water level and waves:



which also suggests that there was some rapid landward movement of the bar to the east of the river mouth between roughly December 1 and 4.  I happened to get some profile data on 5 December as well, and have one profile line that cut through the section of bar visible in this video, Line 156:

You can really see the migration of that bar in my profile data from Line 156:


These data suggest roughly 50 meters of landward migration between September and December!

Interestingly though, the beach at Line 164 (which is outside the field of view in the video, to the east) is far more stable:


Its not abundantly clear to me what drove the bar migration in early December - it wasn't really a period of extreme wind, water level wasn't really all that highFlow was still a bit elevated by early December, but the big peaks had occurred earlier, around Thanksgiving.  And waves, at least as suggested by the buoy out towards Neah Bay, weren't all that big:


This plot is significant wave heights measured all the way out at the mouth of the Strait, and while those wave heights around the 29th of November are indeed sizable (5.5 meters!), by the 4th things had calmed down.  Indeed, it seems like the convergence of forcing was really between November 26 and 29, but by my eye the time-lapse suggests that the bar really moved between Dec 1 and Dec 4.  Very cool...it will take a bit more digging to figure out what really happened here.

Thursday, December 7, 2017

When a King Tide Isn't so royal

Photo of Hollywood Beach taken during the "King Tide" on 6 December 2017
I love me some King Tides, and I love that we've built programs around appreciating and even viewing these sorts of events.  The concept is that we can use these high water events to understand future conditions, or learn something about the complex suite of processes that drives variations in marine water level in our neck of the woods.  I'm 100% in to both of those concepts.


Predicted water level due to astronomical tides in Port Angeles, Washington for the winter 2017-2018
The predicted marine water levels due to the astronomical tides for this winter in Port Angeles, WA (relative to Mean Lower Low Water, or MLLW) are shown above, and four "King Tide" periods stand out as the three humps on the top of the curve, where predicted water level exceeds 7.5 feet.  For reference, the mean higher high water (essentially the daily average high tide) elevation here is 7.0 feet relative to mean lower low water.  So these are pretty high water events.

Predicted (blue) and measured (red) water level at Port Angeles on 6 December 2017
So yesterday's predicted high water level for Port Angeles was 7.8 feet - thats pretty good - and i went down and snapped a pic looking east from the Feiro Marine Life Center (check it out above).  And I have to say, it was pretty unexciting.  What gives?  The measured water level yesterday was considerably lower than predicted...by a full foot.  So the actual water level actually was even lower than the daily high tide.

Predicted (blue), measured (green) and the difference between the two (purple) for Port Angeles for the last year
If we look back even further, and look at a whole year of water level data, we can see that, in fact, water level has reached that 7.5 ft threshold on numerous occasions.  The highest water level in the last year occurred on February 9 of this year.  This one was particularly cool because this particular event was the opposite of what happened yesterday.  It was an astronomical King Tide, with a predicted water level of 7.7 feet...but what actually hit the shoreline was an impressive actual water level of 9.2 feet...which is getting close to the highest observed water for this station (dating back to 1979) of 10.5 feet.  Sadly, no pictures.

Predicted (blue), and measured (green) water level in Port Angeles, WA, and the difference between the two (purple) for February 9, 2017
My take away, though, is that to really get the good King Tide photos its worthwhile looking watching your local tide gauge, and in particular paying attention to what we call the NTR, or "non-tidal residual", which is the difference between the observed and predicted water level (the purple lines on my plots).  If that NTR is high, like 1 ft plus in our area, then get out there!  Heck, if its really high (like 2+ ft), then get out there at any high tide.  

Tuesday, October 24, 2017

Sea Level Rise in the news

A history of long-term relative sea level change in Friday Harbor, Washington - a pattern that our data suggest is not due to land level change...but rather to the sea rising
Is it just me, or is sea level rise breaking through in our neck of the woods?  This week there were multiple articles making the rounds focused on sea level rise in Washington State including
reporting at the Seattle Times and KIRO7 on Zillow's updated sea level rise vulnerability assessment for real estate (which I will get to later) and Chris Dunagan's reporting for the Encyclopedia of Puget Sound on issues surrounding homeowner decision-making in the era of sea level rise and also his piece on SLR planning on Washington State.

Nuisance flooding like this, in Port Townsend on 10 March 2016, is almost certain to become more common and more of a problem in the future.  Photo courtesy of the Local 20/20 King Tides Team
The concept of climate-driven sea level change is nothing new...its been part of the climate change conversation for decades.  What is evolving is our understanding of the processes that drive sea level change (typically referred to as sea level components) over the community planning time-frames of interest.  The Earth system is complex, though, and the problem of interest here is complicated and multi-part:  How do emissions of greenhouse gases integrate with the natural cycles of those gases, how do the resulting concentrations influence the global heat budget, then how is extra heat distributed around and through the globe, and (finally) what are the process and rates at which that heat starts affect the components that lead to sea level rise (for example, how does that head lead to the break down of large masses of land-grounded ice on Antarctica)? 

Antarctica - a huge mass of land-grounded ice (this is an artists rendering of a cut-away view through the ice).  Its future matters to us.  Photo credit:  National Geographic
The evolving understanding of the processes that drive sea level change has led to an intense focus on this problem amongst the scientific community, as evidenced by the publication rate of papers focusing on sea level rise.  I used Web of Science to search for papers with the topics "sea level rise" and "climate change" and came up with this publication distribution through time:


This intense focus on the processes that drive sea level rise, of course, has led to a community planning problem, though; projections of sea level rise, or how much we can expect, change through time.  This isn't surprising if you think about it.  Projecting anything is hard.  As a society we make projections all the time in any number of fields...and many of them don't play out as expected.  In the case of sea level rise, projections will change as our understanding of processes driving sea level rise evolves, and also as we observe sea level rise happening and can compare those observations against projections.

This brings me back around to Zillow's analysis.  I like this approach that they took, where they used their national scope and data-analytics expertise to look at the possible national implications of sea level rise on their core product - homes.  Using a sea level rise of six feet relative to present, they found (perhaps not surprisingly) that places like Florida have a lot at stake.  It also is a reminder, though, that Washington State is not immune from sea level rise (even though we may be less vulnerable on a national scale) - there is a lot of high value infrastructure exposed.

Zillow has taken some criticism though, for the particular sea level they chose to do their analysis with - six feet relative to present sea level.  The Washington Policy Center published a blog, for example, saying that six feet was out of alignment with the most recently published projections by the IPCC.  An early statement in the article sets the tone, "Their projections are, essentially, made up".

Is six feet of sea level rise made up?  Does it "ignore the science", as the title of the Washington Policy Center piece implies?  No, quite the opposite, and here we simply see this problem associated with a rapidly advancing scientific endeavor.  The Zillow analysis uses a very recent NOAA assessment that attempts to assess the likelihood of different levels of sea level rise across the full range of uncertainty (using a very similar approach to what we are doing with the Washington Coastal Resilience Project).  By contrast, the IPCC projection plot shown in the Washington Policy Center blog only communicates a narrower "likely range", which the Washington Policy Center's blog misinterprets as communicating full range of uncertainty.  Zillow nicely acknowledges the uncertainty that the NOAA assessment is trying to communicate by stating, "if the oceans rise six feet – roughly midway between the high end of what the government says is “very likely” (4.3 feet) and the possibility of an 8-foot or greater rise that cannot be excluded." 

Lets dive a bit deeper here.  The "upper ends" of the probability distribution, where sea level rise exceeds the ~2-3 ft (by 2100) best estimate, are driven by places like Antarctica melting a lot more than was previously assumed in past sea level rise projections (ice sheet uncertainties, and their implications, are also touched on in this fascinating recent article by Forbes).  Science seems to be pointing towards these large masses of ice being more sensitive to climate change than has been previously assumed - a conclusion that, if it holds up, will lead to a greater likelihood of higer sea levels represented in future projections.  Its also worth acknowledging that, while 6 feet of sea level rise by 2100 may be unlikely based on NOAA's current assessment (and ours, for that matter), sea level isn't projected to fall in the coming centuries - and we become much more likely to get to 6 feet by, for example, 2150.

And, of course, Zillow could re-run their analysis with a best estimate of 3 feet, and we would still see vulnerabilities emerge, both around the country and in our own neck of the woods.  Despite changing projections, and uncertainty, we gain by planning now to avoid future costly problems.