Monday, June 25, 2018

A land made of sand



Looking north along the shoreline towards the Big Sable lighthouse on the eastern shore of Lake Michigan
A little family vacation this year means a trip to Michigan, and a few days spent in my wife's childhood summertime haunts near Ludington, Michigan.  We've spent most of our time in Ludington State Park, which sits on the incredible Big Sable Point.  As far as I can tell the whole landscape here is basically a big pile of sand blown out of Lake Michigan, which makes for a prime opportunity to check out various sand transport processes at play, and their resulting landforms.  So first off, a reminder (mostly for my benefit) that the vast body of water that we've been gazing out on to our west:


is, indeed fresh:
but the process scales here ARE extraordinary, and very ocean-like in many ways.  There are actually tides at play, though they are small.  But there are larger water level variations (of around 4 feet based on the last 50 years of record) driven by an interaction between precipitation, evaporation, outflow, and seiches (which seem to be driving little 1 inch sub-hourly variations in water level over the last day).  Waves are clearly a force here - I geeked out for a bit on these little lines on the shoreline, each deposited by an individual wave scouring sand from the beach face and pushing it landward.  


at the same time there are signs of erosion everywhere, not only indicated by the seawall built to protect the Big Sable lighthouse (photo at top), but also by the erosional scarp along most of the lake edge:

But wind is clearly the main player here.  My guess is that periods of low lake level lead to drying of shoreline sand, and rapid aeolian transport.  The resulting dunes are impressive:


and clearly mobile (as indicated by the complex stratigraphy exposed on this dune):


Dune grass (an Ammophila species, though I'm not sure which one - but may be native here?) is widespread (and so impressive in its ability to survive in this environment):


and probably contributes in some way to dune stability.  I was struck, though, looking at Google Earth Engine's timelapse, at how LITTLE obvious dune migration there is over the last 30 years:


I have no idea how much dune grass contributes to that stability.  But, as in a lot of locations Ammophila DOES contribute to the creation of a distinctive dune morphology.  Here is a beautiful view looking down the trough between the primary foredune (to the left in the field of view) and the secondary dune (to the right):



Behind the secondary dunes is a wonderland.  Currently the lake is pretty high, and there has been recent rain, so the landscape is peppered with these beautiful little ponds:


Interestingly, in this particular location the ridges between these ponds were actually paved with these gravel cobble lag deposits, which were beautiful...but also a bit odd to try to figure out how they ended up here.  Anyone want to take a stab?







Tuesday, June 12, 2018

Elwha Update

The date is approaching for our annual topo/bathy survey of the Elwha delta and so I figured it would be the right time for a bit of a year in review from my own monthly survey work.  Here are the story-lines as I see them:


1)  The transition of the old estuary.  This isn't new by any stretch, and has been well documented by a variety of investigators (i.e. see this and this).  But I've been struck by the visual transition.  Above, for example, is a shot from this morning (looking south from here) of what used to be a pretty sizable estuarine lagoon.  Here is that same view in February 2013 (this photo was shot from the other side of the picnic table here):




That formally open estuarine lagoon has been rapidly filled with fine sediment, colonized by cattails and other vegetation, and seems well on its way towards becoming a marshy forest.  

2)  The terrestrialization (is that a word?) of the former intertidal near the river mouth, in the zone where the river dumped most of its sediment, this view from 2011 (shot here):

2 August 2011
now looks like this:


That IS the same location.  

3)  And continuing with the theme of transitions, the nourishment of the beach to the east of the floodplain, under the bluffs.  Here is a photo taken today here:



and from the same location back in September 2013:


I've got some profiles and other data from this location all the way at the bottom of this post.


4)  Lets look at some beach profile data, most of it collected over the last year.  I shot the photo below today, of a band of buried wood waste (mulch, small sticks, etc) eroding from the intertidal beach right about here:

This area has been quite erosional since 2015 (see profiles for the last year below), and I'm assuming that this material is made up of deposits from one of the lagoons that formed behind the seaward bar during the peak of dam removal.



Just to the west, closer to the river mouth, the seaward bar has also been quite erosional, but over the last two months it looks as if a new little lower intertidal bar formed, and then welded to the beach face:



As you move away from the river mouth, both west and east, there has been quite a bit of stability to the beach.  Here, for example, are profiles from about here to the west of the river mouth:


and this site to the east, that just a few years ago was eroding at average rates of more than 5 meters/yr:



Over the last year the shoreline position at both of these locations has fluctuated within a window just a few meters wide.

The very far eastern side of the floodplain also seems to be on a trajectory of change.  Here, for example, are beach profiles and shoreline position time-series date back to 2011 from this site:



This area is quite interesting, as it is east and downdrift of a major rip-rap removal and beach restoration project that happened back in August 2016 (see this and this), and sits right next to a subsequent house relocation and armor removal project that happened in August of 2017.  I think that you can see the August 2016 project in the shoreline position time-series above, manifested as that first and tallest spike centered on 2017.  The winter 2018 spike in shoreline position is also interesting, and may be attributable to that second project...or maybe we are seeing some sort of seasonal transport signal at play.  I'm intrigued though, that the section has continued to erode after those projects wrapped up.

By contrast, the overall combination of massive supply of sediment from the dam removal, coupled with the removal of rip-rap in August 2016 that was blocking transport to the east, seems to have led to a shift in the shoreline under the bluffs (here).  Here are the profiles and shoreline position time-series dating back to 2011


and of course the photos set above (comparing today to September 2013) is from this same location. This section of shoreline really took off in the summer of 2016, and while it seems to have the same possible seasonal (maybe?) pattern going on (spring/summer erosion?) the overall trend has been towards nourishment and beach accretion.




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.