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 high.  Flow 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.

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.