Anatomy of a costal storm: January 9th 2024

 

As the winter storm season closes in on us on the coast of Washington, and on the eve of what is shaping up to be a pretty significant storm, I wanted to spend a few minutes looking back at the anatomy of a pretty interesting coastal storm that hit the coast and western and central Strait of Juan de Fuca last winter...on January 9th 2024. This one was notable to me because it was pretty damaging across the Port Angeles waterfront, and ended up shutting down Ediz Hook, a long, sand spit that forms Port Angeles Harbor that I spend a lot of time studying, surveying, and generally thinking about. 

A view along Ediz Hook NOT taken during a storm...April 2012

While Ediz Hook used to be a relatively low sandy spit one of its distinctive features now is a huge rip rap defensive breakwater on its seaward side, part of an Army Corps of Engineers Erosion Control project built in the 1970s. This rip rap raises the elevation of the seaward crest of Ediz Hook to elevations of around 9 to 11 feet above MHHW...pretty darn high...and up until this January 2024 storm I had never observed or heard of anything close to over-topping of this feature.  But this storm did it, sending water and debris over the breakwater, flooding the road that runs along Ediz Hook, and ultimately closing Ediz Hook until the storm subsided and crews could clear the road.  

Flooding of Ediz Hook on 9 January 2024

So what were the ingredients? Like most of these stories it starts with a winter high tide, predicted at about 8.5 feet MLLW, just a shade shy of highest astronomical tide at this site (coming in at 9.2 feet).  Also like most of these stories, that high tide was bolstered by a storm surge of about 1 foot, bringing the observed still water level up t 9.5 feet MLLW.  This is a high tide, but well clear of the record of 10.5 feet MLLW reached in 2003, and not even close to making the top 10 highest water levels recorded at this station since observations started in the 1970s.  

Driven by the high tide and storm surge alone, this storm was a nothing. But layered on top of this high water were waves...but interestingly the wave story has a similar narrative to that for tides and surge: The waves were big, but nowhere near record-breaking.  A wave buoy just to the west of Port Angeles, for example, recorded significant wave heights of just about 10 feet, whereas the New Dungeness buoy in the Strait of Juan de Fuca recorded significant wave heights of about 8.5 feet.  These are big waves, no doubt about it...but nowhere near maximums.  The New Dungeness buoy, for example recorded a maximum significant wave height of over 12 feet during a storm in December of 2006.  

So, like many of the impactful storms on the coast, this one was about a variety of factors coming together and co-occurring...in this case the tide, storm surge and waves.  None of those factors was necessarily extreme in isolation but taken together they created something powerful and noteworthy. This kind of interaction amongst various factors, none of which are extreme or present risks in isolation, poses real challenges in understanding these types of storms and their impacts, accurately forecasting them, and even building a sense for how likely they are to occur in the future. 

Buried silt on the Elwha sea floor

This week I was, once more, part of an annual subtidal survey of the marine community around the Elwha River delta during which we visited our site called, 4SP1, just to the east of the Elwha River mouth, roughly here. This is a place that was buried under 2-3 feet of sand in 2013, as the dam removal pumped out tons of sediment into the Strait of Juan de Fuca.  The site IS still very sandy, here is a bit of a view from this year:

and it does still look very different than it did before dam removal started (check it out in 2011 here).  But this year the site was also obviously different from last in that much of the deep mantle of sand deposited during dam removal had been stripped off.  So that is interesting in and of itself...we've been curious about how the Elwha River delta would evolve in the long-term now that dam removal is long over, and this gives us some indication.  But what really struck me was what was UNDER the remaining thin layer of sand on the seafloor...a few inch thick layer of silt and mud, which you can see in this photo below, with my slate for scale:

And get a sense for the composition in this video.  So what is the big deal?  This is a high current site, where mud and silt generally doesn't stick around.  I think this layer of mud and silt tells us something about how rapid and how massive the delivery of sediment was during the dam removals.  I envision a pulse of very fine material blanketing the sea floor, presumably followed almost immediately (perhaps within a tidal cycle?) by a pulse of sand, both pulses massive enough to blanket the seafloor with many inches of material...

Cabins at risk of coastal bluff erosion removed at Kalaloch in Olympic National Park

 

Some of the cabins at Kalaloch are (or were) quite close to the edge of the coastal bluff. Photo from 6 July 2023 

Eroding coastal bluffs are hard to manage, especially when valuable assets are perched on their edges. Coastal bluffs are by definition tall, and their erosion can be rapid and forced by a variety of processes, so engineering solutions aren't always easy to devise, and are invariably expensive and difficult to maintain. At Kalaloch in Olympic National Park, two factors recently converged to create particularly dangerous problems.  First, rates of erosion of coastal bluffs in a small area just south of Kalaloch Creek accelerated, and second, the locations where those erosion rates accelerated also happened to be developed. Buildings, in this case valuable rentable cabins at Kalaloch Lodge, were put at increased risk and, as a consequence, in March 2024, five cabins were deemed unsafe and removed.

A similar perspective as in the photo above, with cabins removed.  The former cabin sites are marked with the brown burlap.  Photo from 10 April 2024

I was part of efforts that looked for every opportunity to try to understand that erosion, in the hopes that some cause of erosion might be identified that could illuminate a potential solution. As is often the case, though, the best we can do is use our monitoring data to characterize rates of erosion, and how those rates vary along the shoreline, as I did in this recent recorded talk.

    To me, one of the most interesting things that we've done at Kalaloch is to install five Chronolog stations, which encourage visitors to submit photos from a fixed vantage point, which can then be complied into a time-lapse video. Those stations, and the people that have contributed to them, have created a rich visual record of bluff erosion and the removal of at-risk buildings, and other poorly understood coastal processes (like the loss and recruitment of large wood along the beach). 

A Chronolog station at Kalaloch.