Friday, March 24, 2017
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.
perplexing and beautiful stratigraphy, plenty of signs of active erosion, and also plenty of futile efforts to control that erosion:
beach glass! This is why we went...to 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:
Friday, March 3, 2017
|Nuisance flooding in Freeland, Washington on Whidbey Island after the March 10 storm. Unknown photographer, photo courtesy of Island County Department of Natural Resources.|
|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|
|photo courtesy of David Wilkinson|
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:
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|
and on March 20 that buoy in the strait recorded peak average winds from the south on the order of 18 kts: