First, what I got wrong.

I thought maybe more water was entering from the ocean through Deception pass, which is closer to the Skagit river.

But I was mistaken. Even though water enters Deception Pass *very fast*, most of the ocean water enters through the South, through Posession Sound, which is closer to the Snohomish river.

The video linked shows this using the Puget Sound model (which is a really cool model to check out in real life):

https://youtu.be/OEQP5BwVh7A?t=181

#PugetSound
2/n

@guyjantic pointed out it might be a problem of topography, and they were onto something. These topographic pictures show how the area around the mouth of the Skagit is much lower in elevation than around the mouth of the Snohomish. In fact, I5 lays at only ~20 ft above sea level between Mount Vernon and Burlington! Much of the surrounding area is equally low (or lower).

#pnw

3/n

While I'm not sure if the size of the rivers is relevant for what happens during a tsunami, I think it's worth noting the differences in size. I knew the Skagit River was larger, but I had not realized how much. According to the video I posted, the Skagit delivers half of all the fresh water in the Puget Sound! 😮

Wikipedia tells me the Skagit discharges an average of 468 m3/s of water, whereas the Snohomish only does 273 m3/s.

Pictures to follow in a bit, to see how this looks irl!

#pnw
4/n

.. and here are the pictures of the rivers, first the Snohomish, as seen from the Langus Riverfront trail, just behind Everett. Then, the Skagit, as seen from the Skagit Riverwalk in Mount Vernon.

5/n

#pnw
#rivers

Continuing from last week, more river talk! This time thinking about flooding in general, not only in the context of a tsunami.

This thread started because the tsunami alert for the Skagit River showed a risk extending further inland than the risk for the Snohomish River. But the Skagit river itself floods periodically, and what I find interesting is the response from Mount Vernon to address the flood risk. This response may be worth considering in the context of #ClimateAdaptation. #pnw

6/n

Mount Vernon's downtown is located by the Skagit River. It has a path overlooking the water, which changes with the seasons depending on the amount of glacier sediment. It's a pleasant place to hang out.

Here are two pictures of the Skagit Riverwalk. First, as seen from the Riverwalk itself, the other as seen from the boat launch accross the river. Notice the brick walls, and their elevation.
7/n
#pnw #FloodRisks

The brick wall is not only decorative, is a flood protection wall that gets to be assembled when there is risk of the Skagit breaching its banks and flooding Mount Vernon's downtown, which has happened. If you look again at the picture in the post above, the water of the Skagit can reach the walkway and flood the downtown. That's a lot of water 😰
In the second picture below, a close up of the wall where the flood protection system is installed in times of emergency.
8/n

#pnw #FloodRisks