Monday, February 13, 2012

More on 22 January...

We've recently had the opportunity to recover two cameras set up to record time-lapse photos of the Elwha River delta, both of which were recording during the 22 January high-water event that I've written about previously. In this post I'm simply going to post some of the information from those cameras as well as document some of the impacts of that high-water event on the delta.

Again, the event on 22 January had a few characteristics. First, there was a perigean high tide that day, with an additional "non-tidal residual" of about two feet:

That non-tidal residual was probably driven primarily by low sea-level pressure. Here are the air pressure data (the second panel from the top) from the Port Angeles airport from Jan 22 (from Weather Underground):

The peak low air pressure corresponded almost exactly with the peak high tide. The other interesting part of this event was the relatively strong east wind associated with it, which pushed

The first camera is sited on the west side of the river mouth on private property overlooking the river mouth. The higher berm on that side of the river mouth, combined with the relative protection from east waves afforded by the delta itself, seems to have held off most of the sea's energy. This photo was taken right at high water, and in it you can see that the lagoons formed by sediment movement right at the river mouth are full and the berms surrounding them are probably over-topping them. To the left in the image though the high berm fronting the beach doesn't appear to be over-topped anywhere.

Another camera placed on an old communications tower on the east side of the delta did record some of the berm overwash that was evident after the storm. This beach profile, collected just to the east of Charles road on the east side of the delta gives you a sense of what I am talking about. Between 4 January and 27 January the top of the beach set back at least 5m, while the lower foreshore (below about 2m on the profile) shows little sign of change over the same time period:

And the view from the tower at 1:15pm on 22 January looked like this:

You have to sort of know the delta to see where the over-topping is happening in this photo. It might help if you have something to compare it to. This photo is from the following day at the same time.

The combination of high water and strong east wind and waves are driving water over the berm (which is only about 3.5 m above MLLW along much of this shore)along pretty much the entire stretch between the two clumps of trees on the left and right sides of the photo. Our observations suggest that this wide scale overtopping was associated with lots of erosion on the upper part of the beach, and it appears that much of that sediment was pushed back over the berm in to back beach areas:

and finally, to see the whole storm in action check out the entire timelapse video collected from the tower between December 2011 and February 2012:

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