Drawndown

The latest in a long list of steps to be taken in preparation for dam removal on the elwha river was taken a few weeks ago. the power-houses for both dams were turned off, and the water diverted out of the penstocks feeding the turbines, and through the spillways in the dams themselves. The spillways were also fully opened, lowering the levels of both reservoirs by 10-20 feet. These actions exposed even more of the impressive deltas that have built up at the up-stream ends of Lakes Aldwell and Mills, and, seeing as the sediment of the deltas is the beach building sediment of the coming decade I've taken a few opportunities over the last week or two to view those deltas.




The Lake Aldwell delta, 25 June 2011









The Lake Mills delta 25 June 2011













fine sediments (mostly mud) compressed onto the bedrock side of the reservoir. and check out the logs!














shear scarp at the former water level.













cool stratigraphy exposed by the lowered water level, Lake Aldwell delta

Coastal Resilience on the Mississippi Delta

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When we decided that I would be accompanying Christine to the National Conferhttp://www.blogger.com/img/blank.gifence on Volunteering and Service in New Orleans this year I immediately emailed random colleagues with Louisiana Sea Grant in the hopes I could meet some of them. It turned out that Melissa Trosclair Daigle, Jim Wilkins, Kevin Crow (all from the LA Sea Grant Law and Policy Program) and Julie Falgout from Marine Advisory Services did one better, putting together an awesome day of visits to a variety of very interesting sites. Since my whole purpose in coming was to take care of McHenry while Christine conferences, he went along for the ride.

The day started with a trip to the Bonnet Carre' spillway, which allows ACOE managershttp://www.blogger.com/img/blank.gif to divert some section of the flooding Mississippi River into Lake Pontchartrain, thereby protecting down-river communities, particularily New Orleans. The river is currently flooding, and the spillway was in full use, running a few days ago at 316,000 cfs, about 20% of the flow of the river. The diversion will likely last for months, and when the spillway is finally closed back down after the water recedes it will be full of deposited river sedimehttp://www.blogger.com/img/blank.gifnt.

After a lunch of seafood Gumbo and crawfish pistolettes we headed to the next stop, another ACOE project, a shockingly ambitious 1 billion dollar surge barrier designed to be closed down during hurricanes, preventing surge from forcing its way up the Mississipi River Gulf Outlet
and inundating New Orleans and other communities on the river.

From there we headed to the Lower 9th Ward to look at what is still a devastated landscape, with swaths of lots stripped bare. Of interest, the shotgun houses that used to populate these neighborhoods are now replaced in areas with small, clearly innovative houses designed as part of the Make It Right program. Its an interesting juxtaposition - houses as modern and interesting as any in the country next door to ruined empty lots and still-damaged houses marked with the distinctive crosses that responders used in the immediate aftermath of Katrina.

A Rising Tide

The beginning of this week was dedicated to grain size surveys on the beach at the Elwha delta. What that means is that I got up early each day and spent hours taking photos of the ground. To spice things up a bit I decided to try something that I've been thinking about for some time - creating a time lapse of the rising tide. I've got some kinks to work out (need a bigger SD card, for example, since mine filled within 6 hours taking a shot a minute) but the result is very cool. More importantly, it may help me to get at some things I've wondered about, like how wave height and breaking characteristics change as the tide rises over the low tide terrace. We've also talked about using a similar technique to monitor changing grain size and shoreline position. Probably more of this to come.

Signatures of Tsunamis on the Strait of Juan de Fuca

Today I head the opportunity to visit Discovery Bay with Dr. Brian Atwater from the USGS, Carrie Garrison-Lanery, a PhD student at the UW, Lee Whitford from the PT Marine Science Center, and a reporter from the Seattle Times. Carrie was investigating the site as a potential addition to her investigation of earthquake-related subsidence in Puget Sound. I went along to watch the proceedings and figure out if and how we can work with Carrie and Brian to do some education on the tsunami history in this area.

The sand layers that mark numerous tsunamis are clearly visible just inches below the surface of the marsh, and extend to about 8 feet depth, where we ran into what may be the bottom of the shallow bay from thousands of years ago. In total we counted maybe 8-10 sand layers, each perhaps marking an individual tsunami occurring sometime in the past 3000-4000 years.

We started by watching Brian dig a pit, about 3 feet deep, in which you could see two sand layers. Brian then used a corer to pull sediment from beneath the bottom of the pit, revealing further layers. The top three layers were also visible in the side cut of the creek channel draining the uplands. Very cool. Hopefully you can make out the lighter colored sand layers in the photos above...

A cage full of dirt...

Yesterday we dove to set up a pressure sensor for recovery. This is the fourth time that this instrument has been recovered and each of the previous three times the instrument has been recovered by divers, leaving the cage on the bottom. This time was the last, and se we had a boat to pull up the entire thing: cage, instrument and weights. And thank goodness for that because we found the cage chock full of sand and gravel. I've had to dig sand and gravel out of there before, but typically just a little. This time it was filled to the brim and probably would have taken me a full tank of air just to dig the instrument out of there. Interesting, since there was not appreciable accretion on the sea-floor around the cage. Sign of a wave of sediment passing this location?

Time Lapse of PA Harbor during Tsunami

Using CHDK on my bottom of the line Canon PowerShot I shot about 60 photos on a time lapse setting (one every 30 seconds) of Port Angeles Harbor between about 2:30 and 3:00 PM local time. I got lucky - the periods of the tsunami waves propagating through the Strait of Juan de Fuca are about 30 minutes - so I captured a full wave before my POS camera failed. The currents generated within the harbor associated with these waves are fairly minimal, though there is a noticeable current at the entrance - maybe 2-3 knots. NOAA CO-OPS data suggests a wave amplitude at this time of about 50-60 cm. You sort of have to look close - focus first on the dock piling in the near field.

Tsunami on the North Olympic Peninsula

My son is 13 months old. Just after he was born the Chilean tsunami generated a wave that was visible on the shores of Santa Cruz, where we lived at the time. I dragged the family down to a building above the beach and we watched as the waves hit. It was visible, but damage was minimal, and it provided more of an ooh-ahh moment. I posted to this blog the day of that event.

Today's tsunami was much more significant for the west coast. Santa Cruz harbor has experienced damage in its harbor. Initial reports from Crescent City suggest significant damage. Here in Port Angeles I am getting reports of well over a meter (54 inches) of water level fluctuation, though thankfully without enough current to do any damage yet.

For those of us on this side of the Pacific this event will do some damage, but, on the scale of what we may experience in the future, this is a small event. Our thoughts must be first for those killed or missing in Japan, Russian and other parts of Asia most impacted by this earthquake and tsunami. Some of the video coming from Japan and Russia is astounding. Unlike most of the video that emerged from the Indonesian tsunami, much of what we are seeing is hi-def and taken from the air. It provides some insight regarding what we could experience from a Cascadia Subduction zone earthquake generated off of the shores of Oregon and Washington.

NOAA has generated a propagation model for this tsunami, the results of which suggest that Chile will see some of the most damaging wave heights from this event on this side of the Pacific:


The scale that they provide here, I assume (I haven't yet looked into the details of this model) tries to predict the wave height in deeper water. Tsunami waves are hugely long, many kilometers, but in the open ocean their heights can be just tens of centimeters. However, as they approach the continental shelf interactions between the energy propagated in the wave and the bottom causes the wave to slow and the wavelength to shorten. The wave responds by growing in height. My point in providing this brief explanation is to suggest that the scale on this model output shouldn't be taken as suggestive of the wave height at the shoreline.

What comes next are a series of plots taken from the NOAA tides and currents web site, generated by NOAA Center for Operational Oceanographic Products and Services. Each plot has three tracers: In blue is the predicted tidal water level, in red is the observed water level, and in green is the difference between the two. The green one is the one to pay attention to.

On this side of the Pacific it appears as of right now that Crescent City, CA is seeing the largest waves associated with the tsunami



Data from the North Olympic Peninsula illustrates how complex the propagation of these waves are. It appears that Port Angeles is seeing the biggest wave heights (though not by much), suggesting that the Strait of Juan de Fuca may be somehow funneling energy propagating from the Pacific. In Westport amplitudes are smallest:



Moving up the coast La Push saw some slightly larger waves:



but in Neah Bay they initial waves were a bit smaller:



The hydrograph from Port Angeles suggests that we are in the middle of the wave train:



and finally the most recent data from Port Townsend suggests that the wave is just reaching there, and has attenuated since reaching Port Angeles: