Tides at D-Day

The deeper I dig the more I find the history of my field (loosely defined as some mix of coastal oceanography, coastal geology and benthic ecology) fascinating. It turns out that a major turning point in our understanding of both waves and tides was motivated by World War II, and specifically the need to safely land a huge number of soldiers and equipment on the beach at Normandy.

Physics Today just published a really nice historical summary of tidal predictions, and their link to D-Day. It is a suggested read for the coast nerd. Find it here.

time lapse: accelearated learning

I've always been a believer in using photos to track change - in 2004, newly with the Surfrider Foundation, I kicked off a photo monitoring project focusing on the Elwha shoreline. I am also a natural cheap-skate and find that while I do love to play with expensive scientific equipment, I almost love it more when there are novel ways to measure natural systems with cheap, off-the-shelf kind of stuff. Time-lapse photography can be particularly valuable. Even if it doesn't yield quantitative data, it can help us to generate hypotheses or identify processes that are important over timescales that can be hard to observe directly. I experimented a bit with time lapse using CHDK on my Canon point and shoot, but realized that shooting long time-series would be problematic. Recently I was sent a few PlantCams to use to start collecting time-lapse at various points around the Elwha delta. At $80 each, these cameras are CHEAP and, because they are supposedly waterproof and built specifically for time-lapse outdoors, may be perfect for the sort of quick and dirty timelapse photography we have in mind to try to understand how the coast and delta changes over timescales of weeks to months to years. So just tonight I had the chance to pull the stored photos from the test camera that I put on our roof overlooking P.A. harbor:



Now I know what you may be thinking..."Nice timelapse of a tree". I will get better at aiming, I promise.

Lake Mills Delta

Jumped on an opportunity to visit the Lake Mills delta with Tim Randle of the Bureau of Reclamation and Gary Smillie and Brian Cluer of the National Park Service. Relative to the Lake Aldwell delta, the Lake Mills delta is huge - maybe 3-4 times the area, and seems to be composed of coarser sediment in general. Given that it is the primary trap for most of the sediment production in the watershed this makes sense. Overall it is an astonishing feature to visit. Tim, who had visited a month earlier, was shocked by the amount of change - a shifted river channel, new delta lobes, and a rapidly prograding delta front. It is a landscape in motion, with bigger changes coming over the next year...

A series of photos from the morning...

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...