Wednesday, May 29, 2013

Time Lapse of the Ledgewood Slide

A few months back I wrote about a survey of the Ledgewood Slide, a large deep-seated "rotational" slide on the west coast of Whidbey Island. During that survey I left a camera behind, which faithfully collected an image of the toe of the slide every hour during daylight hours. My interest was in determining how quickly the toe of that slide would erode, as well as the processes that are most responsible (high water versus waves, for example). And while survey data would be most useful, the time lapse is a great tool when you can't be there all the time measuring.

I was able to quickly revisit the site over the Memorial Day weekend, and while I didn't have time or tide for a survey I was able to recover the photos. Check it out:

Note that this time lapse was updated on 28 June 2013 to include photos collected through 26 June 2013

There are a few marked episodes of erosion of the toe, occurring over the night on April 4-5, on April 10, and the night of April 28-29. All of these periods fall during spring tides (see water level observations from Port Townsend, below), with high astronomical tidal water level, suggesting that water level plays a critical role. This seems obvious, except to note that the last two days captured by this session, May 24-26, also feature very high tides but no obvious erosion events.

It therefore seems likely that wind, and specifically wind-generated local wind waves, played a role in those erosion events, and the wind data from Port Townsend seems to support this, with some notable spikes around April 4th, 10th and 29th.

Regardless, the bluff toe had changed dramatically. Notably, as the toe of the slide erodes it exposes more of the sand layer that was exposed as a relatively thin (~1-2 m) layer during my survey on 2 April. This material is likely a significant contributor to the budget of adjacent beaches...and it would be cool to get out and do a survey to look at profile and grain size change...just need to find a time to get out.

Here are a few photos I shot on May 26...

Steep and high sand scarps prevail across much of the toe of the slide at this point, which contrasts with the early toe, which was composed of a lot of uplifted clays.

A view from the top of the scarp looking down to the beach...a distance of ~6-7 meters

Another view of the scarp at the toe of the slide on 26 May

The beach to the north of the slide...appears sandier than before

A view of the beach to the south of the slide, taken on 26 May 2013 from the revetment. Below is a photo taken on 2 April 2013 taken from a point looking towards the slide from about MLLW. The photo above was shot from about where the stairs are in view right. Sandier beach?

Tuesday, May 21, 2013

The Changing Elwha Shoreline (continued again)...

Two things made me think its time for another update regarding shoreline change at the Elwha River delta. First I've finally had a few moments to do a bit of work with the profile data I've been collecting approximately twice per month (at four sites around the delta) since I started with Sea Grant in March 2011. Notably I've been wanting to add an analysis specifically looking at movement of the Mean Higher High Water contour as a proxy for the position of the shoreline. As the restoration continues our conceptual models suggest that erosion, especially to the east of the river mouth, should slow down and perhaps reverse as sediment is supplied to the shoreline. Its been very clear since about January that the beach at Line 164 (see map in attached below) was growing dramatically. This site is close enough to the river mouth, though, that it is possible that this accretion is less about alongshore transport processes and more about that site really becoming part of the expanding river mouth.

30 April 2013 aerial image of the Elwha River delta courtesy of Andy Ritchie, Olympic National Park. The four transect lines that I measure topography and grain size on every two weeks are shown in red.

As a result I've been particularly intrigued by patterns of shoreline change at Line 190, which is further to the east and at least a few hundred meters away from the large pile of sediment that deposited in front of the river mouth in December-January this winter. Even with an enhanced sediment supply to the coastal zone, which really kicked off in April of 2012, however, my data from late last year and early this year showed continued erosion at this site. Lately, however, (and this is the second thing that made me feel like its time for an update) I've started to "feel" like that section of the shoreline has stabilized a bit relative to how its been eroding in the recent past. I think that my profile data back me up a bit on that. I see the possibility in these data that rates of erosion at Line 190 (the green line in the lower right hand corner of the figure below) have slowed since about the middle of 2012, and that data from the first half of this year even suggests a possible pattern of accretion developing there.

Profiles from May 2011, 2012 and 2013 from four sites on the Elwha River delta (reference to map at lower left). Relative position of the MHHW contour (positive is accretion, negative is erosion) over time is shown at lower right.

The interesting thing here is that if there is a pattern of beach growth emerging at this site it is happening in a different way than the accretion at Line 164. At Line 164 its all about sand...huge amounts of sand. At Line 190 the entire intertidal zone is seemingly as coarse as its been for a good while. The photo below, for example, shows both an oblique of Line 190 (looking landward from about MLLW) from 2012 and 2013, as well as a grain size image from just about the mean sea level contour on the beach. So what is going on? Not sure, really, but it is possible to imagine that there is alongshore transport of sand, and perhaps gravel, from areas closer to the river mouth that are adding volume to the beach at Line 190...even without an obvious decrease in grain size on the surface of the beach.

Oblique images taken looking landward from about Mean Lower Low Water (top) and grain size images taken at about 1.40 m above MLLW on the beach (bottom) from May 2012 and 2013.

But the title of this post really says it all...this data collection effort will continue in the hopes that we can puzzle out how this dam removal will also act as a beach nourishment...and if it will reverse decades of erosion. This is an important question, since communities all over the nation and the world are increasingly grappling with questions about how to respond to projections of shoreline erosion due to climate change. Changes to the way that society manages sediment delivery to the coastal zone, via rivers primarily, is one possible way that some of that projected erosion of shorelines might be addressed in the future.

Monday, May 20, 2013

Climate Change...there, I said it

The "Keeling Curve" - atmospheric CO2 in the modern era (since 1958). These data underpin one of the lines of evidence that contemporary rising CO2 concentrations are due primarily to human activities.

It seemed like spring was all about climate change, and particularly various efforts around the Olympic Peninsula aimed at preparing for projected changes. I wrapped up two different climate change projects, a large climate impact assessment for the Olympic Coast National Marine Sanctuary, and another that I was a contributor for - a community impact assessment for the Jamestown S'Klallam Tribe. I am pretty proud of this last one - not only did I get to work with some truly phenomenal partners from Adaptation International and the Jamestown Tribe, but I am also proud to have participated in this first comprehensive community assessment to take place in coastal Washington outside of Puget Sound. Another notable event was the Clallam MRC's workshop on ocean acidification, which focused on current and future "acidification" of local marine waters, driven by increasing carbon dioxide concentrations in the atmosphere.

It seems to me that media reporting on climate change has turned a corner of sorts, and I feel that I've seen far more reporting this spring on science and assessment of global climate change. This Reuters article from today on a Nature Geoscience paper is a good example. It suggests that climate models most extreme projections (i.e. on the high end of their uncertainty) regarding atmospheric warming may be too high...seems like a positive, right? But the reason - that the oceans seem to be absorbing more heat than expected, has local ramifications. Even small increases in ocean temperature may have observable impacts including shifts in the range of marine species, and reduced productivity due to increasing stratification between the warmer surface layer and the colder water below it.

The data that set off the 400 ppm media blitz - CO2 concentration measured at Mauna Loa, Hawaii

Another notable item from May - the symbolic reaching of the 400 ppm mark in atmospheric carbon dioxide concentration at the Mauna Loa CO2 observatory that generated quite a bit of media attention. Both the figure at the top of this post, as well as the one just above are atmospheric CO2 concentration data from Mauna Loa. While there is certainly still debate regarding what this threshold means and how we, as a society, should view it, I find it compelling to think about the context: CO2 levels have not been this high certainly since Homo sapiens has been around (see figure below), and pre-date many of our fore-bearers as well. The last time that atmospheric CO2 concentrations appear to have exceeded 400 ppm was during the Pliocene > 2 million years ago.

These data, from the Scripps Institute of Oceanography and posted to, suggest that the current level of atmospheric CO2 is anamalous over the 800,000 year record available by analyzing gases trapped in ice.

In light of this context, it seems worthwhile to at the very least bring the very best science to bear on the problem of projecting future climate, and use that information to plan for those changes. The OCNMS Sanctuary Advisory Committee discussed that very problem at their meeting on Friday, and I see leaders all over the Olympic Peninsula and in Washington State doing the same. I focus on the coastal implications of climate change - and there are many. One of the areas that I am interested in at the moment is the ways in which climate change, primarily through sea level rise and changes in storm pattens and wave climate, may compromise the ability of shorelines to act as effective barriers between communities and the ocean. To that end I've proposed a small shoreline monitoring program for the North Olympic Peninsula, to complement shoreline change data collected in SW Washington and Oregon. I put together the poster below on the program - check it out and let me know what you think...