Monday, April 22, 2013

The Olympic Coast Clean-up 2013: Preliminary Observations increasingly common component of the intertidal ecosystem of the world's coastlines.

Initial estimates from this year's Olympic Coast Cleanup suggest that approximately 15 tons of debris were pulled off of Washington's beaches. A staggering amount, but definitely not a huge increase over previous years. One of the hypotheses out there regarding the potential of increased volumes of debris related to the Tohoku tsunami is that we would see spikes in these clean-up data...and that doesn't appear to be the case this year.

...and the other part of the modern beach, the plastic beverage bottle

This year's clean-up provided the same inspiring examples of community care and investment in the condition of Washington's outer coast. People came from all over the state (and out of the state), made a weekend of it, and dedicated hours and energy to pulling everything from chunks of styrofoam to 50 kg tires off of wilderness beaches. For the past few years I've worked the registration station at Three Rivers, serving beaches north and south of La Push. Many of the faces showing up to register have become familiar, and learning the stories of the people that come to the clean-up is one of the reasons that I love this event so much.

a local contribution to marine debris...likely from commercial fishing off of Washington's coast

Like last year I tried to get a sense of what was pulled off of those beaches in order to assess the degree to which patterns of debris are changing. Again, I was primarily interested in the "production rate" of those beaches, so like last year I turned to data collected by volunteers as they worked the beaches. We totaled 118 volunteers on "our" beaches this year (again: Rialto, First, Second and Third), and based on their estimates each volunteer averaged 19 pounds of debris, with a standard deviation of 14 pounds. Using the standard deviation as a measure of the uncertainty, I use that to estimate a total of 2280±1650 pounds collected over 6.6 miles of beach. On a per mile of beach basis (which is the metric that we attempted to use in our scenario development for the possible impact of tsunami debris), this equates to 0.17±0.12 tons/miles. We've estimated the "baseline" (i.e. before the tsunami debris) debris delivery to the beaches of Washington to be about 0.5 tons/mile. So this is another line of evidence to suggest that the Tohoku tsunami has not led to a significant and sustained spike in the amount of debris making landfall on the beach.

more fishing debris

That being said, its almost certain that some of the debris that was pulled off of the beach was, indeed, "tsunami debris". The first photo of this post shows a sub-sample of the styrofoam bits pulled off of Rialto Beach. There has been much speculation that pulses of styrofoam that made landfall in Washington starting last summer were derived at least in part from insulation material - from homes, businesses and other structures - released into the ocean by the destructive power of the tsunami. This material is particularly worrisome because it breaks apart fairly easily and some suspect has ecological impacts out of proportion with its relatively low mass. We don't know if there is more styrofoam this year than in previous years since those sorts of information aren't tracked carefully.

one of the finds of the day - a huge chunk of styrofoam that appeared to have been a part of an old dock or structure. Chunks of concrete were attached to it.

Another very cool part of this year's clean-up, and one that will hopefully provide much more detailed information on the mass and composition of debris recovered, was the work of a group of Western Washington University students at a selection of beaches (including Third Beach). As part of a project funded by the North Pacific Coast Marine Resource Committee they focused on carefully sorting and weighing debris.

students from Huxley College of Environmental Studies carefully sorted and measured much of the debris off of selected beaches as part of a project funded by the North Pacific Coast Marine Resource Committee

A view of the dumpster at the trailhead of Third Beach near the end of the day

Tuesday, April 16, 2013

Preliminary results from a Ledgewood Slide survey

The ProMark 200 RTK-DGPS system used for this survey leaning one one of the uplifted scarps along the edge of the slide. Those gravels on top of the scarp are the former high intertidal surface, uplifted 2-3 meters.

The Ledgewood Slide on Whidbey Island on March 27th was large enough to destroy at least one house and prompt the evacuation of more, and also to generate at least a blip on the national news scene. Bluffs are a predominant shore type in Washington State, and their failure - whether slow and creeping or large and catastrophic - is one of the many hazards that coastal residents of this state are subject to. Bluff erosion and failure is sort of a double-edged sword though - while a hazard to human infrastructure, the sediment supplied to beaches by bluff erosion is thought to be a building block for beaches and complex coastal habitats. As a result there can be tension between the desire to stabilize bluffs with armoring or other tools, and allow them to erode to support habitat restoration goals. In light of sea level rise projections, climate change projections related to increasing winter precipitation, and on-going construction of infrastructure on coastal bluffs it is likely that this tension will only amplify in the decades ahead.

Rebekah Sexton and Diana McCandless from WA DOE's CMAP program - about to get wet and collect more topography data than you can imagine.

For all of these reasons understanding how, when and why bluffs erode, and what sort of contribution they make to the coastal sediment budget are important research objectives in Washington. The Ledgewood slide, because of its scale and the deep-seated nature of the slide, generated significant interest amongst the small community of coastal geologists, geomorphologists, managers and others who think about these sorts of problems every day (see these two other blog posts on the slide, one by Dan McShane, and the other by the venerable Hugh Shipman, as well as the Washington DNR's Preliminary Report on the slide). As a result I carved aside a day (2 April 2013, six days after the slide) to join a few others from the WA DOE Coastal Monitoring and Analysis Program to investigate the slide. While the DOE staff (Rebekah Sexton and Diana McCandless) focused on collecting high resolution topography data on the beaches adjacent to the slide for post-processing, I decided to focus on collecting real-time topography data on the slide itself. I had two goals: 1) Add to the baseline data set that will allow us to track the evolution of the toe of the slide over time as it interacts with waves and tides, and 2) quantify the volume of sediment delivered to the coastal zone by the slide. Here I am providing some of the preliminary results and analysis from that short survey. To reiterate though, this is just a taster. Others are collecting reams of data and providing insight that should deliver an enhanced perspective on the slide.

The former log line from the high beach, uplifted to approximately 4 m above MHHW.

First, a bit on methods. All of these survey data were collected with a Peninsula College-owned Ashtech ProMark 200 RTK-DGPS system (PM200) on a survey pole (see photo above), receiving corrections through the Washington State Reference Network. Its always ideal to validate the RTK survey data against some other independent spatial data, preferably a monument with good published control. In this instance though there were no monuments adjacent to the site. As an alternative the PM200 survey data were compared to aerial LIDAR collected in 2001-2002 for the area around the slide, and available through the Puget Sound Lidar Consortium. Near the slide site 20-30 points were surveyed along a surface (the road leading down to the parking area north of the slide) that I though was likely there in 2001-2002, highly visible to the LIDAR sensor, and probably fairly stable over that 11 year intervening period. These 20-30 survey points were compared to the nearest individual LIDAR return and the measured elevations differenced to generate this distribution:

So this was good - an average 6 cm offset suggested that the PM200 and the LIDAR from 2001 were relatively close in the vertical...good enough for the purposes of this preliminary survey.

I focused on trying to collect cross-shore profiles from the water line as high as I could get on the slide, both adjacent to and on the slide, and then compared each to the 2001-2002 LIDAR data. Here is an example from a site in the middle of the slide (others are given at the end of this post):

As it turned out I was unable to survey high enough on the slide (due to vegetation) to get over the pre-slide surface (the LIDAR data). The slide toe was pushed 60-80 m seaward and so all of the areas I was surveying on the toe were over formerly sub-tidal or lower intertidal surfaces, and to make matters worse the 2001-2002 LIDAR in this area was collected during relatively high water - somewhere around 1.5 m above MLLW. Needing a pre-slide surface to calculate vertical changes against I turned to Dave Finlayson's Puget Sound DEM (also shown in the figure above). As is clear, though, this is a relatively coarse (10 m horizontal resolution) DEM and only roughly models the actual surface in the area of the slide.

Despite the coarse resolution of the Finlayson DEM it was the best available surface for most of the survey extent. Here are how all of the survey data compare to the DEM:

You can see from this map how I was unable to survey over the former beach surface along most of the slide. For comparison sake here is the comparison to the 2001 LIDAR data:

Since these LIDAR data were collected at relatively high water the only survey points that I collected that overlapped were on the upper beach adjacent to the slide.

Total volume contributed to the coastal zone? Well, kind of hard to get at with these data since I wasn't able to survey to the former MHHW contour and didn't have high resolution bathymetry to work with, not to mention how sparse my survey data were. However, based on the footprint of the slide now in the coastal zone (an estimated 21,260 m2 based on my preliminary survey), and assuming a mean difference between my survey data and the pre-slide surface (a loosely estimated 6 m based on eyeballing the profiles below), I estimate a contribution to the coastal zone (defined here as the area seaward of the former MHHW contour) of ~128,000 m3 of sediment. This is a VERY rough estimate (noting that a better estimate should come later from the higher resolution data collected by WA DOE), but if its close it represents a significant volumetric contribution to the intertidal zone. However, based on observations made of the slide it seemed to be composed of a large fraction of mud and silt which is unlikely to remain on the beach. And, of course, it remains to be seen if and how long it takes Puget Sound to redistribute this sediment.

Of course, one of the more interesting things about this slide was not necessarily its extent, or the volume it contributed to the coastal zone, but in how it slid, and the forms associated with it. I shot this video to try to capture some of the interesting features of the toe of the slide:

and here are the remaining profiles...all ten of them. If you are interested in my raw survey data email me at and I can get them to you.

Thursday, April 4, 2013

The Removal of Washington's Misawa Dock

Today Steve Fradkin from Olympic National Park and I presented a well-attended Studium Generale lecture at Peninsula College in Port Angeles - on marine debris in general and "tsunami debris" in particular. While I babbled on trying to provide some background and context to tsunami debris Steve focused on the implications and removal of the Misawa dock that washed up in Olympic National Park. The Misawa dock gets its name from its point of origin, in Misawa Japan:

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The harbor from which the Misawa docks originated. Of four docks, one did not leave Misawa Harbor, one was recovered on the coast of Oregon, and one was spotted off of Hawaii but subsequently lost.

My favorite part...this great time lapse of the multi-day removal of the dock from the remote beach south of Mosquito Creek. Check it out:

The time lapse makes removal look easy, no?