Showing posts with label whidbey. Show all posts
Showing posts with label whidbey. Show all posts

Wednesday, June 11, 2014

Possession









This small, unadvertised state park at the southern tip of Whidbey is a great place for an early morning walk on the beach below Possession Head, a tall landslide prone bluff that faces south down the Sound.  Wave action erodes the bluff, carrying sediment northward up the southeast side of the island, past this state park, the county boat ramp, and the Glendale pier. Later it sneaks under the Clinton ferry dock, along Brighton Beach, and eventually to Sandy Point.  Much of the sediment probably never makes it, getting detoured to the bottom of Puget Sound by the steep offshore slope, which in some places is not far from shore at all.


The old house at the park is built on what appears to be fill at the mouth of a steep ravine.  The shoreline had been held together by an old timber pile bulkhead for many decades, but by 2004 when I first saw it, it was in serious disrepair. There was discussion of replacing it, but a few years ago the old wall was removed, the bank regraded and planted, and some of the large wood rearranged.  I wondered how this site would behave - fill usually erodes rapidly and this site is exposed to strong oblique waves from the south.  But it looks like it is doing just fine without the wall.  There is some continuing erosion, but not much.


Rounding the corner from one of these south-facing headlands, we often encounter local complications in the beaches.  Small spit-like accretional features are common. Basically, the beach can't turn the corner that fast and it overshoots before gradually reconnecting with the drift-aligned shoreline farther north (in reality it is a little bit more complicated than this).  There's another neat example just a few miles west at Maple Point.

AERIAL VIEW

Here, there is a small accretional bulge right in front of the site and bank erosion is reduced as a result. Thus the success of the bulkhead removal. Sure it would be great if you could apply general principles and regional assessments to beach projects, but in the end, it's all local.

Despite the wide place in the berm, the beach itself is incredibly narrow here. In one spot along here, a good spring low tide will actually expose the edge of the platform - which is abrupt and plunges into several hundred feet of water. I'll come back at one of those tides someday and then post a picture.


Monday, February 17, 2014

West Beach





I was up in Oak Harbor again for Sound Waters (Saturday, Feb 1st), which meant that I had a few hours in the afternoon to work my way down the island. I spent much of that walking below the bluffs south of Swan Lake, turning around when I got a little south of Fort Nugent Road (which is how about how far I got walking north from Hastie Lake (February 2012) on a comparable Saturday afternoon two years ago).


This is a wonderful stretch of 200-250' bluffs, the bulk of which are sandy units that probably belong to the Whidbey formation (lower) and Vashon advance outwash (upper).  As noted previously, wind erosion is significant along here and the homes along the top are built among the perched dunes where this windblown sand collects. The dunes are largely obliterated by the development, but the sand still collects on decks and driveways.

I wish I knew more of the story of these two concrete structures. The one on the beach must have come down fairly recently, although I haven't been down here in a long time so don't know for sure. On Google Earth (image dated 8-25-2011), it is already on the beach. There's another hanging on the edge a short distance north and destined to come down soon.  From their proximity and general similarity, I assume they are a pair - are these observation posts of some sort associated with the island's military history?

AERIAL VIEW

Thursday, October 24, 2013

Ala Spit




My visit to Whiffen Spit two weeks ago had me thinking a lot about Ala Spit, and since I was in the area for meetings and other site visits, I figured it was worth checking out Ala while the tide was still pretty high and I still had a little daylight left. The tide was a little above MHHW and flowing rapidly into the lagoon across the neck of the spit.

Gravel Beach:  Ala Spit  (December 2011 -- from there you can link back to earlier posts)

This site remains one of the more interesting beach restoration stories of the last few years and I suspect is trying to teach us lessons that, if we pay attention, will help us all on future projects.

One of the lessons - the more obvious one - is that beaches can suffer from a number of ills and that successful restoration must address, or at least carefully consider, all of them. Sometimes the challenge is figuring out which problems are most serious and which are secondary.

I think the more complex lesson is about restoring dynamic systems - especially after several decades have gone past.  Removing a stressor does not necessarily take you back to where you would have been had the stressor never been applied. I'm trying to figure out how to use the word "hysteresis" here - because I think it is important. But I need to work longer on this argument than I have time for now -- and there will undoubtedly be other chances!

Google Maps:  AERIAL VIEW





Saturday, July 20, 2013

Ledgewood






I was lucky to visit Ledgewood the afternoon of the big landslide back on March 27th, and then again briefly one week later.  But I hadn't been able to get back until very late on the afternoon of July 10th (this blog is relatively sequential, but rarely live).

Ledgewood:  27 March 2013

My visit was brief, as the tide was rising and I didn't want to get squeezed too tightly between the water and the drift logs hanging over the edge of the old beach - 15' above my head.

The toe of the slide has eroded rapidly this spring and much of the uplifted beach has now been redistributed by waves to the adjacent beaches (see Ian's blog below). Most of the eroding scarp consists of a thick sandy unit.  In the top foot or two there are some gravel layers that are consistent with the upper surface being a raised beach.  The toe of the scarp consists of the deformed dark gray clay that I assume marks the slide surface.  I can't wait to see a more through geologic analysis of this thing -- the thick sand is intriguing and I'd like to hear if folks understand the origin of the clay or its role in the slide.




The scarp has not yet reached the displaced pre-March drift log line.  Maybe some time next fall, the retreating bluff will reach the back of the uplifted beach and begin to work its way into the forest. As this promontory gradually succumbs to waves over the years to come it will probably leave a beach underlain by hummocky clay and covered with fallen trees.

Ian Miller with Sea Grant has been following the slide and has posted observations and time-lapse video on his blog:
http://coastnerd.blogspot.com/2013/07/coastal-sediment-distribution-from.html

If anyone is aware of more geologic information available online, feel free to mention it in a comment.

Google Maps:  AERIAL VIEW



Thursday, July 18, 2013

San de Fuca







A couple of small spits converge on a lagoon (two, actually) here at the northwestern corner of Penn Cove below the community of San de Fuca. Sometimes the place is referred to as Coveland.

There's enough fetch from the east and southeast to maintain the gravel spits, but not enough wave energy to keep the pickleweed (salicornia) from colonizing the more protected parts of the beach.

I couldn't find too much detail online, but I confirmed what I'd been told many years ago that there had once been a small tide-powered saw mill on the site. They apparently built a dam or control structure of some sort at the mouth of the inner lagoon, and it looks like they turned a portion of the spit into more of a dike, but not much is left besides some rusted pipes and some of the foundation of the mill.

Google Maps:  AERIAL VIEW
Ecology Coastal Atlas:  2006 Aerial Photo


Cornet Bay






Last fall, WA State Parks, the NW Straits Foundation, the Island County Marine Resources Committee, and others collaborated to pull out the old creosoted timber bulkhead at Cornet Bay and restore a more natural beach.

When it was first built, I was concerned that the temporary erosion protection extended too low on the beach (see October 2012 post below), but ultimately the high tides of December (including the record one on the 17th) sorted out those details.  It did mean that there was some scrambling this spring to clean up a lot of the mulch that ended up accumulating on the lower beach.

Cornet Bay:  October 2012 Cornet Bay:  March 2008

The high tides were good, in that they helped clarify the upper edge of the new beach. It will take a while for the sediment and the logs to settle into more comfortable positions, but the basic concept is great and I'm looking forward to seeing this place in a few years.

There are some interesting details that bear watching. A lot of large wood has stacked up against the west side of the piers and may require some active management.The small drainage outfall in the middle of the eastern segment may lead to some local erosion of the upper beach and the formation of a small delta on the lower beach.  Invasive plants will try very hard to invade the backshore, testing the persistence of volunteer groups.

Ironically, I suspect the hard parts of the project will fare the poorest. Gravity, and probably children, are already causing a shift of the small rock down the beach.  The rounded cobbles are ahead, but the angular quarry spalls will follow. As the small rock and the beach itself shifts, the logs may be undermined, putting more wear on their metal hardware. The rocky areas around the anchored wood will probably attract the most aggressive of the weeds and will be hard to maintain (and remain hard to walk across).

But again, these are details.  Compare these shots to the ones from before the project.  And then compare them to the ones in a couple of years when the beach and the vegetation have become better established.  In 2004, a bunch of us stood on the old bulkhead and wondered what might be done -- this is better than we could have imagined!

Google Maps:  AERIAL VIEW
Ecology Coastal Atlas:  2006 Aerial Photo


Monday, May 06, 2013

Deception Pass







Much of Puget Sound is nothing but Pleistocene - with Vashon glacial deposits on the surface and older glacial and interglacial sediments peaking out from the lower portions of some of the bluffs.  But at Rocky Point (2009), on the west side of Whidbey Island, and in Skagit Bay (Craft Island 2011, Hope Island 2012), the Mesozoic re-emerges from the basement to form rocky islands and headlands.

Deception Pass, separating the north end of Whidbey Island from Fidalgo Island, is a topographic gap in these older metamorphic rocks, which make up much of the San Juan Islands to the north and west.

AERIAL VIEW

Deception Pass moves a lot of water, including much of Skagit Bay and Saratoga Passage and the currents are fast.  Steep rocky cliffs plunge into deep water in two channels, split by Pass Island.  But there is sediment moving at depth and USGS work has shown a submarine delta of sorts west of the entrance (I know I've seen some bathy from here - but can't find it online). There are pocket beaches on both the Whidbey and Fidalgo sides of Deception Pass, probably consisting of sediment derived from the erosion of overlying glacial drift, although the ones on the south side may also include sediment that has made it around the corner from the sediment rich beaches on northwest Whidbey.




Wednesday, March 27, 2013

Ledgewood Beach











For better and more up-to-date information on the geology of this landslide, see:
DNR's Ear to the Ground:  Whidbey Island Coupeville Landslide

Early this morning (4:15AM, 3-27-2013), a very large landslide occurred up at Ledgewood Beach on Whidbey Island.  This neighborhood is no stranger to slides, but nothing like this has happened in a long time.  The slide was a large rotational failure within the much larger landslide complex that extends along this stretch of shoreline.  It may have been 700-800' long and several hundred feet deep, with the head scarp stepping back several tens of feet into the 200' high upland surface.  The failure surface - based on what we've seen on the beach elsewhere along here, but confirmed by today's observations - is a little below sea level.

AERIAL VIEW
KING5: Huge landslides damage, threaten homes on Whidbey Island


Previous Post on Ledgewood Beach (April 2006)

For a beach wonk, the toe was the coolest part. The shoreline along here was relatively straight prior to the slide and is now marked by a bulge that extends more than 100 feet into Admiralty Inlet.  This is not just a big pile of debris from the slope above, but rather it is the uplifted toe of the rotational landslide.  Distorted dark gray clay is pushed up along the base (the tide was too high to see the lowest portions of the toe), but as the clays pushed up, they simply raised the beach into the air.  The toe bulge is mantled by a remarkably intact sand and gravel beach.  Barnacle covered boulders sit on the surface.  The driftwood still marks yesterday's shoreline, which just happens to be 20' higher and 100' seaward of where it was a few hours ago.  I could still follow a discontinuous band of dead eelgrass and beach wrack, marking an earlier high tide. Sections of the raised beach were broken by tension cracks, or arrayed in a series of terraces (drift logs on the top step, sand and gravel on the middle steps, cobbles on the lowermost steps).






I've posted several entries recently about deep-seated landslides:

South Whidbey State Park, February 2013
Camano Island State Park, November, 2012

These geologic landscape are best reserved for open space or parks, not subdivisions.  In this case, we were very lucky that only one or two homes along the lower bench were affected -- in other places along here it could have been much more serious.

Wednesday, February 06, 2013

South Whidbey State Park








Another State Park -- another deep-seated landslide.  I used Camano Island State Park to illustrate this symbiotic relationship in November (Gravel Beach:  Camano Island SP), but much the same applies to this park on the west side of Whidbey Island.

The trail down to the beach at South Whidbey SP traverses the headscarp of the main slide, then winds through hummocks and around sag ponds, before arriving at the lower bluff, which is where the recent movement has been and which has taken some of the trail along with it.

AERIAL VIEW


This is a wonderful stretch of beach. Bush Point lies to the south, Lagoon Point to the north (Gravel Beach:  last year, same afternoon).  Other than the stairs at the park and a few drain pipes coming down the high bluff south of the park boundary, it's a pretty wild beach.

There are a couple of waterfalls that plunge directly to the beach and both were running full, their streams cutting through the thin sand layer deposited by the previous high tide.  And there is a large glacial erratic.  My petrology is rusty, but I was told once that this was a block of dunite, most likely from Twin Sisters near Mount Baker (anyone want to confirm or refute?)



There are some spectacular landslides - historic ones and new ones - on the bluffs between here and Bush Point.  The sun was going down or I would have checked them out on this hike.  Maybe later this spring.

Side note:  This is my 60th post from Whidbey Island since this little adventure began back at the end of 2005.  'Whidbey' is the most common label on the blog after 'Washington' and 'Puget Sound.'

West Beach





Sound Waters is held every year on the first Saturday of February and whether I stay for the afternoon classes or skip out after lunch to go to the beach, it's always a good day.  This year they moved the venue from Langley to Oak Harbor High School, so I started near the north end of the island and worked my way south.

West Beach was calmer than on my last visit - back on December 17th when a storm coincided with a record high tide and caused a lot of damage to both homes and bulkheads.

Gravel Beach:  17 December 2012


This community is a poster child for imprudent development. It certainly isn't sustainable in the long run, particularly with rising sea levels.  At least not without a great deal of expense and heavy duty fortification.

AERIAL VIEW

It's a wonderful place at low tide on a sunny July afternoon, but events like December's storm are exactly what built this ephemeral spit of land and what will wallop it again and again.  Peat ledges on the foreshore are evidence of the beach's landward retreat.  Tsunami warnings are reminders of the beach's lack of elevation and proximity to shifting plate boundaries.  The old failed seawalls at the south end are a fitting monument.