Sunday, April 22, 2012

Foss Waterway

Tacoma, the City of Destiny, was destined to be built on the hills that rise above the western edge of the Puyallup Delta. The Foss probably began as a tidal slough along this edge, fed by the creeks that emerged from the hills to the south and west. In some ways, this is still what it is, albeit straightened, deepened, and devegetated.  The streams enter through storm drains - two very large ones at the head end, in particular -- cascading across rocks at low tide and into the Sound.

It's hard to define what a natural shoreline is along such an artificial body of water, but the current banks are probably higher and steeper than they were before the waterway was dredged and the adjacent land was filled. In recent years, there have been some efforts to soften the edges a little bit - for habitat, for recreation, for aesthetic variety.

Beaches have been built near the mouth of the Foss where wave action is higher -- without waves, beaches become something else.  These include the tightly constrained gravel pocket beach at Thea's Park and the north-facing beach along the Olympic View shoreline to the east.

On the west side of the Foss, where most of the recent redevelopment has occurred, there have been attempts to build narrow benches into the steep bank, often just below the seawall at the edge of the promenade.  These benches become narrow strips of marsh, perched atop walls made from rows of logs and large boulders.  I can't speak to how much biological value these features add, but they certainly appear more diverse and more interesting than the uniformly rocked banks typically found in such situations.

Figuring out how to do this offers some interesting possibilities for enhancing the inside edges of marinas (which for all practical purposes, the southern part of the Foss Waterway is), but some design issues need be worked on.  For example, perching boulders atop the steep slopes looks like a challenge, since in several places they have toppled, leaving a ragged sheet of geotextile.

More pictures at hshipman: Tacoma

Sunday, April 15, 2012

Dungeness Spit

There are hundreds of spits and barrier beaches on Puget Sound, but the longest and the best known is Dungeness Spit on the Strait of Juan de Fuca, north of Sequim.  It is also the most elegant, composed of a long slender bar, a rapidly growing tip, and a complex series of secondary and tertiary spits along its inner shores.


It's a 4 1/2 mile walk from the base of the spit to the lighthouse and another 1/2 mile out to the end (much of which has formed in the last 150 years).  You can't actually walk to to the tip -- the spit is a National Wildlife Refuge and much is off limits to casual exploration.

Saturday's weather was magnificent, which meant that I returned with hundreds of photos and dozens of possible stories.  In the interests of time, I'm simply going to post some of my favorite pictures and provide a few chapter headings:  The eastward transport of bluff-derived sediment.  The influence of long-period, but low amplitude ocean waves.  Overwash and spit migration.  The growth of the spit since the 1800s.  The configuration of the spits on the bay side.  The distribution and role of large wood. The partitioning of sand and coarser gravel and cobble on the beach face, the berm, and the backside.  The development of beach cusps.

There's even a story about riprap, but fortunately it looks like perhaps it was a mistake that nature is already trying to erase.

George Vancouver called the spit New Dungeness, after t
he original Dungeness, a cuspate foreland located on the English Channel.  Ness is a British term for a low-lying coastal area typically associated with a spit or barrier - so the term "Dungeness Spit" may be a bit redundant.  

There are some more pictures of Saturday's hike to the lighthouse at

Port Williams

This is a beautiful stretch of steep, wonderfully layered bluffs north and west of the entrance to Sequim Bay. I'll have to go back and check the maps, but I believe the geology is late glacial -- till on the bottom, overlain by river gravels, and capped with glacial marine drift (?).  The stratigraphy changes slightly along these bluffs, painting an interesting picture of complex goings on right as the glacier retreated from this area and both sea level and perhaps the Dungeness River were doing something very different than they are today!

(NOTE:  Well, I was right about till on the bottom and glacial marine drift on top, but better geologists than me report that the till at the bottom is Possession, suggesting this sequence covers two glaciations, not just the end of the last one.  And there is a lot of interesting sedimentary detail in here, too, from rip-ups to cross-bedding.)

The bluffs are steep, consistent with higher erosion rates and fairly coherent units.  The fluvial gravels are strongly cemented at the south end, resulting in a near vertical bluff.  Farther north, the gravels are less consolidated and are a distinct slope-forming unit mid-bluff, above the steep till and below the steep upper drift unit. They were so unconsolidated that they were raveling as I walked the beach, cascading over the till and forming beautiful cones on the beach.


Kamus Drive

The wet conditions that led into the winter of 1998-99 must have exceeded some region-wide threshold.  Deep-seated slides reactivated all over Puget Sound, from Olympia to Point Roberts, as well as here on the west side of Fox Island.  At first blush, and perhaps at high tide, this might have looked like a large shallow failure, but low tide revealed that the clay below the tide beach had been raised 10-20 feet in a big arc, marking the toe of a deeper rotational slide.
The initial report that I heard was that a spit-like feature had appeared. When I first saw it - at low tide - the impermable clay ridge had turned the upper beach into large tidepool.

The uplifted clays, although much eroded and/or subsided, still crop out on the beach 13 years later.  The house (
try typing "askew" into Google) remains as it was left.


Pebble Beach

Way back in 2005, I picked as a subtitle for this blog:


This beach on the southwestern side of Fox Island fits that nicely. The beach face is gravel - or at least the surface layer is fairly uniform looking gravel - but beneath the natural armor is a much more diverse mixture of sand, gravel, and broken shell.  There is a distinct break at low tide to a flatter, sandier terrace, although the transition is far from uniform along this beach.  There's a lot of uneveness to this beach - a rolling topography and an irregularity to the low tide terrace.  There are gravel bedforms that contribute to this, but I suspect it is related mainly to the underlying geology.  The gravel-rich bluffs leave little doubt of the source of the beach sediments.

The largest pebble on this beach is 10' high and is called "The Big Rock." It has the remnants of a survey marker on top, along with small divots that may once have supported a tripod.

The development along the beach is limited to a few homes and cabins tucked into low spots along the otherwise high bluffs.  Most of the new development is upland - big homes typical of the high end suburban sprawl that characterizes the Gig Harbor Peninsula.

Madronas (Arbutus menzeii) are a signature tree of many of our bluffs, particularly on dry south facing slopes.  They can hang tenuously on the edges of cliffs for decades. I've seen some that from their size and growth habit have probably been in a perpetual state of falling over the edge for more than a century.  Apparently, the owners of this bluff didn't like them, but I thought we'd moved beyond this kind of thing.


Sunday, April 08, 2012

Camano Head

Camano Head lies at the southeastern tip of Camano Island and rises more than 300' from the beach.  Not unlike Possession Head at the south end of Whidbey Island, Camano Head is marked by a large, deep landslide complex.  The bench is heavily forested and looked broad enough for a small, but very scenic, subdivision (The Homes on Undercliffe?).  Finer grained silts and clays ledge out on the beach near low tide.  Some dip landward, suggesting they lie within the toe of the deep-seated slide.

On a sunny Saturday afternoon, the place seemed pretty benign, but it has not always been so.  Tulalip accounts describe a major landslide in the early 1800s, one that generated a tsunami that reached Hat (Gedney) Island more than two miles to the south, with devastating consequences (History Link, or check a short piece I wrote a number of years ago, The Fall of Camano Head, pp 13-14).

There were no shortage of neat geologic and geomorphic features to check out -- but the tide was starting to come back up and I head to head back. The beaches heading north on both sides of the island are wonderfully sinuous, likely reflecting the shape of the steep submarine topography. The bluffs northwest of Camano Head are not quite as dramatic, but contained many more slides, some beautiful exposures of a gravel-rich till (pre-Vashon, I believe), and a few beach cabins precariously perched atop seawalls at the bottom of the bluffs.