Tuesday, August 28, 2012

McNeil Island

We spent most of the day mapping our way around McNeil Island.  As a result of its prison status, the island has actually avoided the intense waterfront development typical of much of the rest of Puget Sound.  Much of the shoreline consists of remarkably pristine bluffs and forested shorelines, although almost every stream and small estuary has been blocked off or otherwise altered.  We saw strange groin-like structures extending offshore in two places and the remains of old ship or barge hulls on the north side.

The erosion control structures of choice were massive piles of coiled cable (old submarine nets? but they looked like giant mattress springs) and tall stacks of precast Ecology blocks.

This is a place with a complicated history and probably an even more complicated future. It has been both a federal and a state penitentiary and now it's still used to house various types of offenders.  But as the use of the island as a prison has gone down, interest in what happens next goes up.


Hyde Point

This little pair of spits is located just north of Hyde Point on the east side of McNeil Island.  Most of our mapping was from the boat, but we had permission to land and this was a great spot to pull the boat up and wander over to look at the back-barrier marsh.  The aerial view shows the relationship of these two small lagoons - the southern one tucked into a cove in the upland, the northern one enclosed within a hooked spit.


At one time, I suspect these two lagoons may have been connected with everything draining out the north end, but now they seem to be plumbed separately since the southern one has it's own tidal channel.

Gertrude Island

Gertrude is another small island just offshore of McNeil, this one on the north side at the mouth of Still Harbor.  It's off limits to folks like us to protect the seals that haul out on the beaches - particularly at the south end.  The east side is very sheltered, with salicornia growing on the beach and a low bank overhung with trees. The west side is a bit more exposed and there is more evidence of erosion.

The funky little spit at the south end appears to be a low terrace -- the flat surface is well above normal backshore elevations and consists of a low erosional scarp.  Another geologic question goes unanswered!


Pitt Island

Pitt Island is pretty small - a hectare or so of madrone and fir and poison oak sticking out of the narrow channel between the Key Peninsula and McNeil Island.  Wave action from the north (infrequent but significant fetch) and from the south (frequent but sheltered) results in two small cusps at the east and west ends - about the extent of the beach on this island.


This is part of the McNeil Island Corrections (now Commitment) Facility, so we had permission to land (although it took a phone call to remind the guards with the bullhorn on McNeil about that).

Some of these outcrops were a reminder that I don't know my South Sound geology as well as I'd like.

Garry Point

Garry Point is the end of the road in Steveston, where the Fraser River heads out to sea.  I suppose Steveston was originally built on the natural levee along the historic distributary, but now it's simply the bottom left corner of the sprawling city of Richmond.  


Garry Point Park was created with fill (dredged sediment from the river, I assume) and then armored with riprap and shaped to create a series of pocket beaches along the riverside.

Roberts Bank

The Fraser River delta extends out into Georgia Strait, forming the large, shallow Roberts Bank.  The Tsawwassen Ferry Terminal is located at the end of a long causeway that extends across Roberts Bank to end just short of the U.S. border.  A parallel causeway a couple of kilometers to the north serves the large coal and container terminals.


The two jetty-like projections have undoubtedly mucked up circulation and sedimentation patterns in the vicinity, but they sure move a lot of ferry passengers to Vancouver Island and a lot of Rocky Mountain coal to steel plants in Japan and Korea.

Wednesday, August 08, 2012

Livingston Bay

This log-choked salt marsh originally formed behind a tenuous spit, but sometime last century, a dike was built along the general line of the spit, cutting off tidal influence so the area could to be pastured. There have been years of debate about what to do with this site, in part to address a mosquito problem that tidal circulation would help alleviate.  Now the Nature Conservancy is excavating a portion of the old dike and restoring a tidal inlet at the northern end, which should result in much more efficient exchange and a marsh much more similar to what used to be here.

The beach here doesn't amount to much.  Iverson Spit, located a short distance south, is much larger and probably traps a bulk of the sediment transported from Barnum Point.  The limited sand on this beach may come from the reworking of older marsh or tidal flat deposits, although I suppose some sediment may find its way north from Iverson.  Up here at the north end of Port Susan, most of the wave action is from the south, across the broad flats that extend over from the Stilliguamish Delta.


Over the past few years, a new sandy spit has grown north from this site into the marsh.  In a year, the new tidal channel will wind out behind this spit.  The big question will be whether the new channel will allow all those trapped logs to escape, or whether they will simply choke the new channel until a really high tide occurs.