Wednesday, January 27, 2010
The Warm Beach Conference Center is perched on the bluff overlooking the north end of Port Susan and has great views out over the Stilliguamish Delta.
I walked down the hill at lunch to find the beach largely underwater. I'll come back someday when the tide is lower. This is where the beach - which has rolled along for many miles (including Kayak Point (2007, 2009) and the southern part of Warm Beach) - runs out. Or more accurately, the beach runs into the delta. Littoral drift is to the north, driven by southerly storms and fetch, but the delta is growing southwards as the river continues to pump out ground-up chunks of the western Cascades. The beach likely continued farther northward in the past, but the delta has gradually subsumed it, burying the gravelly beach face in finer sediment and eventually, covering it with marsh.
It looks like the beach here was once a spit with a back-barrier wetland between it and the base of the bluff, but now the backshore is heavily forested and the beach is on its last legs.
The old 1800s maps show the Stilli flowing through its northern distributary past Stanwood, but at some point it was directed (yes, it was pushed) into the more southern Hat Slough and has been building a big fan at its mouth ever since. Since the river is constrained by dikes, all the sediment is dumped in one big pile, instead of being distributed more evenly across the landscape, as it probably was naturally. The Mississippi has the same problem. Meaningful restoration may eventually require letting the lower river move around.
Sunday, January 24, 2010
Saturday afternoon - D needed time behind the wheel and I had been itching to visit this site for two months. Tom and Kathy were at the site and gave us the tour, helping us pick our way through thousands of new plantings.
This site is very different now than when I visited last May (South of Frenchman's Cove). The 400' bulkhead that used to define the shoreline has been removed and a low log-covered spit marks its location and encloses the new lagoon. Many thousands of yards of fill have been removed. The stream has been given a new, more natural channel, amidst lots of big logs and root wads. Instead of flowing over the edge of the bulkhead in a flume, it runs into the newly created lagoon and then out into Hood Canal across a rapidly reforming fan.
We don't know just what this place looked like 150 years ago, but we certainly know something about what parts were probably there and what the processes were that shaped those parts. The folks who put this project together put the basic pieces in place and gave them the ability to move. Now it just requires time. The plants will grow, the logs will move around, the dirt will erode in some places and deposit in others. The geometry will look different in 10 years, but it will look real.
It is rare to have an opportunity to completely restore a place. Check out the aerial view linked to the title of this post. Then check it again a couple years when they've updated those air photos.
Tuesday, January 19, 2010
What happens when you add a foot and a half or two feet of sea level rise to a normal January on Puget Sound? You get this past week. Normally inoccuous 12' tides became 14' tides. Tide levels that we normally only see once or twice a year happen every day for a week! The bathtub starts to overflow and places get wet that normally don't.
Thursday morning I went out to Alki Beach. The water was pretty calm - save for the occasional boat wakes. The tide was predicted to be 12.0'. It arrived around 8:30 just short of 14 feet and began to spill out onto the sidewalk. The drain notches in the seawall must be around 14', although the wall isn't quite level and some sections dipped a little lower than others. The sandy berm on the beach must also be just over 14', since it took a little bit of wave action to push the water over the top and back into the volleyball area.
This week, folks on Camano's Driftwood Shores and on Bainbridge's Point Monroe were reminded of their vulnerability to the tides and to the old real estate adage of "location, location, location" (they are both sand spits). King County had problems with one of its pump stations, too.
So what's going on? Starting a little more than a week ago, the observed tides in Seattle started diverging from the predicted ones. And for the last week, the 1.5-2' difference has been pretty continuous. One obvious explanation is a series of low pressure systems that have driven the barometer down and kept it down (atmospheric pressure has a direct effect on sea level). The pressure plummeted at about the same time the tides started rising.
During the 82-82 and in 97-98 El Ninos, sea level on the west coast rose significantly during the winter, bringing many more extreme tides than in normal years. This has been attributed to atmospheric conditions, to warmer ocean water, and to things called Kelvin Waves that raise water levels right along the coast. We don't know yet what is going on this year - and low pressure is certainly the simplest explanation - but stay tuned. And if the pattern persists, and you live on a sand spit, you may want to be prepared to wring out your carpets the first week of February, when even the regular tides are supposed to reach 13'!
The tide plot is from NOAA's Tides and Currents website (Seattle) (most folks around here will want to use Local Time and Feet above MLLW, not Greenwich Time and Meters)! The photos in this post were taken on the morning of the 21st.
The entrance to Drayton Harbor is marked by Semiahmoo Spit and Tongue Point on the south and the town of Blaine on the north. Blaine's waterfront includes a long peninsula that extends out like a spit towards Semiahmoo, but is actually an artificial feature that began as wharves and was then filled in with sediment dredged to create the marina (and with lots of other debris, too). Marine Park is located on the northwestern side of this peninsula, just across the water from the Peace Arch.
The concrete remnants of the old mill form hard points that help define the shape of the shoreline, with small pockets of sediment forming beaches in between. The beaches themselves consist of gravel, coarse sand, bricks, concrete rubble, quarry spalls, and ground up shell. At the northeastern end, there's a marsh and a small stream mouth.
The plan is to make the park more friendly to people and to improve habitat. This will involve removing much of the old debris and resculpting the shoreline, although some of the existing mill relics will be kept to help anchor the restored shoreline and provide for historic interpretation. The existing configuration of the shoreline - the position and orientation of the beaches - will help guide plans for the new shoreline.
There's something about White Rock that makes me expect Thomas the Tank Engine to pull up, loaded with school kids out of British children's novels. Railroad tracks along the beach, a waterfront promenade, and lots of fish'n'chips places. Nothing in Puget Sound feels like this place - Edmonds probably comes closest, but it still isnt the same.
This place really deserves a sunny summer day when the tide is out - with crowds trailing out across the warm sand flats. But all I had was a spare 30 minutes on a gray January day.
The town of White Rock, on the other side of the Peace Arch from Blaine, gets its name from a large glacial erratic perched on the beach. Apparently, the seagulls were responsible for the original white color, but now the town uses real paint.
Blackie Spit is the remnant tip of the larger spit system now occupied by the town of Crescent Beach. It would be neat to see historic maps of this area - partly to see what the whole landform originally looked like and partly to see how much this small spit has changed in response to all the modifications updrift (dike, groins, and so forth).
The beach wraps around the northern end of the spit and but doesn't get very far before running out of steam against the marsh. There's a nice set of trails back into the wetlands behind the spit - probably a great place for birds, though I didn't see too many through the raindrops this morning.
Waves from the south sweep into Canada's Boundary Bay, eroding bluffs and creating spits on both ends of the bay. On the west side, Point Roberts gradually gets reconstituted into Maple Beach, Centennial Beach, and Beach Grove. On the east side, the equivalent landform is Crescent Beach. This appears to have been a large spit (maybe a series of spits) extending northward into the corner of the bay.
Now much of the historic spit and back barrier wetlands have been converted to homes and streets, but the basic feature is still discernible in the aerial view (click the title of the post). Blackie Spit - next post - is about all that remains in a relatively natural state. The berm and backshore along the main part of Crescent Beach has been built up into a dike, in places armored with rock, that protects the low-lying community from storms and high tides.
Crescent Beach is a case study in groins. Larger and smaller, older and newer. Some of wood, some of rock. I guess the basic rationale is that there's a limited amount of sediment moving north along this shoreline and the groins offer a way to slow it up, maintaining beaches that would otherwise go elsewhere. At least for a while - and then they are gone.
Monday, January 18, 2010
Tuesday morning, January 5th, and one of the highest tides of the year was predicted for 8am. The tide arrived at about 13.3' (Seattle gauge). High, although not terribly dramatic. A 13' tide is typically sufficient to begin to flood the berm of some beaches - like the Sculpture Park beach shown here.
We get an average of 8 or so 13' tides every year in Seattle - although the actual number varies. In strong El Nino years, when sea level is higher up and down the west coast, we may get 25-30 (1983 and 1998), but there are also years in which we never get a tide higher than 13'. Our highest tides tend to come with storms and strong low pressure - the highest recorded tide in Seattle is almost 2' higher than this morning's.
In some parts of the world, the highest tides of the year are referred to as King Tides. And speaking of kings, King Canute (paleo Britain, 1000 years ago) did not go to the beach to hold back the tides, as some suggest. He went to the beach to show his overly enthusiastic followers that he did not have the power to control the tides.
Sunday, January 10, 2010
The west side of Vashon, along Colvos Passage, is less exposed to waves than the eastern side of the island and as a result there has been much less redistribution of sediment - less erosion, less opportunity for spit development, less consolidation of littoral cells. The nearshore platform is narrower and the irregular shoreline is divided into many small littoral cells -- short stretches of bluffs eroding and feeding sediment into small coves or to a few small spits and cuspate forelands.
Lisabuela is located on one of these small barriers - although the original morphology is a little confusing and most of the historic wetland is now lawn. The spit appears to have been fed by sediment eroded from the bluffs to the north - which remain a nice example of what natural shorelines tend to look like in this heavily forested part of the world.
Point Robinson is a cuspate foreland, gathering sediment from both the northern and southern shores of Maury Island, although I suspect it receives far more from the southern side (more wave energy and more gravel). It doesn't look like the point is accreting very rapidly these days, suggesting that most of the gravel is moving past and winding up in deep water offshore.
As local bumper stickers remind us, Maury Island is more than just gravel. Yes, but gravel sure explains the geology, the beaches, and much of the island's history! The southeastern shore of the island is pot-marked with large divots, the relics of early 20th century gravel operations. One has become the largest residential development along this side of the island. One is a King County Park. None are currently being mined, but one is slated to be reopened and has become one of the most controversial shoreline sites on Puget Sound.
It is called Point Heyer on the maps but is known locally as KVI Beach, after the radio transmitting tower on the point.
Point Heyer is a recurved spit, shaped primarily by winds and waves out of the north, and is the terminus of a littoral cell that collects sand and gravel from two miles of eroding bluffs and small streams. As usual, most of the wind comes out of the south, but Maury Island limits the fetch, so northern waves have much more influence. The southerly winds are still more than enough to pile the drift logs up into the northern corner of the marsh (within the lagoon itself, wind moves the logs, not the waves).
The spit is hooked around to the west, into Tramp Harbor, and the tidal inlet is pushed to the farthest end. The eastern limb is narrow, consistent with a barrier beach migrating westward in step with the retreating bluff to the north. The western limb is broad, since it is the ultimate resting place for much of this sediment moving down the shore. We often call these landforms accretion beaches or depositional landforms - because they have built over long periods of time seaward of the original coastline. But that doesn't mean they are actively accreting. In this case, the eastern limb is erosional - or at least maintaining a state of dynamic equilibrium (if your house was built on it you would call it erosion), but the western limb is truly accretional.
It's hard to find a tidal marsh in this part of the Sound. There used to be more, but these small estuaries and lagoons were easy targets for early settlers and small industry and most were filled by the early part of the last century.
Once upon a time a small stream ran down this ravine on the east side of Vashon Island, probably running out across the beach through a tangle of fallen trees. Now the stream exits the ravine in a 6' waterfall from the end of a pipe.
The seawall is a classic - complete with a decaying concrete balustrade along the top. The tide during the photos was probably about 11' - 100 years ago, this would have left a wide strip of dry beach, but today the waves are bouncing against the concrete. The 13' tide a couple of hours ago would have been well up on the wall itself.