Saturday, May 21, 2011
The eastern shore of Elliott Bay was once a gravel beach with a steep bluff gradually rising from south to north, perhaps 80-100' high in the vicinity of Bell Street. But one thing leads to another and now the bluff is hidden in the jungle of buildings and roadways between Alaskan Way and Western Avenue. The waterfront was built on piers and wharves, then railroads were built parallel to shore (but over the beach), and then eventually, everything was filled in and the current seawall was built.
Now the seawall is being redesigned, the viaduct is slated for removal, and the city has embarked on a grand and long overdue scheme to redevelop its waterfront into a world-class urban shoreline. Thursday night, James Corner provided additional glimpses into the emerging ideas for this stretch of forested bluff and log-strewn beach at the mouth of the Duwamish River.
Cape George is a large residential development west of Port Townsend. It faces northwest across the mouth of Discovery Bay, looking out over Protection Island and the Strait of Juan de Fuca. Were it not for Protection Island, I suspect the shoreline would look very different, as the island is appropriately named (by George Vancouver back in 1792).
The community's primary link to the beach is a marina and community center built on an old spit and salt marsh - littoral drift is from north to south and sediment that bypasses the jetty is periodically dredged from the channel and placed on the beach immediately south.
The high bluff around the corner to the north has been active this winter, encouraged by the wet weather and stratigraphy that lends itself to hydrologically induced mid-bluff failures. There are massive clays or silts at the toe of the slope - in most cases, the slides have come down from above, although farther northeast, it looks like some historic slides may have cut deeper into this unit. There is a nice contrast between the heavily deformed fine-grained unit at the base and beautiful horizontally laminated sands higher in the bluff.
Small, sheltered beaches often seem much more complicated than big, high energy ones. High energy ocean beaches with abundant sediment are just a simple (hah!) balance of wave energy and sediment mobility - the math is hard, but the geology is straightforward, almost absent. But these protected systems are a messy combination of an inherited landscape, a complex geologic framework, a spatially variable wave environment, the role of mixed grain size, often sediment-limited beaches, and the persistence of past human modifications.
Port Hadlock is located at the south end of Port Townsend Bay - where northerly waves dominate and Tertiary bedrock makes one of its rare Puget Sound appearances. Hadlock Spit extends southward from the boat building school, approaching but missing rocky Skunk Island down near the old alcohol plant (as usual, click on the title of the post for the aerial/map view). The beach beneath the boat yard appears to have built seaward, maybe as a lingering result of more than a century of piers and moored ships (and maybe an abundance of sand from the huge fill up at Irondale?). But this sandy beach narrows rapidly just north, with the tide lines swinging landward as if at the end of a spit (starved by the updrift accretion?). But the gravelly beach continues south. The boat ramp is built below the current beach grade, so sandy gravel constantly accumulates and is removed and put in a pile that then gradually erodes. But despite this miniature bypass operation, the shoreline another hundred yards south is eroding, undermining the road out to the private property on the spit itself.
I have few answers, only ideas and questions. Someday I would love to get together with the regular readers of the blog (all 3 of them?) at the Ajax Cafe to figure this all out (funny hats are optional)!
Monday, May 09, 2011
As the Skagit Delta has expanded into Puget Sound, it has gradually engulfed the small islands that once must have dotted the northern portion of what was once a much larger Skagit Bay. Some of these islands are larger than others - Fidalgo Island, for example, which is only still an island by virtue of the Swinomish Channel. Most of these islands are simply hills now, rising out of the miles of low, flat tulip and mustard seed fields. Some are tiny rock dimples - by sheer luck rising slightly higher than modern sea level - juxtaposing ancient bedrock ledges against acres of tide flat and salt marsh.
If you drive to the west end of Rawlins Road (turn at the Snow Goose farm stand) and park, you can find a half-mile trail that skirts the high marsh out to this rocky knob. And if the tide is low, you can just keep on walking for miles.
This big hunk of metamorphic rock sits on the beach below Scenic Heights, somewhere between Penn Cove and Oak Harbor. I think it can safely be called an erratic - since it sure didn't start here and I can't imagine it having wandered here without the help of ice. It's so big, you can't help but wonder if there is a big divot missing somewhere on the side of a valley in British Columbia.
Longshore drift is from south to north along this beach and is interrupted by the rock and the tiny tombolo that attaches it to the base of the bluff. The beach is wider to the south and the bluff a little less severe. To the north, the apparent lack of sediment results in a much diminished beach and a steeper bluff. The aerial (click on the title of this post) shows a distinct offset in the bluff crest. Jerry Thorsen first pointed out the groin-like nature of this feature to me years ago - as an example of how local details can influence bluff recession patterns.
I need to explore this beach with a better geologist along - one who really understands the complex stratigraphy and sedimentary tales exposed on these spectacular high cliffs. The first, and last, time I walked this beach was with better geologists, but I'm afraid I took too few notes and remember too little.
The cliffs keep getting higher as you round the corner from Penn Cove and the number of layers keeps growing. There are wonderful layered bedded fluvial sediments, presumably from some earlier interglacial floodplain. There are coarse gravels and glacial tills and layers containing giant chunks of other layers - the latter must be a fascinating story. There are peat beds peaking through the cobbles on the mid beach. And there are many small and large boulders - the largest of which I'll save for the next post.
I suppose it is the interplay of easterly and westerly wave action that results in accretion here inside the northeastern corner of Penn Cove. This small barrier beach shelters a brackish wetland, filled with logs that have wandered up Saratoga Passage from the south and become permanently lodged. Like the logs that accumulate in so many of these marshes, most are cut - probably escapees from early log rafting. The cut timbers (telephone poles, basically) float easily and are readily washed over the berm during high tides. Once trapped inside, winds blow them to the north sides of these ponds, where the logs pack together tightly. And they decay very, very slowly. Wood, including some very big wood, is a fundamental component of Salish Sea beaches and marshes, but these dense mats of timber are not likely what would have been found here two centuries ago.
Penn Cove is known for it's mussels. Maybe they cultivate them here because it is such a natural nursery. Or maybe its the enthusiastic cultivation that explains the mussel-covered beaches spilling out of the entrance of Penn Cove. Like the logs, I wonder if the abundance is actually a human legacy.
Long before Captain Thomas Coupe, killer whale round-ups, (an infamous legacy of Penn Cove), and mussel rafts, Monroe's Landing was a gathering place for the Lower Skagit tribe.
The big landslides at Termination Point used to feed the beaches northeastward towards Shine Tidelands and Bywater Bay, but the embankment that supports the west end of the Hood Canal floating bridge cuts across the base of the old spit. This starves the beach at Shine Tidelands, resulting in coarse cobble and an eroding berm. But because the bridge approach acts like a big groin, it traps sediment on the south side and results in a beautiful little swash-aligned pocket beach.
The railroad and the high bluffs make access to the beach between Seattle and Everett a tricky proposition, but there are places where stream valleys, pedestrian overpasses, and public parks conspire to make it possible - Carkeek Park, Picnic Point, and Howarth Park, for example.
The natural stream mouth at Howarth is obscured beneath the railroad grade and the big pile of dirt that surrounds the stair tower -- the creek tumbles out of a long culvert onto the riprap. From the look of the wetland next to the parking lot, this stream might have had a sufficiently low gradient to result in a nice little estuary (probably behind a small spit - sort of like the one down the beach at Merrill and Ring Creek).