Thursday, November 20, 2008
The pocket beach at the sculpture park was looking great, particularly once the sun came out ( just as we were leaving). A mother seal had dropped off her pup on the only backshore in the several miles between the mouth of the Duwamish and Magnolia Bluff (it was probably once a continuous beach, broken only at the head of Smith Cove), and the beach had been cordoned off so he could lounge in the wrack undisturbed. I'm a big advocate of urban beaches, but this is an ecological function that I hadn't considered!
The tide was too high to see much of the lower beach, let alone the low tide "habitat bench" that stretches along this shore in front of both the seawall and the pocket beach. The researchers monitoring the beach report that some gravel is lost offshore as a result of being thrown by kids. Maybe we should invite them (the kids, not the researchers) all back at a really low tide every few years to retrieve it! If it weren't for the low-tide sill, maybe it would come back on its own.
Previous Post: Sculpture Park (January 2007)
And more pictures at hshipman, too.
It used to be a strawberry packing plant, but this site on Eagle Harbor had fallen into disrepair long before the county acquired it some years ago for a future park. The plant was built on lots of fill and lots of pilings next to the mouth of a small creek - now there's a chance to pull much of this out and restore the shoreline while also creating a nice little community park.
The shorelines at the head of Eagle Harbor are too sheltered to form beaches - there's just not enough wave energy to move much coarse-grained sediment. For a beach to form, there's got to be enough wave action to keep the sand and gravel moving around so the marsh can't get a foothold. We looked at Leslie Landing ten years ago when it was first developed and wondered how the shoreline would hold up. No problem - the high tide line is now marked by a narrow band of dense Salicornia.
A new proposal to fix some of the problems at this park on the Tacoma Narrows led me to swing by for a quick stop last week. I was also hoping to see how the stream mouth behaved during a heavy rain, but unfortunately the rain had pretty much stopped by the time I got there. The flow from the outfall structure was way above the normally low levels, but far from what I'd call exciting. Exciting would be if the pipe was full and mud and trees were washing across the park - but that might have made driving down the ravine a bit tricky.
The concrete stream mouth, which marks the end of a pipe a couple hundred feet long (tough for a salmon), acts like a groin to the northerly drift, contributing to the ongoing erosion problems on the north side (but making a nice little sandy beach on the south side). The stream leads to another problem, too. During higher flows at lower tides, the stream erodes the upper beach, carrying sediment down the profile, which may also contribute to downdrift erosion.
This is the"logs-in-bondage" site described two years ago (Narrows Park). Ideally, it would be great to remove the concrete structure and daylight the stream, but this will require a considerable rethink of the park. Meanwhile, folks are looking at modifying the outfall structure slightly, relocating the big logs higher on the profile, and patching the worst of the erosional scars.