Plants, Stone, California Landscapes


Posts Tagged ‘riprap’

Middle Harbor Training Wall Memorial

This little jetty sticking out into the mudflat (click on all of these to see them bigger) is a memorial to one half of the Bay Area’s largest and most ambitious drystone construction, the Oakland Harbor Training Walls. It’s in Oakland’s Middle Harbor Shoreline Park, which is a rather incongruous park. The park is out in the middle of the port surrounded by industrial activity, there’s a ton of lawn which no one ever uses and in fact the geese have turned rather unusable, and there are a bunch of big landscape elements that reference the history of the port: the shade structure in the photo below, a concrete path that marks the footprint of a giant 19,000 square foot building that they took down, and the rock jetty that commemorates the port’s north training wall.

The harbor’s north and south training walls were two long jetties designed to ‘train’ the tide. Unlike a typical riprap jetty made of haphazardly dumped piles of rock designed to absorb wave or tidal energy, each rock in the training wall was fitted by stoneworkers to give the wall a smooth face that would accelerate the water instead of slowing it down. Back in the 1800’s, Oakland’s harbor was shallow and it tended to fill with silt; ships could only enter it during high tide. The idea of the training walls was to channel the tide’s energy so that when the tide went out it would also suck all the silt out with it, reducing the need for dredging. The walls were started in 1874 and took twenty years to build, with some impressive stats: 310,000 tons of stone, 500,000 square feet of wall, 20 feet wide at the base, 8 feet wide at the top, 6 feet above the low water point. The north wall was 9500 feet long, the south wall 12,000. Apparently the walls worked; the signage says the port’s activity went up 2000% after they were built.

The south wall is still there, but the port the north wall out in 2001 when they widened the channel so bigger container ships could use it; as part of the approval process, they used some of the north wall’s rock to build this memorial. I didn’t do all that good with my photos of it (there’s a better one at Oakland Geology) and I might try again some time when the tide is in or I might try to find a good view of the south wall. Honestly, though, I think the appeal is more intellectual than aesthetic.

It looks a little better with some sun flare drama. You can see the contrast between the training wall’s fitted stone (above) and the riprap’s rough faces (below).

Overall, though I said it was incongruous, the park is also pretty cool. The ships and cranes and machinery right next to the park are all impressive. There’s also a habitat planting with some natives struggling against weeds and a path out to a great view of the Bay Bridge and the city. The water area of the middle harbor is being converted into a mudflat, slowly getting filled with the silt from dredging of the channel. It’s a good place to see water birds.

And the park is a great place to see the sunset. Information and a map of the park is here, a historic photo with the training walls visible on the left side is here.