Thursday, November 20, 2008
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.