Wednesday, August 1, 2012

Elwha Sediment and the Shoreline

Besides the aspect of restoring significant salmon habitat, the removal of the dams on the Elwha River has another restoration component. Because the dams were trapping sediment, the shore line along the Strait of Juan de Fuca particularly east of the mouth of the river was starved of a sediment source leading to more rapid shoreline erosion.

Elwha River, Ediz Hook and Port Angeles

At a glance it appears that the Elwha has a large prograding delta in the aerial view above. However, the image is misleading; the delta is much smaller as can be seen by a careful look at the topographic map.

Topography near mouth of the Elwha River.
Click to enlarge and note that the shoreline bluffs are as much as 175 feet high.

I did do some preliminary investigations of the area during the early stages of dam removal planning. For one thing, access to the lower reach of the river will be subject to flooding and alternate road routes needed to be contemplated. Also the community waste water treatment facility had to be thought about. I did some slope stability assessment on the high bluffs to the west of the river. 

While walking the shore I found a curved ivory-like object on the beach gravel. My initial reaction was I had found an exceptionally well preserved mammoth tusk. However, when I turned it over in my hands I noted well spaced homes on one side. this got me thinking of perhaps some sort of whale bone. But the object had a familiar look about it and then I realized I was holding the worn partial rim of a toilet bowl. It took me a bit longer to realize that it was very unlikley that the toilet bolwn floated up onto the beach. At that point I looked up at the bluff slope and realized I was looking at a cross section of a municipal waste landfill that was being eroded by the waves.

Bluffs, landfill and cemetery

Perhaps not the best spot for a landfill or for that matter the nearby cemetery. Since my site visit (predated digital pictures) the landfill has been protected with a rock armoring and some regrading of the slope. With sediment from the Elwha River, perhaps the erosion rate will be lessened.

Oblique view of landfill (Ecology, 1997)

Oblique view post repair work (Ecology 2011)

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