Wednesday, May 31, 2017

Elwha Delta

This is the first of two posts from the mouth of the Elwha. This one is built around photos taken near the tip - on both sides of the river mouth. The next post will be from a little farther east.

The river is currently flowing out into Freshwater Bay on the western side of the delta, although the linked imagery from Google Earth currently doesn't reflect this.


The broad crescent-shaped beach on the west side of the delta seems much simpler than the messy beach on the eastern side of the delta (next post). It has continued to accrete into Freshwater Bay and appears to be doing so in a fairly uniform fashion along its length. I guess this is how I might expect a swash-aligned beach to respond to additional sediment. But the beach on the east side is progressing much less cleanly - perhaps because of its drift alignment and the uneven transfer of sediment along its length. I say perhaps - I often say perhaps - to clarify that this is some speculation based on fairly limited observations. There are others watching this much more carefully and hopefully they will be able to put together a more rigorous story (and maybe a different story) in time.

The Elwha Dam was gone by mid-2012, the Glines Canyon Dam, farther upriver, was out in 2014. Fresh sediment reached the shore very quickly after the lower dam was removed and the new delta built out rapidly for at least four years. That process seems to have now slowed as the initial plugs of sediment flushed through and the reservoir bottoms have begun to stabilize.

The slowing (at least from what I can see) of delta growth provides an opportunity for coastal processes to take over. During the first few years, the beach east of the delta continued to retreat, despite the huge accretion at the river mouth. But in the last year or two, a huge amount of sand has moved east, perhaps as the front of the expanded delta has begun to erode.

Previous posts about the Elwha Delta

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