Elwha Delta

From Salish Sea Wiki


delta progradation following Elwha dam removal

The Elwha Delta is an example of a wave dominated delta, where barrier beach formation controls the configuration of the river outlet. The Elwha has very low indicators of degradation compared to other Puget Sound deltas (Cereghino et al 2012). The greatest source of degradation is the historical damming of the Elwha river, which dramatically reduced sediment supply. Ongoing dam removal has dramatically increased sediment input, and is altering the structure of the delta.

Nearshore Strategies Data Report

Cereghino et al 2012 completed a soundwide analysis to identify and describe river delta sites in Puget Sounds as part of a nearshore ecosystem restoration strategy (using remote sensing data c. 2000-2006). The following narrative of this delta site was developed to support distribution and use of analysis results:

The Elwha Delta in the Juan de Fuca sub-basin historically contained 46 acres of vegetated wetland along a 4 km shoreline. The delta receives flow from a 83,609 square kilometer watershed. These characteristics make this system the 11th largest delta out of 16 systems in Puget Sound.
Simenstad et al 2011 found that this system had lost none of its vegetated tidal wetlands, and 25% of its shoreline length. Of the remaining shoreline, 2% shows some evidence of infrastructure development. In the surrounding uplands, 7% of land is estimated to have greater than 10% impervious surface. Across the watershed, 2% of land is estimated to have greater than 10% impervious surface. Based on these paramters, the site was given a degradation score of 6 out of 100, making it the 16th most degraded delta in Puget Sound. It faces no risk of future development locally, and a low risk of development across the watershed. Approximately 98% of the watershed is currently impounded behind dams.


Efforts

Reporting


Notes

  • Delta progradation has accelerated since first Elwha Dam removal.
  • Barrier beach formation apepars to change the orientation and character of distributary and tidal channel networks.

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