Linking Marine Ecosystem Response to the Removal of Shoreline Armor and Large Dams in the Elwha River and Nearshore Environment of Washington, USA: An Extended Summary

Shaffer, J.A.; Oxborrow, B.; Parks, D.; Bauman, J.; Michel, J., and Maucieri, D., 2024. Linking marine ecosystem response to the removal of shoreline armor and large dams in the Elwha River and Nearshore Environment of Washington, USA: An extended summary. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 890-895. Charlotte (North Carolina), ISSN 0749-0208. We assess the nearshore ecosystem processes and function and restoration response to removal of large scale in-river dams and shoreline-armor. Two nearly century-old large dams in the Elwha River watershed in the Northwestern United States were removed during 2011-2014, which liberated upwards of 18 million tonnes (Mt) or approximately ∼9 million cubic meters of silt, sand and gravel to sediment starved, armored and unarmored shorelines. Within one-year of the initiation of dam removal, unarmored shorelines in the drift cell broadened, flattened, sediment fined, and large woody debris (LWD) volumes increased, all significantly. Armored shorelines continued to be steep and coarse-grained. Beginning two years after dam removals approximately 4700 m3 of large riprap (shoreline armor) was removed from over 650 meters of the armored Elwha River east delta reach drift cell. Following armor removal, previously eroding shorelines broadened, sediment fined at the project site, LWD volumes increased significantly, and beach wrack metrics resembled non-armored beaches at the treatment reaches. Invertebrate communities also responded to both dam and armor removal, and showed increasing trends along the armor removal site every year of the study. We therefore conclude that armoring impairs ecosystem function along dam removal shorelines; and that removal of shoreline armoring along with dam removals can result in drift cell scale ecosystem restoration.