Alongshore Transport of Large Woody Debris on the Elwha River Delta

In the Elwha River watershed, large woody debris is being tracked in association with the removal of the Glines Canyon and Elwha Dams. In 2011, 25 logs were tagged on the Elwha River delta east of the river mouth along 2 km of beach on the Strait of Juan de Fuca. Logs greater than 3 meters long and 30 cm in diameter were tagged with 3 cm aluminum disks stamped with an identification number. Two comprehensive surveys of the entire delta were conducted in September 2011 and October 2012. 12 shorter surveys across approximately 700 m of the shoreline were also completed. GPS coordinates from all the log surveys were mapped in a geographic information system. 13 logs were missing from the study area by October 2012, either because they were buried by new sediment or moved out of the study area. One additional log recruited to the beach from a separate study tracking 1,700 logs upstream on the Elwha River. For each log observed more than once, the distance traveled between surveys, the rate in meters per day, and the direction of movement in degrees, was calculated. Of the logs that remained in the study area, the maximum distance traveled was 985 meters in 11 months. The minimum rate of movement was 0 m/day and the maximum was 6.6 m/day. The mean movement for all logs in all surveys was 0.4 m/day. The median direction of all movements was 108 degrees. These data are useful in determining the degree to which large woody debris are stable in the intertidal system, and inform questions regarding their role in protecting the beach from erosion. These data may also be used to assess the utility of large wood as a “soft armoring” shore protection solution along drift cells dominated by alongshore transport