Title

Change in Woody Debris Following the World’s Largest Dam Removal, Elwha River, Washington

Presenter Information

Spencer Baumgartner
Bryon Free

Document Type

Oral Presentation

Location

SURC Ballroom C/D

Start Date

15-5-2014

End Date

15-5-2014

Keywords

Dam removal, Fluvial geomorphology, Woody debris

Abstract

This research documents the fluctuation of logs and other woody debris in the Elwha River, Washington, in the year following the initiation of the sediment release from the removal of the Glines Canyon Dam. Fluctuations in the amount and position of large woody debris were documented over a one-year period at four sites that had been previously selected for separate studies of sediment and channel changes. Branches, logs, and trees, known as woody debris, that have accumulated in the reservoir for 85 years were released during the removal of the dam. We hypothesized that this influx of new woody debris into the river would influence the course of the Elwha River channel over time. Log jams and large woody debris in the river channel from 1.4 to 8 kilometers downstream of the dam were mapped using ArcGIS 10.2 along with orthographic photos, provided by the National Parks Service. All visible individual logs on a 1:1000 scale were mapped and measured. A group of four or more logs in close proximity to one another was mapped as a log jam. Logs within a jam that had clear termini and line of sight were also measured for length. The results show small alterations to the Elwha River channel path, an increase in woody debris quantity for the first ten months, and an increase in the average length of woody debris over the study period. The sites exhibiting the greatest changes were located 1.4 and 4 kilometers downstream of the dam.

Poster Number

38

Faculty Mentor(s)

Ely, Lisa

Additional Mentoring Department

Geological Sciences

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Change in Woody Debris Following the World’s Largest Dam Removal, Elwha River, Washington

SURC Ballroom C/D

This research documents the fluctuation of logs and other woody debris in the Elwha River, Washington, in the year following the initiation of the sediment release from the removal of the Glines Canyon Dam. Fluctuations in the amount and position of large woody debris were documented over a one-year period at four sites that had been previously selected for separate studies of sediment and channel changes. Branches, logs, and trees, known as woody debris, that have accumulated in the reservoir for 85 years were released during the removal of the dam. We hypothesized that this influx of new woody debris into the river would influence the course of the Elwha River channel over time. Log jams and large woody debris in the river channel from 1.4 to 8 kilometers downstream of the dam were mapped using ArcGIS 10.2 along with orthographic photos, provided by the National Parks Service. All visible individual logs on a 1:1000 scale were mapped and measured. A group of four or more logs in close proximity to one another was mapped as a log jam. Logs within a jam that had clear termini and line of sight were also measured for length. The results show small alterations to the Elwha River channel path, an increase in woody debris quantity for the first ten months, and an increase in the average length of woody debris over the study period. The sites exhibiting the greatest changes were located 1.4 and 4 kilometers downstream of the dam.