Quantifying Channel Responses to the Removal of the Glines Canyon Dam in the Middle Reach of the Elwha River, Washington

The removal of the Glines Canyon and Elwha Dams on the Elwha River, Washington in 2011-2013 is the largest dam-removal project in United States history. The objective of my research is to quantify the sediment deposition and channel changes following the removal of the Glines Canyon Dam. An estimated seven to eight million cubic meters of sand, gravel, and large woody debris will be released into the river within a year after dam removal is completed in April 2013. Previous observations and models have shown that the majority of the sediment deposition following a dam removal occurs within the first two kilometers below the breach. However, these observations and estimates have been made on sediment reservoirs that are one-third the size of the Glines Canyon reservoir. My hypotheses are that within the first year: 1) initial sediment deposition will occur two kilometers below the dam and will propagate several kilometers further downstream; 2) sediment distribution will fill riffles and pools with coarse sediment; and 3) the increase in sediment and new large woody debris will cause lateral channel migration in key areas along the river corridor, such as adjacent to mid-channel bars. My current observations show that the sediment in the river has aggraded the channel, it is consequently filling in the riffles, and pools as far as six kilometers downstream of the dam. It is also evident that the channel is widening during this deposition period but is subject to change as water flows increase with the spring melt