Largest Dam Removal in History Scientifically Characterized

SEATTLE — The effects of dam removal are better known as a result of several new studies released this week by government, tribal and university researchers. The scientists worked together to characterize the effects of the largest dam removal project in U.S. history occurring on the Elwha River of Washington State. New findings suggest that dam removal can change landscape features of river and coasts, which have ecological implications downstream of former dam sites.

“These studies not only give us a better understanding of the effects of dam removal, but show the importance of collaborative science across disciplines and institutions,” said Suzette Kimball, acting director of the U.S. Geological Survey.

Five peer-reviewed papers, with authors from the U.S. Geological Survey, Reclamation, National Park Service, Washington Sea Grant, NOAA Fisheries, the Lower Elwha Klallam Tribe, and the University of Washington, provide detailed observations and insights about the changes in the river’s landforms, waters and coastal zone during the first two years of dam removal. During this time, massive amounts of sediment were eroded from the drained reservoirs and transported downstream through the river and to the coast.

One finding that intrigued scientists was how efficiently the river eroded and moved sediment from the former reservoirs; over a third of the 27 million cubic yards of reservoir sediment, equivalent to about 3000 Olympic swimming pools filled with sediment, was eroded into the river during the first two years even though the river’s water discharge and peak flows were moderate compared to historical gaging records.

This sediment release altered the river’s clarity and reshaped the river channel while adding new habitats in the river and at the coast. In fact, the vast majority of the new sediment was discharged into the coastal waters of the Strait of Juan de Fuca, where the river mouth delta expanded seaward by hundreds of feet.

“The expansion of the river mouth delta is very exciting, because we are seeing the rebuilding of an estuary and coast that were rapidly eroding prior to dam removal,” said USGS research scientist and lead author of the synthesis paper, Dr. Jonathan Warrick. …

Elwha_over_time
Aerial photos of the Elwha River mouth before and during dam removal. Photos show (A) the river mouth wetlands before dam removal, (B) the turbid coastal plume that occurred during much of the dam removal project, and (C) the expansion of the river mouth delta by sediment deposition. Photos provided by Ian Miller of Washington Sea Grant, Jonathan Felis of USGS, and Neal and Linda Chism of LightHawk

Read the full article here and five peer-reviewed papers here.