The effects of dam removal are better known as a result of
several new studies released this week by government, tribal and university
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. 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
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 3,000
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, Jonathan Warrick.
Although the primary goal of the dam removal project is to
reintroduce spawning salmon runs to the pristine upper reaches of the Elwha
River within Olympic National Park, the new studies suggest that dam removal
can also have ecological implications downstream of the former dam sites.
These implications include a renewal of the sand, gravel and
wood supplies to the river and to the coast, restoring critical processes for
maintaining salmon habitat to river, estuarine and coastal ecosystems.
“These changes to sediment and wood supplies are important
to understand because they affect the river channel form, and the channel form
provides important habitat to numerous species of the region,” stated USGS
research scientist and river study lead author, Amy East.
The final stages of dam removal occurred during the summer
of 2014. Some sediment erosion from the former reservoirs will likely continue.
The Elwha Project and research teams are continuing to monitor how quickly the
river returns to its long-term restored condition.
“We look forward to seeing when the sediment supplies
approach background levels,” said Reclamation engineer and co-author, Jennifer
Bountry, “because this will help us understand the length of time that dam
removal effects will occur.”
The five new papers can be found in Elsevier’s peer-reviewed
journal, Geomorphology, and they focus on the following topics of the
large-scale dam removal on the Elwha River:
-- Erosion of reservoir sediment http://www.sciencedirect.com/science/article/pii/S0169555X15000306
-- Fluvial sediment load http://www.sciencedirect.com/science/article/pii/S0169555X14006369
-- River channel and floodplain geomorphic change http://www.sciencedirect.com/science/article/pii/S0169555X14004553
-- Coastal geomorphic change http://www.sciencedirect.com/science/article/pii/S0169555X15000148
-- Source-to-sink sediment budget and synthesis http://www.sciencedirect.com/science/article/pii/S0169555X15000227