The Lake Aldwell reservoir is starting to look like a river again. It’s just one of the changes to the Elwha River system that the Lower Elwha Klallam Tribe has been watching with great anticipation since removal of the river’s two fish-blocking dams began in September.
By Nov. 1, the 108-foot-tall Elwha Dam had been lowered by 48 feet and the 210-foot-tall Glines Canyon dam by 32 feet. Water from the reservoirs has been spilling over the deconstructed dams, changing the hydrology of the reservoirs as well as the lower river. Only the last five miles of the river were free flowing before dam removal began.
“Since the Elwha Dam is about 40 percent gone, the reservoir behind it, Lake Aldwell, isn’t really a reservoir anymore,” said Mike McHenry, the tribe’s habitat program manager. “It’s starting to look like a river channel. The delta at the south end of the reservoir is more exposed and sediment is being transported downriver.”
In addition, construction crews have removed remnants of nearly 100 year old pilings from Lake Aldwell. Also removed was a logboom that prevented boats from going over the dam. The wood was allowed to flow downriver with the expectation that it will contribute to salmon habitat in the lower river.
“Following the big rains we had in late November, the river was flowing at 10,000 cubic feet per second at one point,” McHenry said. “A lot of dynamic stuff is happening with the high flows.”
Near the mouth of the river, the tribe has noticed a small increase of fine sediments building in the estuaries.
“The fine sediment plume from the mouth of the river into the Strait is much more pronounced than prior to removal activities. Its configuration varies during the course of the day,” said Matt Beirne, the tribe’s environmental coordinator. “We haven’t seen significant sediment deposition in the estuary just yet, but we have seen elevated turbidity levels from the finer fraction of sediment.
“Although the removal of the dams appears to be ahead of schedule, we don’t expect to see significant sediment deposition within the estuary until we experience greater mobilizing flows through the system.”
For nearly 100 years, fish have been blocked from the upper Elwha River watershed by the two dams, which were built without fish ladders. More than 20 million cubic yards of sediment have built up behind the dams, most of which will be allowed to flow downriver and alter the riverbed.
The dams are owned by the federal government; the Olympic National Park is spearheading the removal effort. The project to remove the structures and restore the Elwha River ecosystem, estimated at $350 million, is the largest dam removal project to date in the United States. The project is expected to be finished by 2014.
