[env-trinity] TRRP responds to gravel bed concerns

[Tom Stokely]

 http://www.trinityjournal.com/news/local/article_fe763b54-ef2d-11eb-9603-832ca8e5c3ea.html
TRRP responds to gravel bed concerns

Work has essentially been completed on a project that got the attention of several people near the Trinity River Hatchery in Lewiston. Photos posted on social media showed heavy equipment moving gravel into the Trinity River, which raised questions and concerns among those who saw them.
According to Lisa Navarro at the Trinity River Restoration Program, the project to augment gravel beds into the river near the hatchery has been going on since July 15 and concluded on the morning of July 23. She said the program added 6,200 cubic yards of gravel below the dam that will serve as a salmon nesting area.

“This is a good thing,” she said. “They were also doing background tests and turbidity tests to mitigate any damage there.”

One concern was over the amount of dirt flowing downstream from the project site. TRRP Science Coordinator James Lee explained that turbidity is basically measure of how murky the water is when dirt and sediment mixes in it.

“The North Coast Regional Water Quality Control Board has standards that can be measured,” he said, explaining that the project has used a full-time turbidity monitor. “They would measure the turbidity about every 15 minutes. If the turbidity got near the maximum allowed by the state, they would stop until the water cleared.

Lee explained that turbidity needs to be minimized so aquatic life in the riverbed wouldn’t be covered and smothered and so light can reach the bottom.

He said that after the next flood, some of the gravel will move downstream, which would be the natural occurrence if the dam was not slowing the upstream water. He said research has been done to track the distance gravels will flow downstream and it was found to be less than ¼ mile, depending on the conditions. He said researchers used tagged rocks in the gravel to measure the movement.

“It was really eye-opening to see it didn’t go far after the floods after it was placed,” he said, noting that it may move to just below the downstream bridge in several years’ time.

Navarro explained that the gravel is essential for salmon to use for egg-laying, and the last time gravel was placed in that area was 2007. She said the dams cut off the introduction of new gravel and that recent years’ floods washed it away. She said the Yurok Tribe had a good team working on the project, which was approved by several state regulatory agencies.

Lee noted that while the gravel serves as an egg bed for salmon, it also encourages aquatic insects the salmon feed on. He said the area was a main spawning bed, but that has declined over time.

“So what we are really trying to do is encourage and allow spawning there,” he said. “We expect to see spawning there this fall and we also expect more fresh reds (baby salmon) than last year.”

Lee said that while most of the work is done in the area, some erosion control and seeding work will occur to correct any damage that was done by the heavy equipment.

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