About half as much water pulsed through the Coeur d’Alene River last week as during the benchmark flood of 1974.
That will come as a surprise to many Kingston and Cataldo residents who had 4 feet of water in their homes. They swore the flooding was as bad or worse than 22 years ago.
They’re not necessarily wrong, according to scientists who met Wednesday in Coeur d’Alene.
“When you hear folks up there saying it was higher than the ‘74 flood, that may be so,” said Paul Woods of the U.S. Geological Survey.
He noted that the depth of water, known as the “stage,” is different from the flow, which is measured in cubic feet per second (cfs).
“You could have lower flow, but higher stage because the river can’t handle it,” he said.
The river is shallower because there’s more rock in the stream bed than there was two decades ago, scientists say. They blame erosion caused by unstable stream banks and faster runoff.
In the 1974 flood, 79,000 cfs flowed past the USGS measuring gauge at Cataldo. At its peak last week, the flow was above 40,000 cfs.
The Geological Survey scientists aren’t sure of that second figure yet, and may never be because the automated streamflow gauge may have been washed downstream. They haven’t been able to reach it yet.
The gauge upstream at Enaville definitely disappeared.
The measuring stick used to tell the height of the water at Cataldo couldn’t be read during the flood. But the level apparently reached a record 53 feet.
The flooding dominated conversation at Wednesday’s meeting of the Coeur d’Alene Interagency Group. It includes scientists, land managers and others interested in cleaning up mining wastes and restoring streams in the Coeur d’Alene River basin.
Among other flood-related comments: While the main river did not reach an all-time high, the South Fork experienced record flows. So did Pine Creek, one of its main tributaries.
Floods flush mining wastes into the river system. While figures aren’t available from last week, a smaller flood one year ago washed as much lead and zinc into the water as would normally occur during an entire year, said Mike Beckwith of the Geological Survey.
His figures from Feb. 21, 1995, showed 69 tons of lead and 42 tons of zinc per day moving in the water at Harrison, which lies at the mouth of the river on Lake Coeur d’Alene.
At Pinehurst, just downstream of the Bunker Hill Superfund site on the South Fork, the figures were 16 tons of lead, 11 tons of zinc. At Enaville on the North Fork, where there’s been less mining, the figures were .9 tons of lead, 1.7 tons of zinc.
The three floods that have occurred in the last 12 months complicate efforts to clean up heavy metals. David Fortier of the Bureau of Land Management, which owns land along Pine Creek, noted that nature has been sweeping away tailings before they can be moved from the stream.
So far, streambank stabilization and cleanup efforts at Nine Mile Creek and Elizabeth Park have withstood flooding. But it’s too early to tell in other places, such as the Cataldo boat ramp.
Last year, officials tried two methods for stopping erosion at the ramp below Old Mission State Park. One method involved using heavy equipment to place logs below the riverbank. The logs were held in place by cables. It didn’t work.
After the Nov. 30-Dec. 1 flood, Mike Stevenson of the Bureau of Land Management visited the boat ramp and was crushed to find the logs “sticking straight up from the water like an obscene hand gesture.”
The other method survived the fall flood. It involved driving posts into the riverbed and filling in between them with willow cuttings. The log work cost $2,000; the willow project, done with the help of student volunteers, cost $200.
Marti Calabretta, coordinator of the Silver Valley Natural Resource Trust Fund, noted that massive flooding probably wouldn’t have happened before people stripped the riverbanks of vegetation.
Capt. John Mullan, assigned to find a military road through the region in the 1860s, deemed the river valley unsuitable because it was a cedar swamp, she said. “We did this to ourselves.”
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