Flood of the Century: Clark Fork River
This story package is featured in the December 2011 issue of Canoe & Kayak, available on newsstands now.
By Doug Ammons
When last winter’s record snowpack began to melt in western Montana, pushing the Clark Fork River above flood stage for nearly two months, hundreds of people gathered on the bridges in downtown Missoula to stare wide-eyed as the river flexed its muscle. This was the first runoff since the Milltown dam had been removed.
The dam was built in 1906 at the confluence of the Blackfoot and Clark Fork rivers to store and generate power. Ironically, the flood of 1908 deposited so much sediment behind the dam that it was never able to do much of either. It stood for more than 100 years, accumulating sediments toxic with arsenic, cadmium, lead, copper and zinc, all washed down from upstream mines and smelters. The poisons killed fish by the millions, gradually seeped into the aquifer, and contaminated wells in Missoula, seven miles below the dam site. The Clark Fork became the country’s largest Superfund site, stretching along 110 river miles.
Engineers rerouted the headwaters into holding ponds and bird habitat. They dredged more than 6 million cubic yards of tainted mud from the reservoir. Mostly, though, they got out of the river’s way. In the summer of 2010, they knocked down the Milltown Dam and a smaller dam just upstream on the Blackfoot. When the flood came in the spring of 2011, nature had her way with both rivers for the first time in more than a century.
The unleashed rivers cut down through 20 or 30 feet of cobble bars and sediment. The effect was most dramatic on the lower Blackfoot, where over about the distance of mile, it completely changed multiple bends, rearranged the river bottom, dropped the water level, undercut banks, and laid bare old bedrock ledges and huge boulders, long buried. It unearthed thousands of logs buried during the great log drives from the turn of the 20th Century, when gigantic matchsticked logjams filled the river for miles. Buried for all this time, the river freed thousands of old-growth logs, pushing them up to 60 miles downstream, through and below Missoula.
The stretch of the Clark Fork from above the dam site down into Missoula was transformed as well. Huge new cobble bars appeared right where the Milltown dam powerhouse, spillway, and concrete riprap once stood. The river stripped all the accumulated mud and sludge and algae from the riverbed and replaced it with acres of fine sand and perfectly sorted, multi-colored gravel beds. The river looks like a clean mountain stream again. Paddling along in disbelief, I saw great blue herons, osprey, deer, and a bear drinking in the river; and around one corner, two baby bald eagles shrieking in joy as they learned to fly in the blustery afternoon winds. Before our eyes, the river was reborn.
—Doug Ammons is author of Laugh of the Water Nymph and Whitewater Philosophy. See the immediate revitalizing effects of dam removal with Andy Maser’s incredible time-lapse footage of the recent Condit Dam removal on Washington’s White Salmon River.