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British Columbia residents facing a flood emergency this weekend can partly blame 19th-century gold miners for their woes.
Two Canadian scientists have shown how the Fraser River — the waterway at the heart of British Columbia’s history, and currently the focus of a flood threat in Abbotsford and elsewhere in B.C.’s Lower Mainland — was significantly altered by 19th-century fortune seekers, whose dumped mine tailings from the Fraser’s gold-rich banks and tributaries accumulated at critical points along the southern course of the river and continue inching toward its Pacific outlet today.
The study of the ongoing “geomorphic impact” of 1800s-era placer mining in the Fraser watershed, co-authored by UBC researchers Andrew Nelson and Michael Church and published in the latest Geological Society of America (GSA) Bulletin, argues that present-day flood and fishery management for the 1,375-kilometre river — B.C.’s longest — need to account better for the “legacy effects” of the Gold Rush and carefully distinguish between the pre-1858, “natural” state of the Fraser’s riverbed and its post-Rush condition.
Millions of tonnes of gravel flushed into the Fraser by miners as early as 154 years ago have been “accumulating in the river in the Lower Mainland throughout the 20th century,” Church told Postmedia News. “Because this raises the river bed, it also raises the water surface for a given flow, so — at high flows — the protection from flooding afforded by the dikes becomes slowly less effective.”
The discovery of gold near Quesnel in 1858 saw an estimated 30,000 gold miners from the U.S. and elsewhere pour into the B.C. interior in a feverish quest for riches.
While the initial rush petered out in a few years, subsequent discoveries spawned the famous Cariboo Gold Rush and other pulses of mining activity that kickstarted the political and economic development of mainland B.C., with the Fraser River at the centre of the action.
Miners panned for gold or used stream-fed sluice boxes to separate the precious metal from worthless sand, gravel or bigger rocks dug up along the shore. The waste material was typically disposed of in the river, gradually flushing downstream.
“The apparent impact of any given individual mine along the river was limited, especially because the river actively ‘washed the sediment away,’ ” Nelson told Postmedia News. “In so doing, however, the river eventually concentrated the sediment from hundreds of mines into a smaller area, resulting in the downstream impact that is observed today.”
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