Salvaging Beetle-killed Trees Leads to Flooding

Killing or removing most of a watershed's forests dramatically alters the rate and amount of water flowing across the landscape.

This is clearly evident in Baker Creek, a 1570 km² watershed in central British Columbia near Quesnel.

Mountain pine beetles and logging altered the Baker Creek drainage from 13 percent of the forested area harvested by 1970 to one-third of the forest harvested and another half of the area attacked by beetles as of 2005.

The transformed vegetation causes spring snowmelt to fill creeks with 31 percent more water and the flow rate to peak at volumes 61 percent higher than typical of 25 years earlier. Floods of over 100 m³/sec that used to occur once every 20 years are now expected to happen every four years.

But salvaging the beetle-killed trees triggers the landscape to release even more water all at once. The most likely scenario for 2017 under current provincial policy would leave 20 percent of the watershed unlogged. Hydrological modelling indicates that these forest conditions would produce peak stream flows that are 92 percent higher in volume and overall water yields 52 percent greater than what occurred in 1970.

In comparison, forest modifications that had accumulated as of 1996 produced negligible increases in water flow, when only 2 percent of the forests had been infested by beetles and 28 percent of the watershed was logged

The gentle, plateau landscape of the north-facing Baker drainage allows most of its snow to melt over one brief period. This accentuates any repercussions that changes to the forest have on water flowing in creeks.

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