Mid-winter flooding, high late-summer flows all signs of changing water regime
By Bob Berwyn
SUMMIT COUNTY — Widespread lodgepole pine mortality has increased both the abundance and timing of runoff in streams and irrigation ditches, Blue River water commissioner Scott Hummer said this week at a meeting of the Summit Forest Health Task Force.
His local observations reflect a recent Colorado State University study showing at least a short-term runoff increase, probably because there are hardly any live trees left to drink up the water. Other studies have been inconclusive, and some researcher speculate that, if there is any increase in runoff, it will be very short-lived, as other vegetation fills in the forest floor beneath the dead lodgepole overstory.
“Based on my observations, that’s a pretty reliable number,” Hummer said, adding that he’s also seen changes in the timing of the runoff. For example, some residents of the Three Peaks neighborhood in Silverthorne last winter saw flooding in the middle of the winter.
Hummer said wetlands in the area became totally saturated during the winter and started discharging water into a historic irrigation ditch that subsequently over-flowed into the subdivision. There’s no empirical evidence that beetle-kill caused the flooding, but if the extensive lodgepole pine forests above the area stop absorbing water — well, it has to go somewhere.
Hummer also said ranchers are reporting streams flowing higher and later in the season than anyone in the Lower Blue has seen, going back four or five generations, which could also be a sign that the vast stands of dead lodgepoles are not taking up nearly as much water as they once did.
Other speakers at the task force meeting included Don Kennedy, a Denver Water environmental scientist who described the costly remediation required after the Buffalo Creek and Hayman fires in 1996 and 2002.
Despite the fact that local officials keep trying to link the pine beetle epidemic with an increased risk of catastrophic fire, there’s very little scientific evidence to support that claim. The Buffalo Creek and Hayman fires burned in areas where pine beetles play no role whatsoever in the forest ecology, Kennedy said.
“It’s like ball-bearings on hillside ready to roll down … with no needles on the surface of the ground, it results in debris flows after a quarter-inch rainstorm,” Kennedy said, adding that the 1996 Buffalo Creek fire was huge wakeup call for Denver Water. A moderate rainstorm a couple of months after the fire deposited 10 years worth of sediments in the watershed.