From The Greeley Tribune (Trevor Reid):
With five of Greeley’s six high mountain reservoirs in the burn area, erosion is expected to carry sediment into Greeley’s water supply. Left untreated, that could affect the city’s water quality. But officials are already planning to make sure that doesn’t happen.
“When fires burn, if they’re hot enough, they can actually burn underbrush and soil,” said Adam Jokerst, Greeley’s deputy director of Water Resources, adding that vegetation is burned up as well. “With the lack of the vegetation … you can get increased erosion when it rains or when the snow melts.”
That erosion carries sediment into the Poudre River, which pulls water from the reservoirs to supply water for the city. Water with high sediment content can be harder to treat, Jokerst said, but it is possible to treat safely.
For better or for worse, Jokerst said, Greeley water officials have a lot of experience handling erosion into the water supply after dealing with the impacts of the High Park Fire in 2012. That fire burned more than 87,000 acres, making it the sixth-largest in state history.
There are at least a few steps to take to mitigate erosion impacts: aerial mulching, felling trees and adding flocculants during the treatment process. For aerial mulching, crews drop shredded wheat chips or straw from a helicopter. The mulch reduces erosion and helps with revegetation. Cutting down the burned trees and letting them fall into the gullies and rills — the channels created in the soil by water erosion — prevents stormwater and meltwater from carrying added erosion into the water supply.
Jokerst said it’s common to see the water get murkier during the runoff season every year. To provide clean, clear drinking water when that happens, crews use more flocculants, which are chemicals that help to separate the water from the sediment, in the treatment process. If there’s very high sediment content at the Bellvue Treatment Plant, officials can turn off the plant so it stop pulling water from the Poudre, Jokerst said. The city can then use the Boyd Treatment Plant…
If the fire keeps on into snowfall season in the winter, Jokerst said crews will have to wait until the spring to start on erosion control measures. Greeley officials are working with the city of Fort Collins, Northern Water and the Coalition for the Poudre River Watershed, a nonprofit Jokerst said will be a key entity in the post-fire recovery.