“The ash will be disappearing soon, but erosion along the river will continue — through summer 2013. We’ll see lower erosion rates by 2014,” said MacDonald, who specializes in watershed science.
It could take three years for relief in the harder-hit spur canyons, engineers told Solley. Rebuilding should wait, they said.
While the ash in the river is not harmful to rafters or even swimmers, except for its power to obscure potentially dangerous debris, the fish have much more serious problems.
The 2002 Hayman fire caused the loss of 70 percent of adult fish in the the South Platte River, said Colorado Parks and Wildife aquatic biologist Ken Kehmeier . The South Platte still hasn’t responded well to efforts to repopulate the fish, he said.
“We still hear complaints from anglers on the South Platte. The Poudre fire will be that bad or worse,” Kehmeier said, partly because there are no large reservoirs filtering out heavy sediments to the benefit of the river downstream.
“We know we’re losing fish now, but the impacts could last more than 10 years,” Kehmeier said. “It’s a devastating thing. It’s a lengthy recovery process, and we will be continually working for years to bring the fishery back.”
One of the early efforts to save fish was made during the fire, when officials evacuated 100,000 small fish over two days from the Watson Lake Rearing Unit in Bellvue. The fish left the hatchery in a semi truck outfitted with seven 500-gallon tanks. Some were released in Horsetooth, Carter and Flatiron reservoirs. Others went to Chatfield State Park’s hatchery, Kehmeier said.
Now as storm runoff from burned areas hits the river, some sediment and ash is carried along and some settles, dropping into the small spaces between river rocks and gravel, smothering insects and other invertebrates that are food for fish.
The river’s pH changes, Kehmeier said. Ash makes it more basic. Yet in some parts of the river researchers are seeing the water become more acidic, possibly because of decomposing pine needles. The shifts in pH are one more stress on fish.
Note from Sharon: I’m not trying to say that we shouldn’t have fires, which are “natural” and we couldn’t stop ‘em if we tried. My point is that we ought to be clear-eyed about their costs and benefits when we manage them, which we will always do, as long as there are people in the woods and people using the water from the woods. I wonder if seeing them through the “timber wars” lens keeps us from seeing clearly.