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Science & Environment

Debris Flow From California's Rough Fire Threatens Lakes Downstream

RENEE MONTAGNE, HOST:

Let's move from powerful music and ads to powerful weather. Storms related to El Nino are dumping large amounts of snow and rain in the mountains of central California. A lot of that precipitation is falling on an area that was devastated by the giant fire last summer, dubbed the Rough Fire. It burned 150,000 acres. Now dirt and debris are flowing into lakes. Valley Public Radio's Ezra David Romero reports.

EZRA DAVID ROMERO, BYLINE: Pine Flat Lake, in the hills of the Sierra Nevada, east of Fresno, is rising about half a foot a day. Recent rain and snow are slowly filling it up.

JEROMY CALDWELL: The storms have been fairly regularly spaced. And they have been bringing some much-needed water into the lake.

ROMERO: That's Jeremy Caldwell. He runs the daily operations of the reservoir, in the hills of Fresno County.

(SOUNDBITE OF MOTORBOAT ENGINE HUMMING)

ROMERO: Caldwell pilots a motorboat to the far end of the lake. With heavy storms expected this winter, he's anticipating lots of water to flow in.

(SOUNDBITE OF MOTORBOAT ENGINE HUMMING)

CALDWELL: We're at the upper end of the lake, just below the Trimmer boat ramp.

ROMERO: At the moment, Pine Flat Lake is about 20 percent full and still has room for 260 billion gallons of water. The U.S. Army Corps Of Engineers says the water flowing into the lake poses a twofold problem. First, they are worried that lots of brush, logs and groundcover from the Rough Fire burn area will flow into the lake. That debris can be harmful to people fishing or skiing. Caldwell says the Corp has a solution for debris.

CALDWELL: We have a floating boom. And as you can see, we have got some smaller debris now that is being caught. The larger debris can cause hazards to boaters. It can also cause problems with operation of the dam.

ROMERO: The boom spans the width of the lake. It's made out of long, orange plastic buoys. Hanging from each one is a two-foot metal grate stopping the debris flow. That's a pretty big log right there.

CALDWELL: It is pretty long. So it could cause some problems for a boater that happened to hit it.

ROMERO: Sediment is the other problem. Eventually, it builds up on lake floor, which means the reservoir holds less water.

CALDWELL: There is additional settlement expected to come into the lake because of the fire. You see some brown-colored, fine sediment that's building up along the river.

ROMERO: At this point, there's not much that can be done to stop the dirt from washing into the lake. Steve Haugen is in charge of making sure all the farms that need water from the Kings River get it. He says the consequences that come with the increased sediment from storms over a burn area are huge.

STEVE HAUGEN: We can get upwards of 2,000 acre-feet worth of sediment coming into Pine Flat. That settles on the bottom and displaces 2,000 acre-feet of water.

ROMERO: And that's just from one storm. It may not seem like that much of a loss, but with such low reservoir levels, every drop matters. All that water is already allocated to farmers and towns downstream. And a lower holding capacity means less water for them.

HAUGEN: What happens in the burn scar area impacts everything downstream - sediment, water quality, ability to store water, how it's used.

ROMERO: Haugen says the problem with increased sediment flows doesn't just go away after El Nino ends.

HAUGEN: We won't know the full extent of that problem until probably five to 10 years out, as that sediment makes its way down through the river system. The consequences of these fires are long duration.

ROMERO: Haugen says the sediment dissolves in the lake water, eventually makes it out of the dam into growers' fields, and over time can clog farm machinery and water pumps. For NPR News, I'm Ezra David Romero in Fresno. Transcript provided by NPR, Copyright NPR.