http://www.insidedenver.com/drmn/sta...522232,00.html

Log dams don't halt erosion
Burned areas need mulch and seedlings, expert tells meeting

By Jim Erickson, Rocky Mountain News
November 4, 2002

Building log dams across hillsides to control erosion in the wake of wildfires
is far less effective than soil experts had long assumed.

In some cases, log dams don't help at all.

For nearly 20 years, fire rehabilitation teams have used "log erosion barriers"
in an attempt to trap soil and keep it from washing off hillsides during
rainstorms.

But experiments at the site of the Hi Meadow Fire near Bailey, the Bobcat Fire
northwest of Loveland, and at burned areas in several other states have cast
doubt on the technique's value, said Peter R. Robichaud, a U.S. Forest Service
research engineer who began testing log dams in 1998.

When it came time to rehabilitate land charred in the June 2002 Hayman Fire
southwest of Denver, log dams were rejected altogether. The 138,000-acre Hayman
Fire was the largest and most destructive wildfire in Colorado history.

"We're finding that some of these older techniques just aren't that effective,
including log erosion barriers," said Ken Kanaan, who led the Hayman emergency
rehabilitation team.

"It's time-consuming, it takes specially trained people to do the work, and
it's just not as effective as mulching and some of our other rehab treatments,"
he said.

The Hayman rehab team finished its 2002 work Oct. 18 and spent $14.7 million,
Kanaan said.

"This was the most popularly used erosion control method, but there was little
to no research to support that it worked or didn't work," University of
Colorado researcher John Gartner said of log barriers.

Gartner studied the site of the Hi Meadow Fire, which burned 10,800 acres in
June 2000. He presented his findings this week at a Denver meeting of the
Geological Society of America.

Gartner compared severely burned areas where log dams were installed to burned
areas that received no treatment. Fences were placed at the bottom of hillsides
to trap sediment.

"My data shows that the log barriers don't make a difference in the amount of
sediment coming down off the hill slope and trapped at the base," he said.

Colorado State University graduate student Joe Wagenbrenner conducted a similar
study at the site of the Bobcat Fire, which burned 10,400 acres in June 2000.

A single large storm on Aug. 16 of that year filled the log barriers with
sediment, he said. During subsequent storms, "All the sediment went straight
down the hill," he said.

In 2000 and 2001, there was no significant difference in the amount of sediment
trapped below untreated hillsides and hillsides fitted with log barriers
immediately after the fire, Wagenbrenner said at this week's Denver geology
meeting.

At the Hayman Fire, rehab workers relied mainly on seeding and mulching,
blanketing the ground with grass seed, wood fibers and straw to hold the soil
when summer rains hit. They tried to keep ash and dirt out of streams that feed
the South Platte River, which supplies drinking water to Denver.

A green slurry called called hydro-mulch was sprayed by helicopter and truck
onto about 3,100 severely burned acres at the Hayman. Hydro-mulch is a mix of
recycled wood fibers, grass seed, water and a binding agent.

Ground crews used rakes and harrow-equipped ATVs to break up water-repellent
soils in severely burned areas. Then grass seed was spread across 13,800 acres.


An airplane spread grass seed over another 19,835 acres, and helicopters
dropped dry straw onto 7,700 seeded acres.

Robichaud and several other researchers have established long-term research
plots at the Hayman to test the effectiveness of the various erosion-control
methods used there.