USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
The 1980 Polallie Creek Debris Flow and Subsequent Dam-Break Flood, East Fork
Hood River Basin, Oregon
--
Gary L. Gallino and Thomas C. Pierson, 1984,
The 1980 Polallie Creek Debris Flow and Subsequent Dam-Break
Flood, East Fork Hood River Basin, Oregon:
U.S. Geological Survey Open-File Report 84-578, 37p.
Introduction
At approximately 9 p.m. on December 25, 1980, a disastrous debris flow burst
out of Polallie Creek Canyon, killed the lone camper in the old section of
Polallie Creek campground, located at the confluence of Polallie Creek and East
Fork Hood River, and temporarily dammed the East Fork Hood River (fig. 1).
-- (Web note: not available) --
Deposition of this debris mass set the stage for a dam-burst flood that swept
down the East Fork Hood River Canyon minutes later. Damage or destroyed were
approximately 5 mi of Oregon Highway 35 (Mount Hood Highway), including three
bridges, a state park, and a campground. The estimated $13 million in damage
caused by this flood prompted the Governor of Oregon to declare parts of Hood
River County as disaster areas.
A slope failure in the unconsolidated volcanic deposits at the oversteepened
head of Polallie Creek Canyon started the chain of events. The landslide was
rapidly transformed into a debris flow which surged down the canyon, tearing
loose trees, boulders, and easily erodible channel deposits, and incorporating
it all into the flow. The magnitude of this rapidly moving debris wave grew
steadily as it flowed down Polallie Creek Canyon, until it emptied into the East
Fork Hood River and formed a temporary dam.
This study was initiated to document the Polallie Creek debris flow and
subsequent flood event, to describe the triggering mechanism and characteristics
of the debris flow, and to test and compare some of the analytical tools
available to study these events.
Historically, many debris flows in mountain watersheds have been analyzed as
water floods, even though the major component of the fluid was solids (Costa and
Jarrett, 1981). This can result in computed peak discharges and storm runoff
amounts that are too large, as this report will show. In this report,
comparisons are made between the unadjusted synthesized peak water discharges
derived from (1) comparisons with ungaged adjacent basins and gaged streams
draining Mount Hood, (2) discharges computed from hydraulic formulas, and (3)
compositional data on the debris-flow slurry.
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03/03/06, Lyn Topinka