DESCRIPTION:
Experimental Debris-Flow Flume

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Debris-Flow Flume, Annotated

Scientific understanding of debris flows has been hampered by their unpredictable timing, location and magnitude, which make systematic observation and measurement of natural events both difficult and dangerous. Consequently, in 1991 the U.S. Geological Survey (USGS), in cooperation with the U.S. Forest Service, constructed a flume to conduct controlled experiments on debris flows. Located about 45 miles east of Eugene, Oregon, in the Cascades Range foothills near the headquarters of the H.J. Andrews Experimental Forest, Blue River Ranger District, Willamette National Forest, this unique facility provides research opportunities available nowhere else.

The flume is a reinforced concrete channel 95 meters (310 feet) long, 2 meters (6.6 feet) wide, and 1.2 meters (4 feet) deep that slopes 31 degrees (60 percent), an angle typical of terrain where natural debris flows originate. Twelve large bolts grouted into deep boreholes and tensioned to concrete pads adjoining the flume help anchor the structure to the underlying soil and rock. Removable glass windows built into the side of the flume allow flows to be observed and photographed as they sweep past. Eighteen data-collection ports in the floor of the flume permit measurements of forces due to particles sliding and colliding at the base of flows.

To create a debris flow, up to 20 cubic meters (about 40 tons) of sediment are placed behind a steel gate at the head of the flume, saturated with water from subsurface channels and surface sprinklers, and then released. Alternatively, a sloping mass of sediment can be placed behind a retaining wall at the flume head and watered until slope failure occurs. The ensuing debris flow descends the flume and forms a deposit on a nearly flat runout surface at the flume base. The flume design thus accommodates research on all stages of the debris-flow process, from initiation through deposition. Experiments can be conducted using a variety of materials, from mixtures of well-sorted gravel and water to heterogeneous natural slope debris. Experimental materials are recycled by excavating deposits with a front-end loader, placing them in a dump truck, and hauling them back to the staging area at the head of the flume.

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