Trapping Efficiencies For Four Types of Pressure-Difference Bedload Samplers

Bedload-trapping efficiencies (coefficients) were derived for four types of pressure-difference bedload samplers at the St. Anthony Falls Laboratory, University of Minnesota, in January-March, 2006. A Helley-Smith (intake-nozzle width and height of 76.2 mm x 76.2 mm), BLH-84 (76.2 mm x 76.2 mm), Elwha (203 mm x 102 mm) and Toutle River-2 (TR-2; 305 mm x 152 mm) were deployed by hand-held rod in the main flume during the first two phases of the StreamLab06 experiments. The trapping-efficiency tests, which were conceived, designed and administered by the U.S. Geological Survey, took place in the sediment-recirculating main flume. Representatives from the St. Anthony Falls Laboratory, National Center for Earth-surface Dynamics, Federal Interagency Sediment Project, Bureau of Reclamation, academia and the private sector joined the U.S. Geological Survey in the implementation of the tests. The 7-phase StreamLab06 experiments were made possible and supported by the National Center for Earth-surface Dynamics, University of Minnesota.

Six combinations of sampler type and bed composition were tested. The BLH-84, Elwha, and Helley-Smith samplers were deployed on a sand bed (D50 = 1.0 mm) during five steady flows ranging from 2.0-3.6 m3/s. The BLH-84, Elwha, and Toutle River-2 samplers were deployed on a gravel bed (D50 = 11.2 mm) at four steady flows ranging from 4.0-5.5 m3/s. Thirty-seven trials – tests of a given bedload sampler for a given steady flow and bed composition – took place.

The submitted paper will include the trapping coefficients for each bedload sampler-and-bed composition tested.