John Gray
John Gray
Principal, GraySedimentology, LLC
Title: TRAPPING COEFFICIENTS FOR 4 TYPES OF PRESSURE-DIFFERENCE BEDLOAD SAMPLERS
Abstract:
The reliability of transport data produced by a bedload sampler is in part predicated on the efficiency by which the sampler traps bedload. Absent technically supportable trapping efficiencies (coefficients), a bedload sampler’s trapping coefficient is typically assumed to equal unity (i.e., to trap bedload without bias).
Bedload-trapping coefficients were derived for four types of pressure-difference bedload samplers from data collected at the St. Anthony Falls Laboratory, University of Minnesota, in January-March 2006 (figure). 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 sediment-recirculating and -weighing Main Flume over a range of steady flows.
All but the Helley-Smith sampler have expansion ratios (nozzle exit area divided by intake area) of 1.4. That for the Helley-Smith is 3.22.
The BLH-84, Elwha, and Helley-Smith samplers were deployed on a sand bed (D50 = 1.0 mm). The BLH-84, Elwha, and TR-2 samplers were deployed on a gravel bed (D50 = 11.2 mm).
Thirty-seven trials – tests of the trapping efficiency of a bedload sampler for a given steady flow and bed composition – took place. A total of 2,030 manually collected and weighed bedload samples, and some 3.8-million automated mass measurements produced by five contiguous weigh drums in a slot spanning the width of the flume, were used to calculate trapping coefficients for the samplers using four analytical techniques.
Provisional results indicate that the sand- and gravel-trapping efficiencies calculated for the BLH-84 were about 85 percent of unity, or slightly sub-efficient. Those for the other three samplers tested were super-efficient, with coefficients ranging from about 150- to 300-percent of unity. Verified sampler-specific trapping coefficients may be used to adjust historical as well as contemporary bedload-transport rates produced by these types of samplers deployed atop beds with compositions similar to those used in these tests.
Biography:
John is a Prodigal Son of Illinois, including the State, the University of, and the USGS offices in Dekalb and Urbana. He grew up on the "wrong side of the tracks" in the Chicago suburb of Lombard.
A week after receiving his bachelor degree in Biology/Chemistry from Northern Illinois University in 1976, he came on-board with the U.S. Geological Survey (USGS) Water Resources Division, Dekalb Subdistrict Office, then located on the NIU campus.
After transferring to Urbana in 1982, he started undergraduate coursework toward a U of I CEE Master's Degree, taking his first course from Dr. William Ackermann. After finishing his graduate coursework in 1987 under Dr. Ben C. Yen, he transferred to the USGS Tucson District Office. In 1991 he relocated yet again on a 2-year assignment to the USGS National Center in Reston, Virginia, as the "Staff Assistant to the USGS Director." Twenty-two years later...he retired from USGS Reston office, having served the last 17 years as the USGS Office of Surface Water's "National Sedimentologist."
John earned his Ph.D. in Civil Engineering from Virginia Tech in May 2019, some 5 years after retiring from the USGS. Please don't ask him to explain why a then-67-year-old "student" would suffer through that most-humbling process.
John remains affiliated with the USGS as a "scientist emeritus" and is the Principal of GraySedimentology, LLC, consulting in fluvial sedimentology, geomorphology, water quality, and limnology.
Without further ado, I welcome John 'home' with the following quote from his then: 3-year old daughter Jackie..."Go 'Yini!"