Data from thirteen field tests were used to compare bedload samplers. During each field test, 23 to 63 individual samples were collected. During most tests, the same number of samples was collected for each bedload sampler tested. Most field tests were conducted by sampling alternately with differently designed samplers at one common point on the bed. Sampling times ranged from 4 to 60 seconds, sampling intervals ranged from about 3 to 5 minutes, and sampling periods ranged from about 2.5 to 4 hours.
Flow velocities and depth were measured at the sampling vertical once during each field test. During different tests, measured velocities ranged from 2.12 to 3.16 meters per second, depths ranged from 0.55 to 1.46 meters, and computed Froude numbers ranged from 0.61 to 0.97. Individual sampled bedload rates ranged from 0.004 to 15.9 kilograms per second-meter and were variable through a range of at least two orders of magnitude during a sampling period. During different tests, calculated mean sampled bedload rates ranged fro 0.076 to 9.09 kilograms per second-meter. Bedload sediment collected during different field tests had mean intermediate particle diameters that ranged from 0.93 to 36.2 millimeters.
Evaluation of field performance for each of the 6 bedload samplers tested showed that only the Toutle River-1 and Toutle River-2 bedload samplers were stable in high-energy flow without the use of a stayline. However, use of a stayline improved the stability of all bedload samplers tested.
The sampling ratio of each pair of samplers tested was computed by dividing the mean bedload transport rate sampled by one sampler by the mean rate sampled by a second sampler. Ratios of sampled bedload rates between all sampler pairs ranged from 0.40 to 5.73. These ratios provide insight into relative sampling characteristics of bedload samplers during high-energy flow. The Toutle River-2 bedload sampler was developed in this study for sampling bedload under conditions of high velocity and turbulence and high sediment transport rates. This sampler has a mass of 100 kilograms, overall length of 1.52 meters, nozzle entrance that is 305 millimeters wide and 152 millimeters high, and hydraulic efficiency estimated at 1.40. The Toutle River-1 bedload sampler appears to provide representative bedload samples of bedload consisting of a mixture of sediment in the size range between 1.0 and 128.0 millimeters.
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