US BL 84 Sampler - The US BL 84 was designed by the Federal Interagency Sedimentation project to collect bedload particles up to 38 mm at mean velocities up to 9.8 feet per second. The sampling box has a 3 in by 3 in entrance with a 4.2 in by 4.2 in exit for an area expansion ratio of 1.4. The collection net is 0.25 mm. The collection box is connected to a stabilizing tail section by three arching tubes, two horizontal and one verticle. The overall length of the sampler is 36 in. and it weighs 32 pounds. Samples are collected by setting the sampler on the stream bottom for a specific time interval at a specific number of equidistant verticles. The ratio of the cross section to the sampled section (number of verticles times 3 inch) and the time can be used to estimate the total bedload at that cross section from the sampled bedload.