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.