Sounding weights are used in
streams where discharge measurements are made by suspension
techniques from bridges, cableways or boats. The sounding weight is
suspended below the current meter to keep it stationary in the
water. The USGS Columbus-type or "C"-type weights are streamlined to
minimize resistance to flowing water and are longer than the current
meter, thereby offering some protection from bridge piers and
flowing debris. The added length also produces better directional
and stabilizing characteristics than that obtained with other
weights. The hanger slot is shaped to allow the hanger to tilt
forward 15 degrees and backward 5 degrees from the vertical. This
prevents the meter from coming into contact with, and being damaged
by, the weight. These weights come in 15, 30, 50, 75, 100, 150, 200
and 300-pound (7, 14, 23, 34, 45, 68, 91 and 136 kg) sizes. The
15-pound (7 kg) weight is cast from brass, but all others are cast
from lead and have aluminum tailfins. All are properly balanced and
tested by an approved method before shipment. The weights can be
epoxy coated if required.