MEASUREMENT IN THE MEANS OF CONVEYANCE: Basically two parameters are
measured to quantify hopper load contents: volume and weight. Either one of these two
parameters is used as a production evaluation tool, or both are measured simultaneously to
calculate the dredged material's average density or some derivative thereof (i.e., tons dry solids).
Methods and equipment used to measure these parameters range from manually sounding the
hopper volume with a weighted tape, to measuring and calculating hopper density with an
automated measuring/monitoring system i.e., the Silent Inspector.
Hopper manual sounding methods. Since the
first hopper dredge, the General Moultrie, was
used to dredge the Charleston, South Carolina
Bar in 1857, the volume of material in the
hopper has been measured to calculate
production (the General Moultrie with a 19-in.-
diam drag pipe averaged 328 yd3 per day).
Sounding of the hopper at various locations with
a lead line was the primary method of measuring
the volume of material being transported in the
hopper, and this method is still in use today (see
This photograph was taken on a hopper dredge
working in coarse-grained material (medium-
sized sand) on the Columbia River Bar, managed
by the Portland District. Soundings, or ullage
measurements, are usually taken at six to eight
different locations around the hopper using
conveniently located reference points (i.e.,
walkways or coaming tops). The soundings are
then averaged together. The resulting value is
applied to an ullage table or equation that Figure 2. Sounding hopper to measure load
equates ullage distance to volume of material in
the hopper. Depending on the number of
soundings taken and care taken by the sounder, this measurement method can be quite accurate
as long as the dredged material provides a surface with sufficient bearing strength to support the
sounding lead (i.e., in a sand load). After loading is completed and the sand settles out quickly
with a layer of water over it, this measurement method compensates for the water layer by the
lead penetrating through the water layer till it rests upon the sand surface. Rullens (1993)
concludes that when sand is dredged, the half-sphere "sounding" method (a sounding lead with
specific mass and dimensions that will be described later) gives an unambiguous indication of
the top of the solids mass and that this method is suitable to measure payable dredged quantities.
Another advantage of this method is that the measuring equipment is inexpensive and simple.
Disadvantages of the half-sphere sounding method include: