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Table 1. Example Hopper Dredge Uncertainty Calculations1
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REFERENCES - doert60015
ERDC TN-DOER-T6
September 2004
from these analyses that accurate instrument calibration, along with a thorough knowledge of the
properties of the water, and to a much lesser degree mineral density, is necessary to ensure the
highest degree of production measurement accuracy. This conclusion is also graphically illus-
trated in the sensitivity analysis plot.
In addition to the limitations previously described for hopper level sensors and the weight
measurement method (both used to measure the average hopper load density), additional TDS
measurement error can be induced by "dry" sand loading. The TDS equation is based on the
density relationship between water and solids in a completely saturated slurry (water between all
the solid particles). Fluid mud loads meet this criterion, but there are loading situations when the
entire load is not saturated, such as with sand loads with unsaturated portions of the hopper load.
These unsaturated portions can be due to an uneven loading surface (ridges) above the "water
plane" (see Figure 7), or by water draining through the sand and out leaking seals, or over the
weirs. As was shown in the sensitivity and uncertainty analyses above, measurements of the
hopper volume and vessel's draft (displacement) have the most effect on the accuracy of the final
TDS calculated value. TDS measurement error is proportional to the volume of unsaturated
dredged material (and respective absence of water in this volume).
SUMMARY:
Research to improve dredging contract management, economics (cost
optimization), and contaminated sediments management (document dredging and placement
locations) is currently being conducted by the Innovative Technologies Focus Area of the DOER
Program. This technical note describes currently used hopper and bin load measurement methods
and analysis procedures and discusses their respective capabilities and limitations. Subsequent
DOER technical notes from this Focus Area will refer back to this document as a basis for
defining system requirements in the development of improved hopper and bin measurement
technologies.
POINTS OF CONTACT: For additional information on TDS measurement or the Silent
Inspector System, contact Mr. Timothy Welp (601-634-2083,
usace.army.mil) or Mr. James Rosati (601-634-2022, ),
and/or the DOER Program Manager, Dr. Robert M. Engler (601-634-3624, Robert.M.
). This technical note should be cited as follows:
Welp, T., Rosati, J. and Howell, G.  (2004). "Status of current hopper and bin
measurement technologies," DOER Technical Notes Collection (ERDC TN-DOER-T6),
U.S.  Army  Engineer  Research  and  Development  Center,  Vicksburg,  MS.
REFERENCES
Herbich, J. B., Lee, J. Y., Trivedi, D. R., Wilkinson, G., and De Hert, D. O. (1992). "Survey and evaluation of
production meter instrumentation and uses," WES Contract Report DACW-39-89-K-0003, Texas A&M
Research Foundation.
Jorgeson, J. D., and Scott, H. L. (1994). "An automated system for hopper dredge monitoring," Technical Report
HL-94-12, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
14

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