Past Corps TDS Experience

ERDC TN-DOER-I2

July 2000

TDS may encounter a problem with sandy material (mounding)in the hopper but is suitable

in silty material.

TDS was a fair and accurate measurement method for determining payable dredged quantities

in areas of heavy erosion or siltation.

Performance of hopper dredges operating in the Euro-channel, Maas-channel, and EuroPort

entrance was improved and there had been a reduction in total capacity of dredges required.

Past Corps TDS Experience. An example of previous Corps experience with hopper dredge

instrumentation and data collection, the Dredge Data Logging System (DDLS), is presented by

Burke (1989) and McDonnell and Tillman (1992). The first DDLS was designed to monitor hopper

dredge production and position data and, although it did not incorporate hopper level sensors

(necessary for TDS determination), the system recorded vessel draft. Scott (1992) investigated the

use of acoustic hopper level sensors and concluded that they "maintained their calibration through-

out the two months of testing (and that) the data from the hopper sensors had good resolution, with

minimal signal noise."

Jorgeson and Scott (1994) and Scott et al. (1995) describe an instrumentation package of acoustic

and pressure sensors to monitor real-time dredge displacement and hopper volume and indirectly

measure the density or TDS value of the dredged material in the hopper. This package was designed,

fabricated, tested, and evaluated for effectiveness in providing data to dredge personnel for the

purpose of increasing dredge efficiency. "The results indicate that sufficient knowledge and

technology existed for developing a comprehensive hopper dredge monitoring system" (Scott et al.

1995).

Alexander, Murphy, and Scott (1996) developed DDLS specifications and quality assurance tests

for hydraulic pipeline dredges, hopper dredges (incorporating draft and hopper level sensors), and

mechanical dredges and scows (with draft and bin level sensors) for the Oakland Harbor Deepening

Project in the U.S. Army Engineer District, San Francisco. The project was accomplished with

mechanical dredges with scows and the scow draft and bin-level sensors were used to calculate

dredged material density. A conclusion from this dredging contract was that "DDLS methods

provide a fair and accurate assessment of project activities for both the dredging project sponsors

and contractors" (Alexander, Murphy, and Scott 1996). Cox, Maresca, and Rosati (1996) present

the Silent Inspector (SI) system technical manual developed during the Dredging Research Program

(DRP). TDS data was collected on the Corps dredge Essayons under this program.

The design of the Corps instrumentation and data collection system, specifications for contractors,

and quality assurance procedures were built upon the aggregate knowledge from various sources

that include these past Corps experiences, Corps dredging management and inspection expertise,

and European and Asian experiences and documentation.

RECENT DOER TDS STUDIES: The Corps dredge McFarland and B+B Dredging Company

dredge Columbus have been instrumented to collect TDS data in different geographical and

geological locations. The DOER work unit has installed TDS instrumentation on the McFarland,

while the TDS system on the Columbus is required in a rental contract with the U.S. Army Engineer

District, Mobile.