Initial Corps Experience with Tons Dry Solids (TDS) Measurement

ERDC TN-DOER-I2

July 2000

Initial Corps Experience with

Tons Dry Solids (TDS) Measurement

PURPOSE: This technical note describes the Tons Dry Solids (TDS) measurement method and

summarizes the initial experiences of the U.S. Army Corps of Engineers with its use on Corps and

contractor hopper dredges. Subsequent technical notes will describe further TDS measurement

developments that evolve from these experiences.

BACKGROUND: In the Corps' dredging program, unit price construction contracting is the

preferred method of accomplishing dredging work. With hopper dredges, the unit price can be

based on volume, area, time, or bin measurements. The Instrumentation Focus Area of the Corps'

Dredging Operations and Environmental Research (DOER) Program is currently investigating the

applicability of the TDS bin measurement methodology for payment purposes. This methodology

has been used in Europe since 1988 and was originally developed in The Netherlands for use in the

Port of Rotterdam.

INTRODUCTION: TDS measures the volume and weight of the hopper load to determine the

quantity of dry solids that the load contains. By applying the values for the dry solid specific density

and in situ water density in a formula with the hopper load weight and volume (which indirectly

measures the average density of the hopper load), the total quantity of the dry solids can be

calculated.

TDS has promise for the Corps where dredging conditions render hydrographic surveys too

inaccurate to determine work accomplished by the contractor. There are times and/or locations

where hydrographic surveying cannot be used for payment purposes: on dynamic ocean entrance

bars where the bottom changes quickly, or in fluid mud locations (naturally occurring fluff or

sediment suspended from dredging activities) that affect echo sounding. In fluid mud, small changes

in sensitivity (or signal gain) settings can result in large variations in the echo return point (depth)

and no definitive methods exist to fully compensate for them (Headquarters, U.S. Army Corps of

Engineers, 1994).

Because TDS measures the amount of dry solids material that is actually being transported, the

performance of the dredge can be determined for contract management purposes, and TDS

measurement provides feedback to the dredge crew and management for optimizing production.

TDS also allows sediment removal to be described in terms of mass balance, improving the

understanding of dredged material fate.

TDS Requirements. As stated earlier, the data requirements for computing TDS are as follows:

Density of in situ water.

Specific density of dry particles.